Magnetization reversal in ferromagnetic wires patterned with antiferromagnetic gratings

NASA Astrophysics Data System (ADS)

Sani, S. R.; Liu, F.; Ross, C. A.

2017-04-01

The magnetic reversal behavior is examined for exchange-biased ferromagnetic/antiferromagnetic nanostructures consisting of an array of 10 nm thick Ni80Fe20 stripes with width 200 nm and periodicity 400 nm, underneath an orthogonal array of 10 nm thick IrMn stripes with width ranging from 200 nm to 500 nm and periodicity from 400 nm to 1 μm. The Ni80Fe20 stripes show a hysteresis loop with one step when the IrMn width and spacing are small. However, upon increasing the IrMn width and spacing, the hysteresis loops showed two steps as the pinned and unpinned sections of the Ni80Fe20 stripes switch at different fields. Micromagnetic modeling reveals the influence of geometry on the reversal behavior.

Buffer layer dependence of magnetoresistance effects in Co2Fe0.4Mn0.6Si/MgO/Co50Fe50 tunnel junctions

NASA Astrophysics Data System (ADS)

Sun, Mingling; Kubota, Takahide; Takahashi, Shigeki; Kawato, Yoshiaki; Sonobe, Yoshiaki; Takanashi, Koki

2018-05-01

Buffer layer dependence of tunnel magnetoresistance (TMR) effects was investigated in Co2Fe0.4Mn0.6Si (CFMS)/MgO/Co50Fe50 magnetic tunnel junctions (MTJs). Pd, Ru and Cr were selected for the buffer layer materials, and MTJs with three different CFMS thicknesses (30, 5, and 0.8 nm) were fabricated. A maximum TMR ratio of 136% was observed in the Ru buffer layer sample with a 30-nm-thick CFMS layer. TMR ratios drastically degraded for the CFMS thickness of 0.8 nm, and the values were 26% for Cr buffer layer and less than 1% for Pd and Ru buffer layers. From the annealing temperature dependence of the TMR ratios, amounts of interdiffusion and effects from the lattice mismatch were discussed.

Exchange-coupled Fe3O4/CoFe2O4 nanoparticles for advanced magnetic hyperthermia

NASA Astrophysics Data System (ADS)

Robles, J.; Das, R.; Glassell, M.; Phan, M. H.; Srikanth, H.

2018-05-01

We report a systematic study of the effects of core and shell size on the magnetic properties and heating efficiency of exchange-coupled Fe3O4/CoFe2O4 core/shell nanoparticles. The nanoparticles were synthesized using thermal decomposition of organometallic precursors. Transmission electron microscopy (TEM) confirmed the formation of spherical Fe3O4 and Fe3O4/CoFe2O4 nanoparticles. Magnetic measurements showed high saturation magnetization for the nanoparticles at room temperature. Increasing core diameter (6.4±0.7, 7.8±0.1, 9.6±1.2 nm) and/or shell thickness (˜1, 2, 4 nm) increased the coercive field (HC), while an optimal value of saturation magnetization (MS) was achieved for the Fe3O4 (7.8±0.1nm)/CoFe2O4 (2.1±0.1nm) nanoparticles. Magnetic hyperthermia measurements indicated a large increase in specific absorption rate (SAR) for 8.2±1.1 nm Fe3O4/CoFe2O4 compared to Fe3O4 nanoparticles of same size. The SAR of the Fe3O4/CoFe2O4 nanoparticles increased from 199 to 461 W/g for 800 Oe as the thickness of the CoFe2O4 shell was increased from 0.9±0.5 to 2.1±0.1 nm. The SAR enhancement is attributed to a combination of the large MS and the large HC. Therefore, these Fe3O4/CoFe2O4 core/shell nanoparticles can be a good candidate for advanced hyperthermia application.

Metastable bcc phase formation in 3d ferromagnetic transition metal thin films sputter-deposited on GaAs(100) substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Minakawa, Shigeyuki, E-mail: s-minakawa@futamoto.elect.chuo-u.ac.jp; Ohtake, Mitsuru; Futamoto, Masaaki

2015-05-07

Co{sub 100−x}Fe{sub x} and Ni{sub 100−y}Fe{sub y} (at. %, x = 0–30, y = 0–60) films of 10 nm thickness are prepared on GaAs(100) substrates at room temperature by using a radio-frequency magnetron sputtering system. The detailed growth behavior is investigated by in-situ reflection high-energy electron diffraction. (100)-oriented Co and Ni single-crystals with metastable bcc structure are formed in the early stage of film growth, where the metastable structure is stabilized through hetero-epitaxial growth. With increasing the thickness up to 2 nm, the Co and the Ni films start to transform into more stable hcp and fcc structures through atomic displacements parallel to bcc(110) slide planes,more » respectively. The stability of bcc phase is improved by adding a small volume of Fe atoms into a Co film. The critical thickness of bcc phase formation is thicker than 10 nm for Co{sub 100−x}Fe{sub x} films with x ≥ 10. On the contrary, the stability of bcc phase for Ni-Fe system is less than that for Co-Fe system. The critical thicknesses for Ni{sub 100−y}Fe{sub y} films with y = 20, 40, and 60 are 1, 3, and 5 nm, respectively. The Co{sub 100−x}Fe{sub x} single-crystal films with metastable bcc structure formed on GaAs(100) substrates show in-plane uniaxial magnetic anisotropies with the easy direction along GaAs[011], similar to the case of Fe film epitaxially grown on GaAs(100) substrate. A Co{sub 100−x}Fe{sub x} film with higher Fe content shows a higher saturation magnetization and a lower coercivity.« less

Non-local detection of spin dynamics via spin rectification effect in yttrium iron garnet/SiO{sub 2}/NiFe trilayers near simultaneous ferromagnetic resonance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soh, Wee Tee, E-mail: a0046479@u.nus.edu; Ong, C. K.; Peng, Bin

2015-08-15

The spin rectification effect (SRE), a phenomenon that generates dc voltages from ac microwave fields incident onto a conducting ferromagnet, has attracted widespread attention due to its high sensitivity to ferromagnetic resonance (FMR) as well as its relevance to spintronics. Here, we report the non-local detection of yttrium iron garnet (YIG) spin dynamics by measuring SRE voltages from an adjacent conducting NiFe layer up to 200 nm thick. In particular, we detect, within the NiFe layer, SRE voltages stemming from magnetostatic surface spin waves (MSSWs) of the adjacent bulk YIG which are excited by a shorted coaxial probe. These non-localmore » SRE voltages within the NiFe layer that originates from YIG MSSWs are present even in 200 nm-thick NiFe films with a 50 nm thick SiO{sub 2} spacer between NiFe and YIG, thus strongly ruling out the mechanism of spin-pumping induced inverse spin Hall effect in NiFe as the source of these voltages. This long-range influence of YIG dynamics is suggested to be mediated by dynamic fields generated from YIG spin precession near YIG/NiFe interface, which interacts with NiFe spins near the simultaneous resonance of both spins, to generate a non-local SRE voltage within the NiFe layer.« less

Giant magnetoresistance (GMR) behavior of electrodeposited NiFe/Cu multilayers: Dependence of non-magnetic and magnetic layer thicknesses

NASA Astrophysics Data System (ADS)

Kuru, Hilal; Kockar, Hakan; Alper, Mursel

2017-12-01

Giant magnetoresistance (GMR) behavior in electrodeposited NiFe/Cu multilayers was investigated as a function of non-magnetic (Cu) and ferromagnetic (NiFe) layer thicknesses, respectively. Prior to the GMR analysis, structural and magnetic analyses of the multilayers were also studied. The elemental analysis of the multilayers indicated that the Cu and Ni content in the multilayers increase with increasing Cu and NiFe layer thickness, respectively. The structural studies by X-ray diffraction revealed that all multilayers have face centred cubic structure with preferred (1 1 0) crystal orientation as their substrates. The magnetic properties studied with the vibrating sample magnetometer showed that the magnetizations of the samples are significantly affected by the layer thicknesses. Saturation magnetisation, Ms increases from 45 to 225 emu/cm3 with increasing NiFe layer thickness. The increase in the Ni content of the multilayers with a small Fe content causes an increase in the Ms. And, the coercivities ranging from 2 to 24 Oe are between the soft and hard magnetic properties. Also, the magnetic easy axis of the multilayers was found to be in the film plane. Magnetoresistance measurements showed that all multilayers exhibited the GMR behavior. The GMR magnitude increases with increasing Cu layer thickness and reaches its maximum value of 10% at the Cu layer thickness of 1 nm, then it decreases. And similarly, the GMR magnitude increases and reaches highest value of pure GMR (10%) for the NiFe layer thickness of 3 nm, and beyond this point GMR decreases with increasing NiFe layer thickness. Some small component of the anisotropic magnetoresistance was also observed at thin Cu and thick NiFe layer thicknesses. It is seen that the highest GMR values up to 10% were obtained in electrodeposited NiFe/Cu multilayers up to now. The structural, magnetic and magnetoresistance properties of the NiFe/Cu were reported via the variations of the thicknesses of Cu and NiFe layers with stressing the role of layer thicknesses on the high GMR behavior.

Shape induced magnetic vortex state in hexagonal ordered cofe nanodot arrays using ultrathin alumina shadow mask

NASA Astrophysics Data System (ADS)

Sellarajan, B.; Saravanan, P.; Ghosh, S. K.; Nagaraja, H. S.; Barshilia, Harish C.; Chowdhury, P.

2018-04-01

The magnetization reversal process of hexagonal ordered CoFe nanodot arrays was investigated as a function of nanodot thickness (td) varying from 10 to 30 nm with fixed diameter. For this purpose, ordered CoFe nanodots with a diameter of 80 ± 4 nm were grown by sputtering using ultra-thin alumina mask. The vortex annihilation and the dynamic spin configuration in the ordered CoFe nanodots were analyzed by means of magnetic hysteresis loops in complement with the micromagnetic simulation studies. A highly pinched hysteresis loop observed at 20 nm thickness suggests the occurrence of vortex state in these nanodots. With increase in dot thickness from 10 to 30 nm, the estimated coercivity values tend to increase from 80 to 175 Oe, indicating irreversible change in the nucleation/annihilation field of vortex state. The measured magnetic properties were then corroborated with the change in the shape of the nanodots from disk to hemisphere through micromagnetic simulation.

Spectral ellipsometry as a method for characterization of nanosized films with ferromagnetic layers

NASA Astrophysics Data System (ADS)

Hashim, H.; Singkh, S. P.; Panina, L. V.; Pudonin, F. A.; Sherstnev, I. A.; Podgornaya, S. V.; Shpetnyi, I. A.; Beklemisheva, A. V.

2017-11-01

Nanosized films with ferromagnetic layers are widely used in nanoelectronics, sensor systems and telecommunications. Their properties may strongly differ from those of bulk materials that is on account of interfaces, intermediate layers and diffusion. In the present work, spectral ellipsometry and magnetooptical methods are adapted for characterization of the optical parameters and magnetization processes in two- and three-layer Cr/NiFe, Al/NiFe and Cr(Al)/Ge/NiFe films onto a sitall substrate for various thicknesses of Cr and Al layers. At a layer thickness below 20 nm, the complex refractive coefficients depend pronouncedly on the thickness. In two-layer films, remagnetization changes weakly over a thickness of the top layer, but the coercive force in three-layer films increases by more than twice upon remagnetization, while increasing the top layer thickness from 4 to 20 nm.

Thickness dependencies of structural and magnetic properties of cubic and tetragonal Heusler alloy bilayer films

NASA Astrophysics Data System (ADS)

Ranjbar, R.; Suzuki, K. Z.; Sugihara, A.; Ando, Y.; Miyazaki, T.; Mizukami, S.

2017-07-01

The thickness dependencies of the structural and magnetic properties for bilayers of cubic Co-based Heusler alloys (CCHAs: Co2FeAl (CFA), Co2FeSi (CFS), Co2MnAl (CMA), and Co2MnSi (CMS)) and D022-MnGa were investigated. Epitaxy of the B2 structure of CCHAs on a MnGa film was achieved; the smallest thickness with the B2 structure was found for 3-nm-thick CMS and CFS. The interfacial exchange coupling (Jex) was antiferromagnetic (AFM) for all of the CCHAs/MnGa bilayers except for unannealed CFA/MnGa samples. A critical thickness (tcrit) at which perpendicular magnetization appears of approximately 4-10 nm for the CMA/MnGa and CMS/MnGa bilayers was observed, whereas this thickness was 1-3 nm for the CFA/MnGa and CFS/MnGa films. The critical thickness for different CCHAs materials is discussed in terms of saturation magnetization (Ms) and the Jex .

Effect of MgO spacer and annealing on interface and magnetic properties of ion beam sputtered NiFe/Mg/MgO/CoFe layer structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhusan Singh, Braj; Chaudhary, Sujeet

2012-09-15

The effect of variation in the thickness of ion assisted ion beam sputtered MgO spacer layer deposited at oxygen ion assisted energy of 50 eV on the extent of magnetic coupling of NiFe and CoFe layers in Si/NiFe(10 nm)/Mg(1 nm)/MgO(2,4,6 nm)/CoFe(10 nm) sandwich structure is investigated. At MgO spacer layer thickness of 4 nm, the separate reversal of magnetizations of the two ferromagnetic layers is observed in the hystresis loop recorded along easy direction. This results in a 3.5 Oe wide plateau like region during magnetization reversal, which became 4.5 Oe at 6 nm thin MgO. At 2 nm thinmore » MgO, the absence of plateau during magnetization reversal region revealed ferromagnetic coupling between the two ferromagnetic layers, which is understood to arise due to the growth of very thin and low density (1.22 gm/cc) MgO spacer layer, indicating the presence of pinholes as revealed by x-ray reflectometry. After vaccum annealing (200 Degree-Sign C/1 h), the plateau region for 4 and 6 nm thin MgO case decreased to 1.5 Oe and 2.0 Oe, respectively, due to enhanced interface roughness/mixing. In addition, an enhancement of the in-plane magnetic anisotropy is also observed.« less

Size-tunable drug-delivery capsules composed of a magnetic nanoshell.

PubMed

Fuchigami, Teruaki; Kitamoto, Yoshitaka; Namiki, Yoshihisa

2012-01-01

Nano-sized FePt capsules with two types of ultrathin shell were fabricated using a template method for use in a nano-scale drug delivery system. One capsule was composed of an inorganic-organic hybrid shell of a water-soluble polymer and FePt nanoparticles, and the other capsule was composed of a network of fused FePt nanoparticles. We demonstrated that FePt nanoparticles selectively accumulated on the polymer molecules adsorbed on the template silica particles, and investigated the morphologies of the particle accumulation by changing the concentration of the polymer solution with which the template particles were treated. Capsular size was reduced from 340 to less than 90 nm by changing the size of the silica template particles, and the shell thickness was controlled by changing the amount of FePt nanoparticles adsorbed on the template particles. The hybrid shell was maintained by the connection of FePt nanoparticles and polymer molecules, and the shell thickness was 10 nm at the maximum. The FePt network shell was fabricated by hydrothermal treatment of the FePt/polymer-modified silica composite particles. The FePt network shell was produced from only the FePt alloy, and the shell thickness was 3 nm. Water-soluble anti-cancer drugs could be loaded into the hollow space of FePt network capsules, and lipid-coated FePt network capsules loaded with anti-cancer drugs showed cellular toxicity. The nano-sized capsular structure and the ultrathin shell suggest applicability as a drug carrier in magnetically guided drug delivery systems.

Size-tunable drug-delivery capsules composed of a magnetic nanoshell

PubMed Central

Fuchigami, Teruaki; Kitamoto, Yoshitaka; Namiki, Yoshihisa

2012-01-01

Nano-sized FePt capsules with two types of ultrathin shell were fabricated using a template method for use in a nano-scale drug delivery system. One capsule was composed of an inorganic-organic hybrid shell of a water-soluble polymer and FePt nanoparticles, and the other capsule was composed of a network of fused FePt nanoparticles. We demonstrated that FePt nanoparticles selectively accumulated on the polymer molecules adsorbed on the template silica particles, and investigated the morphologies of the particle accumulation by changing the concentration of the polymer solution with which the template particles were treated. Capsular size was reduced from 340 to less than 90 nm by changing the size of the silica template particles, and the shell thickness was controlled by changing the amount of FePt nanoparticles adsorbed on the template particles. The hybrid shell was maintained by the connection of FePt nanoparticles and polymer molecules, and the shell thickness was 10 nm at the maximum. The FePt network shell was fabricated by hydrothermal treatment of the FePt/polymer-modified silica composite particles. The FePt network shell was produced from only the FePt alloy, and the shell thickness was 3 nm. Water-soluble anti-cancer drugs could be loaded into the hollow space of FePt network capsules, and lipid-coated FePt network capsules loaded with anti-cancer drugs showed cellular toxicity. The nano-sized capsular structure and the ultrathin shell suggest applicability as a drug carrier in magnetically guided drug delivery systems. PMID:23507895

Synthesis and magnetic properties of the thin film exchange spring system of MnBi/FeCo

NASA Astrophysics Data System (ADS)

Sabet, S.; Hildebrandt, E.; Alff, L.

2017-10-01

Manganese bismuth thin films with a nominal thickness of ∼40 nm were grown at room temperature onto quartz glass substrate in a DC magnetron sputtering unit. In contrast to the usual multilayer approach, the MnBi films were deposited using a single sputtering target with a stoichiometry of Mn55Bi45 (at. %). A subsequent in-situ annealing step was performed in vacuum in order to form the ferromagnetic LTP of MnBi. X-ray diffraction confirmed the formation of a textured LTP MnBi hard phase after annealing at 330 °C. This film shows a maximum saturation magnetization of 530 emu/cm3, high out-of-plane coercivity of 15 kOe induced by unreacted bismuth. The exchange coupling effect was investigated by deposition of a second layer of FeCo with 1 nm and 2 nm thickness onto the LTP MnBi films. The MnBi/FeCo double layer showed as expected higher saturation magnetization with increasing thickness of the FeCo layer while the coercive field remained constant. The fabrication of the MnBi/FeCo double layer for an exchange spring magnet was facilitated by deposition from a single stoichiometric target.

Composition gradient, structure, stress, roughness and magnetic properties of 5-500 nm thin NiFe films obtained by electrodeposition

NASA Astrophysics Data System (ADS)

Gong, Jie; Riemer, Steve; Kautzky, Michael; Tabakovic, Ibro

2016-01-01

The composition gradients of 5-500 nm thin NiFe films on Cu and NiP substrates obtained by electrodeposition in stirred plating solutions at pH 3.0 on 8 in wafers were studied. It was found that the average elemental composition of the NiFe changes during electrodeposition with steep downturns of Fe-content, from 58 to 50 wt% Fe, in composition gradient zone near the substrate interface in the thickness range 5-250 nm depending on the electrode substrate (Cu and NiP). The increase of Fe-content in the composition gradient zone is accompanied by the increase of coercivity, Hc, magnetic flux saturation, Bs, saturation magnetostriction, λs, increase of dimensionless roughness, ρrms, and change of stress, σ. The coercivity (easy and hard axis) follows the Neel's relation Hc=ct-n (t is thickness and c is a constant). The mechanisms related to the change of coercivity of the NiFe films deposited on different substrates (Cu and NiP) are discussed in terms of material properties of these films.

Large exchange bias induced by polycrystalline Mn3Ga antiferromagnetic films with controlled layer thickness

NASA Astrophysics Data System (ADS)

Wu, Haokaifeng; Sudoh, Iori; Xu, Ruihan; Si, Wenshuo; Vaz, C. A. F.; Kim, Jun-young; Vallejo-Fernandez, Gonzalo; Hirohata, Atsufumi

2018-05-01

Polycrystalline Mn3Ga layers with thickness in the range from 6–20 nm were deposited at room temperature by a high target utilisation sputtering. To investigate the onset of exchange-bias, a ferromagnetic Co0.6Fe0.4 layer (3.3–9 nm thick) capped with 5 nm Ta, were subsequently deposited. X-ray diffraction measurements confirm the presence of Mn3Ga (0 0 0 2) and (0 0 0 4) peaks characteristic of the D019 antiferromagnetic structure. The 6 nm thick Mn3Ga film shows the largest exchange bias of 430 Oe at 120 K with a blocking temperature of 225 K. The blocking temperature is found to decrease with increasing Mn3Ga thickness. These results in combination with x-ray reflectivity measurements confirm that the quality of the Mn3Ga/Co0.6Fe0.4 interface controls the exchange bias, with the sharp interface with the 6-nm-thick Mn3Ga inducing the largest exchange bias. The magneto-crystalline anisotropy for 6 nm thick Mn3Ga thin film sample is calculated to be . Such a binary antiferromagnetic Heusler alloy is compatible with the current memory fabrication process and hence has a great potential for antiferromagnetic spintronics.

Hf thickness dependence of spin-orbit torques in Hf/CoFeB/MgO heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ramaswamy, Rajagopalan; Qiu, Xuepeng; Dutta, Tanmay

We have studied the spin-orbit torques in perpendicularly magnetized Hf/CoFeB/MgO system, by systematically varying the thickness of Hf underlayer. We have observed a sign change of effective fields between Hf thicknesses of 1.75 and 2 nm, indicating that competing mechanisms, such as the Rashba and spin Hall effects, contribute to spin-orbit torques in our system. For larger Hf thicknesses (>2 nm), both the components of spin-orbit torques arise predominantly from the bulk spin Hall effect. We have also confirmed these results using spin-orbit torque induced magnetization switching measurements. Our results could be helpful in designing Hf based SOT devices.

Dependence of spin pumping and spin transfer torque upon Ni81Fe19 thickness in Ta/Ag /Ni 81Fe19/Ag/Co 2MnGe /Ag /Ta spin-valve structures

NASA Astrophysics Data System (ADS)

Durrant, C. J.; Shelford, L. R.; Valkass, R. A. J.; Hicken, R. J.; Figueroa, A. I.; Baker, A. A.; van der Laan, G.; Duffy, L. B.; Shafer, P.; Klewe, C.; Arenholz, E.; Cavill, S. A.; Childress, J. R.; Katine, J. A.

2017-10-01

Spin pumping has been studied within Ta / Ag / Ni81Fe19 (0-5 nm) / Ag (6 nm) / Co2MnGe (5 nm) / Ag / Ta large-area spin-valve structures, and the transverse spin current absorption of Ni81Fe19 sink layers of different thicknesses has been explored. In some circumstances, the spin current absorption can be inferred from the modification of the Co2MnGe source layer damping in vector network analyzer ferromagnetic resonance (VNA-FMR) experiments. However, the spin current absorption is more accurately determined from element-specific phase-resolved x-ray ferromagnetic resonance (XFMR) measurements that directly probe the spin transfer torque (STT) acting on the sink layer at the source layer resonance. Comparison with a macrospin model allows the real part of the effective spin mixing conductance to be extracted. We find that spin current absorption in the outer Ta layers has a significant impact, while sink layers with thicknesses of less than 0.6 nm are found to be discontinuous and superparamagnetic at room temperature, and lead to a noticeable increase of the source layer damping. For the thickest 5-nm sink layer, increased spin current absorption is found to coincide with a reduction of the zero frequency FMR linewidth that we attribute to improved interface quality. This study shows that the transverse spin current absorption does not follow a universal dependence upon sink layer thickness but instead the structural quality of the sink layer plays a crucial role.

Increased magnetic damping in ultrathin films of Co2FeAl with perpendicular anisotropy

NASA Astrophysics Data System (ADS)

Takahashi, Y. K.; Miura, Y.; Choi, R.; Ohkubo, T.; Wen, Z. C.; Ishioka, K.; Mandal, R.; Medapalli, R.; Sukegawa, H.; Mitani, S.; Fullerton, E. E.; Hono, K.

2017-06-01

We estimated the magnetic damping constant α of Co2FeAl (CFA) Heusler alloy films of different thicknesses with an MgO capping layer by means of time-resolved magneto-optical Kerr effect and ferromagnetic resonance measurements. CFA films with thicknesses of 1.2 nm and below exhibited perpendicular magnetic anisotropy arising from the presence of the interface with MgO. While α increased gradually with decreasing CFA film thickness down to 1.2 nm, it was increased substantially when the thickness was reduced further to 1.0 nm. Based on the microstructure analyses and first-principles calculations, we attributed the origin of the large α in the ultrathin CFA film primarily to the Al deficiency in the CFA layer, which caused an increase in the density of states and thereby in the scatterings of their spins.

Magnetization reversal process and evaluation of thermal stability factor in Cu doped granular L10 FePt films

NASA Astrophysics Data System (ADS)

Jain, S.; Papusoi, C.; Admana, R.; Yuan, H.; Acharya, R.

2018-05-01

Curie temperature TC distributions and magnetization reversal mechanism in Cu doped L10 FePt granular films is investigated as a function of film thickness in the range of ˜5-12 nm with Cu mol. % varying in the range of 0%-6%. It is shown that Cu doping increases the FePt tetragonality and chemical ordering. For Cu doped FePt-X films, coercivity (HC) exhibits a non-monotonic behavior with increasing film thickness, i.e., HC increases initially up to tcr ˜ 7 nm, and decreases thereafter. We attribute this behavior to the change in magnetization reversal mechanism from coherent to an incoherent (domain-wall driven) mode. While in un-doped films, the domain-walls nucleate at the grain boundaries, in doped films the Cu atoms may act as domain-wall nucleation and pinning sites, isolating magnetic spin clusters of reduced dimensionality with respect to the physical grain size. This is experimentally supported by a much poorer dependence of the AC susceptibility (both, real and imaginary components) on the film thickness above 7 nm than in the case of un-doped films. The formation of magnetic spin clusters inside the grains as a consequence of the reduced coupling between Fe-Fe and Fe-Pt-Fe atoms with increasing Cu doping can explain the experimentally evidenced reduction of both, the film Curie temperature, TC, and intrinsic anisotropy energy density, KC, with increasing Cu doping.

Small-Angle Neutron Scattering Studies of Magnetic Correlation Lengths in Nanoparticle Assemblies

NASA Astrophysics Data System (ADS)

Majetich, Sara

2009-03-01

Small-angle neutron scattering (SANS) measurements of ordered arrays of surfactant-coated magnetic nanoparticle reveal characteristic length scales associated with interparticle and intraparticle magnetic ordering. The high degree of uniformity in the monodisperse nanoparticle size and spacing leads to a pronounced diffraction peak and allows for a straightforward determination of these length scales [1]. There are notable differences in these length scales depending on the particle moment, which depends on the material (Fe, Co, Fe3O4) and diameter, and also on whether the metal particle core is surrounded by an oxide shell. For 8.5 nm particles containing an Fe core and thick Fe3O4 shell, evidence of a spin flop phase is seen in the magnetite shell when a field is applied , but not when the shell thickness is ˜0.5 nm [2]. 8.0 nm particles with an e-Co core and 0.75 nm CoO shell show no exchange bias effects while similar particles with a 2 nm thick shell so significant training effects below 90 K. Polarized SANS studied of 7 nm Fe3O4 nanoparticle assemblies show the ability to resolve the magnetization components in 3D. [4pt] [1] M. Sachan, C. Bonnoit, S. A. Majetich, Y. Ijiri, P. O. Mensah-Bonsu, J. A. Borchers, and J. J. Rhyne, Appl. Phys. Lett. 92, 152503 (2008). [0pt] [2] Yumi Ijiri, Christopher V. Kelly, Julie A. Borchers, James J. Rhyne, Dorothy F. Farrell, Sara A. Majetich, Appl. Phys. Lett. 86, 243102-243104 (2005). [0pt] [3] K. L. Krycka, R. Booth, J. A. Borchers, W. C. Chen, C. Conlon, T. Gentile, C. Hogg, Y. Ijiri, M. Laver, B. B. Maranville, S. A. Majetich, J. Rhyne, and S. M. Watson, Physica B (submitted).

Ultra-thin L1{sub 0}-FePt for perpendicular anisotropy L1{sub 0}-FePt/Ag/[Co/Pd]{sub 30} pseudo spin valves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ho, Pin; Chow, Gan Moog; Chen, Jing-Sheng, E-mail: msecj@nus.edu.sg

2014-05-07

Perpendicular anisotropy L1{sub 0}-FePt/Ag/[Co/Pd]{sub 30} pseudo spin valves (PSVs) with ultra-thin L1{sub 0}-FePt alloy free layer possessing high anisotropy and thermal stability have been fabricated and studied. The thickness of the L1{sub 0}-FePt layer was varied between 2 and 4 nm. The PSV became increasingly decoupled with reduced L1{sub 0}-FePt thickness due to the larger difference between the coercivity of the L1{sub 0}-FePt and [Co/Pd]{sub 30} films. The PSV with an ultra-thin L1{sub 0}-FePt free layer of 2 nm displayed a high K{sub u} of 2.21 × 10{sup 7} ergs/cm{sup 3}, high thermal stability of 84 and a largest giant magnetoresistance of 0.54%.

Magnetoresistance of layered structures with alternating in-plane and perpendicular anisotropies

NASA Astrophysics Data System (ADS)

Stobiecki, F.; Szymański, B.; Luciński, T.; Dubowik, J.; Urbaniak, M.; Röll, K.

2004-11-01

The magnetic properties of (Ni83Fe17/Au/Co/Au) multilayers with different thickness of Au (0.5⩽tAu⩽3 nm) and Co (0.2⩽tCo⩽1.5 nm) layers were characterized. For tAu⩾1.5 nm independent magnetization reversal of Ni-Fe and Co was found. Increase of tCo for (Ni83Fe17-2 nm/Au-3 nm/Co-tCo/Au-3 nm)15 multilayers results in a sequence of transformations in the magnetic properties due to changes in Co microstructure: from superparamagnetic to ferromagnetic clusters at tCo≈0.3 nm, from discontinuous to continuous layers at tCo≈0.6 nm and from perpendicular to in-plane anisotropy at tCo≈1.2 nm.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wan, Li; Thompson, Gregory, E-mail: gthompson@eng.ua.edu

A series of 40–2 nm bilayer spacing Ti/Fe multilayers were sputter-deposited. As the length scale of individual Ti layers equaled to 2 nm, Ti phase transforms from a hexagonal close packed (hcp)-to-body centered cubic (bcc) crystal structures for equal layer thicknesses in Ti/Fe multilayers. Further equal reductions in bilayer spacing to less than 1 nm resulted in an additional transformation from a crystalline to amorphous structure. Atom probe tomography reveals significant intermixing between layers which contributes to the observed phase transformations. Real-time, intrinsic growth stress measurements were also performed to relate the adatom mobility to these phase transformations. For the hcp Ti/bcc Femore » multilayers of equivalent volume fractions, the multilayers undergo an overall tensile stress state to a compressive stress state with decreasing bilayer thickness for the multilayers. When the above phase transformations occurred, a modest reduction in the overall compressive stress of the multilayer was noted. Depending on the Fe thickness, the Ti growth was observed to be a tensile to compressive growth change to a purely compressive growth for thinner bilayer spacing. Fe retained a tensile growth stress regardless of the bilayer spacing studied.« less

Dependence of spin pumping and spin transfer torque upon Ni 81 Fe 19 thickness in Ta / Ag / Ni 81 Fe 19 / Ag / Co 2 MnGe / Ag / Ta spin-valve structures

DOE PAGES

Durrant, C. J.; Shelford, L. R.; Valkass, R. A. J.; ...

2017-10-18

Spin pumping has been studied within Ta / Ag / Ni 81Fe 19 (0–5 nm) / Ag (6 nm) / Co 2MnGe (5 nm) / Ag / Ta large-area spin-valve structures, and the transverse spin current absorption of Ni 81Fe 19 sink layers of different thicknesses has been explored. In some circumstances, the spin current absorption can be inferred from the modification of the Co 2MnGe source layer damping in vector network analyzer ferromagnetic resonance (VNA-FMR) experiments. However, the spin current absorption is more accurately determined from element-specific phase-resolved x-ray ferromagnetic resonance (XFMR) measurements that directly probe the spin transfermore » torque (STT) acting on the sink layer at the source layer resonance. Comparison with a macrospin model allows the real part of the effective spin mixing conductance to be extracted. We find that spin current absorption in the outer Ta layers has a significant impact, while sink layers with thicknesses of less than 0.6 nm are found to be discontinuous and superparamagnetic at room temperature, and lead to a noticeable increase of the source layer damping. For the thickest 5-nm sink layer, increased spin current absorption is found to coincide with a reduction of the zero frequency FMR linewidth that we attribute to improved interface quality. Furthermore, this study shows that the transverse spin current absorption does not follow a universal dependence upon sink layer thickness but instead the structural quality of the sink layer plays a crucial role.« less

Dependence of spin pumping and spin transfer torque upon Ni 81 Fe 19 thickness in Ta / Ag / Ni 81 Fe 19 / Ag / Co 2 MnGe / Ag / Ta spin-valve structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Durrant, C. J.; Shelford, L. R.; Valkass, R. A. J.

Spin pumping has been studied within Ta / Ag / Ni 81Fe 19 (0–5 nm) / Ag (6 nm) / Co 2MnGe (5 nm) / Ag / Ta large-area spin-valve structures, and the transverse spin current absorption of Ni 81Fe 19 sink layers of different thicknesses has been explored. In some circumstances, the spin current absorption can be inferred from the modification of the Co 2MnGe source layer damping in vector network analyzer ferromagnetic resonance (VNA-FMR) experiments. However, the spin current absorption is more accurately determined from element-specific phase-resolved x-ray ferromagnetic resonance (XFMR) measurements that directly probe the spin transfermore » torque (STT) acting on the sink layer at the source layer resonance. Comparison with a macrospin model allows the real part of the effective spin mixing conductance to be extracted. We find that spin current absorption in the outer Ta layers has a significant impact, while sink layers with thicknesses of less than 0.6 nm are found to be discontinuous and superparamagnetic at room temperature, and lead to a noticeable increase of the source layer damping. For the thickest 5-nm sink layer, increased spin current absorption is found to coincide with a reduction of the zero frequency FMR linewidth that we attribute to improved interface quality. Furthermore, this study shows that the transverse spin current absorption does not follow a universal dependence upon sink layer thickness but instead the structural quality of the sink layer plays a crucial role.« less

Dependency of tunneling magneto-resistance on Fe insertion-layer thickness in Co{sub 2}Fe{sub 6}B{sub 2}/MgO-based magnetic tunneling junctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chae, Kyo-Suk; Samsung Electronics Co., Ltd., San #16 Banwol-dong, Hwasung-City, Gyeonggi-Do 445-701; Park, Jea-Gun, E-mail: parkjgL@hanyang.ac.kr

For Co{sub 2}Fe{sub 6}B{sub 2}/MgO-based perpendicular magnetic tunneling junctions spin valves with [Co/Pd]{sub n}-synthetic-antiferromagnetic (SyAF) layers, the tunneling-magneto-resistance (TMR) ratio strongly depends on the nanoscale Fe insertion-layer thickness (t{sub Fe}) between the Co{sub 2}Fe{sub 6}B{sub 2} pinned layer and MgO tunneling barrier. The TMR ratio rapidly increased as t{sub Fe} increased up to 0.4 nm by improving the crystalline linearity of a MgO tunneling barrier and by suppressing the diffusion of Pd atoms from a [Co/Pd]{sub n}-SyAF. However, it abruptly decreased by further increasing t{sub Fe} in transferring interfacial-perpendicular magnetic anisotropy into the IMA characteristic of the Co{sub 2}Fe{sub 6}B{sub 2}more » pinned layer. Thus, the TMR ratio peaked at t{sub Fe} = 0.4 nm: i.e., 120% at 29 Ωμm{sup 2}.« less

Thickness-dependent multiferroic behavior of BiFe0.75Cr0.25O3 films over Pt(111)/Ti/SiO2/Si substrate

NASA Astrophysics Data System (ADS)

William, R. V.; Sivaprakash, P.; Marikani, A.; Reddy, V. Raghavendra; Arumugam, S.

2018-02-01

We present here the experimental results of BiFe0.75Cr0.25O3 (BFCO) thin film deposited by sol-gel spin coating technique directly on Pt(111)/Ti/SiO2/Si substrate at different thicknesses. The crystal structure of BFCO has been investigated using X-ray diffraction which acts as a double perovskite structure with high crystallinity obtained at 400 °C. Further microscopic studies such as scanning electron microscope (SEM) with EDAX, transmission electron microscope (TEM) were also used in identifying the grain size and particle distribution over Pt (111) substrate. Atomic force microscopy (AFM) on the films at a different thickness (- 80 to - 250 nm) reveals that the surface roughness and other amplitude parameters increases with the increase in thickness signifying an increase of grain size with thickness. Increase in grain size and substrate clamping effect between the BFCO film and the substrate induces change in ferroelectric polarization and dielectric properties in relation to thickness effect. Similarly, decrease in magnetization from 9.241 emu/cm3 (- 80 nm) to 5.7791 emu/cm3 (- 250 nm) is attributed to the formation of anti-sites and anti-phase boundaries in the films. In addition, temperature dependence of magnetization reveals ferromagnetic super-exchange interaction of BFCO which is unlike the spin structure of antiferromagnetic BiFeO3.

Analyzing the Boundary Thermal Resistance of Epitaxially Grown Fe2VAl/W Layers by Picosecond Time-Domain Thermoreflectance

NASA Astrophysics Data System (ADS)

Hiroi, Satoshi; Choi, Seongho; Nishino, Shunsuke; Seo, Okkyun; Chen, Yanna; Sakata, Osami; Takeuchi, Tsunehiro

2018-06-01

To gain deep insight into the mechanism of phonon scattering at grain boundaries, we investigated the boundary thermal resistance by using picosecond pulsed-laser time-domain thermoreflectance for epitaxially grown W/Fe2VAl/W films. By using radio-frequency magnetron sputtering, we prepared a series of the three-layer films whose Fe2VAl thickness ranged from 1 nm to 37 nm. The fine oscillation of reflectivity associated with the top W layer clearly appeared in synchrotron x-ray reflectivity measurements, indicating a less obvious mixture of elements at the boundary. The areal heat diffusion time, obtained from the time-domain thermoreflectance signal in the rear-heating front-detection configuration, reduced rapidly in samples whose Fe2VAl layer was thinner than 15 nm. The ˜ 10% mismatch in lattice constant between Fe2VAl and W naturally produced the randomly distributed lattice stress near the boundary, causing an effective increase of boundary thermal resistance in the thick samples, but the stress became homogeneous in the thinner layers, which reduced the scattering probability of phonons.

Magnetoresistance of antiferromagnetic Ir22Mn78-pinned spin filter specular spin valves

NASA Astrophysics Data System (ADS)

Hwang, J. Y.; Kim, M. Y.; Rhee, J. R.; Lee, S. S.; Hwang, D. G.; Yu, S. C.; Lee, H. B.

2004-06-01

Specular spin valves (SSVs) having the spin filter layer (SFL) in contact with the ultrathin free layer of composition Ta3/NiFe2/IrMn7/CoFe1/(NOL1)/CoFe2/Cu1.8/CoFe(tF)/Cu(tSF)/(NOL2)/Ta3.5 (in nm) deposited by magnetron sputtering were studied. For these antiferromagnetic Ir22Mn78-pinned spin filter specular spin valve (SFSSV) films, an optimal magnetoresistance (MR) ratio of 11.9% was obtained when both the free layer thickness (tF) and the SFL thickness (tSF) were 1.5 nm, and a MR ratio higher than 11% was maintained even when tF was reduced to 1.0 nm. This was due to an increase of specular electrons by the nano-oxide layer (NOL) and of current shunting through the SFL. Moreover, the interlayer coupling field (Hint) between the free layer and pinned layer could be explained by considering the RKKY and magnetostatic coupling. The coercivity of the free layer (Hcf) was significantly reduced as compared to traditional spin valves (TSV), and remained as low as 4 Oe when tF varied from 1 to 4 nm. It was found that the SFL made it possible to reduce the free layer thickness and enhance the MR ratio without degrading the soft magnetic property of the free layer.

Synthesis of Nanomaterials by the Pulsed Plasma in Liquid and their Bio-medical Applications

NASA Astrophysics Data System (ADS)

Omurzak, E.; Abdullaeva, Z.; Satyvaldiev, A.; Zhasnakunov, Z.; Kelgenbaeva, Z.; Akai Tegin, R. Adil; Syrgakbek kyzy, D.; Doolotkeldieva, T.; Bobusheva, S.; Mashimo, T.

2018-01-01

Pulsed plasma in liquid is a simple, ecologically friendly, cost-efficient method based on electrical discharge between two metal electrodes submerged into a dielectric liquid. We synthesized carbon-encapsulated Fe (Fe@C) magnetic nanoparticles with low cytotoxicity using pulsed plasma in a liquid. Body-centered cubic Fe core nanoparticles showed good crystalline structures with an average size between 20 and 30 nm were encapsulated in onion-like carbon coatings with a thickness of 2-10 nm. Thermal gravimetric analysis showed a high stability of the as-synthesized samples under thermal treatment and oxidation. Cytotoxicity measurements showed higher cancer cell viability than samples synthesized by different methods. Carbon coated ZnO nanorods with about 20 nm thickness and 150 nm length were synthesized by this method using different surfactant materials such as cetyl trimethylammonium bromide (CTAB) and sodium dodecyl sulphate (SDS). Cu and Ag nanoparticles of about 10 nm in size were also synthesized by the pulsed plasma in aquatic solution of 0.2 % gelatine as surfactant material. These nanoparticles showed high antibacterial activity for Erwinia amylovora and Escherichia coli.

All-optical measurement of interlayer exchange coupling in Fe/Pt/FePt thin films

NASA Astrophysics Data System (ADS)

Berk, C.; Ganss, F.; Jaris, M.; Albrecht, M.; Schmidt, H.

2018-01-01

Time Resolved Magneto Optic Kerr Effect spectroscopy was used to all-optically study the dynamics in exchange coupled Fe(10 nm)/Pt(x = 0-5 nm)/FePt (10 nm) thin films. As the Pt spacer decreases, the effective magnetization of the layers is seen to evolve towards the strong coupling limit where the two films can be described by a single effective magnetization. The coupling begins at x = 1.5 nm and reaches a maximum exchange coupling constant of 2.89 erg/cm2 at x = 0 nm. The films are ferromagnetically coupled at all Pt thicknesses in the exchange coupled regime (x ≤ 1.5 nm). A procedure for extracting the interlayer exchange constant by measuring the magnetic precession frequencies at multiple applied fields and angles is outlined. The dynamics are well reproduced using micromagnetic simulations.

Shell thickness-dependent microwave absorption of core-shell Fe3O4@C composites.

PubMed

Du, Yunchen; Liu, Wenwen; Qiang, Rong; Wang, Ying; Han, Xijiang; Ma, Jun; Xu, Ping

2014-08-13

Core-shell composites, Fe3O4@C, with 500 nm Fe3O4 microspheres as cores have been successfully prepared through in situ polymerization of phenolic resin on the Fe3O4 surface and subsequent high-temperature carbonization. The thickness of carbon shell, from 20 to 70 nm, can be well controlled by modulating the weight ratio of resorcinol and Fe3O4 microspheres. Carbothermic reduction has not been triggered at present conditions, thus the crystalline phase and magnetic property of Fe3O4 micropsheres can be well preserved during the carbonization process. Although carbon shells display amorphous nature, Raman spectra reveal that the presence of Fe3O4 micropsheres can promote their graphitization degree to a certain extent. Coating Fe3O4 microspheres with carbon shells will not only increase the complex permittivity but also improve characteristic impedance, leading to multiple relaxation processes in these composites, thus the microwave absorption properties of these composites are greatly enhanced. Very interestingly, a critical thickness of carbon shells leads to an unusual dielectric behavior of the core-shell structure, which endows these composites with strong reflection loss, especially in the high frequency range. By considering good chemical homogeneity and microwave absorption, we believe the as-fabricated Fe3O4@C composites can be promising candidates as highly effective microwave absorbers.

Studies on high-moment soft magnetic FeCo/Co thin films

NASA Astrophysics Data System (ADS)

Fu, Yu; Yang, Zheng; Matsumoto, Mitsunori; Liu, Xiao-Xi; Morisako, Akimitsu

2006-06-01

The dependences of soft magnetic properties and microstructures of the sputtered FeCo (=Fe65Co35) films on Co underlayer thickness tCo, FeCo thickness tFeCo, substrate temperature Ts and target-substrate spacing dT-S are studied. FeCo single layer generally shows a high coercivity with no obvious magnetic anisotropy. Excellent soft magnetic properties with saturation magnetization μ0Ms of 2.35 T and hard axis coercivity Hch of 0.25 kA/m in FeCo films can be achieved by introducing a Co underlayer. It is shown that sandwiching a Co underlayer causes a change in orientation and reduction in grain size from 70 nm to about 10 nm in the FeCo layer. The magnetic softness can be explained by the Hoffmann's ripple theory due to the effect of grain size. The magnetic anisotropy can be controlled by changing dT-S and a maximum of 14.3 kA/m for anisotropic field Hk is obtained with dT-S=18.0 cm.

Modifying exchange-spring behavior of CoPt/NiFe bilayer by inserting a Pt or Ru spacer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsu, Jen-Hwa, E-mail: jhhsu@phys.ntu.edu.tw; Tsai, C. L.; Lee, C.-M.

2015-05-07

We herein explore the possibility of obtaining tunable tilted magnetic anisotropy in ordered-CoPt (5 nm)/NiFe(t{sub NiFe}) bilayers through modifying their exchange spring behavior by inserting Pt and Ru-spacers. The tuning process of tilt angle magnetization of NiFe-layer was systematically investigated by varying the Pt or Ru thickness (t{sub Pt} or t{sub Ru}) from 0 to 8 nm at different thicknesses of NiFe (t{sub NiFe} = 1.5, 4.0, and 6.0 nm). Polar magneto-optic Kerr effect (p-MOKE) studies reveal that the bilayers grown in absence of spacers exhibit almost a rectangular hysteresis loop. With the insertion of Pt-spacer, the loop becomes more and more tilted as t{submore » Pt} increases; whereas, in the case of Ru-spacer, the nature of the loops is not simply changing in one direction. The estimated SQR{sub ⊥} (= θ{sub r}/θ{sub s}) values from the p-MOKE loops are found to monotonically decrease with increasing t{sub Pt} when t{sub Pt} ≦ 4 nm. In contrast, in the case of Ru-spacer, an oscillatory behavior for the SQR{sub ⊥} values is apparent when t{sub Ru} ≦ 4 nm. As a result, an oscillatory tilted angle of NiFe spin configuration was obtained in the case of Ru-spacer; while a decoupling effect was prominent for the Pt-spacer. The results of present study reveal that the insertion of Pt and Ru-spacers as an appropriate means for realizing tunable tilted magnetic anisotropy in the CoPt/NiFe exchange springs.« less

Large lattice mismatch effects on the epitaxial growth and magnetic properties of FePt films

NASA Astrophysics Data System (ADS)

Deng, Jinyu; Dong, Kaifeng; Yang, Ping; Peng, Yingguo; Ju, Ganping; Hu, Jiangfeng; Chow, Gan Moog; Chen, Jingsheng

2018-01-01

Heteroepitaxial film growth is crucial for magnetic and electronic devices. In this work, we reported the effects of the large lattice mismatch and film thickness on the epitaxial growth and magnetic properties of FePt films on ZrxTi1-xN (0 0 1) intermediate layer. FePt films with different thickness were deposited on ZrTiN intermediate layers with various doping concentration of TiN in ZrN. The increase in doping concentration of TiN caused a decrease in the lattice parameters of ZrTiN intermediate layer. It was found that (0 0 1) epitaxy of FePt 10 nm films was only achieved on ZrTiN intermediate layer when the TiN composition was ≥25 vol%, while (0 0 1) texture of 5 nm films was achieved on ZrTiN intermediate layer with a minimum of 50 vol% TiN composition. The in-plane lattice constants of FePt and Zr0.70Ti0.30N (25 vol% TiN) were 3.870 Å and 4.476 Å, respectively, which resulted in a lattice mismatch as large as 15.7%. These large lattice mismatch heterostructures adopted 7/6 domain matching epitaxy. The magneto-crystalline anisotropy of FePt films was improved with the increase in lattice mismatch. Intrinsic magnetic properties were extrapolated for FePt (30 nm)/Zr0.70Ti0.30N (30 nm)/TaN (30 nm)/MgO, and the Ms(0 K) and K1(0 K) were 1042 emu/cc and 5.10 × 107 erg/cc, respectively, which is comparable to that of bulk L10 FePt.

Preparation and magnetic properties of cylindrical NiFe films and antidot arrays.

PubMed

Sanz, R; Navas, D; Vazquez, M; Hernández-Vélez, M; Ross, C A

2010-10-01

Continuous NiFe (Permalloy) cylindrical films and arrays of cylindrical NiFe antidots 7 nm thick have been prepared by sputtering onto cylindrical aluminum wires and onto wires anodized to form a porous anodic alumina layer. The antidots are arranged in a close-packed pattern determined by the hexagonal pore arrangement in the porous alumina, with period 103 nm and diameter 42 nm. Hysteresis loops were measured at different angles with respect to the cylinder axis and indicate an easy plane normal to the radius of the wire. The antidots enhance the coercivity compared to the continuous cylindrical film.

Innovative soft magnetic multilayers with enhanced in-plane anisotropy and ferromagnetic resonance frequency for integrated RF passive devices

NASA Astrophysics Data System (ADS)

Falub, Claudiu V.; Bless, Martin; Hida, Rachid; MeduÅa, Mojmír; Ammann, Arnold

2018-04-01

We present an innovative, economical method for manufacturing soft magnetic materials that may pave the way for integrated thin film magnetic cores with dramatically improved properties. Soft magnetic multilayered thin films based on the Fe-28%Co20%B (at.%) and Co-4.5%Ta4%Zr (at.%) amorphous alloys are deposited on 8" bare Si and Si/200nm-thermal-SiO2 wafers in an industrial, high-throughput Evatec LLS EVO II magnetron sputtering system. The multilayers consist of stacks of alternating 80-nm-thick ferromagnetic layers and 4-nm-thick Al2O3 dielectric interlayers. Since in our dynamic sputter system the substrate cage rotates continuously, such that the substrates face different targets alternatively, each ferromagnetic sublayer in the multilayer consists of a fine structure comprising alternating CoTaZr and FeCoB nanolayers with very sharp interfaces. We adjust the thickness of these individual nanolayers between 0.5 and 1.5 nm by changing the cage rotation speed and the power of each gun, which is an excellent mode to engineer new, composite ferromagnetic materials. Using X-ray reflectometry (XRR) we reveal that the interfaces between the FeCoB and CoTaZr nanolayers are perfectly smooth with roughness of 0.2-0.3 nm. Kerr magnetometry and B-H looper measurements for the as-deposited samples show that the coercivity of these thin films is very low, 0.2-0.3 Oe, and gradually scales up with the thickness of FeCoB nanolayers, i.e. with the increase of the overall Fe content from 0 % (e.g. CoTaZr-based multilayers) to 52 % (e.g. FeCoB-based multilayers). We explain this trend in the random anisotropy model, based on considerations of grain size growth, as revealed by glancing angle X-ray diffraction (GAXRD), but also because of the increase of magnetostriction with the increase of Fe content as shown by B-H looper measurements performed on strained wafers. The unexpected enhancement of the in-plane anisotropy field from 18.3 Oe and 25.8 Oe for the conventional CoTaZr- and FeCoB-based multilayers, respectively, up to ˜48 Oe for the nanostructured multilayers with FeCoB/CoTaZr nano-bilayers is explained based on interface anisotropy contribution. These novel soft magnetic multilayers, with enhanced in-plane anisotropy, allow operation at higher frequencies, as revealed by broadband (between 100 MHz and 10 GHz) RF measurements that exhibit a classical Landau-Lifschitz-Gilbert (LLG) behavior.

Permanent magnetic properties of NdFe12Nx sputtered films epitaxially grown on V buffer layer

NASA Astrophysics Data System (ADS)

Sato, T.; Ohsuna, T.; Yano, M.; Kato, A.; Kaneko, Y.

2017-08-01

To clarify the magnetic properties of the NdFe12Nx compound, which shows promise as a high-performance permanent magnet material, NdFe12Nx epitaxial films fabricated by using a V underlayer on MgO (100) single-crystalline substrates were investigated. Nd-Fe films deposited on a V underlayer consist of NdFe12 grains, which have a c-axis orientation perpendicular to the film plane, as well as α-Fe and Nd2Fe17 phases. In the Nd-Fe-N film obtained by subsequent nitridation of the Nd-Fe film, NdFe12Nx grains grew as the dominant phase, and the volume fractions of α-Fe phases dropped below 5%. A Nd-Fe-N film with a thickness of 50 nm exhibits a saturation magnetization (Ms) of 1.7 T, an anisotropy field (HA) of ˜60 kOe, a magnetocrystalline anisotropy energy (K1) of ˜4.1 MJ/m3, and a coercivity (Hc) of 1.7 kOe. The Hc of a Nd-Fe-N film with a thickness of 25 nm is 4.3 kOe. These results indicate that NdFe12Nx compounds have a superior Ms compared to Nd-Fe-B magnets, while the enhancement in Hc is indispensable.

STRESS-INDUCED ASYMMETRIC MAGNETOIMPEDANCE EFFECT IN Ni80Fe20/Cu COMPOSITE WIRES

NASA Astrophysics Data System (ADS)

Lv, Wenxing; Li, Xin; Xie, Wenhui; Zhao, Qiang; Zhao, Zhenjie

The magnetoimpedance effect of Ni80Fe20/Cu composited wires was experimentally investigated by varying the Ni80Fe20 coating thickness. An asymmetric MI behavior with a tunable linear region around zero magnetic field by altering the thickness of Ni80Fe20 layer was demonstrated. And the MI behavior was governed by the different anisotropy induced by the residual local stress in the multi-layer region. In addition, our investigation also suggested that the interactions between interface phase and outer phase of coating layer decreased with thickness, resulting in the domination of the asymmetric MI characteristic. For thickness of 485nm, the sensitivity was up to 225%/Oe from -2 Oe to 2 Oe, providing a promising candidate for linear sensor application.

Magnetic characteristics and nanostructures of FePt granular films with GeO2 segregant

NASA Astrophysics Data System (ADS)

Ono, Takuya; Moriya, Tomohiro; Hatayama, Masatoshi; Tsumura, Kaoru; Kikuchi, Nobuaki; Okamoto, Satoshi; Kitakami, Osamu; Shimatsu, Takehito

2017-01-01

To realize a granular film composed of L10-FePt grains with high uniaxial magnetic anisotropy energy, Ku, and segregants for energy-assisted magnetic recording, a FePt-GeO2/FePt-C stacked film was investigated in the engineering process. The FePt-GeO2/FePt-C stacked film fabricated at a substrate temperature of 450 °C realized uniaxial magnetic anisotropy, Kugrain , of about 2.5 × 107 erg/cm3, which is normalized by the volume fraction of FePt grains, and a granular structure with an averaged grain size of 7.7 nm. As the thickness of the FePt-GeO2 upper layer was increased to 9 nm, the Ku values were almost constant. That result differs absolutely from the thickness dependences of the other oxide segregant materials such as SiO2 and TiO2. Such differences on the oxide segregant are attributed to their chemical bond. The strong covalent bond of GeO2 is expected to result in high Ku of the FePt-GeO2/FePt-C stacked films.

The role of the non-magnetic material in spin pumping and magnetization dynamics in NiFe and CoFeB multilayer systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruiz-Calaforra, A., E-mail: ruiz@physik.uni-kl.de; Brächer, T.; Lauer, V.

2015-04-28

We present a study of the effective magnetization M{sub eff} and the effective damping parameter α{sub eff} by means of ferromagnetic resonance spectroscopy on the ferromagnetic (FM) materials Ni{sub 81}Fe{sub 19} (NiFe) and Co{sub 40}Fe{sub 40}B{sub 20} (CoFeB) in FM/Pt, FM/NM, and FM/NM/Pt systems with the non-magnetic (NM) materials Ru, Cr, Al, and MgO. Moreover, for NiFe layer systems, the influence of interface effects is studied by way of thickness dependent measurements of M{sub eff} and α{sub eff}. Additionally, spin pumping in NiFe/NM/Pt is investigated by means of inverse spin Hall effect (ISHE) measurements. We observe a large dependence ofmore » M{sub eff} and α{sub eff} of the NiFe films on the adjacent NM layer. While Cr and Al do not induce a large change in the magnetic properties, Ru, Pt, and MgO affect M{sub eff} and α{sub eff} in different degrees. In particular, NiFe/Ru and NiFe/Ru/Pt systems show a large perpendicular surface anisotropy and a significant enhancement of the damping. In contrast, the magnetic properties of CoFeB films do not have a large influence of the NM adjacent material and only CoFeB/Pt systems present an enhancement of α{sub eff}. However, this enhancement is much more pronounced in NiFe/Pt. By the introduction of the NM spacer material, this enhancement is reduced. Furthermore, a difference in symmetry between NiFe/NM/Pt and NiFe/NM systems in the output voltage signal from the ISHE measurements reveals the presence of spin pumping into the Pt layer in all-metallic NiFe/NM/Pt and NiFe/Pt systems.« less

Infrared extinction and microwave absorption properties of hybrid Fe3O4@SiO2@Ag nanospheres synthesized via a facile seed-mediated growth route.

PubMed

Chen, Yongpeng; Li, Shichuan; Wei, Xuebin; Tang, Runze; Zhou, Zunning

2018-06-21

Fe3O4@SiO2@Ag ternary hybrid nanoparticles were synthesized via a facile seed-mediated growth route. X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) measurements were used to characterize the as-prepared product. The results indicated that the nanoparticles exhibited excellent magnetic properties and an extremely dense structure with Ag layer thicknesses of 30 nm, 40 nm, and 50 nm. Furthermore, the microwave shielding effectiveness exceeded 20 dB over almost the entire frequency range (2-18 GHz), and the effectiveness obviously improved as the thickness of the Ag layer increased. In addition, the IR extinction coefficient of the nanoparticles was calculated by a finite-difference time-domain (FDTD) method, which showed that the nanoparticles can inherit the extinction performance of pure silver when the Ag shell thickness was 30 nm. Specifically, after assembling into chains, the peak position of the IR extinction curves displayed a significant redshift and an intensity increase as the number of nanoparticles increased in the chain, which dramatically promoted the IR extinction capability. As a result, the Fe3O4@SiO2@Ag nanoparticles are expected to be used as a new multispectral interference material. © 2018 IOP Publishing Ltd.

Perpendicular magnetic anisotropy and magnetization dynamics in oxidized CoFeAl films

PubMed Central

Wu, Di; Zhang, Zhe; Li, Le; Zhang, Zongzhi; Zhao, H. B.; Wang, J.; Ma, B.; Jin, Q. Y.

2015-01-01

Half-metallic Co-based full-Heusler alloys with perpendicular magnetic anisotropy (PMA), such as Co2FeAl in contact with MgO, are receiving increased attention recently due to its full spin polarization for high density memory applications. However, the PMA induced by MgO interface can only be realized for very thin magnetic layers (usually below 1.3 nm), which would have strong adverse effects on the material properties of spin polarization, Gilbert damping parameter, and magnetic stability. In order to solve this issue, we fabricated oxidized Co50Fe25Al25 (CFAO) films with proper thicknesses without employing the MgO layer. The samples show controllable PMA by tuning the oxygen pressure (PO2) and CFAO thickness (tCFAO), large perpendicular anisotropy field of ~8.0 kOe can be achieved at PO2 = 12% for the sample of tCFAO = 2.1 nm or at PO2 = 7% for tCFAO = 2.8 nm. The loss of PMA at thick tCFAO or high PO2 results mainly from the formation of large amount of CoFe oxides, which are superparamagnetic at room temperature but become hard magnetic at low temperatures. The magnetic CFAO films, with strong PMA in a relatively wide thickness range and small intrinsic damping parameter below 0.028, would find great applications in developing advanced spintronic devices. PMID:26190066

Facile deposition of gold nanoparticles on core-shell Fe3O4@polydopamine as recyclable nanocatalyst

NASA Astrophysics Data System (ADS)

Zhao, Yan; Yeh, Yaowen; Liu, Rui; You, Jinmao; Qu, Fengli

2015-07-01

A simple and green method for the controllable synthesis of core-shell Fe3O4 polydopamine nanoparticles (Fe3O4@PDA NPs) with tunable shell thickness and their application as a recyclable nanocatalyst support is presented. Magnetite Fe3O4 NPs formed in a one-pot process by the hydrothermal approach with a diameter of ˜240 nm were coated with a polydopamine shell layer with a tunable thickness of 15-45 nm. The facile deposition of Au NPs atop Fe3O4@PDA NPs was achieved by utilizing PDA as both the reducing agent and the coupling agent. The satellite nanocatalysts exhibited high catalytic performance for the reduction of p-nitrophenol. Furthermore, the recovery and reuse of the catalyst was demonstrated 8 times without detectible loss in activity. The synergistic combination of unique features of PDA and magnetic nanoparticles establishes these core-shell NPs as a versatile platform for potential applications.

First principles calculation for Gilbert damping constants in ferromagnetic/non-magnetic junctions

NASA Astrophysics Data System (ADS)

Hiramatsu, R.; Miura, D.; Sakuma, A.

2018-05-01

We evaluated an intrinsic α in ferromagnetic (FM)/non-magnetic (NM) junctions from first principles (FM = Co, Fe, and Ni and NM = Cu, Pd, and Pt) to investigate the effects of the inserted NM layer. α is calculated by liner muffin-tin orbital methods based on the torque-correlation model. We confirmed that Gilbert damping is enhanced and saturated as NM thickness increases, and that the enhancement is greater in NM materials having a stronger spin-orbital interaction. By contrast, the calculated FM thickness dependences of α show that Gilbert damping tends to decrease and be saturated as the FM thickness increases. Under the torque-correlation model, the dependences of α on FM and NM thickness can be explained by considering the electronic structure of the total system, including junction interfaces, which exhibit similar behaviors derived by spin pumping theory.

Nanoscale Inhomogeneous Superconductivity in Fe(Te1-xSex) Probed by Nanostructure Transport.

PubMed

Yue, Chunlei; Hu, Jin; Liu, Xue; Sanchez, Ana M; Mao, Zhiqiang; Wei, Jiang

2016-01-26

Among iron-based superconductors, the layered iron chalcogenide Fe(Te1-xSex) is structurally the simplest and has attracted considerable attention. It has been speculated from bulk studies that nanoscale inhomogeneous superconductivity may inherently exist in this system. However, this has not been directly observed from nanoscale transport measurements. In this work, through simple micromechanical exfoliation and high-precision low-energy ion milling thinning, we prepared Fe(Te0.5Se0.5) nanoflakes with various thicknesses and systematically studied the correlation between the thickness and superconducting phase transition. Our result revealed a systematic thickness-dependent evolution of superconducting transition. When the thickness of the Fe(Te0.5Se0.5) flake is reduced to less than the characteristic inhomogeneity length (around 12 nm), both the superconducting current path and the metallicity of the normal state in Fe(Te0.5Se0.5) atomic sheets are suppressed. This observation provides the first transport evidence for the nanoscale inhomogeneous nature of superconductivity in Fe(Te1-xSex).

The Fabrication and High-Efficiency Electromagnetic Wave Absorption Performance of CoFe/C Core-Shell Structured Nanocomposites

NASA Astrophysics Data System (ADS)

Wan, Gengping; Luo, Yongming; Wu, Lihong; Wang, Guizhen

2018-03-01

CoFe/C core-shell structured nanocomposites (CoFe@C) have been fabricated through the thermal decomposition of acetylene with CoFe2O4 as precursor. The as-prepared CoFe@C was characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, and thermogravimetric analysis. The results demonstrate that the carbon shell in CoFe@C has a poor crystallization with a thickness about 5-30 nm and a content approximately 48.5 wt.%. Due to a good combination between intrinsic magnetic properties and high-electrical conductivity, the CoFe@C exhibits not only excellent absorption intensity but also wide frequency bandwidth. The minimum RL value of CoFe@C can reach - 44 dB at a thickness of 4.0 mm, and RL values below - 10 dB is up to 4.3 GHz at a thickness of 2.5 mm. The present CoFe@C may be a potential candidate for microwave absorption application.

Transport properties of ultrathin BaFe1.84Co0.16As2 superconducting nanowires

NASA Astrophysics Data System (ADS)

Yuan, Pusheng; Xu, Zhongtang; Li, Chen; Quan, Baogang; Li, Junjie; Gu, Changzhi; Ma, Yanwei

2018-07-01

Superconducting nanowire single-photon detectors (SNSPDs) have an absolute advantage over other types of single-photon detectors, except for the low operating temperature. Therefore, much effort has been devoted to finding high-temperature superconducting materials that are suitable for preparing SNSPDs. Copper-based and MgB2 ultrathin superconducting nanowires have already been reported. However, the transport properties of iron-based ultrathin superconducting nanowires have not been studied. In this work, a 10 nm thick × 200 nm wide × 30 μm long high-quality superconducting nanowire was fabricated from ultrathin BaFe1.84Co0.16As2 films by a lift-off process. The precursor BaFe1.84Co0.16As2 film with a thickness of 10 nm and root-mean-square roughness of 1 nm was grown on CaF2 substrates by pulsed laser deposition. The nanowire shows a high superconducting critical temperature {T}{{c}}{{zero}} = 20 K with a narrow transition width of ΔT = 2.5 K and exhibits a high critical current density J c of 1.8 × 107 A cm-2 at 10 K. These results of ultrathin BaFe1.84Co0.16As2 nanowire will attract interest in electronic applications, including SNSPDs.

Reduction of conductance mismatch in Fe/Al2O3/MoS2 system by tunneling-barrier thickness control

NASA Astrophysics Data System (ADS)

Hayakawa, Naoki; Muneta, Iriya; Ohashi, Takumi; Matsuura, Kentaro; Shimizu, Jun’ichi; Kakushima, Kuniyuki; Tsutsui, Kazuo; Wakabayashi, Hitoshi

2018-04-01

Molybdenum disulfide (MoS2) among two-dimensional semiconductor films is promising for spintronic devices because it has a longer spin-relaxation time with contrasting spin splitting than silicon. However, it is difficult to fabricate integrated circuits by the widely used exfoliation method. Here, we investigate the contact characteristics in the Fe/Al2O3/sputtered-MoS2 system with various thicknesses of the Al2O3 film. Current density increases with increasing thickness up to 2.5 nm because of both thermally-assisted and direct tunneling currents. On the other hand, it decreases with increasing thickness over 2.5 nm limited by direct tunneling currents. These results suggest that the Schottky barrier width can be controlled by changing thicknesses of the Al2O3 film, as supported by calculations. The reduction of conductance mismatch with this technique can lead to highly efficient spin injection from iron into the MoS2 film.

Collective magnetic response of inhomogeneous nanoisland FeNi films around the percolation transition

NASA Astrophysics Data System (ADS)

Kovaleva, Natalia N.; Bagdinov, Anton V.; Stupakov, Alexandr; Dejneka, Alexandr; Demikhov, Evgenii I.; Gorbatsevich, Alexandr A.; Pudonin, Fedor A.; Kugel, Kliment I.; Kusmartsev, Feodor V.

2018-04-01

By using superconducting quantum interference device (SQUID) magnetometry, we investigated anisotropic high-field ( H ≲ 7T) low-temperature (10 K) magnetization response of inhomogeneous nanoisland FeNi films grown by rf sputtering deposition on Sitall (TiO2) glass substrates. In the grown FeNi films, the FeNi layer nominal thickness varied from 0.6 to 2.5 nm, across the percolation transition at the d c ≃ 1.8 nm. We discovered that, beyond conventional spin-magnetism of Fe21Ni79 permalloy, the extracted out-of-plane magnetization response of the nanoisland FeNi films is not saturated in the range of investigated magnetic fields and exhibits paramagnetic-like behavior. We found that the anomalous out-of-plane magnetization response exhibits an escalating slope with increase in the nominal film thickness from 0.6 to 1.1 nm, however, it decreases with further increase in the film thickness, and then practically vanishes on approaching the FeNi film percolation threshold. At the same time, the in-plane response demonstrates saturation behavior above 1.5-2T, competing with anomalously large diamagnetic-like response, which becomes pronounced at high magnetic fields. It is possible that the supported-metal interaction leads to the creation of a thin charge-transfer (CT) layer and a Schottky barrier at the FeNi film/Sitall (TiO2) interface. Then, in the system with nanoscale circular domains, the observed anomalous paramagnetic-like magnetization response can be associated with a large orbital moment of the localized electrons. In addition, the inhomogeneous nanoisland FeNi films can possess spontaneous ordering of toroidal moments, which can be either of orbital or spin origin. The system with toroidal inhomogeneity can lead to anomalously strong diamagnetic-like response. The observed magnetization response is determined by the interplay between the paramagnetic- and diamagnetic-like contributions.

Intrinsic superconducting transport properties of ultra-thin Fe1+ y Te0.6Se0.4 microbridges

NASA Astrophysics Data System (ADS)

Sun, HanCong; Lv, YangYang; Lu, DaChuan; Yang, ZhiBao; Zhou, XianJing; Hao, LuYao; Xing, XiangZhuo; Zou, Wei; Li, Jun; Shi, ZhiXiang; Xu, WeiWei; Wang, HuaBing; Wu, PeiHeng

2017-11-01

We investigated the superconducting properties of Fe1+ y Te0.6Se0.4 single-crystalline microbridges with a width of 4 μm and thicknesses ranging from 20.8 to 136.2 nm. The temperature-dependent in-plane resistance of the bridges exhibited a type of metal-insulator transition in the normal state. The critical current density ( J c) of the microbridge with a thickness of 136.2 nm was 82.3 kA/cm2 at 3K and reached 105 kA/cm2 after extrapolation to T = 0 K. The current versus voltage characteristics of the microbridges showed a Josephson-like behavior with an obvious hysteresis. These results demonstrate the potential application of ultra-thin Fe-based microbridges in superconducting electronic devices such as bolometric detectors.

Spin-valve Josephson junctions for cryogenic memory

NASA Astrophysics Data System (ADS)

Niedzielski, Bethany M.; Bertus, T. J.; Glick, Joseph A.; Loloee, R.; Pratt, W. P.; Birge, Norman O.

2018-01-01

Josephson junctions containing two ferromagnetic layers are being considered for use in cryogenic memory. Our group recently demonstrated that the ground-state phase difference across such a junction with carefully chosen layer thicknesses could be controllably toggled between zero and π by switching the relative magnetization directions of the two layers between the antiparallel and parallel configurations. However, several technological issues must be addressed before those junctions can be used in a large-scale memory. Many of these issues can be more easily studied in single junctions, rather than in the superconducting quantum interference device (SQUID) used for phase-sensitive measurements. In this work, we report a comprehensive study of spin-valve junctions containing a Ni layer with a fixed thickness of 2.0 nm and a NiFe layer of thickness varying between 1.1 and 1.8 nm in steps of 0.1 nm. We extract the field shift of the Fraunhofer patterns and the critical currents of the junctions in the parallel and antiparallel magnetic states, as well as the switching fields of both magnetic layers. We also report a partial study of similar junctions containing a slightly thinner Ni layer of 1.6 nm and the same range of NiFe thicknesses. These results represent the first step toward mapping out a "phase diagram" for phase-controllable spin-valve Josephson junctions as a function of the two magnetic layer thicknesses.

Magnetic glass-film based on single-nanosize 𝜺 -Fe2O3 nanoparticles

NASA Astrophysics Data System (ADS)

Yoshikiyo, Marie; Namai, Asuka; Nakagawa, Kosuke; Ohkoshi, Shin-ichi

2017-05-01

We report a magnetic thin film of single-nanosize ɛ-Fe2O3 in SiO2 matrix. The glass-film was prepared by sintering a silica coated iron oxide hydroxide on a quartz substrate in air. The glass-film consists of ɛ-Fe2O3 of 8.8 nm size, and its thickness was 570 nm (0.57 μm) with a roughness of 10 nm (0.01 μm). UV-vis spectrum showed that the glass-film has small absorbance of 0.043 at 500 nm. The magneto-optical effect was investigated, and Faraday ellipticity showed a magnetic hysteresis loop with a coercive field of 3.0 ± 0.2 kOe. Furthermore, single-nanosize ɛ-Fe2O3 without silica was prepared as a reference sample, and ferroelectricity was observed. Therefore, the present thin glass-film consists of single-nanosize ferroelectric-ferromagnetic nanoparticles.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zohar, S.; Choi, Y.; Love, D. M.

We use X-ray Excited Luminescence Microscopy to investigate the elemental and layer resolved magnetic reversal in an interlayer exchange coupled (IEC) epitaxial Fe/Cr wedge/Co heterostructure. The transition from strongly coupled parallel Co-Fe reversal for Cr thickness t(Cr) < 0.34 nm to weakly coupled layer independent reversal for t(Cr) > 1.5 nm is punctuated at 0.34 < t(Cr) < 1.5 nm by a combination of IEC guided domain wall motion and stationary zig zag domain walls. Domain walls nucleated at switching field minima are guided by IEC spatial gradients and collapse at switching field maxima.

L10 FePtCu bit patterned media

NASA Astrophysics Data System (ADS)

Brombacher, C.; Grobis, M.; Lee, J.; Fidler, J.; Eriksson, T.; Werner, T.; Hellwig, O.; Albrecht, M.

2012-01-01

Chemically ordered 5 nm-thick L10 FePtCu films with strong perpendicular magnetic anisotropy were post-patterned by nanoimprint lithography into a dot array over a 3 mm-wide circumferential band on a 3 inch Si wafer. The dots with a diameter of 30 nm and a center-to-center pitch of 60 nm appear as single domain and reveal an enhanced switching field as compared to the continuous film. We demonstrate successful recording on a single track using shingled writing with a conventional hard disk drive write/read head.

Co7Fe3 and Co7Fe3@SiO2 Nanospheres with Tunable Diameters for High-Performance Electromagnetic Wave Absorption.

PubMed

Chen, Na; Jiang, Jian-Tang; Xu, Cheng-Yan; Yuan, Yong; Gong, Yuan-Xun; Zhen, Liang

2017-07-05

Ferromagnetic metal/alloy nanoparticles have attracted extensive interest for electromagnetic wave-absorbing applications. However, ferromagnetic nanoparticles are prone to oxidization and producing eddy currents, leading to the deterioration of electromagnetic properties. In this work, a simple and scalable liquid-phase reduction method was employed to synthesize uniform Co 7 Fe 3 nanospheres with diameters ranging from 350 to 650 nm for high-performance microwave absorption application. Co 7 Fe 3 @SiO 2 core-shell nanospheres with SiO 2 shell thicknesses of 30 nm were then fabricated via a modified Stöber method. When tested as microwave absorbers, bare Co 7 Fe 3 nanospheres with a diameter of 350 nm have a maximum reflection loss (RL) of 78.4 dB and an effective absorption with RL > 10 dB from 10 to 16.7 GHz at a small thickness of 1.59 mm. Co 7 Fe 3 @SiO 2 nanospheres showed a significantly enhanced microwave absorption capability for an effective absorption bandwidth and a shift toward a lower frequency, which is ascribed to the protection of the SiO 2 shell from direct contact among Co 7 Fe 3 nanospheres, as well as improved crystallinity and decreased defects upon annealing. This work illustrates a simple and effective method to fabricate Co 7 Fe 3 and Co 7 Fe 3 @SiO 2 nanospheres as promising microwave absorbers, and the design concept can also be extended to other ferromagnetic alloy particles.

Dependency of anti-ferro-magnetic coupling strength on Ru spacer thickness of [Co/Pd]{sub n}-synthetic-anti-ferro-magnetic layer in perpendicular magnetic-tunnel-junctions fabricated on 12-inch TiN electrode wafer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chae, Kyo-Suk; Samsung Electronics Co., Ltd., San #16 Banwol-dong, Hwasung-City, Gyeonggi-Do 445-701; Shim, Tae-Hun

We investigated the Ru spacer-thickness effect on the anti-ferro-magnetic coupling strength (J{sub ex}) of a [Co/Pd]{sub n}-synthetic-anti-ferro-magnetic layer fabricated with Co{sub 2}Fe{sub 6}B{sub 2}/MgO based perpendicular-magnetic-tunneling-junction spin-valves on 12-in. TiN electrode wafers. J{sub ex} peaked at a certain Ru spacer-thickness: specifically, a J{sub ex} of 0.78 erg/cm{sup 2} at 0.6 nm, satisfying the J{sub ex} criteria for realizing the mass production of terra-bit-level perpendicular-spin-transfer-torque magnetic-random-access-memory. Otherwise, J{sub ex} rapidly degraded when the Ru spacer-thickness was less than or higher than 0.6 nm. As a result, the allowable Ru thickness variation should be controlled less than 0.12 nm to satisfy the J{sub ex} criteria. However,more » the Ru spacer-thickness did not influence the tunneling-magneto-resistance (TMR) and resistance-area (RA) of the perpendicular-magnetic-tunneling-junction (p-MTJ) spin-valves since the Ru spacer in the synthetic-anti-ferro-magnetic layer mainly affects the anti-ferro-magnetic coupling efficiency rather than the crystalline linearity of the Co{sub 2}Fe{sub 6}B{sub 2} free layer/MgO tunneling barrier/Co{sub 2}Fe{sub 6}B{sub 2} pinned layer, although Co{sub 2}Fe{sub 6}B{sub 2}/MgO based p-MTJ spin-valves ex-situ annealed at 275 °C achieved a TMR of ∼70% at a RA of ∼20 Ω μm{sup 2}.« less

Characteristics of a thick film ethanol gas sensor made of mechanically treated LaFeO3 powder

NASA Astrophysics Data System (ADS)

Suhendi, Endi; Witra, Hasanah, Lilik; Syarif, Dani Gustaman

2017-05-01

In this work, fabrication of LaFeO3 thick film ceramics for ethanol gas sensor made of mechanically treated (milling) powder was studied. The thick films were fabricated using screen printing technique from LaFeO3 powder treated by HEM (High Energy Milling). The films were baked at 800°C for one hour and analyzed using XRD and SEM. Sensitivity of the films was studied by measuring resistance of them at various temperatures in a chamber containing air with and without ethanol gas. Data of XRD showed that the thick film crystalizes in orthorombic structure with space group of Pn*a. SEM data showed that the films consisted of small grains with grain size of about 225 nm. According to the electrical data, the LaFeO3 thick films that produced in this work could be applied as ethanol gas with operating temperature of about 275°C.

On gate stack scalability of double-gate negative-capacitance FET with ferroelectric HfO2 for energy efficient sub-0.2 V operation

NASA Astrophysics Data System (ADS)

Jang, Kyungmin; Saraya, Takuya; Kobayashi, Masaharu; Hiramoto, Toshiro

2018-02-01

We have investigated the gate stack scalability and energy efficiency of double-gate negative-capacitance FET (DGNCFET) with a CMOS-compatible ferroelectric HfO2 (FE:HfO2). Analytic model-based simulation is conducted to investigate the impacts of ferroelectric characteristic of FE:HfO2 and gate stack thickness on the I on/I off ratio of DGNCFET. DGNCFET has wider design window for the gate stack where higher I on/I off ratio can be achieved than DG classical MOSFET. Under a process-induced constraint with sub-10 nm gate length (L g), FE:HfO2-based DGNCFET still has a design point for high I on/I off ratio. With an optimized gate stack thickness for sub-10 nm L g, FE:HfO2-based DGNCFET has 2.5× higher energy efficiency than DG classical MOSFET even at ultralow operation voltage of sub-0.2 V.

Development of flexible Ni80Fe20 magnetic nano-thin films

NASA Astrophysics Data System (ADS)

Vopson, M. M.; Naylor, J.; Saengow, T.; Rogers, E. G.; Lepadatu, S.; Fetisov, Y. K.

2017-11-01

Flexible magnetic Ni80Fe20 thin films with excellent adhesion, mechanical and magnetic properties have been fabricated using magnetron plasma deposition. We demonstrate that flexible Ni80Fe20 thin films maintain their non-flexible magnetic properties when the films are over 60 nm thick. However, when their thickness is reduced, the flexible thin films display significant increase in their magnetic coercive field compared to identical films coated on a solid Silicon substrate. For a 15 nm flexible Ni80Fe20 film coated onto 110 μm Polyvinylidene fluoride polymer substrate, we achieved a remarkable 355% increase in the magnetic coercive field relative to the same film deposited onto a Si substrate. Experimental evidence, backed by micro-magnetic modelling, indicates that the increase in the coercive fields is related to the larger roughness texture of the flexible substrates. This effect essentially transforms soft Ni80Fe20 permalloy thin films into medium/hard magnetic films allowing not only mechanical flexibility of the structure, but also fine tuning of their magnetic properties.

Size effect in the spin glass magnetization of thin AuFe films as studied by polarized neutron reflectometry.

PubMed

Saoudi, M; Fritzsche, H; Nieuwenhuys, G J; Hesselberth, M B S

2008-02-08

We used polarized neutron reflectometry to determine the temperature dependence of the magnetization of thin AuFe films with 3% Fe concentration. We performed the measurements in a large magnetic field of 6 T in a temperature range from 295 to 2 K. For the films in the thickness range from 500 to 20 nm we observed a Brillouin-type behavior from 295 K down to 50 K and a constant magnetization of about 0.9 micro(B) per Fe atom below 30 K. However, for the 10 nm thick film we observed a Brillouin-type behavior down to 20 K and a constant magnetization of about 1.3 micro(B) per Fe atom below 20 K. These experiments are the first to show a finite-size effect in the magnetization of single spin-glass films in large magnetic fields. Furthermore, the ability to measure the deviation from the paramagnetic behavior enables us to prove the existence of the spin-glass state where other methods relying on a cusp-type behavior fail.

Annealing and thickness effects on magnetic properties of Co2FeAl alloy films

NASA Astrophysics Data System (ADS)

Wang, Ke; Xu, Zhan; Ling, Fujin; Wang, Yahong; Dong, Shuo

2018-03-01

Co2FeAl (CFA) films in a wide thickness range between 2 and 100 nm are sputtered at room temperature. Perpendicular magnetic anisotropy (PMA) is achieved in the annealed structure of Pd/CFA/MgO with CFA thickness ranging between 2.3 and 4.9 nm. PMA as high as 2 × 106 erg/cm3 is demonstrated in the structures annealed in the temperature range between 300 and 350 °C. Positive contributions to the PMA made by the interfaces of Pd/CFA and CFA/MgO are identified. For the as-deposited structure of MgO/CFA/Ta with thick CFA alloy up to 5 nm or above a high effective saturation magnetization of 983.9 ± 30.1 emu/cc is derived from the fitting and an in-plane uniaxial magnetic anisotropy of 104 erg/cm3 in magnitude is revealed by angular dependent magnetic measurements. In addition to the increase in saturation magnetization, a fourfold cubic magnetic anisotropy is found to develop with annealing, in line with the improvement of the crystalline structure confirmed by X-ray diffraction measurements. Out results provide some useful information for the design of the CFA-based magnetoelectronic devices.

The influence of interface on spin pumping effect in Ni{sub 80}Fe{sub 20} /Tb bilayer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yue, Jinjin; Jiang, Sheng; Zhang, Dong

2016-05-15

Focusing on the interface effect of the Ni{sub 80}Fe{sub 20} (Py)/terbium (Tb) bilayer, the influence of interface on the magnetization dynamic damping is investigated systematically. Two series of Py (12 nm)/Tb (d nm) films with and without copper (Cu) (1 nm) interlayer are deposited on silicon (Si) substrates by DC magnetron sputtering at room temperature. From vibrating sample magnetometer (VSM) measurements, the saturation magnetization (M{sub s}) decreases with increasing Tb thickness in Py/Tb bilayer while the decrease of M{sub s} is suppressed efficiently by inserting a Cu layer with even 1 nm of thickness. From the frequency dependence of ferromagneticmore » resonance (FMR) linewidth, we can obtain the Gilbert damping coefficient (α), α is found to exhibit an extreme enhancement in comparison to the single Py layer and shows an increasing trend with increasing Tb thickness. By inserting the Cu layer, α decreases significantly. From theoretical fitting, the spin diffusion length (λ{sub SD}) and spin mixing conductance (g{sup ↑↓}) are determined. It shows that the interface structure influences the spin mixing conductance but not the spin diffusion length.« less

Exchange coupling and microwave absorption in core/shell-structured hard/soft ferrite-based CoFe2O4/NiFe2O4 nanocapsules

NASA Astrophysics Data System (ADS)

Feng, Chao; Liu, Xianguo; Or, Siu Wing; Ho, S. L.

2017-05-01

Core/shell-structured, hard/soft spinel-ferrite-based CoFe2O4/NiFe2O4 (CFO/NFO) nanocapsules with an average diameter of 17 nm are synthesized by a facile two-step hydrothermal process using CFO cores of ˜15 nm diameter as the hard magnetic phase and NFO shells of ˜1 nm thickness as the soft magnetic phase. The single-phase-like hysteresis loop with a high remnant-to-saturation magnetization ratio of 0.7, together with a small grain size of ˜16 nm, confirms the existence of exchange-coupling interaction between the CFO cores and the NFO shells. The effect of hard/soft exchange coupling on the microwave absorption properties is studied. Comparing to CFO and NFO nanoparticles, the finite-size NFO shells and the core/shell structure enable a significant reduction in electric resistivity and an enhancement in dipole and interfacial polarizations in the CFO/NFO nanocapsules, resulting in an obvious increase in dielectric permittivity and loss in the whole S-Ku bands of microwaves of 2-18 GHz, respectively. The exchange-coupling interaction empowers a more favorable response of magnetic moment to microwaves, leading to enhanced exchange resonances in magnetic permeability and loss above 10 GHz. As a result, strong absorption, as characterized by a large reflection loss (RL) of -20.1 dB at 9.7 GHz for an absorber thickness of 4.5 mm as well as a broad effective absorption bandwidth (for RL<-10 dB) of 8.4 GHz (7.8-16.2 GHz) at an absorber thickness range of 3.0-4.5 mm, is obtained.

Correlations among magnetic, electrical and magneto-transport properties of NiFe nanohole arrays.

PubMed

Leitao, D C; Ventura, J; Teixeira, J M; Sousa, C T; Pinto, S; Sousa, J B; Michalik, J M; De Teresa, J M; Vazquez, M; Araujo, J P

2013-02-13

In this work, we use anodic aluminum oxide (AAO) templates to build NiFe magnetic nanohole arrays. We perform a thorough study of their magnetic, electrical and magneto-transport properties (including the resistance R(T), and magnetoresistance MR(T)), enabling us to infer the nanohole film morphology, and the evolution from granular to continuous film with increasing thickness. In fact, different physical behaviors were observed to occur in the thickness range of the study (2 nm < t < 100 nm). For t < 10 nm, an insulator-to-metallic crossover was visible in R(T), pointing to a granular film morphology, and thus being consistent with the presence of electron tunneling mechanisms in the magnetoresistance. Then, for 10 nm < t < 50 nm a metallic R(T) allied with a larger anisotropic magnetoresistance suggests the onset of morphological percolation of the granular film. Finally, for t > 50 nm, a metallic R(T) and only anisotropic magnetoresistance behavior were obtained, characteristic of a continuous thin film. Therefore, by combining simple low-cost bottom-up (templates) and top-down (sputtering deposition) techniques, we are able to obtain customized magnetic nanostructures with well-controlled physical properties, showing nanohole diameters smaller than 35 nm.

Synthesis of core-shell iron nanoparticles via a new (novel) approach

NASA Astrophysics Data System (ADS)

Chaudhary, Rakesh P.; Koymen, Ali R.

2014-03-01

Carbon-encapsulated iron (Fe) nanoparticles were synthesized by a newly developed method in toluene. Transmission Electron Microscopy (TEM) and High Resolution Transmission Electron Microscopy (HRTEM) of the as prepared sample reveal that core-shell nanostructures have been formed with Fe as core and graphitic carbon as shell. Fe nanoparticles with diameter 11nm to 102 nm are encapsulated by 6-8 nm thick graphitic carbon layers. There was no iron carbide formation observed between the Fe core and the graphitic shell. The Fe nanoparticles have body centered cubic (bcc) crystal structure. The magnetic hysteresis loop of the as synthesized powder at room temperature showed a saturation magnetization of 9 Am2 kg-1. After thermal treatment crystalline order of the samples improved and hence saturation magnetization increased to 24 Am2kg-1. We foresee that the carbon-encapsulated Fe nanoparticles are biologically friendly and could have potential applications in Magnetic Resonance Imaging (MRI) and Photothermal cancer therapy.

Anisotropy of the upper critical field and its thickness dependence in superconducting FeSe electric-double-layer transistors

NASA Astrophysics Data System (ADS)

Shiogai, Junichi; Kimura, Shojiro; Awaji, Satoshi; Nojima, Tsutomu; Tsukazaki, Atsushi

2018-05-01

Anisotropy of superconductivity is one of the fundamental physical parameters for understanding layered iron-based superconductors (IBSs). Here we investigated the anisotropic response of resistive transition as a function of thickness (d ) in iron selenide (FeSe) based electric-double-layer transistors (EDLTs) on SrTi O3 , which exhibit superconducting transition temperatures Tc as high as 40 K below d =10 nm . According to the analyses of the in-plane (Hc2 //) and out-of-plane (Hc2 ⊥) upper critical fields (Hc 2) and the magnetic field angle dependence of the resistance (Rs-θ ) in ultrathin condition, we found that the anisotropy factor ɛ0=Hc2 ///Hc2 ⊥ is 7.4 in the thin limit of d ˜1 nm , which is larger than that of bulk IBSs. In addition, we observed the shorter out-of-plane coherence length ξc of 0.19 nm compared to the c -axis lattice constant, which implies the confinement of the order parameter in the one unit cell FeSe. These findings suggest that high-Tc superconductivity in the ultrathin FeSe-EDLT exhibits an anisotropic three-dimensional (3D) or quasi-two-dimensional (2D) nature rather than the pure 2D one, leading to the robust superconductivity. Moreover, we carried out the systematic evaluation of the anisotropic Hc 2 against thickness reduction in the FeSe channel. The in-plane Hc 2 as a function of normalized temperature T /Tc is almost independent of d until the thin limit condition. On the other hand, the out-of-plane Hc 2 near T /Tc˜1 decreases with increasing d , resulting in the increase of ɛ0 at around Tc to 32.0 at the thick condition of d =9.3 nm , which is also confirmed by Rs-θ measurements. The counterintuitive behavior can be attributed to the degree of coupling strength between two electron-rich layers possessing a high superconducting order parameter induced by electrostatic gating at the top interface and charge transfer from SrTi O3 substrates at the bottom interface. Besides a large Hc2 ⊥ for d =9.3 nm exceeding 20 T even at T =0.8 Tc , we observe the decoupling crossover of the two superconducting layers at low temperature, which is a unique feature for the high-Tc FeSe-EDLT on SrTi O3 .

X-ray absorption fine structure and x-ray diffraction studies of crystallographic grains in nanocrystalline FePd:Cu thin films

NASA Astrophysics Data System (ADS)

Krupinski, M.; Perzanowski, M.; Polit, A.; Zabila, Y.; Zarzycki, A.; Dobrowolska, A.; Marszalek, M.

2011-03-01

FePd alloys have recently attracted considerable attention as candidates for ultrahigh density magnetic storage media. In this paper we investigate FePd thin alloy film with a copper admixture composed of nanometer-sized grains. [Fe(0.9 nm)/Pd(1.1 nm)/Cu(d nm)]×5 multilayers were prepared by thermal deposition at room temperature in UHV conditions on Si(100) substrates covered by 100 nm SiO2. The thickness of the copper layer has been changed from 0 to 0.4 nm. After deposition, the multilayers were rapidly annealed at 600 °C in a nitrogen atmosphere, which resulted in the creation of the FePd:Cu alloy. The structure of alloy films obtained this way was determined by x-ray diffraction (XRD), glancing angle x-ray diffraction, and x-ray absorption fine structure (EXAFS). The measurements clearly showed that the L10 FePd:Cu nanocrystalline phase has been formed during the annealing process for all investigated copper compositions. This paper concentrates on the crystallographic grain features of FePd:Cu alloys and illustrates that the EXAFS technique, supported by XRD measurements, can help to extend the information about grain size and grain shape of poorly crystallized materials. We show that, using an appropriate model of the FePd:Cu grains, the comparison of EXAFS and XRD results gives a reasonable agreement.

Femtosecond Measurements Of Size-Dependent Spin Crossover In FeII(pyz)Pt(CN)4 Nanocrystals

DOE PAGES

Sagar, D. M.; Baddour, Frederick G.; Konold, Patrick; ...

2016-01-07

We report a femtosecond time-resolved spectroscopic study of size-dependent dynamics in nanocrystals (NCs) of Fe(pyz)Pt(CN) 4. We observe that smaller NCs (123 or 78 nm cross section and < 25 nm thickness) exhibit signatures of spin crossover (SCO) with time constants of ~ 5-10 ps whereas larger NCs with 375 nm cross section and 43 nm thickness exhibit a weaker SCO signature accompanied by strong spectral shifting on a ~20 ps time scale. For the small NCs, the fast dynamics appear to result from thermal promotion of residual low-spin states to high-spin states following nonradiative decay, and the size dependencemore » is postulated to arise from differing high-spin vs low-spin fractions in domains residing in strained surface regions. The SCO is less efficient in larger NCs owing to their larger size and hence lower residual LS/HS fractions. Our results suggest that size-dependent dynamics can be controlled by tuning surface energy in NCs with dimensions below ~25 nm for use in energy harvesting, spin switching, and other applications.« less

Effect of Mg interlayer on perpendicular magnetic anisotropy of CoFeB films in MgO/Mg/CoFeB/Ta structure

NASA Astrophysics Data System (ADS)

Ma, Q. L.; Iihama, S.; Kubota, T.; Zhang, X. M.; Mizukami, S.; Ando, Y.; Miyazaki, T.

2012-09-01

The effects of Mg metallic interlayer on the magnetic properties of thin CoFeB films in MgO/Mg (tMg)/CoFeB (1.2 nm)/Ta structures were studied in this letter. Our experimental result shows that the CoFeB film exhibits perpendicular magnetic anisotropy (PMA) when the CoFeB and MgO layers are separated by a metallic Mg layer with a maximum thickness of 0.8 nm. The origin of PMA was discussed by considering the preferential transmission of the Δ1 symmetry preserved by the Mg interlayer in crystallized MgO/Mg/CoFeB/Ta. In addition, the thin Mg interlayer also contributes to enhancing the thermal stability and reducing the effective damping constant and coercivity of the CoFeB film.

Improvement of perpendicular anisotropy of columnar FePt-ZrO2-C films with FePt insert layer

NASA Astrophysics Data System (ADS)

Dong, Kaifeng; Mo, Wenqin; Jin, Fang; Song, Junlei; Cheng, Weimin; Wang, Haiwei

2018-05-01

The effects of various thicknesses of FePt insert layer on the microstructure and magnetic properties of FePt-ZrO2-C thin films have been investigated. It is found that with inserting 0.4 nm FePt films between the TiON intermediate layer and FePt-ZrO2-C layer, the perpendicular anisotropy indicated by Hc⊥/Hc//ratio would increase from 4 to 13.1, suggesting the perpendicular anisotropy could be improved a lot with using FePt insert layer. Simultaneously, the FePt grains of FePt-ZrO2-C thin films maintained columnar structure and the grain isolation could also be improved in a certain degree. With further increase of the FePt insert layer thickness, although the perpendicular anisotropy was still larger than that without FePt insert layer, the grain size of the FePt-ZrO2-C films would increase and the isolation would be deteriorated.

Tuning exchange bias in Fe/γ-Fe{sub 2}O{sub 3} core-shell nanoparticles: Impacts of interface and surface spins

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khurshid, Hafsa, E-mail: hkhurshi@usf.edu, E-mail: phanm@usf.edu, E-mail: sharihar@usf.edu; Phan, Manh-Huong, E-mail: hkhurshi@usf.edu, E-mail: phanm@usf.edu, E-mail: sharihar@usf.edu; Mukherjee, Pritish

A comparative study has been performed of the exchange bias (EB) effect in Fe/γ-Fe{sub 2}O{sub 3} core-shell nanoparticles with the same thickness of the γ-Fe{sub 2}O{sub 3} shell (∼2 nm) and the diameter of the Fe core varying from 4 nm to 11 nm. Transmission electron microscopy (TEM) and high-resolution TEM confirmed the high quality of the core-shell nanostructures. A systematic analysis of magnetization versus magnetic field measurements under zero-field-cooled and field-cooled regimes using the Meiklejohn-Bean model and deconvoluting superparamagnetic and paramagnetic contribution to the total magnetic moment Langevin function shows that there exists a critical particle size (∼10 nm), above which the spinsmore » at the interface between Fe and γ-Fe{sub 2}O{sub 3} contribute primarily to the EB, but below which the surface spin effect is dominant. Our finding yields deeper insight into the collective contributions of interface and surface spins to the EB in core-shell nanoparticle systems, knowledge of which is the key to manipulating EB in magnetic nanostructures for spintronics applications.« less

Ledge-type Co/L1{sub 0}-FePt exchange-coupled composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Speliotis, Th.; Giannopoulos, G.; Niarchos, D.

2016-06-21

FePt-based exchange-coupled composites consisting of a magnetically hard L1{sub 0}-FePt phase exchange-coupled with a soft ferromagnetic material are promising candidates for future ultra-high density (>1 Tbit/in{sup 2}) perpendicular magnetic recording media, also being of interest for other applications including spin torque oscillators and micro-electro-mechanical systems, among others. In this paper, the effect of the thickness of a soft Co layer (3 < th{sub Co} < 20 nm) on the magnetic behavior of ledge-type fcc(100)-Co/L1{sub 0}(001)-FePt composites deposited on an MgO (100) substrate is systematically studied by combining morpho-structural analyses and angular magnetization measurements. Starting from a film consisting of isolated L1{submore » 0}(001)–FePt islands, the ledge-type structure was obtained by depositing a Co layer that either covered the FePt islands or filled-up the inter-island region, gradually forming a continuous layer with increasing Co thickness. A perpendicular anisotropy was maintained up to th{sub Co} ∼ 9.5 nm and a significant reduction in the coercivity (about 50% for th{sub Co} ∼ 3 nm) with the increase in th{sub Co} was observed, indicating that, by coupling hard FePt and soft Co phases in a ledge-type configuration, the writability can be greatly improved. Recoil loops' measurements confirmed the exchange-coupled behavior, reinforcing a potential interest in these systems for future magnetic recording media.« less

Computer simulation of single-phase nanocrystalline permanent magnets

NASA Astrophysics Data System (ADS)

Griffiths, M. K.; Bishop, J. E. L.; Tucker, J. W.; Davies, H. A.

1998-03-01

Demagnetizing curves have been calculated numerically for three-dimensional micromagnetic model assemblies of randomly oriented, magnetically hard, exchange coupled, uniaxial nanocrystals as typified by rapidly quenched Nd 2Fe 14B. The curves were obtained as a sequence of static equilibrium states in an incrementally changing applied field. The magnetization distribution in each state was obtained by minimizing the sum of the exchange, anisotropy and Zeeman energies of the assembly, using a modified LaBonte method, with computational elements as small as 1.11 nm (roughly {1}/{4} the domain wall thickness in Nd 2Fe 14B). For computational economy, internal dipolar interactions were ignored in the energy minimization. For a material with the magnetic constants of stoichiometric Nd 2Fe 14B, tests showed that these interactions contribute less than 3% to the energy. On increasing the model grain size from 4.4 to 36 nm, the reduced remanence fell from 76 to 54% and the reduced intrinsic coercivity μ0iHCMS/ KU increased from 0.16 to 0.46 (just under half the Stoner-Wohlfarth value); both sets of results are in reasonable agreement with experimental values. The energy product, evaluated for Nd 2Fe 14B, ranged from ˜224 kJ/m 3 for 10 nm grains to ˜128 kJ/m 3 for 36 nm grains. For grain sizes ⩾20 nm, spatial magnetization variation was confined to domain walls centred on the grain boundaries. For grain sizes decreasing below about twice the domain wall thickness, spatial magnetization variation extended to the interior of the grains and exhibited increasingly long-range correlations.

Evolution of magnetic properties in the vicinity of the Verwey transition in Fe3O4 thin films

NASA Astrophysics Data System (ADS)

Liu, X. H.; Liu, W.; Zhang, Z. D.

2017-09-01

We have systematically studied the evolution of magnetic properties, especially the coercivity and the remanence ratio in the vicinity of the Verwey transition temperature (TV), of high-quality epitaxial Fe3O4 thin films grown on MgO (001), MgAl2O4 (MAO) (001), and SrTiO3 (STO) (001) substrates. We observed rapid change of magnetization, coercivity, and remanence ratio at TV, which are consistent with the behaviors of resistivity versus temperature [ρ (T )] curves for the different thin films. In particular, we found quite different magnetic behaviors for the thin films on MgO from those on MAO and STO, in which the domain size and the strain state play very important roles. The coercivity is mainly determined by the domain size but the demagnetization process is mainly dependent on the strain state. Furthermore, we observed a reversal of remanence ratio at TV with thickness for the thin films grown on MgO: from a rapid enhancement for 40-nm- to a sharp drop for 200-nm-thick film, and the critical thickness is about 80 nm. Finally, we found an obvious hysteretic loop of coercivity (or remanence ratio) with temperature around TV, corresponding to the hysteretic loop of the ρ (T ) curve, in Fe3O4 thin film grown on MgO.

Thin film bismuth iron oxides useful for piezoelectric devices

DOEpatents

Zeches, Robert J.; Martin, Lane W.; Ramesh, Ramamoorthy

2016-05-31

The present invention provides for a composition comprising a thin film of BiFeO.sub.3 having a thickness ranging from 20 nm to 300 nm, a first electrode in contact with the BiFeO.sub.3 thin film, and a second electrode in contact with the BiFeO.sub.3 thin film; wherein the first and second electrodes are in electrical communication. The composition is free or essentially free of lead (Pb). The BFO thin film is has the piezoelectric property of changing its volume and/or shape when an electric field is applied to the BFO thin film.

Electrical spin injection into GaAs based light emitting diodes using perpendicular magnetic tunnel junction-type spin injector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tao, B. S.; Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190; Barate, P.

Remanent electrical spin injection into an InGaAs/GaAs based quantum well light emitting diode is realized by using a perpendicularly magnetized MgO/CoFeB/Ta/CoFeB/MgO spin injector. We demonstrate that the Ta interlayer plays an important role to establish the perpendicular magnetic anisotropy and the thickness of Ta interlayer determines the type of exchange coupling between the two adjacent CoFeB layers. They are ferromagnetically or antiferromagnetically coupled for a Ta thickness of 0.5 nm or 0.75 nm, respectively. A circular polarized electroluminescence (P{sub c}) of about 10% is obtained at low temperature and at zero magnetic field. The direction of the electrically injected spins is determinedmore » only by the orientation of the magnetization of the bottom CoFeB layer which is adjacent to the MgO/GaAs interface. This work proves the critical role of the bottom CoFeB/MgO interface on the spin-injection and paves the way for the electrical control of spin injection via magnetic tunnel junction-type spin injector.« less

Generic Superconducting Inhomogeneity in Single Crystal Fe(Te1-xSex) Probed by Nanostructure-transport

NASA Astrophysics Data System (ADS)

Yue, Chunlei; Hu, Jin; Liu, Xue; Mao, Zhiqiang; Wei, Jiang

2015-03-01

We have investigated the nano-scale electronic properties of the iron-based unconventional superconductor Fe(Te1-xSex) with optimal Se content x = 0.5. Using the microexfoliation method and ion milling thinning, we successfully produced Fe(Te1-xSex) devices with thickness varying from 90nm down to 12nm. Our transport measurements revealed a suppression of superconductivity coinciding with the loss of normal state metallicity. Through the simulation of the formation of superconducting region in nano-scale thin flakes, we show that our observation is in line with the nano-scale inhomogeneity proposed for this material; therefore it provides a more direct evidence for the nano-scale inhomogeneous superconductivity in Fe(Te1-xSex) .

Bio-Inspired Hierarchical Nanofibrous Fe3O4-TiO2-Carbon Composite as a High-Performance Anode Material for Lithium-Ion Batteries.

PubMed

Li, Shun; Wang, Mengya; Luo, Yan; Huang, Jianguo

2016-07-13

A bioinspired hierarchical nanofibrous Fe3O4-TiO2-carbon composite was fabricated by employing natural cellulose substance (e.g., filter paper) as both the scaffold and the carbon source and showed improved electrochemical performances when it is employed as an anode material for lithium-ion batteries. FeOOH nanoparticles were first grown uniformly onto the surface of the titania thin-layer precoated cellulose nanofibers, and thereafter, the as-prepared FeOOH-TiO2-cellulose composite was calcined and carbonized in argon atmosphere at 500 °C for 6 h to produce the Fe3O4-TiO2-carbon composite. The resultant composite possesses a hierarchical structure that was faithfully inherited from the initial cellulose substance, which was composed of titania-coated carbon fibers with corncob-like shaped Fe3O4 nanoparticles immobilized on the surfaces. The diameter of the composite nanofiber is ca. 100-200 nm, and the diameter of the Fe3O4 nanoparticle is about 30 nm, which is coated with an ultrathin carbon layer with a thickness about 3 nm. This composite displayed superior lithium-ion storage performance. It showed a first-cycle discharge capacity of 1340 mAh/g, delivering a stable reversible capacity of ca. 525 mAh/g after 100 charge-discharge cycles at a current density of 100 mA/g, and the efficiency is as high as ca. 95% of the theoretical value. This is much higher than those of the commercial Fe3O4 powder (160 mAh/g) and the Fe3O4-carbon counter material (310 mAh/g). It was demonstrated that the thin titania precoating layer (thickness ca. 3-5 nm) is necessary for the high content loading of the Fe3O4 nanoparticles onto the carbon nanofibers. Owing to the unique three-dimensional porous network structure of the carbon-fiber scaffold, together with the ultrathin outer carbon-coating layer, the composite showed significantly improved cycling stability and rate capability.

Structure and magnetic properties of Co2FeSi film deposited on Si/SiO2 substrate with Cr buffer layer

NASA Astrophysics Data System (ADS)

Chatterjee, Payel; Basumatary, Himalay; Raja, M. Manivel

2018-05-01

Co2FeSi thin films of 25 nm thickness with 50 nm thick Cr buffer layer was deposited on thermally oxidized Si substrates. Structural and magnetic properties of the films were studied as a function of annealing temperature and substrate temperatures. While the coercivity increases with increase in annealing temperature, it is found to decrease with increase in substrate temperature. A minimum coercivity of 18 Oe has been obtained for the film deposited at 550°C substrate temperature. This was attributed to the formation of L12 phase as observed from the GIXRD studies. The films with a good combination of soft magnetic properties and L21 crystal structure are suitable for spintronic applications.

Effect of heat treatment on interface driven magnetic properties of CoFe films

NASA Astrophysics Data System (ADS)

Singh, Akhilesh Kr.; Hsu, Jen-Hwa

2017-06-01

We report systematic studies on non-magnetic Ta underlayer and cap layer driven microstructural and magnetic properties at a wide temperature range for CoFe films. All the films were grown at room temperature and post annealed at different annealing temperatures (TA = 200 °C, 250 °C, 300 °C, 350 °C, 400 °C and 450 °C). The in-plane magnetic hysteresis (M-H) loops of 10 nm thick CoFe single layer films, grown directly on thermally oxidized Si substrate, exhibit anisotropic nature for TA above 250 °C. However, the CoFe (10 nm) films grown on the 5 nm thick Ta underlayer show reduced anisotropy. Moreover, with underlayer and cap layers (2 nm) the anisotropy is disappeared. The in-plane coercivity (HC) shows a strong variation with TA, underlayer and cap layers. HC increases significantly with Ta underlayer and cap layers. The out of plane M-H loops exhibit increase in the remanence magnetization and squareness with both Ta underlayer and cap layers due to transition of in-plane magnetization component to the out of plane direction. The atomic force microscopic observations revealed that grain/particle size and shape depend strongly on TA and Ta layers. Moreover, a large reduction in the surface roughness is observed with the Ta cap layer. The magnetic domain patterns depend on the TA, and Ta layers. However, for Ta/CoFe/Ta films no clear domains were observed for all the TA. Hence, the Ta cap layers not only protect the CoFe magnetic layer against the heat treatment, but also show a smooth surface at a wide temperature range. These results could be discussed on the basis of random anisotropy model, TA, underlayer and cap layers driven microstructure and magnetization orientation of the CoFe films.

Static magnetism and thermal switching in randomly oriented L10 FePt thin films

NASA Astrophysics Data System (ADS)

Lisfi, A.; Pokharel, S.; Alqarni, A.; Akioya, O.; Morgan, W.; Wuttig, M.

2018-05-01

Static magnetism and thermally activated magnetic relaxation were investigated in granular FePt films (20 nm-200 nm thick) with random magnetic anisotropy through hysteresis loop, torque curve and magnetization time dependence measurements. While the magnetism of thicker film (200 nm thick) is dominated by a single switching of the ordered L10 phase, thinner film (20 nm) displays a double switching, which is indicative of the presence of the disordered cubic phase. The pronounced behavior of double switching in thinner film suggests that the film grain boundary is composed of soft cubic magnetic phase. The magnetic relaxation study reveals that magnetic viscosity S of the films is strongly dependent on the external applied field and exhibits a maximum value (12 kAm) around the switching field and a vanishing behavior at low (1 kOe) and large (12 kOe) fields. The activation volume of the thermal switching was found to be much smaller than the physical volume of the granular structure due to the incoherent rotation mode of the magnetization reversal mechanism, which is established to be domain wall nucleation.

Reduced temperature-dependent thermal conductivity of magnetite thin films by controlling film thickness

PubMed Central

2014-01-01

We report on the out-of-plane thermal conductivities of epitaxial Fe3O4 thin films with thicknesses of 100, 300, and 400 nm, prepared using pulsed laser deposition (PLD) on SiO2/Si substrates. The four-point probe three-omega (3-ω) method was used for thermal conductivity measurements of the Fe3O4 thin films in the temperature range of 20 to 300 K. By measuring the temperature-dependent thermal characteristics of the Fe3O4 thin films, we realized that their thermal conductivities significantly decreased with decreasing grain size and thickness of the films. The out-of-plane thermal conductivities of the Fe3O4 films were found to be in the range of 0.52 to 3.51 W/m · K at 300 K. For 100-nm film, we found that the thermal conductivity was as low as approximately 0.52 W/m · K, which was 1.7 to 11.5 order of magnitude lower than the thermal conductivity of bulk material at 300 K. Furthermore, we calculated the temperature dependence of the thermal conductivity of these Fe3O4 films using a simple theoretical Callaway model for comparison with the experimental data. We found that the Callaway model predictions agree reasonably with the experimental data. We then noticed that the thin film-based oxide materials could be efficient thermoelectric materials to achieve high performance in thermoelectric devices. PMID:24571956

Grain size engineering for ferroelectric Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films by an insertion of Al{sub 2}O{sub 3} interlayer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Han Joon; Park, Min Hyuk; Kim, Yu Jin

2014-11-10

The degradation of ferroelectric (FE) properties of atomic layer deposited Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films with increasing thickness was mitigated by inserting 1 nm-thick Al{sub 2}O{sub 3} interlayer at middle position of the thickness of the FE film. The large P{sub r} of 10 μC/cm{sup 2}, which is 11 times larger than that of single layer Hf{sub 0.5}Zr{sub 0.5}O{sub 2} film with equivalent thickness, was achieved from the films as thick as 40 nm. The Al{sub 2}O{sub 3} interlayer could interrupt the continual growth of Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films, and the resulting decrease of grain size prevented the formation of non-ferroelectricmore » monoclinic phase. The Al{sub 2}O{sub 3} interlayer also largely decreased the leakage current of the Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films.« less

Ion irradiation-induced easy-cone anisotropy in double-MgO free layers for perpendicular magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

Teixeira, B. M. S.; Timopheev, A. A.; Caçoilo, N. F. F.; Auffret, S.; Sousa, R. C.; Dieny, B.; Alves, E.; Sobolev, N. A.

2018-05-01

We have used the ferromagnetic resonance in the X-band (9.37 GHz) to investigate the effect of 400 keV Ar+ irradiation on the perpendicular magnetic anisotropy (PMA) and Gilbert damping parameter, α, of double-MgO free layers designed for application in perpendicular magnetic tunnel junctions. The samples comprised a MgO/Fe72Co8B20/X(0.2 nm)/Fe72Co8B20/MgO layer stack, where X stands for an ultrathin Ta or W spacer. Samples with two different total FeCoB layer thicknesses, tFCB = 3.0 nm and tFCB = 2.6 nm, were irradiated with ion fluences ranging from 1012 cm-2 to 1016 cm-2. The effective first-order PMA field, BK1, decreased nearly linearly with the logarithm of the fluence for both FeCoB thicknesses and spacer elements. The decrease in BK1, which is likely caused by an ion-induced intermixing at the FeCoB/MgO interfaces, resulted in a reorientation of the magnetization of the free layers with tFCB = 2.6 nm, initially exhibiting a perpendicular easy-axis anisotropy. For intermediate fluences, 1013 cm-2 and 1014 cm-2, easy-cone states with different cone angles could be induced in the free layer with a W spacer. Importantly, no corresponding increase in the Gilbert damping was observed. This study shows that ion irradiation can be used to tune the easy-cone anisotropy in perpendicular magnetic tunnel junctions, which is interesting for spintronic applications such as spin-torque magnetic memory devices, oscillators, and sensors.

Silicon induced stability and mobility of indium zinc oxide based bilayer thin film transistors

NASA Astrophysics Data System (ADS)

Chauhan, Ram Narayan; Tiwari, Nidhi; Liu, Po-Tsun; Shieh, Han-Ping D.; Kumar, Jitendra

2016-11-01

Indium zinc oxide (IZO), silicon containing IZO, and IZO/IZO:Si bilayer thin films have been prepared by dual radio frequency magnetron sputtering on glass and SiO2/Si substrates for studying their chemical compositions and electrical characteristics in order to ascertain reliability for thin film transistor (TFT) applications. An attempt is therefore made here to fabricate single IZO and IZO/IZO:Si bilayer TFTs to study the effect of film thickness, silicon incorporation, and bilayer active channel on device performance and negative bias illumination stress (NBIS) stability. TFTs with increasing single active IZO layer thickness exhibit decrease in carrier mobility but steady improvement in NBIS; the best values being μFE ˜ 27.0, 22.0 cm2/Vs and ΔVth ˜ -13.00, -6.75 V for a channel thickness of 7 and 27 nm, respectively. While silicon incorporation is shown to reduce the mobility somewhat, it raises the stability markedly (ΔVth ˜ -1.20 V). Further, IZO (7 nm)/IZO:Si (27 nm) bilayer based TFTs display useful characteristics (field effect mobility, μFE = 15.3 cm2/Vs and NBIS value, ΔVth =-0.75 V) for their application in transparent electronics.

Fabrication of Fe3O4@mSiO2 Core-Shell Composite Nanoparticles for Drug Delivery Applications

NASA Astrophysics Data System (ADS)

Uribe Madrid, Sergio I.; Pal, Umapada; Kang, Young Soo; Kim, Junghoon; Kwon, Hyungjin; Kim, Jungho

2015-05-01

We report the synthesis of Fe3O4@mSiO2 nanostructures of different meso-silica (mSiO2) shell thickness, their biocompatibility and behaviors for loading and release of a model drug ibuprofen. The composite nanostructures have superparamagnetic magnetite cores of 208 nm average size and meso-silica shells of 15 to 40 nm thickness. A modified Stöber method was used to grow the meso-silica shells over the hydrothermally grown monodispersed magnetite particles. The composite nanoparticles show very promising drug holding and releasing behaviors, which depend on the thickness of meso-silica shell. The biocompatibility of the meso-silica-coated and uncoated magnetite nanoparticles was tested through cytotoxicity assay on breast cancer (MCF-7), ovarian cancer (SKOV3), normal human lung fibroblasts MRC-5, and IMR-90 cells. The high drug holding capacity and reasonable biocompatibility of the nanostructures make them ideal agents for targeted drug delivery applications in human body.

Joining thick section aluminum to steel with suppressed FeAl intermetallic formation via friction stir dovetailing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reza-E-Rabby, Md.; Ross, Kenneth; Overman, Nicole R.

A new solid-phase technique called friction stir dovetailing (FSD) has been developed for joining thick section aluminum to steel. In FSD, mechanical interlocks are formed at the aluminum-steel interface and are reinforced by metallurgical bonds where intermetallic growth has been uniquely suppressed. Lap shear testing shows superior strength and extension at failure compared to popular friction stir approaches where metallurgical bonding is the only joining mechanism. High resolution microscopy revealed the presence of a 40-70 nm interlayer having a composition of 76.4 at% Al, 18.4 at% Fe, and 5.2 at% Si, suggestive of limited FeAl3 intermetallic formation.

1D Magnetic Materials of Fe3O4 and Fe with High Performance of Microwave Absorption Fabricated by Electrospinning Method

PubMed Central

Han, Rui; Li, Wei; Pan, Weiwei; Zhu, Minggang; Zhou, Dong; Li, Fa-shen

2014-01-01

Fe3O4 and Fe nanowires are successfully fabricated by electrospinning method and reduction process. Wiry microstructures were achieved with the phase transformation from α-Fe2O3 to Fe3O4 and Fe by partial and full reduction, while still preserving the wire morphology. The diameters of the Fe3O4 and Fe nanowires are approximately 50–60 nm and 30–40 nm, respectively. The investigation of microwave absorption reveals that the Fe3O4 nanowires exhibit excellent microwave absorbing properties. For paraffin-based composite containing 50% weight concentration of Fe3O4 nanowires, the minimum reflection loss reaches −17.2 dB at 6.2 GHz with the matching thickness of 5.5 mm. Furthermore, the calculation shows that the modulus of the ratio between the complex permittivity and permeability |ε/μ| is far away from unity at the minimum reflection loss point, which is quite different from the traditional opinions. PMID:25510415

Surface structure of MgO underlayer with Ti diffusion for (002) oriented L10 FePt-based heat assisted magnetic recording media

NASA Astrophysics Data System (ADS)

Hinata, Sintaro; Jo, Shin; Saito, Shin

2018-05-01

Surface morphology of the MgO layer and magnetic properties of FePt-C layer deposited on the MgO were investigated for the FePt-based heat assisted magnetic recording media. Stacking structure of the underlayer for the FePt-C layer was MgO (0-5 nm)/Cr80Mn20 (0-30 nm)/Cr50Ti50 (0-50 nm)/glass sub.. Surface observation result for the MgO film by using an atomic force microscope revealed the existence of nodules with a height of about 2 nm and a network-like convex structure with a height difference of about sub nm (boundary wall, BW) on the MgO crystal grain boundary. Density of the nodules largely depends on the surface roughness of the CrTi layer, RaCrTi and it is suppressed from 10 to 2/0.5 μm2 by reducing RaCrTi from 420 to 260 pm. Height of the BW depends on thickness of the MgO layer, tMgO and it can be suppressed by reducing tMgO to less than 4 nm. From the cross-sectional energy dispersive x-ray mapping, it is clarified that the BW is formed by atomic diffusion of Ti atoms from CrTi layer due to the substrate heating process, and a compound consists of Mg, Ti and O atoms. This BW can be used as a template to magnetically isolate the FePt column in the FePt-based granular film, such as FePt-SiO2, if the size of the BW is reduced to less than 10 nm. M-H loop of the FePt-C granular film deposited on the underlayer showed that the nodule and BW induce oxidation of the FePt grains, and reduction of intergranular exchange coupling.

Solvothermal synthesis of Fe{sub 7}C{sub 3} and Fe{sub 3}C nanostructures with phase and morphology control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williams, Brent; Clifford, Dustin; Carpenter, Everett E., E-mail: aelgendy@vcu.edu, E-mail: ecarpenter2@vcu.edu

A phase transition, from orthorhombic Fe{sub 3}C to hexagonal Fe{sub 7}C{sub 3}, was observed using a wet synthesis mediated by hexadecyltrimethylammonium chloride (CTAC). In this study, CTAC has been shown to control carbide phase, morphology, and size of the iron carbide nanostructures. Fe{sub 7}C{sub 3} hexagonal prisms were formed with an average diameter of 960 nm, the thickness of 150 nm, and Fe{sub 3}C nanostructures with an approximate size of 50 nm. Magnetic studies show ferromagnetic behavior with M{sub s} of 126 emu/g, and H{sub c} of 170 Oe with respect to Fe{sub 7}C{sub 3} and 95 emu/g and 590 Oe with respect to Fe{sub 3}C. Themore » thermal studies using high temperature x-ray diffraction show stability of Fe{sub 7}C{sub 3} up to 500 °C. Upon slow cooling, the Fe{sub 7}C{sub 3} phase is recovered with an intermediate oxide phase occurring around 300 °C. This study has demonstrated a simple route in synthesizing iron carbides for an in depth magnetic study and crystal phase transition study of Fe{sub 7}C{sub 3} at elevated temperatures.« less

Encapsulation of α-Fe2O3 nanoparticles in graphitic carbon microspheres as high-performance anode materials for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Zhang, Hongwei; Sun, Xiaoran; Huang, Xiaodan; Zhou, Liang

2015-02-01

A novel ``spray drying-carbonization-oxidation'' strategy has been developed for the fabrication of α-Fe2O3-graphitic carbon (α-Fe2O3@GC) composite microspheres, in which α-Fe2O3 nanoparticles with sizes of 30-50 nm are well-encapsulated by onion-like graphitic carbon shells with a thickness of 5-10 nm. In the constructed composite, the α-Fe2O3 nanoparticles act as the primary active material, providing a high capacity. Meanwhile, the graphitic carbon shells serve as the secondary active component, structural stabilizer, interfacial stabilizer, and electron-highway. As a result, the synthesized α-Fe2O3@GC nanocomposite exhibits a superior lithium-ion battery performance with a high reversible capacity (898 mA h g-1 at 400 mA g-1), outstanding rate capability, and excellent cycling stability. Our product, in terms of the facile and scalable preparation process and excellent electrochemical performance, demonstrates its great potential as a high-performance anode material for lithium-ion batteries.A novel ``spray drying-carbonization-oxidation'' strategy has been developed for the fabrication of α-Fe2O3-graphitic carbon (α-Fe2O3@GC) composite microspheres, in which α-Fe2O3 nanoparticles with sizes of 30-50 nm are well-encapsulated by onion-like graphitic carbon shells with a thickness of 5-10 nm. In the constructed composite, the α-Fe2O3 nanoparticles act as the primary active material, providing a high capacity. Meanwhile, the graphitic carbon shells serve as the secondary active component, structural stabilizer, interfacial stabilizer, and electron-highway. As a result, the synthesized α-Fe2O3@GC nanocomposite exhibits a superior lithium-ion battery performance with a high reversible capacity (898 mA h g-1 at 400 mA g-1), outstanding rate capability, and excellent cycling stability. Our product, in terms of the facile and scalable preparation process and excellent electrochemical performance, demonstrates its great potential as a high-performance anode material for lithium-ion batteries. Electronic supplementary information (ESI) available: XRD pattern, XPS spectrum, CV curves, TEM and SEM images, and table. See DOI: 10.1039/c4nr06771a

Influence of Ionic Strength on the Deposition of Metal-Phenolic Networks.

PubMed

Guo, Junling; Richardson, Joseph J; Besford, Quinn A; Christofferson, Andrew J; Dai, Yunlu; Ong, Chien W; Tardy, Blaise L; Liang, Kang; Choi, Gwan H; Cui, Jiwei; Yoo, Pil J; Yarovsky, Irene; Caruso, Frank

2017-10-10

Metal-phenolic networks (MPNs) are a versatile class of self-assembled materials that are able to form functional thin films on various substrates with potential applications in areas including drug delivery and catalysis. Different metal ions (e.g., Fe III , Cu II ) and phenols (e.g., tannic acid, gallic acid) have been investigated for MPN film assembly; however, a mechanistic understanding of the thermodynamics governing MPN formation remains largely unexplored. To date, MPNs have been deposited at low ionic strengths (<5 mM), resulting in films with typical thicknesses of ∼10 nm, and it is still unclear how a bulk complexation reaction results in homogeneous thin films when a substrate is present. Herein we explore the influence of ionic strength (0-2 M NaCl) on the conformation of MPN precursors in solution and how this determines the final thickness and morphology of MPN films. Specifically, the film thickness increases from 10 nm in 0 M NaCl to 12 nm in 0.5 M NaCl and 15 nm in 1 M NaCl, after which the films grow rougher rather than thicker. For example, the root-mean-square roughness values of the films are constant below 1 M NaCl at 1.5 nm; in contrast, the roughness is 3 nm at 1 M NaCl and increases to 5 nm at 2 M NaCl. Small-angle X-ray scattering and molecular dynamics simulations allow for comparisons to be made with chelated metals and polyelectrolyte thin films. For example, at a higher ionic strength (2 M NaCl), sodium ions shield the galloyl groups of tannic acid, allowing them to extend away from the Fe III center and interact with other MPN complexes in solution to form thicker and rougher films. As the properties of films determine their final performance and application, the ability to tune both thickness and roughness using salts may allow for new applications of MPNs.

Multilayer Ni/Fe thin films as oxygen evolution catalysts for solar fuel production

NASA Astrophysics Data System (ADS)

Biset-Peiró, M.; Murcia-López, S.; Fàbrega, C.; Morante, J. R.; Andreu, T.

2017-03-01

The slow kinetics and high overpotential of the oxygen evolution reaction is one of the main limiting factors to achieve the minimum required performances of the so-called photoelectrochemical water splitting systems. An oxygen evolution catalyst (OEC) becomes essential in order to perform this process with higher efficiency. Herein, we report the physical, optical and electrochemical characterization of multilayer Ni/Fe thin films as earth-abundant OEC, to avoid the use of platinum group metals (PGM). Uniform films of thicknesses ranging from 1 to 10 nm were fabricated by sequential and alternate thermal evaporation of Ni and Fe. It was found that the successive deposition allows the fabrication of a Ni terminated surface that does not need activation due to the Fe underlayer. The lowest overpotential achieved for NiFe was 370 mV at 10 mA cm-2 and a Tafel slope of 37 mV dec-1 with 1 nm thickness and 95% transmittance. Finally, NiFe OEC was implemented on top of Mo:BiVO4 photoanodes which resulted in a reduction of the open circuit potential of 0.2 V and up to five fold increase of the oxidation efficiency at 0.7 VRHE. The results presented facilitate the practical implementation of BiVO4 photoanodes in tandem configuration for bias free photoassisted water splitting.

Crossover from disordered to core-shell structures of nano-oxide Y{sub 2}O{sub 3} dispersed particles in Fe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Higgins, M. P.; Wang, L. M.; Gao, F., E-mail: gaofeium@umich.edu

Molecular dynamic simulations of Y{sub 2}O{sub 3} in bcc Fe and transmission electron microscopy (TEM) observations were used to understand the structure of Y{sub 2}O{sub 3} nano-clusters in an oxide dispersion strengthened steel matrix. The study showed that Y{sub 2}O{sub 3} nano-clusters below 2 nm were completely disordered. Y{sub 2}O{sub 3} nano-clusters above 2 nm, however, form a core-shell structure, with a shell thickness of 0.5–0.7 nm that is independent of nano-cluster size. Y{sub 2}O{sub 3} nano-clusters were surrounded by off-lattice Fe atoms, further increasing the stability of these nano-clusters. TEM was used to corroborate our simulation results and showed a crossover frommore » a disordered nano-cluster to a core-shell structure.« less

Heusler alloys with bcc tungsten seed layers for GMR junctions

NASA Astrophysics Data System (ADS)

Frost, William; Hirohata, Atsufumi

2018-05-01

We demonstrate that polycrystalline Co2FeSi Heusler alloys films can be grown with perpendicular anisotropy without the use of an MgO interface. By heating the substrate to 400 °C prior to deposition and using a tungsten seed layer perpendicular anisotropy is induced in the Heusler layer. This is maintained as the thickness of the Co2FeSi is increased up to 12.5 nm. The layers with thickness dependent coercivity can be implemented into a giant magnetoresistance structure leading to spin-valve behaviour without the need for an exchange biased pinned layer.

Effect of epitaxial strain on ferroelectric polarization in multiferroic BiFeO3 films

NASA Astrophysics Data System (ADS)

Kim, Dae Ho; Lee, Ho Nyung; Biegalski, Michael D.; Christen, Hans M.

2008-01-01

Multiferroic BiFeO3 epitaxial films with thicknesses ranging from 40to960nm were grown by pulsed laser deposition on SrTiO3 (001) substrates with SrRuO3 bottom electrodes. X-ray characterization shows that the structure evolves from angularly distorted tetragonal with c /a≈1.04 to more bulklike distorted rhombohedral (c/a≈1.01) as the strain relaxes with increasing thickness. Despite this significant structural evolution, the ferroelectric polarization along the body diagonal of the distorted pseudocubic unit cells, as calculated from measurements along the normal direction, barely changes.

Low-current-density spin-transfer switching in Gd{sub 22}Fe{sub 78}-MgO magnetic tunnel junction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kinjo, Hidekazu, E-mail: kinjou.h-lk@nhk.or.jp; Machida, Kenji; Aoshima, Ken-ichi

2014-05-28

Magnetization switching of a relatively thick (9 nm) Gd-Fe free layer was achieved with a low spin injection current density of 1.0 × 10{sup 6} A/cm{sup 2} using MgO based magnetic tunnel junction devices, fabricated for light modulators. At about 560 × 560 nm{sup 2} in size, the devices exhibited a tunneling magnetoresistance ratio of 7%. This low-current switching is mainly attributed to thermally assisted spin-transfer switching in consequence of its thermal magnetic behavior arising from Joule heating.

Fabrication by Electrophoretic Deposition of Nano-Fe3O4 and Fe3O4@SiO2 3D Structure on Carbon Fibers as Supercapacitor Materials

NASA Astrophysics Data System (ADS)

Hajalilou, Abdollah; Abouzari-Lotf, Ebrahim; Etemadifar, Reza; Abbasi-Chianeh, Vahid; Kianvash, Abbas

2018-05-01

Core-shell nanostructured magnetic Fe3O4@SiO2 with particle size ranging from 3 nm to 40 nm has been synthesized via a facile precipitation method. Tetraethyl orthosilicate was employed as surfactant to prepare core-shell structures from Fe3O4 nanoparticles synthesized from pomegranate peel extract using a green method. X-ray diffraction analysis, Fourier-transform infrared and ultraviolet-visible (UV-Vis) spectroscopies, transmission electron microscopy, and scanning electron microscopy with energy-dispersive spectroscopy were employed to characterize the samples. The prepared Fe3O4 nanoparticles were approximately 12 nm in size, and the thickness of the SiO2 shell was 4 nm. Evaluation of the magnetic properties indicated lower saturation magnetization for Fe3O4@SiO2 powder ( 11.26 emu/g) compared with Fe3O4 powder ( 13.30 emu/g), supporting successful wrapping of the Fe3O4 nanoparticles by SiO2. As-prepared powders were deposited on carbon fibers (CFs) using electrophoretic deposition and their electrochemical behavior investigated. The rectangular-shaped cyclic voltagrams of Fe3O4@CF and Fe3O4@C@CF samples indicated electrochemical double-layer capacitor (EDLC) behavior. The higher specific capacitance of 477 F/g for Fe3O4@C@CF (at scan rate of 0.05 V/s in the potential range of - 1.13 to 0.45 V) compared with 205 F/g for Fe3O4@CF (at the same scan rate in the potential range of - 1.04 to 0.24 V) makes the former a superior candidate for use in energy storage applications.

Spin pumping damping and magnetic proximity effect in Pd and Pt spin-sink layers

NASA Astrophysics Data System (ADS)

Caminale, M.; Ghosh, A.; Auffret, S.; Ebels, U.; Ollefs, K.; Wilhelm, F.; Rogalev, A.; Bailey, W. E.

2016-07-01

We investigated the spin pumping damping contributed by paramagnetic layers (Pd, Pt) in both direct and indirect contact with ferromagnetic Ni81Fe19 films. We find a nearly linear dependence of the interface-related Gilbert damping enhancement Δ α on the heavy-metal spin-sink layer thicknesses tN in direct-contact Ni81Fe19 /(Pd, Pt) junctions, whereas an exponential dependence is observed when Ni81Fe19 and (Pd, Pt) are separated by 3 nm Cu. We attribute the quasilinear thickness dependence to the presence of induced moments in Pt, Pd near the interface with Ni81Fe19 , quantified using x-ray magnetic circular dichroism measurements. Our results show that the scattering of pure spin current is configuration-dependent in these systems and cannot be described by a single characteristic length.

Scaling of anomalous Hall effect in Ta/CoFeB/MgAl2O4/Ta multilayers

NASA Astrophysics Data System (ADS)

Wu, Yong; Zhang, Qimeng; Meng, Kangkang; Chen, Jikun; Xu, Xiaoguang; Miao, Jun; Jiang, Yong

2017-06-01

The anomalous Hall effect (AHE) is studied in Ta/CoFeB/MgAl2O4/Ta multilayers with different thicknesses of MgAl2O4 (t), which causes in-plane magnetic anisotropy (IMA) for t = 1.0 nm and perpendicular magnetic anisotropy (PMA) for t ≥ 1.2 nm. Conventional scaling was demonstrated to be not inadequate in our case. The origin of the AHE in Ta/CoFeB/MgAl2O4/Ta multilayers is mainly an extrinsic mechanism. The contribution of skew scattering (SS) is unneglectable, and both the SS and side jump are enhanced when the magnetic anisotropy changes from IMA to PMA, indicating that the oxidation at the interface of CoFeB/MgAl2O4 has a dominant influence on the AHE.

Uniform, dense arrays of vertically aligned, large-diameter single-walled carbon nanotubes.

PubMed

Han, Zhao Jun; Ostrikov, Kostya

2012-04-04

Precisely controlled reactive chemical vapor synthesis of highly uniform, dense arrays of vertically aligned single-walled carbon nanotubes (SWCNTs) using tailored trilayered Fe/Al(2)O(3)/SiO(2) catalyst is demonstrated. More than 90% population of thick nanotubes (>3 nm in diameter) can be produced by tailoring the thickness and microstructure of the secondary catalyst supporting SiO(2) layer, which is commonly overlooked. The proposed model based on the atomic force microanalysis suggests that this tailoring leads to uniform and dense arrays of relatively large Fe catalyst nanoparticles on which the thick SWCNTs nucleate, while small nanotubes and amorphous carbon are effectively etched away. Our results resolve a persistent issue of selective (while avoiding multiwalled nanotubes and other carbon nanostructures) synthesis of thick vertically aligned SWCNTs whose easily switchable thickness-dependent electronic properties enable advanced applications in nanoelectronic, energy, drug delivery, and membrane technologies.

Depth resolved lattice-charge coupling in epitaxial BiFeO3 thin film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Hyeon Jun; Lee, Sung Su; Kwak, Jeong Hun

2016-12-01

For epitaxial films, a critical thickness (t c) can create a phenomenological interface between a strained bottom layer and a relaxed top layer. Here, we present an experimental report of how the tc in BiFeO 3 thin films acts as a boundary to determine the crystalline phase, ferroelectricity, and piezoelectricity in 60 nm thick BiFeO 3/SrRuO 3/SrTiO 3 substrate. We found larger Fe cation displacement of the relaxed layer than that of strained layer. In the time-resolved X-ray microdiffraction analyses, the piezoelectric response of the BiFeO 3 film was resolved into a strained layer with an extremely low piezoelectric coefficientmore » of 2.4 pm/V and a relaxed layer with a piezoelectric coefficient of 32 pm/V. The difference in the Fe displacements between the strained and relaxed layers is in good agreement with the differences in the piezoelectric coefficient due to the electromechanical coupling.« less

Depth resolved lattice-charge coupling in epitaxial BiFeO3 thin film

PubMed Central

Lee, Hyeon Jun; Lee, Sung Su; Kwak, Jeong Hun; Kim, Young-Min; Jeong, Hu Young; Borisevich, Albina Y.; Lee, Su Yong; Noh, Do Young; Kwon, Owoong; Kim, Yunseok; Jo, Ji Young

2016-01-01

For epitaxial films, a critical thickness (tc) can create a phenomenological interface between a strained bottom layer and a relaxed top layer. Here, we present an experimental report of how the tc in BiFeO3 thin films acts as a boundary to determine the crystalline phase, ferroelectricity, and piezoelectricity in 60 nm thick BiFeO3/SrRuO3/SrTiO3 substrate. We found larger Fe cation displacement of the relaxed layer than that of strained layer. In the time-resolved X-ray microdiffraction analyses, the piezoelectric response of the BiFeO3 film was resolved into a strained layer with an extremely low piezoelectric coefficient of 2.4 pm/V and a relaxed layer with a piezoelectric coefficient of 32 pm/V. The difference in the Fe displacements between the strained and relaxed layers is in good agreement with the differences in the piezoelectric coefficient due to the electromechanical coupling. PMID:27929103

Double-pinned magnetic tunnel junction sensors with spin-valve-like sensing layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Z. H.; Huang, L.; Feng, J. F., E-mail: jiafengfeng@iphy.ac.cn

2015-08-07

MgO magnetic tunnel junction (MTJ) sensors with spin-valve-like sensing layers of Ir{sub 22}Mn{sub 78} (6)/Ni{sub 80}Fe{sub 20} (t{sub NiFe} = 20–70)/Ru (0.9)/Co{sub 40}Fe{sub 40}B{sub 20} (3) (unit: nm) have been fabricated. A linear field dependence of magnetoresistance for these MTJ sensors was obtained by carrying out a two-step field annealing process. The sensitivity and linear field range can be tuned by varying the thickness of NiFe layer and annealing temperature, and a high sensitivity of 37%/mT has been achieved in the MTJ sensors with 70 nm NiFe at the optimum annealing temperature of 230 °C. Combining the spin-valve-like sensing structure and a soft magneticmore » NiFe layer, MTJ sensors with relatively wide field sensing range have been achieved and could be promising for showing high sensitivity magnetic field sensing applications.« less

Profound Interfacial Effects in CoFe2O4/Fe3O4 and Fe3O4/CoFe2O4 Core/Shell Nanoparticles

NASA Astrophysics Data System (ADS)

Polishchuk, Dmytro; Nedelko, Natalia; Solopan, Sergii; Ślawska-Waniewska, Anna; Zamorskyi, Vladyslav; Tovstolytkin, Alexandr; Belous, Anatolii

2018-03-01

Two sets of core/shell magnetic nanoparticles, CoFe2O4/Fe3O4 and Fe3O4/CoFe2O4, with a fixed diameter of the core ( 4.1 and 6.3 nm for the former and latter sets, respectively) and thickness of shells up to 2.5 nm were synthesized from metal chlorides in a diethylene glycol solution. The nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, and magnetic measurements. The analysis of the results of magnetic measurements shows that coating of magnetic nanoparticles with the shells results in two simultaneous effects: first, it modifies the parameters of the core-shell interface, and second, it makes the particles acquire combined features of the core and the shell. The first effect becomes especially prominent when the parameters of core and shell strongly differ from each other. The results obtained are useful for optimizing and tailoring the parameters of core/shell spinel ferrite magnetic nanoparticles for their use in various technological and biomedical applications.

Magnetization dynamics of Ni80Fe20 nanowires with continuous width modulation

NASA Astrophysics Data System (ADS)

Xiong, L. L.; Kostylev, M.; Adeyeye, A. O.

2017-06-01

A systematic investigation of the magnetization reversal and the dynamic behaviors of uncoupled Ni80Fe20 nanowires (NWs) with artificial continuous width modulation is presented. In contrast with the single resonance mode observed in the homogeneous NWs from the broadband ferromagnetic resonance spectroscopy, the NWs with continuous width modulation display three to five distinct resonance modes with increasing wire thickness in the range from 5 to 70 nm due to the nonuniform demagnetizing field. The highest frequency mode and the frequency difference between the two distinct highest modes are shown to be markedly sensitive to the NW thickness. Interestingly, we found that these modes can be described in terms of the quantization of the standing spin waves due to confined varied width. In addition, the easy axis coercive field for the width modulated NWs is much higher than homogeneous NWs of the same thickness when less than 70 nm. Our experimental results are in good qualitative agreement with the micromagnetic simulations. The results may find potential applications in the design and optimization of tunable magnonic filters.

Interfacial Dzyaloshinskii-Moriya interaction sign in Ir/Co2FeAl systems investigated by Brillouin light scattering

NASA Astrophysics Data System (ADS)

Belmeguenai, M.; Gabor, M. S.; Roussigné, Y.; Petrisor, T.; Mos, R. B.; Stashkevich, A.; Chérif, S. M.; Tiusan, C.

2018-02-01

C o2FeAl (CFA) ultrathin films, of various thicknesses (0.9 nm ≤tCFA≤1.8 nm ), have been grown by sputtering on Si substrates, using Ir as a buffer layer. The magnetic properties of these structures have been studied by vibrating sample magnetometry (VSM), miscrostrip ferromagnetic resonance (MS-FMR), and Brillouin light scattering (BLS) in the Damon-Eshbach geometry. VSM characterizations show that films are mostly in-plane magnetized and the saturating field perpendicular to the film plane increases with decreasing CFA thickness suggesting the existence of a perpendicular interface anisotropy. The presence of a magnetic dead layer of 0.44 nm has been detected by VSM. The MS-FMR with the magnetic field applied perpendicularly to the film plane has been used to determine the gyromagnetic factor. The BLS measurements reveal a pronounced nonreciprocal spin wave propagation, due to the interfacial Dzyaloshinskii-Moriya interaction (DMI) induced by the Ir interface with CFA, which increases with decreasing CFA thickness. The DMI sign has been found to be the same (negative) as that of Pt/Co, in contrast to the ab initio calculation on Ir/Co, where it is found to be positive. The thickness dependence of the effective DMI constant shows the existence of two regimes similarly to that of the perpendicular anisotropy constant. The surface DMI constant Ds was estimated to be -0.37 pJ /m for the thickest samples, where a linear thickness dependence of the effective DMI constant has been observed.

Fluoride Thin Films: from Exchange Bias to Multferroicity

NASA Astrophysics Data System (ADS)

Johnson, Trent A.

This dissertation concerns research into the growth and characterization fluoride thin films by molecular beam epitaxy. After a discussion of relevant background material and experimental procedures in the first two chapters, we study exchange bias in magnetic multilayers incorporating the uniaxial antiferromagnet FeF2, grown to varying thicknesses, sandwiched between ferromagnetic Co layers with fixed thicknesses of 5 and 20 nm. Several bilayers with only the 20 nm thick Co layer were grown for comparative study. The samples were grown on Al2O3 (112¯0) substrates at room temperature. In-situ RHEED and x-ray diffraction indicated the films were polycrystalline. The films were determined to have low surface and interlayer roughness, as determined by AFM and x-ray reflectivity. After field-cooling to below the Neel temperature of FeF2 in a magnetic field of 1 kOe, magnetic hysteresis loops were measured as a function of temperature. We found that both layers had a negative exchange bias, with the exchange bias of the thinner layer larger than that of the thicker layer. In addition, the coercivity below the blocking temperature TB of the thinner layer was significantly larger than that of the thick layer, even though the coercivity of the two layers was the same for T > TB. The exchange bias effect, manifested by a shift in these hysteresis loops, showed a strong dependence on the thickness of the antiferromagnet. Anisotropic magnetoresistance measurements provided additional insight into the magnetization reversal mechanism within the ferromagnets. The thickness dependent exchange anisotropy of trilayer and bilayer samples is explained by adapting a random field model to the antiferromagnet/ferromagnet interface. Finally, We investigate the temperature dependent growth, as well as the magnetic and ferroelectric properties of thin films of the multiferroic compounds BaMF4, where M = Fe, Co, Ni. The films were grown to thicknesses of 50 or 100 nm on single crystal Al2O3 (0001) substrates. X-ray diffraction showed that this family of films grew epitaxially in the (010) orientation, but were twinned in the plane, with three domain orientations rotated by 120 degrees relative to one another. Measurements of the remanent hysteresis via interdigitated electrodes showed that the compounds M = Co, and Ni were ferroelectric, but no switching behavior was observed in the Fe system at electric fields up to 400 kV/cm. Measurements of the field-cooled and zero-field-cooled magnetic moment confirmed low temperature antiferromagnetic behavior, and found new weak ferromagnetic phases induced by strain.

Effect of double layer thickness on magnetoelectric coupling in multiferroic BaTiO3-Bi0.95Gd0.05FeO3 multilayers

NASA Astrophysics Data System (ADS)

Hohenberger, S.; Lazenka, V.; Temst, K.; Selle, S.; Patzig, C.; Höche, T.; Grundmann, M.; Lorenz, M.

2018-05-01

The effect of double-layer thickness and partial substitution of Bi3+ by Gd3+ is demonstrated for multiferroic BaTiO3–BiFeO3 2–2 heterostructures. Multilayers of 15 double layers of BaTiO3 and Bi0.95Gd0.05FeO3 were deposited onto (0 0 1) oriented SrTiO3 substrates by pulsed laser deposition with various double layer thicknesses. X-ray diffraction and high resolution transmission electron microscopy investigations revealed a systematic strain tuning with layer thickness via coherently strained interfaces. The multilayers show increasingly enhanced magnetoelectric coupling with reduced double layer thickness. The maximum magnetoelectric coupling coefficient was measured to be as high as 50.8 V cm‑1 Oe‑1 in 0 T DC bias magnetic field at room temperature, and 54.9 V cm‑1 Oe‑1 above 3 T for the sample with the thinnest double layer thickness of 22.5 nm. This enhancement is accompanied by progressively increasing perpendicular magnetic anisotropy and compressive out-of-plane strain. To understand the origin of the enhanced magnetoelectric coupling in such multilayers, the temperature and magnetic field dependency of is discussed. The magnetoelectric performance of the Gd3+ substituted samples is found to be slightly enhanced when compared to unsubstituted BaTiO3–BiFeO3 multilayers of comparable double-layer thickness.

Chiral bobbers and skyrmions in epitaxial FeGe/Si(111) films

NASA Astrophysics Data System (ADS)

Ahmed, Adam S.; Rowland, James; Esser, Bryan D.; Dunsiger, Sarah R.; McComb, David W.; Randeria, Mohit; Kawakami, Roland K.

2018-04-01

We report experimental and theoretical evidence for the formation of chiral bobbers—an interfacial topological spin texture—in FeGe films grown by molecular beam epitaxy. After establishing the presence of skyrmions in FeGe/Si(111) thin-film samples through Lorentz transmission electron microscopy and the topological Hall effect, we perform magnetization measurements that reveal an inverse relationship between the film thickness and the slope of the susceptibility (d χ /d H ). We present evidence for the evolution as a function of film thickness L from a skyrmion phase for L LD/2 , where LD˜70 nm is the FeGe pitch length. We show using micromagnetic simulations that chiral bobbers, earlier predicted to be metastable, are in fact the stable ground state in the presence of an additional interfacial Rashba Dzyaloshinskii-Moriya interaction.

Field-dependent magnetization of BiFeO 3 in ultrathin La 0.7Sr 0.3MnO 3/BiFeO 3 superlattice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fitzsimmons, Michael R.; Jia, Quanxi X.; Singh, Surendra

2015-12-02

We report the observation of field-induced magnetization of BiFeO 3 (BFO) in an ultrathin La 0.7Sr 0.3MnO 3 (LSMO)/BFO superlattice using polarized neutron reflectivity (PNR). The depth dependent structure and magnetic characterization of subnano layer thick (thickness ~ 0.7 nm each) LSMO/BFO hetrostructure is carried out using X-ray reflectivity and PNR techniques. Our PNR results indicate parallel alignment of magnetization as well as enhancement in magnetic moment across LSMO/BFO interfaces. The study showed an increase in average magnetization on increasing applied magnetic field at 10K. As a result, we observed a saturation magnetization of 110 ± 15 kA/m (~0.8 μmore » B/Fe) for ultrathin BFO layer (~2 unit cell) sandwiched between ultrathin LSMO layers (~ 2 unit cell).« less

Epitaxial Fe{sub 3}Pt/FePt nanocomposites on MgO and SrTiO{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casoli, F., E-mail: casoli@imem.cnr.it; Nasi, L.; Cabassi, R.

We have exploited the pseudomorphic growth of the magnetically soft Fe{sub 3}Pt phase on top of L1{sub 0}-FePt to obtain fully epitaxial soft/hard nanocomposites on both MgO(100) and SrTiO{sub 3}(100). The magnetic properties of this new nanocomposite system, driven by the soft/hard exchange-coupling, can be tailored by varying soft phase thickness, soft phase magnetic anisotropy and substrate. Coercivity is strongly reduced by the addition of the soft phase, a reduction which is definitely affected by the nominal composition of the soft phase and by the substrate choice; similarly is the magnetic phase diagram of the composite system. Coercive field decreasesmore » down to 21% of the hard layer value for Fe{sub 3}Pt(5 nm)/FePt(3.55 nm) nanocomposites on SrTiO{sub 3}; this maximum coercivity reduction was obtained with a nominal atomic content of Fe in the soft phase of 80%.« less

[100]-Oriented LiFePO4 Nanoflakes toward High Rate Li-Ion Battery Cathode.

PubMed

Li, Zhaojin; Peng, Zhenzhen; Zhang, Hui; Hu, Tao; Hu, Minmin; Zhu, Kongjun; Wang, Xiaohui

2016-01-13

[100] is believed to be a tough diffusion direction for Li(+) in LiFePO4, leading to the belief that the rate performance of [100]-oriented LiFePO4 is poor. Here we report the fabrication of 12 nm-thick [100]-oriented LiFePO4 nanoflakes by a simple one-pot solvothermal method. The nanoflakes exhibit unexpectedly excellent electrochemical performance, in stark contrast to what was previously believed. Such an exceptional result is attributed to a decreased thermodynamic transformation barrier height (Δμb) associated with increased active population.

Magnetic domain wall engineering in a nanoscale permalloy junction

NASA Astrophysics Data System (ADS)

Wang, Junlin; Zhang, Xichao; Lu, Xianyang; Zhang, Jason; Yan, Yu; Ling, Hua; Wu, Jing; Zhou, Yan; Xu, Yongbing

2017-08-01

Nanoscale magnetic junctions provide a useful approach to act as building blocks for magnetoresistive random access memories (MRAM), where one of the key issues is to control the magnetic domain configuration. Here, we study the domain structure and the magnetic switching in the Permalloy (Fe20Ni80) nanoscale magnetic junctions with different thicknesses by using micromagnetic simulations. It is found that both the 90-° and 45-° domain walls can be formed between the junctions and the wire arms depending on the thickness of the device. The magnetic switching fields show distinct thickness dependencies with a broad peak varying from 7 nm to 22 nm depending on the junction sizes, and the large magnetic switching fields favor the stability of the MRAM operation.

Magnetic properties of superparamagnetic nanoparticles loaded into silicon nanotubes.

PubMed

Granitzer, Petra; Rumpf, Klemens; Gonzalez, Roberto; Coffer, Jeffery; Reissner, Michael

2014-01-01

In this work, the magnetic properties of silicon nanotubes (SiNTs) filled with Fe3O4 nanoparticles (NPs) are investigated. SiNTs with different wall thicknesses of 10 and 70 nm and an inner diameter of approximately 50 nm are prepared and filled with superparamagnetic iron oxide nanoparticles of 4 and 10 nm in diameter. The infiltration process of the NPs into the tubes and dependence on the wall-thickness is described. Furthermore, data from magnetization measurements of the nanocomposite systems are analyzed in terms of iron oxide nanoparticle size dependence. Such biocompatible nanocomposites have potential merit in the field of magnetically guided drug delivery vehicles. 61.46.Fg; 62.23.Pq; 75.75.-c; 75.20.-g.

Low power loss and field-insensitive permeability of Fe-6.5%Si powder cores with manganese oxide-coated particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Junnan, E-mail: junnanli1991@163.com, E-mail: rzhgong@hust.edu.cn; Wang, Xian; Xu, Xiaojun

Fe-6.5%Si alloy powders coated with manganese oxides using an innovative in situ process were investigated. The in-situ coating of the insulating oxides was realized with a KMnO{sub 4} solution by a chemical process. The insulating manganese oxides with mixed valance state were verified by X-ray photoelectron spectroscopy analysis. The thickness of the insulating layer on alloy particles was determined to be in a range of 20–210 nm, depending upon the KMnO{sub 4} concentration. The powder core loss and the change in permeability under a DC-bias field were measured at frequencies ranging from 50 to 100 kHz. The experiments indicated that themore » Fe-6.5%Si powder cores with a 210 nm-thick manganese oxide layer not only showed a low core loss of 459 mW/cm{sup 3} at 100 kHz but also showed a small reduction in permeability (μ(H)/μ(0) = 85% for μ = 42) at a DC-bias field of 80 Oe. This work has defined a novel pathway to realizing low core loss and field-insensitive permeability for Fe-Si powder cores.« less

Iron silicide formation at different layers of (Fe/Si)3 multilayered structures determined by conversion electron Mössbauer spectroscopy

NASA Astrophysics Data System (ADS)

Badía-Romano, L.; Rubín, J.; Magén, C.; Bürgler, D. E.; Bartolomé, J.

2014-07-01

The morphology and the quantitative composition of the Fe-Si interface layer forming at each Fe layer of a (Fe/Si)3 multilayer have been determined by means of conversion electron Mössbauer spectroscopy (CEMS) and high-resolution transmission electron microscopy (HRTEM). For the CEMS measurements, each layer was selected by depositing the Mössbauer active 57Fe isotope with 95% enrichment. Samples with Fe layers of nominal thickness dFe = 2.6 nm and Si spacers of dSi = 1.5 nm were prepared by thermal evaporation onto a GaAs(001) substrate with an intermediate Ag(001) buffer layer. HRTEM images showed that Si layers grow amorphous and the epitaxial growth of the Fe is good only for the first deposited layer. The CEMS spectra show that at all Fe/Si and Si/Fe interfaces a paramagnetic c-Fe1-xSi phase is formed, which contains 16% of the nominal Fe deposited in the Fe layer. The bottom Fe layer, which is in contact with the Ag buffer, also contains α-Fe and an Fe1-xSix alloy that cannot be attributed to a single phase. In contrast, the other two layers only comprise an Fe1-xSix alloy with a Si concentration of ≃0.15, but no α-Fe.

Preparation of Nd-Fe-B/α-Fe nano-composite thick-film magnets on various substrates using PLD with high laser energy density above 10 J/cm2

NASA Astrophysics Data System (ADS)

Nakano, M.; Kondo, H.; Yamashita, A.; Yanai, T.; Itakura, M.; Fukunaga, H.

2018-05-01

PLD (Pulsed Laser Deposition) method with high laser energy density (LED) above 10 J/cm2 followed by a flash annealing enabled us to obtain isotropic nano-composite thick-film magnets with (BH)max ≧ 80 kJ/m3 on polycrystalline Ta substrates. We also have demonstrated that a dispersed structure composed of α-Fe together with Nd2Fe14B phases with the average grain diameter of approximately 20 nm could be formed on the Ta substrates. In this study, we tried to enhance the (BH)max value by controlling the microstructure due to the usage of different metal based substrates with each high melting point such as Ti, Nb, and W. Although it was difficult to vary the microstructure and to improve the magnetic properties of the films deposited on the substrates, we confirmed that isotropic thick-film magnets with (BH)max ≧ 80 kJ/m3 based on the nano-dispersed α-Fe and Nd2Fe14B phases could be obtained on various metal substrates with totally different polycrystalline structure. On the other hand, the use of a glass substrate lead to the deterioration of magnetic properties of a film prepared using the same preparation process.

Ultrafine Ti4+ doped α-Fe2O3 nanorod array photoanodes with high charge separation efficiency for solar water splitting

NASA Astrophysics Data System (ADS)

Liu, Yilin; Liu, Jie; Luo, Wenjun; Wen, Xin; Liu, Xiaokang; Zou, Zhigang; Huang, Wei

2017-06-01

Hematite (α-Fe2O3) is a promising photoanode material for solar water splitting due to its suitable band gap, earth-abundance, excellent stability and non-toxicity. However, a short hole diffusion length limits its performance. A nanorod array structure can shorten hole transfer distance to photoelectrode/electrolyte interface and decrease recombination of photo-generated carriers. However, average diameters of all previously reported nanorods are over 50 nm, thus being too thick for holes to transfer to the interface. It is still a big challenge to prepare a Fe2O3 nanorod array photoelectrode with finer diameter. In this study, we prepare an ultrafine α-Fe2O3 nanorod array film with average diameter about 25 nm by calcining γ-FeOOH for the first time. The ultrafine nanorod array photoanode indicates much higher carrier separation efficiency and performance than a conventional nanorod array film.

Layer thickness dependence of the current-induced effective field vector in Ta|CoFeB|MgO.

PubMed

Kim, Junyeon; Sinha, Jaivardhan; Hayashi, Masamitsu; Yamanouchi, Michihiko; Fukami, Shunsuke; Suzuki, Tetsuhiro; Mitani, Seiji; Ohno, Hideo

2013-03-01

Current-induced effective magnetic fields can provide efficient ways of electrically manipulating the magnetization of ultrathin magnetic heterostructures. Two effects, known as the Rashba spin orbit field and the spin Hall spin torque, have been reported to be responsible for the generation of the effective field. However, a quantitative understanding of the effective field, including its direction with respect to the current flow, is lacking. Here we describe vector measurements of the current-induced effective field in Ta|CoFeB|MgO heterostructrures. The effective field exhibits a significant dependence on the Ta and CoFeB layer thicknesses. In particular, a 1 nm thickness variation of the Ta layer can change the magnitude of the effective field by nearly two orders of magnitude. Moreover, its sign changes when the Ta layer thickness is reduced, indicating that there are two competing effects contributing to it. Our results illustrate that the presence of atomically thin metals can profoundly change the landscape for controlling magnetic moments in magnetic heterostructures electrically.

Growth, structure, morphology, and magnetic properties of Ni ferrite films

PubMed Central

2013-01-01

The morphology, structure, and magnetic properties of nickel ferrite (NiFe2O4) films fabricated by radio frequency magnetron sputtering on Si(111) substrate have been investigated as functions of film thickness. Prepared films that have not undergone post-annealing show the better spinel crystal structure with increasing growth time. Meanwhile, the size of grain also increases, which induces the change of magnetic properties: saturation magnetization increased and coercivity increased at first and then decreased. Note that the sample of 10-nm thickness is the superparamagnetic property. Transmission electron microscopy displays that the film grew with a disorder structure at initial growth, then forms spinel crystal structure as its thickness increases, which is relative to lattice matching between substrate Si and NiFe2O4. PMID:23622034

Growth, structure, morphology, and magnetic properties of Ni ferrite films.

PubMed

Dong, Chunhui; Wang, Gaoxue; Guo, Dangwei; Jiang, Changjun; Xue, Desheng

2013-04-27

The morphology, structure, and magnetic properties of nickel ferrite (NiFe2O4) films fabricated by radio frequency magnetron sputtering on Si(111) substrate have been investigated as functions of film thickness. Prepared films that have not undergone post-annealing show the better spinel crystal structure with increasing growth time. Meanwhile, the size of grain also increases, which induces the change of magnetic properties: saturation magnetization increased and coercivity increased at first and then decreased. Note that the sample of 10-nm thickness is the superparamagnetic property. Transmission electron microscopy displays that the film grew with a disorder structure at initial growth, then forms spinel crystal structure as its thickness increases, which is relative to lattice matching between substrate Si and NiFe2O4.

Role of the Heat Sink Layer Ta for Ultrafast Spin Dynamic Process in Amorphous TbFeCo Thin Films

NASA Astrophysics Data System (ADS)

Ren, Y.; Zhang, Z. Z.; Min, T.; Jin, Q. Y.

The ultrafast demagnetization processes (UDP) in Ta (t nm)/TbFeCo (20 nm) films have been studied using the time-resolved magneto-optical Kerr effect (TRMOKE). With a fixed pump fluence of 2 mJ/cm2, for the sample without a Ta underlayer (t=0nm), we observed the UDP showing a two-step decay behavior, with a relatively longer decay time (τ2) around 3.0 ps in the second step due to the equilibrium of spin-lattice relaxation following the 4f occupation. As a 10nm Ta layer is deposited, the two-step demagnetization still exists while τ2 decreases to ˜1.9ps. Nevertheless, the second-step decay (τ2=0ps) disappears as the Ta layer thickness is increased up to 20 nm, only the first-step UDP occurs within 500 fs, followed by a fast recovery process. The rapid magnetization recovery rate strongly depends on the pump fluence. We infer that the Ta layer provides conduction electrons involving the thermal equilibrium of spin-lattice interaction and serves as heat bath taking away energy from spins of TbFeCo alloy film in UDP.

Evolution of the interfacial perpendicular magnetic anisotropy constant of the Co2FeAl/MgO interface upon annealing

NASA Astrophysics Data System (ADS)

Conca, A.; Niesen, A.; Reiss, G.; Hillebrands, B.

2018-04-01

We investigate a series of films with different thickness of the Heusler alloy Co2FeAl in order to study the effect of annealing on the interface with a MgO layer and on the bulk magnetic properties. Our results reveal that while the perpendicular interface anisotropy constant K\\perpS is zero for the as-deposited samples, its value increases with annealing up to a value of 1.14 +/- 0.07 mJ m‑2 for the series annealed at 320 °C and of 2.01 +/- 0.7 mJ m‑2 for the 450 °C annealed series owing to a strong modification of the interface during the thermal treatment. This large value ensures a stabilization of a perpendicular magnetization orientation for an extrapolated thickness below 1.7 nm. The data additionally shows that the in-plane biaxial anisotropy constant has a different evolution with thickness in as-deposited and annealed systems. The Gilbert damping parameter α shows minima for all series for a thickness of 40 nm and an absolute minimum value of 2.8+/-0.1×10-3 . The thickness dependence is explained in terms of an inhomogeneous magnetization state generated by the interplay between the different anisotropies of the system and by the crystalline disorder.

The discovery of silicon oxide nanoparticles in space-weathered of Apollo 15 lunar soil grains

NASA Astrophysics Data System (ADS)

Gu, Lixin; Zhang, Bin; Hu, Sen; Noguchi, Takaaki; Hidaka, Hiroshi; Lin, Yangting

2018-03-01

Space weathering is an important process on the Moon and other airless celestial bodies. The most common space weathering effects are amorphization of the top surface of soil grains and formation of nanophase iron particles (npFe) within the partially amorphous rims. Hence, space weathering significantly affects optical properties of the surface of the Moon and other airless celestial bodies. Transmission electron microscope (TEM) analysis of Apollo 15 soil grains displays npFe (≤5 nm in size) embedded in the space-weathered rim (∼60 nm in thickness) of a pyroxene grain, consistent with previous studies. In contrast, submicron-sized fragments that adhere to the pyroxene grain show distinct space weathering features. Silicon oxide nanoparticles (npSiOx) were observed with npFe in a submicron-sized Mg-Fe silicate fragment. This is the first discovery of npSiOx as a product of space weathering. The npSiOx and the coexisting npFe are ∼10-25 nm in size, significantly larger than the typical npFe in the space weathered rim of the pyroxene grain. The coexisting npSiOx and npFe were probably formed directly in micrometeorite shock-induced melt, instead of in a solar-wind generated vapor deposit or irradiated rim. This new observation will shed light on space weathering processes on the Moon and airless celestial bodies.

Surface plasmon resonance enhanced light absorption and wavelength tuneable in gold-coated iron oxide spherical nanoparticle

NASA Astrophysics Data System (ADS)

Dasri, Thananchai; Chingsungnoen, Artit

2018-06-01

Surface plasmon in nano-sized particles, such as gold, silver, copper and their composites, has recently attracted a great deal of attention due to its possible uses in many applications, especially in life sciences. It is desirable for application devices with a tenability of surface plasmon wavelength and optical properties enhancement. This article presents enhanced optical light absorption and tunable wavelength in gold-coated magnetite (Fe3O4@Au core-shell) nanoparticles embedded in water using the theoretical method of discrete dipole approximation (DDA). The absorption spectra in the wavelengths from 350 to 900 nm were found to be the spectra obtained from Fe3O4@Au core-shell nanoparticles, and when compared with pure Fe3O4 nanoparticles, the surface plasmon resonance can be enhanced and tuned over the entire visible spectrum (viz. 350-800 nm) of the electromagnetic spectrum by varying the Au shell thickness (2-5 nm). Similarly, the Faraday rotation spectra can also be obtained.

Interplay between out-of-plane anisotropic L1{sub 1}-type CoPt and in-plane anisotropic NiFe layers in CoPt/NiFe exchange springs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saravanan, P.; Defence Metallurgical Research Laboratory, Hyderabad 500058; Hsu, Jen-Hwa, E-mail: jhhsu@phys.ntu.edu.tw

2014-06-28

Films of L1{sub 1}-type CoPt/NiFe exchange springs were grown with different NiFe (Permalloy) layer thickness (t{sub NiFe} = 0–10 nm). X-ray diffraction analysis reveals that the characteristic peak position of NiFe(111) is not affected by the CoPt-layer—confirming the absence of any inter-diffusion between the CoPt and NiFe layers. Magnetic studies indicate that the magnetization orientation of NiFe layer can be tuned through varying t{sub NiFe} and the perpendicular magnetic anisotropy of L1{sub 1}-type CoPt/NiFe films cannot sustain for t{sub NiFe} larger than 3.0 nm due to the existence of exchange interaction at the interface of L1{sub 1}-CoPt and NiFe layers. Magnetic force microscopy analysismore » on the as-grown samples shows the changes in morphology from maze-like domains with good contrast to hazy domains when t{sub NiFe} ≥ 3.0 nm. The three-dimensional micro-magnetic simulation results demonstrate that the magnetization orientation in NiFe layer is not uniform, which continuously increases from the interface to the top of NiFe layer. Furthermore, the tilt angle of the topmost NiFe layers can be changed over a very wide range from a small number to about 75° by varying t{sub NiFe} from 1 to 10 nm. It is worth noting that there is an abrupt change in the magnetization direction at the interface, for all the t{sub NiFe} investigated. The results of present study demonstrate that the tunable tilted exchange springs can be realized with L1{sub 1}-type CoPt/NiFe bilayers for future applications in three-axis magnetic sensors or advanced spintronic devices demanding inclined magnetic anisotropy.« less

Magnetization reversal in epitaxial exchange-biased IrMn/FeGa bilayers with anisotropy geometries controlled by oblique deposition

NASA Astrophysics Data System (ADS)

Zhang, Yao; Zhan, Qingfeng; Zuo, Zhenghu; Yang, Huali; Zhang, Xiaoshan; Dai, Guohong; Liu, Yiwei; Yu, Ying; Wang, Jun; Wang, Baomin; Li, Run-Wei

2015-05-01

We fabricated epitaxial exchange biased (EB) IrMn/FeGa bilayers by oblique deposition and systematically investigated their magnetization reversal. Two different configurations with the uniaxial magnetic anisotropy Ku parallel and perpendicular to the unidirectional anisotropy Ke b were obtained by controlling the orientation of the incident FeGa beam during deposition. A large ratio of Ku/Ke b was obtained by obliquely depositing the FeGa layer to achieve a large Ku while reducing the IrMn thickness to obtain a small Ke b. Besides the previously reported square loops, conventional asymmetrically shaped loops, and one-sided and two-sided two-step loops, unusual asymmetrically shaped loops with a three-step magnetic transition for the descending branch and a two-step transition for the ascending branch and biased three-step loops were observed at various field orientations in the films of both IrMn (tIrMn=1.5 to 20 nm)/FeGa (10 nm) with Ku⊥ Ke b and IrMn (tIrMn≤2 nm)/FeGa (10 nm) with Ku|| Ke b . Considering the geometries of anisotropies, a model based on domain wall nucleation and propagation was employed to quantitatively describe the angular dependent behaviors of IrMn/FeGa bilayers. The biased three-step magnetic switching was predicted to take place when | Ku|> ɛ90°+Ke b , where ɛ90° is the 90° domain wall nucleation energy, and the EB leads to the appearance of the unusual asymmetrically shaped hysteresis loops.

Growth of Ferromagnetic Epitaxial Film of Hexagonal FeGe on (111) Ge Surface

NASA Astrophysics Data System (ADS)

Kumar, Dushyant; Joshi, P. C.; Hossain, Z.; Budhani, R. C.

2014-03-01

The realization of semiconductors showing ferromagnetic order at easily accessible temperatures has been of interest due to their potential use in spintronic devices where long spin life times are of key interest. We have realized the growth of FeGe thin films on Ge (111) wafers using pulsed laser deposition (PLD). The stoichiometric and single phase FeGe target used in PLD chamber has been made by arc melting. A typical θ-2 θ diffraction spectra performed on 40 nm thick FeGe film suggests the stabilization of β-Ni2In (B82-type) hexagonal phase with an epitaxial orientation of (0001)FeGe ||(111)Ge and [11-20]FeGe ||[-110]Ge. SEM images shows a granular structure with the formation of very large grains of about 100 to 500 nm in lateral dimension. The magnetization vs. temperature data taken from SQUID reveal the TC of ~ 270K. Since, PLD technique makes it easier to stabilize the B82 (Ni2In) hexagonal phase in thin FeGe films, this work opens opportunities to reinvestigate many conflicting results on various properties of the FeGe system.

Multiple resonance peaks of FeCo thin films with NiFe underlayer

NASA Astrophysics Data System (ADS)

Zhong, Xiaoxi; Soh, Wee Tee; Phuoc, Nguyen N.; Liu, Ying; Ong, C. K.

2015-01-01

Under zero external magnetic fields, single-layer FeCo thin films exhibit no ferromagnetic resonance (FMR) peaks, while multiple FMR peaks were obtained by growing FeCo thin films on NiFe underlayers with various thicknesses up to 50 nm. Comprehensive investigations of the dynamic magnetic properties and origin of the peaks were conducted through measurements of microwave permeability via a shorted microstrip perturbation technique. Through fitted values of saturation magnetization Ms, uniaxial anisotropy HKsta, and rotatable anisotropy HKrot extracted from the FMR experiments, it was found that two of the three resonance peaks originate from FeCo, and the third from NiFe. The two magnetic phases of FeCo grains are found to have different values of HKrot and explained by the exchange interaction between FeCo and NiFe grains.

Reversible susceptibility studies of magnetization switching in FeCoB synthetic antiferromagnets

NASA Astrophysics Data System (ADS)

Radu, Cosmin; Cimpoesu, Dorin; Girt, Erol; Ju, Ganping; Stancu, Alexandru; Spinu, Leonard

2007-05-01

In this paper we present a study of switching characteristics of a series of synthetic antiferromagnet (SAF) structures using reversible susceptibility experiments. Three series of SAF samples were considered in our study with (t1, t2), the thickness of the FeCoB layers of (80nm, 80nm), (50nm, 50nm), and (80nm, 20nm) and with the interlayer of Ru ranging from 0to2nm. A vector vibrating sample magnetometer was used to measure the hysteresis loops along the different directions in the plane of the samples. The reversible susceptibility experiments were performed using a resonant method based on a tunnel diode oscillator. We showed that the switching peaks in the susceptibility versus field plots obtained for different orientations of the applied dc field can be used to construct the switching diagram of the SAF structure. The critical curve constitutes the fingerprint of the switching behavior and provides information about micromagnetic and structural properties of SAF which is an essential component of modern magnetic random access memories.

Investigation of magnetization dynamics damping in Ni80Fe20/Nd-Cu bilayer at room temperature

NASA Astrophysics Data System (ADS)

Fan, Wei; Fu, Qiang; Qian, Qian; Chen, Qian; Liu, Wanling; Zhou, Xiaochao; Yuan, Honglei; Yue, Jinjin; Huang, Zhaocong; Jiang, Sheng; Kou, Zhaoxia; Zhai, Ya

2018-05-01

Focusing on the Ni80Fe20 (Py)/Nd-Cu bilayers, the magnetization dynamic damping from spin pumping effect is investigated systematically by doping itinerant Cu in rear earth metal Nd. Various Ta/Py/Nd1-xCux/Ta/Si films with x = 0%, 16%, 38%, 46% and 58% are prepared by magnetron sputtering. For every content of Cu, the thickness of Nd-Cu layer is changed from 1 nm to 32 nm. The damping coefficient increases with increasing the thickness of Nd-Cu layer, which shows the trend of the spin pumping behavior. Also, with increasing Cu concentration in the Nd-Cu layer, the damping coefficient decreases, implying that the spin-orbit coupling in Nd-Cu layer is indeed cut down by high itinerant of Cu dopants. It is interesting that the spin diffusion length (λSD) in the Nd-Cu layer for different Cu dopants is not found to increase monotonously.

Magnetic-plasmonic multilayered nanorods

NASA Astrophysics Data System (ADS)

Thumthan, Orathai

Multilayered nanorods which consist of alternating magnetic layers separated by Au layers combine two distinctive properties, magnetic properties and surface plasmonic resonance (SPR) properties into one nano-entity. Their magnetic properties are tunable by changing the layer thickness, varying from single domain to superparamagnetic state. Superparamagnetic is a key requirement for magnetic nanoparticles for bioapplications. Superparamagnetic nanoparticles exhibit high magnetic moments at low applied magnetic field while retain no magnetic moments when magnetic field is removed preventing them from aggregation due to magnetic attraction. Au layers in the nanorods provide anchorage sites for functional group attachment. Also, Au nanodisks exhibit SPR properties. The SPR peak can be tuned from 540 nm to 820 nm by controlling the thickness of magnetic segments while keeping Au thickness constant. In this research, there are three types of multilayered nanorod have been fabricated: Au/NiFe nanorods, Au/Fe nanorods, and Au/Co nanorods. These magnetic nanorods were fabricated by templated electrodeposition into the channels in Anodic Aluminum Oxide (AAO) membrane. The setup for AAO fabrication was developed as a part of this research. Our fabricated AAO membrane has channels with a diameter ranging from 40nm to 80 nm and a thickness of 10um to 12um. Magnetic properties of nanorods such as saturation field, saturation moment, coercivity and remanence are able to manipulate through their shape anisotropy. The magnetization will be easier in long axis rather than short axis of particle. In addition, Au nanodisks in the nanorod structure are not only serving as anchorage sites for functional groups but also provide SPR properties. Under irradiation of light Au nanodisks strongly absorb light at SPR frequency which ranging from 540 nm to 820 nm by controlling the thickness of magnetic segments while keeping Au thickness constant. The SPR tunability of nanorods in near-infrared region can be used in in-vivo biomedical applications such as photo thermal therapy because tissue has an absorption maximum in the infrared range. The magnetic nanorods were explored for the following two applications: 1) as active component orientation-tunable ferrogel for cell culture matrix, 2) as MRI contrast agent. The results show that Au/NiFe magnetic nanorods can be aligned along applied magnetic field. Using MTT assay for 3T3 fibroblast cells, the biocompatibility of Au/Co nanorods was investigated. It shows that cell proliferation after 72 hours of incubation with nanorods decreases as the concentration of nanorods increases. However, cell viability quantified by counting dead cell/live cell reveals that only few cells died after three days of incubation. Au/Co multilayered nanorods were tested as T2 MRI-contrast agent, and a very large relaxivity was observed. In summary, we have successfully fabricated multilayered nanorods with tunability in both magnetic and SPR properties. These nanorods can potentially be used in biological and biomedical fields.

Impact of fluorine based reactive chemistry on structure and properties of high moment magnetic material

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Xiaoyu, E-mail: xiaoyu.yang@wdc.com; Chen, Lifan; Han, Hongmei

The impact of the fluorine-based reactive ion etch (RIE) process on the structural, electrical, and magnetic properties of NiFe and CoNiFe-plated materials was investigated. Several techniques, including X-ray fluorescence, 4-point-probe, BH looper, transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS), were utilized to characterize both bulk film properties such as thickness, average composition, Rs, ρ, Bs, Ms, and surface magnetic “dead” layers' properties such as thickness and element concentration. Experimental data showed that the majority of Rs and Bs changes of these bulk films were due to thickness reduction during exposure to the RIE process. ρ and Msmore » change after taking thickness reduction into account were negligible. The composition of the bulk films, which were not sensitive to surface magnetic dead layers with nano-meter scale, showed minimum change as well. It was found by TEM and EELS analysis that although both before and after RIE there were magnetic dead layers on the top surface of these materials, the thickness and element concentration of the layers were quite different. Prior to RIE, dead layer was actually native oxidation layers (about 2 nm thick), while after RIE dead layer consisted of two sub-layers that were about 6 nm thick in total. Sub-layer on the top was native oxidation layer, while the bottom layer was RIE “damaged” layer with very high fluorine concentration. Two in-situ RIE approaches were also proposed and tested to remove such damaged sub-layers.« less

Thermoelectric properties of Zn4Sb3/CeFe(4-x)CoxSb12 nano-layered superlattices modified by MeV Si ion beam

NASA Astrophysics Data System (ADS)

Budak, S.; Guner, S.; Minamisawa, R. A.; Muntele, C. I.; Ila, D.

2014-08-01

We prepared multilayers of superlattice thin film system with 50 periodic alternating nano-layers of semiconducting half-Heusler β-Zn4Sb3 and skutterudite CeFe2Co2Sb12 compound thin films using ion beam assisted deposition (IBAD) with Au layers deposited on both sides as metal contacts. The deposited multilayer thin films have alternating layers about 5 nm thick. The total thickness of the multilayer system is 275 nm. The superlattices were then bombarded by 5 MeV Si ion at six different fluences to form nano-cluster structures. The film thicknesses and composition were monitored by Rutherford backscattering spectrometry (RBS) before and after MeV ion bombardment. We have measured the thermoelectric efficiency, Figure of Merit ZT, of the fabricated device by measuring the cross plane thermal conductivity by the 3rd harmonic (3ω) method, the cross plane Seebeck coefficient, and the electrical conductivity using the van der Pauw method before and after the MeV ion bombardments. We reached the remarkable thermoelectric Figure of Merit results at optimal fluences.

The growth temperature and measurement temperature dependences of soft magnetic properties and effective damping parameter of (FeCo)-Al alloy thin films

NASA Astrophysics Data System (ADS)

Ariake, Yusuke; Wu, Shuang; Kanada, Isao; Mewes, Tim; Tanaka, Yoshitomo; Mankey, Gary; Mewes, Claudia; Suzuki, Takao

2018-05-01

The soft magnetic properties and effective damping parameters of Fe73Co25Al2 alloy thin films are discussed. The effective damping parameter αeff measured by ferromagnetic resonance for the 10 nm-thick sample is nearly constant (≈0.004 ± 0.0008) for a growth temperature Ts from ambient to 200 °C, and then tends to decrease for higher temperatures and αeff is 0.002 ± 0.0004 at Ts = 300 °C. For the 80 nm-thick sample, the αeff seems to increase with Ts from αeff = 0.001 ± 0.0002 at Ts = ambient to αeff = 0.002 ± 0.0004. The αeff is found nearly constant (αeff = 0.004 ± 0.0008) over a temperature range from 10 to 300 K for the 10 nm films with the different Ts (ambient, 100 and 200 °C). Together with an increasing non-linearity of the frequency dependence of the linewidth at low Ts, extrinsic contributions such as two-magnon scattering dominate the observed temperature dependence of effective damping and linewidth.

Sustainable Interfaces between Si Anodes and Garnet Electrolytes for Room-Temperature Solid-State Batteries.

PubMed

Chen, Cheng; Li, Quan; Li, Yiqiu; Cui, Zhonghui; Guo, Xiangxin; Li, Hong

2018-01-17

Solid-state batteries (SSBs) have seen a resurgence of research interests in recent years for their potential to offer high energy density and excellent safety far beyond current commercialized lithium-ion batteries. The compatibility of Si anodes and Ta-doped Li 7 La 3 Zr 2 O 12 (Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 , LLZTO) solid electrolytes and the stability of the Si anode have been investigated. It is found that Si layer anodes thinner than 180 nm can maintain good contact with the LLZTO plate electrolytes, leading the Li/LLZTO/Si cells to exhibit excellent cycling performance with a capacity retention over 85% after 100 cycles. As the Si layer thickness is increased to larger than 300 nm, the capacity retention of Li/LLZTO/Si cells becomes 77% after 100 cycles. When the thickness is close to 900 nm, the cells can cycle only for a limited number of times because of the destructive volume change at the interfaces. Because of the sustainable Si/LLZTO interfaces with the Si layer anodes with a thickness of 180 nm, full cells with the LiFePO 4 cathodes show discharge capacities of 120 mA h g -1 for LiFePO 4 and 2200 mA h g -1 for the Si anodes at room temperature. They cycle 100 times with a capacity retention of 72%. These results indicate that the combination between the Si anodes and the garnet electrolytes is a promising strategy for constructing high-performance SSBs.

Experimental Investigation of Space Radiation Processing in Lunar Soil Ilmenite: Combining Perspectives from Surface Science and Transmission Electron Microscopy

NASA Technical Reports Server (NTRS)

Christoffersen, R.; Keller, L. P.; Rahman, Z.; Baragiola, R.

2010-01-01

Energetic ions mostly from the solar wind play a major role in lunar space weathering because they contribute structural and chemical changes to the space-exposed surfaces of lunar regolith grains. In mature mare soils, ilmenite (FeTiO3) grains in the finest size fraction have been shown in transmission electron microscope (TEM) studies to exhibit key differences in their response to space radiation processing relative to silicates [1,2,3]. In ilmenite, solar ion radiation alters host grain outer margins to produce 10-100 nm thick layers that are microstructurally complex, but dominantly crystalline compared to the amorphous radiation-processed rims on silicates [1,2,3]. Spatially well-resolved analytical TEM measurements also show nm-scale compositional and chemical state changes in these layers [1,3]. These include shifts in Fe/Ti ratio from strong surface Fe-enrichment (Fe/Ti >> 1), to Fe depletion (Fe/Ti < 1) at 40-50 nm below the grain surface [1,3]. These compositional changes are not observed in the radiation-processed rims on silicates [4]. Several mechanism(s) to explain the overall relations in the ilmenite grain rims by radiation processing and/or additional space weathering processes were proposed by [1], and remain under current consideration [3]. A key issue has concerned the ability of ion radiation processing alone to produce some of the deeper- penetrating compositional changes. In order to provide some experimental constraints on these questions, we have performed a combined X-ray photoelectron spectroscopy (XPS) and field-emission scanning transmission electron (FE-STEM) study of experimentally ion-irradiated ilmenite. A key feature of this work is the combination of analytical techniques sensitive to changes in the irradiated samples at depth scales going from the immediate surface (approx.5 nm; XPS), to deeper in the grain interior (5-100 nm; FE-STEM).

Fe implantation effect in the 6H-SiC semiconductor investigated by Mössbauer spectrometry

NASA Astrophysics Data System (ADS)

Diallo, M. L.; Diallo, L.; Fnidiki, A.; Lechevallier, L.; Cuvilly, F.; Blum, I.; Viret, M.; Marteau, M.; Eyidi, D.; Juraszek, J.; Declémy, A.

2017-08-01

P-doped 6H-SiC substrates were implanted with 57Fe ions at 380 °C or 550 °C to produce a diluted magnetic semiconductor with an Fe homogeneous concentration of about 100 nm thickness. The magnetic properties were studied with 57Fe Conversion Electron Mössbauer Spectrometry at room temperature (RT). Results obtained by this technique on annealed samples prove that ferromagnetism in 57Fe-implanted SiC for Fe concentrations close to 2% and 4% is mostly due to Fe atoms diluted in the matrix. In contrast, for Fe concentrations close to 6%, it also comes from Fe in magnetic phase nano-clusters. This study allows quantifying the Fe amount in the interstitial and substitutional sites and the nanoparticles and shows that the majority of the diluted Fe atoms are substituted on Si sites inducing ferromagnetism up to RT.

Strategic coating of NdFeB magnets with Dy to improve the coercivity of permanent magnets

DOE PAGES

Ucar, Huseyin; Parker, David S.; Nlebedim, I. C.; ...

2015-12-25

Here, we present a method, supported by theoretical analysis, for optimizing the usage of the critical rare earth element dysprosium in Nd 2Fe 14B (NdFeB)-based permanent magnets. In this method, we use Dy selectively in locations such as magnet edges and faces, where demagnetization factors are most significant, rather than uniformly throughout the bulk sample. A 200 nm thick Dy film was sputtered onto commercial N-38, NdFeB magnets with a thickness of 3 mm and post-annealed at temperatures from 600 - 700 C. Magnets displayed enhanced coercivities after post-annealing. Furthermore, our experimental results indicate as large as a 5 percentmore » increase in the energy product of NdFeB magnets, achieved for a total Dy weight percentage of 0.06 percent, much less than that used in commercial grade Dy-NdFeB magnets. Finally, by assuming all Dy diffused into NdFeB magnets, the improvement in energy product corresponds to a saving of over 1% Dy (critical element). Magnets manufactured using this technique will therefore be higher performing and significantly less expensive than those made presently.« less

Magnetic response of hybrid ferromagnetic and antiferromagnetic core-shell nanostructures

NASA Astrophysics Data System (ADS)

Khan, U.; Li, W. J.; Adeela, N.; Irfan, M.; Javed, K.; Wan, C. H.; Riaz, S.; Han, X. F.

2016-03-01

The synthesis of FeTiO3-Ni(Ni80Fe20) core-shell nanostructures by a two-step method (sol-gel and DC electrodeposition) has been demonstrated. XRD analysis confirms the rhombohedral crystal structure of FeTiO3(FTO) with space group R3&cmb.macr;. Transmission electron microscopy clearly depicts better morphology of nanostructures with shell thicknesses of ~25 nm. Room temperature magnetic measurements showed significant enhancement of magnetic anisotropy for the permalloy (Ni80Fe20)-FTO over Ni-FTO core-shell nanostructures. Low temperature magnetic measurements of permalloy-FeTiO3 core-shell structure indicated a strong exchange bias mechanism with magnetic coercivity below the antiferromagnetic Neel temperature (TN = 59 K). The exchange bias is attributed to the alignment of magnetic moments in the antiferromagnetic material at low temperature. Our scheme opens a path towards optimum automotive systems and wireless communications wherein broader bandwidths and smaller sizes are required.The synthesis of FeTiO3-Ni(Ni80Fe20) core-shell nanostructures by a two-step method (sol-gel and DC electrodeposition) has been demonstrated. XRD analysis confirms the rhombohedral crystal structure of FeTiO3(FTO) with space group R3&cmb.macr;. Transmission electron microscopy clearly depicts better morphology of nanostructures with shell thicknesses of ~25 nm. Room temperature magnetic measurements showed significant enhancement of magnetic anisotropy for the permalloy (Ni80Fe20)-FTO over Ni-FTO core-shell nanostructures. Low temperature magnetic measurements of permalloy-FeTiO3 core-shell structure indicated a strong exchange bias mechanism with magnetic coercivity below the antiferromagnetic Neel temperature (TN = 59 K). The exchange bias is attributed to the alignment of magnetic moments in the antiferromagnetic material at low temperature. Our scheme opens a path towards optimum automotive systems and wireless communications wherein broader bandwidths and smaller sizes are required. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07946b

Hysteresis and change of transition temperature in thin films of Fe([Me{sub 2}Pyrz]{sub 3}BH){sub 2}, a new sublimable spin-crossover molecule

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davesne, V.; Gruber, M.; Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Str. 1, 76131 Karlsruhe

2015-05-21

Thin films of the spin-crossover (SCO) molecule Fe([Me{sub 2}Pyrz]{sub 3}BH){sub 2} (Fe-pyrz) were sublimed on Si/SiO{sub 2} and quartz substrates, and their properties investigated by X-ray absorption and photoemission spectroscopies, optical absorption, atomic force microscopy, and superconducting quantum interference device. Contrary to the previously studied Fe(phen){sub 2}(NCS){sub 2}, the films are not smooth but granular. The thin films qualitatively retain the typical SCO properties of the powder sample (SCO, thermal hysteresis, soft X-ray induced excited spin-state trapping, and light induced excited spin-state trapping) but present intriguing variations even in micrometer-thick films: the transition temperature decreases when the thickness is decreased,more » and the hysteresis is affected. We explain this behavior in the light of recent studies focusing on the role of surface energy in the thermodynamics of the spin transition in nano-structures. In the high-spin state at room temperature, the films have a large optical gap (∼5 eV), decreasing at thickness below 50 nm, possibly due to film morphology.« less

Observation of hidden atomic order at the interface between Fe and topological insulator Bi2Te3.

PubMed

Sánchez-Barriga, Jaime; Ogorodnikov, Ilya I; Kuznetsov, Mikhail V; Volykhov, Andrey A; Matsui, Fumihiko; Callaert, Carolien; Hadermann, Joke; Verbitskiy, Nikolay I; Koch, Roland J; Varykhalov, Andrei; Rader, Oliver; Yashina, Lada V

2017-11-22

To realize spintronic devices based on topological insulators (TIs), well-defined interfaces between magnetic metals and TIs are required. Here, we characterize atomically precisely the interface between the 3d transition metal Fe and the TI Bi 2 Te 3 at different stages of its formation. Using photoelectron diffraction and holography, we show that after deposition of up to 3 monolayers Fe on Bi 2 Te 3 at room temperature, the Fe atoms are ordered at the interface despite the surface disorder revealed by our scanning-tunneling microscopy images. We find that Fe occupies two different sites: a hollow adatom deeply relaxed into the Bi 2 Te 3 quintuple layers and an interstitial atom between the third (Te) and fourth (Bi) atomic layers. For both sites, our core-level photoemission spectra and density-functional theory calculations demonstrate simultaneous chemical bonding of Fe to both Te and Bi atoms. We further show that upon deposition of Fe up to a thickness of 20 nm, the Fe atoms penetrate deeper into the bulk forming a 2-5 nm interface layer containing FeTe. In addition, excessive Bi is pushed down into the bulk of Bi 2 Te 3 leading to the formation of septuple layers of Bi 3 Te 4 within a distance of ∼25 nm from the interface. Controlling the magnetic properties of the complex interface structures revealed by our work will be of critical importance when optimizing the efficiency of spin injection in TI-based devices.

Sharp transition from ripple patterns to a flat surface for ion beam erosion of Si with simultaneous co-deposition of iron

NASA Astrophysics Data System (ADS)

Zhang, K.; Brötzmann, M.; Hofsäss, H.

2012-09-01

We investigate pattern formation on Si by sputter erosion under simultaneous co-deposition of Fe atoms, both at off-normal incidence, as function of the Fe surface coverage. The patterns obtained for 5 keV Xe ion irradiation at 30° incidence angle are analyzed with atomic force microscopy. Rutherford backscattering spectroscopy of the local steady state Fe content of the Fe-Si surface layer allows a quantitative correlation between pattern type and Fe coverage. With increasing Fe coverage the patterns change, starting from a flat surface at low coverage (< 2×1015 Fe/cm2) over dot patterns (2-8×1015 Fe/cm2), ripples patterns (8-17×1015 Fe/cm2), pill bug structures (1.8×1016 Fe/cm2) and a rather flat surface with randomly distributed weak pits at high Fe coverage (>1.8×1016 Fe/cm2). Our results confirm the observations by Macko et al. for 2 keV Kr ion irradiation of Si with Fe co-deposition. In particular, we also find a sharp transition from pronounced ripple patterns with large amplitude (rms roughness ˜ 18 nm) to a rather flat surface (rms roughness ˜ 0.5 nm). Within this transition regime, we also observe the formation of pill bug structures, i.e. individual small hillocks with a rippled structure on an otherwise rather flat surface. The transition occurs within a very narrow regime of the steady state Fe surface coverage between 1.7 and 1.8×1016 Fe/cm2, where the composition of the mixed Fe-Si surface layer of about 10 nm thickness reaches the stoichiometry of FeSi2. Phase separation towards amorphous iron silicide is assumed as the major contribution for the pattern formation at lower Fe coverage and the sharp transition from ripple patterns to a flat surface.

Large magnetization and high Curie temperature in highly disordered nanoscale Fe2CrAl thin films

NASA Astrophysics Data System (ADS)

Dulal, Rajendra P.; Dahal, Bishnu R.; Forbes, Andrew; Pegg, Ian L.; Philip, John

2017-02-01

We have successfully grown nanoscale Fe2CrAl thin films on polished Si/SiO2 substrates using an ultra-high vacuum deposition with a base pressure of 9×10-10 Torr. The thickness of thin films ranges from 30 to 100 nm. These films exhibit cubic crystal structure with lattice disorder and display ferromagnetic behavior. The Curie temperature is greater than 400 K, which is much higher than that reported for bulk Fe2CrAl. The magnetic moments of the films varies from 2.5 to 2.8 μB per formula unit, which is larger than the reported bulk values. Thus, the disordered nanoscale Fe2CrAl films exhibit strong Fe-Fe exchange interactions through Fe-Cr-Fe and Fe-Al-Fe layers, resulting in both a large magnetization and a high Curie temperature.

Effects of surface topography on magnetization reversal of magnetic thin films.

PubMed

Girgis, E; Pogossian, S P; Benkhedar, M L

2006-04-01

The influence of the created surface roughness on the coercivity of magnetic thin films has been investigated. The magnetic thin films (CoFe and alternatively NiFe) are sputtered on top of smooth substrates that were previously covered with an array of considerably rougher lines with one of these materials Pt, Cu, CoFe, and NiFe. The lines have been patterned using optical lithography into arrays that are deposited with different thicknesses varying between 5 nm-15 nm. The lines have been designed to have a very rough edge and seated in two different angles relative to the wafer edge (zero and 45 degrees). Magneto-optic Kerr effect (MOKE) measurements showed two distinct switching fields in the hysteresis loops that are due to magnetic domain wall trapping created by the surface roughness. The magnetization reversal showed a strong dependence on the height, the orientation angle, and the material's type of the created surface roughness (the lines).

Formation and investigation of ultrathin layers of Co2FeSi ferromagnetic alloy synthesized on silicon covered with a CaF2 barrier layer

NASA Astrophysics Data System (ADS)

Grebenyuk, G. S.; Gomoyunova, M. V.; Pronin, I. I.; Vyalikh, D. V.; Molodtsov, S. L.

2016-03-01

Ultrathin (∼2 nm) films of Co2FeSi ferromagnetic alloy were formed on silicon by solid-phase epitaxy and studied in situ. Experiments were carried out in an ultrahigh vacuum (UHV) using substrates of Si(1 1 1) single crystals covered with a 5 nm thick CaF2 barrier layer. The elemental and phase composition as well as the magnetic properties of the synthesized films were analyzed by photoelectron spectroscopy using synchrotron radiation and by magnetic linear dichroism in photoemission of Fe 3p and Co 3p electrons. The study shows that the synthesis of the Co2FeSi ferromagnetic alloy occurs in the temperature range of 200-400 °C. At higher temperatures, the films become island-like and lose their ferromagnetic properties, as the CaF2 barrier layer is unable to prevent a mass transfer between the film and the Si substrate, which violates the stoichiometry of the alloy.

In situ study of heavy ion irradiation response of immiscible Cu/Fe multilayers

DOE PAGES

Chen, Youxing; Li, Nan; Bufford, Daniel Charles; ...

2016-04-09

By providing active defect sinks that capture and annihilate radiation induced defect clusters immiscible metallic multilayers with incoherent interfaces can effectively reduce defect density in ion irradiated metals. Although it is anticipated that defect density within the layers should vary as a function of distance to the layer interface, there is, to date, little in situ TEM evidence to validate this hypothesis. In our study monolithic Cu films and Cu/Fe multilayers with individual layer thickness, h, of 100 and 5 nm were subjected to in situ Cu ion irradiation at room temperature to nominally 1 displacement-per-atom inside a transmission electronmore » microscope. Rapid formation and propagation of defect clusters were observed in monolithic Cu, whereas fewer defects with smaller dimensions were generated in Cu/Fe multilayers with smaller h. Moreover, in situ video shows that the cumulative defect density in Cu/Fe 100 nm multilayers indeed varies, as a function of distance to the layer interfaces, supporting a long postulated hypothesis.« less

Hierarchically MnO2-Nanosheet Covered Submicrometer-FeCo2O4-Tube Forest as Binder-Free Electrodes for High Energy Density All-Solid-State Supercapacitors.

PubMed

Zhu, Baogang; Tang, Shaochun; Vongehr, Sascha; Xie, Hao; Meng, Xiangkang

2016-02-01

The current problem of the still relatively low energy densities of supercapacitors can be effectively addressed by designing electrodes hierarchically on micro- and nanoscale. Herein, we report the synthesis of hierarchically porous, nanosheet covered submicrometer tube forests on Ni foam. Chemical deposition and thermal treatment result in homogeneous forests of 750 nm diameter FeCo2O4 tubes, which after hydrothermal reaction in KMnO4 are wrapped in MnO2-nanosheet-built porous covers. The covers' thickness can be adjusted from 200 to 800 nm by KMnO4 concentration. An optimal thickness (380 nm) with a MnO2 content of 42 wt % doubles the specific capacitance (3.30 F cm(-2) at 1.0 mA cm(-2)) of the bare FeCo2O4-tube forests. A symmetric solid-state supercapacitor made from these binder-free electrodes achieves 2.52 F cm(-2) at 2 mA cm(-2), much higher than reported for capacitors based on similar core-shell nanowire arrays. The large capacitance and high cell voltage of 1.7 V allow high energy and power densities (93.6 Wh kg(-1), 10.1 kW kg(-1)). The device also exhibits superior rate capability (71% capacitance at 20 mA cm(-2)) and remarkable cycling stability with 94% capacitance retention being stable after 1500 cycles.

Electronic and magnetic properties of iron doped zirconia: Theory and experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Debernardi, A., E-mail: alberto.debernardi@mdm.imm.cnr.it; Sangalli, D.; Lamperti, A.

We systematically investigated, both theoretically and experimentally, Zr{sub 1−x}Fe{sub x}O{sub 2−y} ranging from diluted (x ≈ 0.05) up to large (x ≈ 0.25) Fe concentration. By atomic layer deposition, we grew thin films of high-κ zirconia in cubic phase with Fe uniformly distributed in the film, as proven by time of flight secondary ion mass spectrometry and transmission electron microscopy measurements. Iron is in Fe{sup 3+} oxidation state suggesting the formation of oxygen vacancies with y concentration close to x/2. By ab-initio simulations, we studied the phase diagram relating the stability of monoclinic vs. tetragonal phase as a function of Fe doping and filmmore » thickness: the critical thickness at which the pure zirconia is stabilized in the tetragonal phase is estimated ranging from 2 to 6 nm according to film morphology. Preliminary results by X-ray magnetic circular dichroism and alternating gradient force magnetometry are discussed in comparison to ab initio data enlightening the role of oxygen vacancies in the magnetic properties of the system.« less

Effect of film thickness on NO2 gas sensing properties of sprayed orthorhombic nanocrystalline V2O5 thin films

NASA Astrophysics Data System (ADS)

Mane, A. A.; Moholkar, A. V.

2017-09-01

The nanocrystalline V2O5 thin films with different thicknesses have been grown onto the glass substrates using chemical spray pyrolysis (CSP) deposition method. The XRD study shows that the films exhibit an orthorhombic crystal structure. The narrow scan X-ray photoelectron spectrum of V-2p core level doublet gives the binding energy difference of 7.3 eV, indicating that the V5+ oxidation state of vanadium. The FE-SEM micrographs show the formation of nanorods-like morphology. The AFM micrographs show the high surface area to volume ratio of nanocrystalline V2O5 thin films. The optical study gives the band gap energy values of 2.41 eV, 2.44 eV, 2.47 eV and 2.38 eV for V2O5 thin films deposited with the thicknesses of 423 nm, 559 nm, 694 nm and 730 nm, respectively. The V2O5 film of thickness 559 nm shows the NO2 gas response of 41% for 100 ppm concentration at operating temperature of 200 °C with response and recovery times of 20 s and 150 s, respectively. Further, it shows the rapid response and reproducibility towards 10 ppm NO2 gas concentration at 200 °C. Finally, NO2 gas sensing mechanism based on chemisorption process is discussed.

Field dependent magnetic anisotropy of Ga0.2Fe0.8 thin films

NASA Astrophysics Data System (ADS)

Resnick, Damon A.; McClure, A.; Kuster, C. M.; Rugheimer, P.; Idzerda, Y. U.

2011-04-01

Using longitudinal MOKE in combination with a variable strength rotating magnetic field, called the rotational MOKE (ROTMOKE) method, we show that the magnetic anisotropy for a Ga0.2Fe0.8 single crystal film with a thickness of 17 nm, grown on GaAs (001) with a thick ZnSe buffer layer, depends linearly on the strength of the applied magnetic field. The torque moment curves generated using ROTMOKE are well fit with a model that accounts for the uniaxial, cubic, or fourfold anisotropy, as well as additional terms with a linear dependence on the applied magnetic field. The uniaxial and cubic anisotropy fields, taken from both the hard and the easy axis scans, are seen to remain field independent. The field dependent terms are evidence of a large affect of the magnetostriction and its contribution to the effective magnetic anisotropy in GaxFe1-x thin films.

Dependence of Brillouin Light Scattering Spectra on the number of Bilayers in Fe/Ag Multilayer Specimens

NASA Astrophysics Data System (ADS)

From, Milton; Cheng, Li; Altounian, Zaven

2001-03-01

We have measured the Brillouin Light Scattering (BLS) spectra of [Fe/Ag] x N sputtered multilayers as a function of N, the number of bilayers in the multilayer. The thickness of the Fe and Ag layers was 1.5 nm and data was collected for samples with N = 5, 10, 25, and 40.The BLS instrument used was a 4-pass Fabry-Perot interferometer operated in the back-scattering geometry with 514.5 nm laser light. The number of peaks seen in the BLS spectra are seen to increase with N. Two peaks are seen for N=5, and four peaks are seen for N=10 and 25. For N = 40, we see two broad manifold peaks and a sharp surface mode peak. This N dependence and the detailed dependence of peak frequency on applied magnetic field are in good agreement with theoretical calculations.

Finite-size effects and magnetic exchange coupling in thin CoO layers

NASA Astrophysics Data System (ADS)

Ambrose, Thomas Francis

Finite size effects in CoO have been observed in CoO/SiOsb2 multilayers. The Neel temperatures of the CoO layers, as determined by dc susceptibility measurements, follow a finite-size scaling relation with a shift exponent lambda = 1.55 ± 0.05. This determined exponent is close to the theoretical value for finite size scaling in an Ising system. The value of the zero temperature correlation length has also been determined to be 18A, while antiferromagnetic ordering persists down to a CoO layer thickness of 10A. The properties of exchange biasing have been extensively studied in NiFe/CoO bilayers. The effects of the cooling field (Hsb{FC}), up to 50 kOe, on the resultant exchange field (Hsb{E}) and coercivity (Hsb{C}) have been examined. The value of Hsb{E} increases rapidly at low cooling fields (Hsb{FC} < 1kOe) and levels off for Hsb{FC} larger than 4 kOe. The value of Hsb{C} also depends upon Hsb{FC}, but less sensitively. The bilayer thickness also influences exchange biasing. We find that Hsb{E} varies inversely proprotional to both tsb{FM} and tsb{AF} where tsb{FM} and tsb{AF} are the ferromagnetic and antiferromagnetic layer thickness respectively. Because of the 1/tsb{AF}, the simple picture of interfacial coupling between ferromagnet and antiferromagnet spins appears to be inadequate. The assertion of long range coupling between ferromagnetic and antiferromagnetic layers has been verified by the observation of antiferromagnetic exchange coupling across spacer layers in NiFe/NM/CoO trilayers, where NM is a non-magnetic material. Exchange biasing has been observed in trilayers with metallic spacer layers up to 50A thick using Ag, Cu and Au, while no exchange field was observed for insulating spacer layers of any thickness using Alsb2Osb3, SiOsb2 and MgO. The temperature dependence of Hsb{E} and Hsb{C} and the effect of the deposition order have been studied in a series of bilayer (NiFe/CoO and CoO/NiFe) and trilayer (NiFe/CoO/NiFe) films. A profound difference in Hsb{E} was observed in samples with NiFe deposited on top of CoO compared to samples with CoO deposited on top of NiFe. When CoO is on top of NiFe Hsb{E} varies linearly with temperature, while for samples with NiFe on top of CoO Hsb{E} has a plateau followed by a rapid decrease. These distinct temperature dependences have been reproduced in NiFe/CoO/NiFe trilayers which contain both geometries. Structural analysis using Transmission Electron Microscopy indicate no apparent differences in the top and bottom interfaces. The angular dependence of the exchange coupling in a NiFe/CoO bilayer has been measured. Both Hsb{E} and Hsb{C} with unidirectional and uniaxial characteristics, respectively, are integral parts of the exchange coupling. The values of Hsb{E} can be expressed by a series of odd angle cosine terms, while the values of Hsb{C} can be expressed by a series of even angle cosine terms. Finally, exchange biasing has been used to "spin engineer" ferromagnetic layers in NiFe/CoO/NiFe trilayers. Four different spin structures have been observed. A phase diagram, for the four spin structures and the conditions with which each spin structure is obtained, has been determined. (Abstract shortened by UMI.)

Spin wave filtering and guiding in Permalloy/iron nanowires

NASA Astrophysics Data System (ADS)

Silvani, R.; Kostylev, M.; Adeyeye, A. O.; Gubbiotti, G.

2018-03-01

We have investigated the spin wave filtering and guiding properties of periodic array of single (Permalloy and Fe) and bi-layer (Py/Fe) nanowires (NWs) by means of Brillouin light scattering measurements and micromagnetic simulations. For all the nanowire arrays, the thickness of the layers is 10 nm while all NWs have the same width of 340 nm and edge-to-edge separation of 100 nm. Spin wave dispersion has been measured in the Damon-Eshbach configuration for wave vector either parallel or perpendicular to the nanowire length. This study reveals the filtering property of the spin waves when the wave vector is perpendicular to the NW length, with frequency ranges where the spin wave propagation is permitted separated by frequency band gaps, and the guiding property of NW when the wave vector is oriented parallel to the NW, with spin wave modes propagating in parallel channels in the central and edge regions of the NW. The measured dispersions were well reproduced by micromagnetic simulations, which also deliver the spatial profiles for the modes at zero wave vector. To reproduce the dispersion of the modes localized close to the NW edges, uniaxial anisotropy has been introduced. In the case of Permalloy/iron NWs, the obtained results have been compared with those for a 20 nm thick effective NW having average magnetic properties of the two materials.

Spin pumping in ion-beam sputtered C o2FeAl /Mo bilayers: Interfacial Gilbert damping

NASA Astrophysics Data System (ADS)

Husain, Sajid; Kumar, Ankit; Barwal, Vineet; Behera, Nilamani; Akansel, Serkan; Svedlindh, Peter; Chaudhary, Sujeet

2018-02-01

The spin-pumping mechanism and associated interfacial Gilbert damping are demonstrated in ion-beam sputtered C o2FeAl (CFA)/Mo bilayer thin films employing ferromagnetic resonance spectroscopy. The dependence of the net spin-current transportation on Mo layer thickness, 0 to 10 nm, and the enhancement of the net effective Gilbert damping are reported. The experimental data have been analyzed using spin-pumping theory in terms of spin current pumped through the ferromagnet/nonmagnetic metal interface to deduce the real spin-mixing conductance and the spin-diffusion length, which are estimated to be 1.56 (±0.30 ) ×1019m-2 and 2.61 (±0.15 )nm , respectively. The damping constant is found to be 8.8 (±0.2 ) ×10-3 in the Mo(3.5 nm)-capped CFA(8 nm) sample corresponding to an ˜69 % enhancement of the original Gilbert damping 5.2 (±0.6 ) ×10-3 in the Al-capped CFA thin film. This is further confirmed by inserting the Cu dusting layer which reduces the spin transport across the CFA/Mo interface. The Mo layer thickness-dependent net spin-current density is found to lie in the range of 1 -4 MA m-2 , which also provides additional quantitative evidence of spin pumping in this bilayer thin-film system.

Self-organized nano-structuring of CoO islands on Fe(001)

NASA Astrophysics Data System (ADS)

Brambilla, A.; Picone, A.; Giannotti, D.; Riva, M.; Bussetti, G.; Berti, G.; Calloni, A.; Finazzi, M.; Ciccacci, F.; Duò, L.

2016-01-01

The realization of nanometer-scale structures through bottom-up strategies can be accomplished by exploiting a buried network of dislocations. We show that, by following appropriate growth steps in ultra-high vacuum molecular beam epitaxy, it is possible to grow nano-structured films of CoO coupled to Fe(001) substrates, with tunable sizes (both the lateral size and the maximum height scale linearly with coverage). The growth mode is discussed in terms of the evolution of surface morphology and chemical interactions as a function of the CoO thickness. Scanning tunneling microscopy measurements reveal that square mounds of CoO with lateral dimensions of less than 25 nm and heights below 10 atomic layers are obtained by growing few-nanometers-thick CoO films on a pre-oxidized Fe(001) surface covered by an ultra-thin Co buffer layer. In the early stages of growth, a network of misfit dislocations develops, which works as a template for the CoO nano-structuring. From a chemical point of view, at variance with typical CoO/Fe interfaces, neither Fe segregation at the surface nor Fe oxidation at the buried interface are observed, as seen by Auger electron spectroscopy and X-ray Photoemission Spectroscopy, respectively.

Nano-structured variable capacitor based on P(VDF-TrFE) copolymer and carbon nanotubes

NASA Astrophysics Data System (ADS)

Lakbita, I.; El-Hami, K.

2018-02-01

A newly organic capacitor was conceived with a variable capacitance using the inverse piezoelectric effect. The device consists of two parallel plates of carbon nanotubes (CNTs), known for their large surface area, high sensitivity and high electric conductivity, separated by a thin film of a dielectric layer of Polyinylidene fluoride and trifluoroehtylene (P(VDF-TrFE)) promising material for piezoelectric and ferroelectric properties. The obtained architecture is the CNT/PVDF-TrFE/CNT capacitor device. In this study, an ultra-thin film of P(VDF-TrFE) (54/46) with thickness of 20 nm was elaborated on highly oriented pyrolytic graphite (HOPG) by spin-coating. The morphology of the ultra-thin film and the mechanical behavior of CNT/P(VDF-TrFE)/CNT system were studied using the atomic force microscopy (AFM) combined with a lock-in amplifier in contact mode. All changes in applied voltage induce a change in thin film thickness according to the inverse piezoelectric effect that affect, consequently the capacitance. The results showed that the ratio of capacitance change ΔC to initial capacitance C0 is ΔC/C0=5%. This value is sufficient to use P(VDF-TrFE) as variable organic capacitor.

Magnetic microstructure and magnetic properties of uniaxial itinerant ferromagnet Fe 3GeTe 2

DOE PAGES

León-Brito, Neliza; Bauer, Eric Dietzgen; Ronning, Filip; ...

2016-08-28

Here, magnetic force microscopy was used to observe the magnetic microstructure of Fe 3GeTe 2 at 4 K on the (001) surface. The surface magnetic structure consists of a two-phase domain branching pattern that is characteristic for highly uniaxial magnets in the plane perpendicular to the magnetic easy axis. The average surface magnetic domain width D s = 1.3 μm determined from this pattern, in combination with intrinsic properties calculated from bulk magnetization data (the saturation magnetization M s = 376 emu/cm 3 and the uniaxial magnetocrystalline anisotropy constant K u = 1.46 × 10 7 erg/cm 3), was usedmore » to determine the following micromagnetic parameters for Fe 3GeTe 2 from phenomenological models: the domain wall energy γ w = 4.7 erg/cm 2, the domain wall thickness δ w = 2.5 nm, the exchange stiffness constant A ex = 0.95 × 10 –7 erg/cm, the exchange length l ex = 2.3 nm, and the critical single domain particle diameter d c = 470 nm.« less

Sub-natural width resonances in Cs vapor confined in micrometric thickness optical cell

NASA Astrophysics Data System (ADS)

Cartaleva, S.; Krasteva, A.; Sargsyan, A.; Sarkisyan, D.; Slavov, D.; Vartanyan, T.

2013-03-01

We present here the behavior of Electromagnetically Induced Transparency (EIT), Velocity Selective Optical Pumping (VSOP) resonances and Velocity Selective Excitation (VSE) resonances observed in Cs vapor confined in а micrometric optical cell (MC) with thickness L = 6λ, λ = 852nm. For comparison of behavior of VSE resonance another conventional optical cell with thickness L=2.5 cm is used. Cells are irradiated in orthogonal to their windows directions by probe beam scanned on the Fg = 4 → Fe= 3, 4, 5 set of transitions and pump beam fixed at the Fg = 3 → Fe = 4 transition, on the D2 line of Cs. The enhanced absorption (fluorescence) narrow VSOP resonance at the closed transition transforms into reduced absorption (fluorescence) one with small increase of atomic concentration or light intensity. A striking difference appears between the VSE resonance broadening in L = 6λ and conventional L = 2.5cm cells.

Effect of Steel Galvanization on the Microstructure and Mechanical Performances of Planar Magnetic Pulse Welds of Aluminum and Steel

NASA Astrophysics Data System (ADS)

Avettand-Fènoël, M.-N.; Khalil, C.; Taillard, R.; Racineux, G.

2018-07-01

For the first time, planar joints between pure aluminum and galvanized or uncoated DP450 steel joints have been developed via magnetic pulse welding. Both present a wavy interface. The microstructure of the interfacial zone differs according to the joint. With uncoated steel, the interface is composed of discrete 2.5- µm-thick FeAl3 intermetallic compounds and Fe penetration lamellae, whereas the interface of the pure Al-galvanized steel joint is bilayered and composed of a 10-nm-thick (Al)Zn solid solution and a few micrometers thick aggregate of Al- and Zn-based grains, arranged from the Al side to the Zn coating. Even if the nature of the interfacial zone differs with or without the steel coating, both welds present rather similar maximum tensile forces and ductility in shear lap testing.

Effect of Steel Galvanization on the Microstructure and Mechanical Performances of Planar Magnetic Pulse Welds of Aluminum and Steel

NASA Astrophysics Data System (ADS)

Avettand-Fènoël, M.-N.; Khalil, C.; Taillard, R.; Racineux, G.

2018-05-01

For the first time, planar joints between pure aluminum and galvanized or uncoated DP450 steel joints have been developed via magnetic pulse welding. Both present a wavy interface. The microstructure of the interfacial zone differs according to the joint. With uncoated steel, the interface is composed of discrete 2.5-µm-thick FeAl3 intermetallic compounds and Fe penetration lamellae, whereas the interface of the pure Al-galvanized steel joint is bilayered and composed of a 10-nm-thick (Al)Zn solid solution and a few micrometers thick aggregate of Al- and Zn-based grains, arranged from the Al side to the Zn coating. Even if the nature of the interfacial zone differs with or without the steel coating, both welds present rather similar maximum tensile forces and ductility in shear lap testing.

Thickness-dependent enhancement of damping in C o2FeAl /β -Ta thin films

NASA Astrophysics Data System (ADS)

Akansel, Serkan; Kumar, Ankit; Behera, Nilamani; Husain, Sajid; Brucas, Rimantas; Chaudhary, Sujeet; Svedlindh, Peter

2018-04-01

In the present work C o2FeAl (CFA) thin films were deposited by ion beam sputtering on Si (100) substrates at the optimized deposition temperature of 300 °C. A series of CFA films with different thicknesses (tCFA), 8, 10, 12, 14, 16, 18, and 20 nm, were prepared and all samples were capped with a 5-nm-thick β-Ta layer. The thickness-dependent static and dynamic properties of the films were studied by SQUID magnetometry, in-plane as well as out-of-plane broadband vector network analyzer-ferromagnetic resonance (FMR) measurements, and angle-dependent cavity FMR measurements. The saturation magnetization and the coercive field were found to be weakly thickness dependent and lie in the range 900-950 kA/m and 0.53-0.87 kA/m, respectively. The effective damping parameter (αeff) extracted from in-plane and out-of-plane FMR results reveals a 1/tCFA dependence, the values for the in-plane αeff being larger due to two-magnon scattering (TMS). The origin of the αeff thickness dependence is spin pumping into the nonmagnetic β-Ta layer and in the case of the in-plane αeff, also a thickness-dependent TMS contribution. From the out-of-plane FMR results, it was possible to disentangle the different contributions to αeff and to the extract values for the intrinsic Gilbert damping (αG) and the effective spin-mixing conductance (geff↑↓) of the CFA/ β-Ta interface, yielding αG=(1.1 ±0.2 ) ×10-3 and geff↑↓=(2.90 ±0.10 ) ×1019m-2 .

Faraday rotation enhancement of gold coated Fe2O3 nanoparticles: comparison of experiment and theory.

PubMed

Dani, Raj Kumar; Wang, Hongwang; Bossmann, Stefan H; Wysin, Gary; Chikan, Viktor

2011-12-14

Understanding plasmonic enhancement of nanoscale magnetic materials is important to evaluate their potential for application. In this study, the Faraday rotation (FR) enhancement of gold coated Fe(2)O(3) nanoparticles (NP) is investigated experimentally and theoretically. The experiment shows that the Faraday rotation of a Fe(2)O(3) NP solution changes from approximately 3 rad/Tm to 10 rad/Tm as 5 nm gold shell is coated on a 9.7 nm Fe(2)O(3) core at 632 nm. The results also show how the volume fraction normalized Faraday rotation varies with the gold shell thickness. From the comparison of experiment and calculated Faraday rotation based on the Maxwell-Garnett theory, it is concluded that the enhancement and shell dependence of Faraday rotation of Fe(2)O(3) NPs is a result of the shifting plasmon resonance of the composite NP. In addition, the clustering of the NPs induces a different phase lag on the Faraday signal, which suggests that the collective response of the magnetic NP aggregates needs to be considered even in solution. From the Faraday phase lag, the estimated time of the full alignment of the magnetic spins of bare (cluster size 160 nm) and gold coated NPs (cluster size 90 nm) are found to be 0.65 and 0.17 μs. The calculation includes a simple theoretical approach based on the Bruggeman theory to account for the aggregation and its effect on the Faraday rotation. The Bruggeman model provides a qualitatively better agreement with the experimentally observed Faraday rotation and points out the importance of making a connection between component properties and the average "effective" optical behavior of the Faraday medium containing magnetic nanoparticles. © 2011 American Institute of Physics

Effect of heavy metal layer thickness on spin-orbit torque and current-induced switching in Hf|CoFeB|MgO structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akyol, Mustafa; Department of Physics, University of Çukurova, Adana 01330; Jiang, Wanjun

We study the heavy metal layer thickness dependence of the current-induced spin-orbit torque (SOT) in perpendicularly magnetized Hf|CoFeB|MgO multilayer structures. The damping-like (DL) current-induced SOT is determined by vector anomalous Hall effect measurements. A non-monotonic behavior in the DL-SOT is found as a function of the thickness of the heavy-metal layer. The sign of the DL-SOT changes with increasing the thickness of the Hf layer in the trilayer structure. As a result, in the current-driven magnetization switching, the preferred direction of switching for a given current direction changes when the Hf thickness is increased above ∼7 nm. Although there might bemore » a couple of reasons for this unexpected behavior in DL-SOT, such as the roughness in the interfaces and/or impurity based electric potential in the heavy metal, one can deduce a roughness dependence sign reversal in DL-SOT in our trilayer structure.« less

Fabrication of graphene oxide decorated with Fe3O4@SiO2 for immobilization of cellulase

NASA Astrophysics Data System (ADS)

Li, Yue; Wang, Xiang-Yu; Jiang, Xiao-Ping; Ye, Jing-Jing; Zhang, Ye-Wang; Zhang, Xiao-Yun

2015-01-01

Fe3O4@SiO2-graphene oxide (GO) composites were successfully fabricated by chemical binding of functional Fe3O4@SiO2 and GO and applied to immobilization of cellulase via covalent attachment. The prepared composites were further characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. Fe3O4 nanoparticles (NPs) were monodisperse spheres with a mean diameter of 17 ± 0.2 nm. The thickness of SiO2 layer was calculated as being 6.5 ± 0.2 nm. The size of Fe3O4@SiO2 NPs was 24 ± 0.3 nm, similar to that of Fe3O4@SiO2-NH2. Fe3O4@SiO2-GO composites were synthesized by linking of Fe3O4@SiO2-NH2 NPs to GO with the catalysis of EDC and NHS. The prepared composites were used for immobilization of cellulase. A high immobilization yield and efficiency of above 90 % were obtained after the optimization. The half-life of immobilized cellulase (722 min) was 3.34-fold higher than that of free enzyme (216 min) at 50 °C. Compared with the free cellulase, the optimal temperature of the immobilized enzyme was not changed; but the optimal pH was shifted from 5.0 to 4.0, and the thermal stability was enhanced. The immobilized cellulase could be easily separated and reused under magnetic field. These results strongly indicate that the cellulase immobilized onto the Fe3O4@SiO2-GO composite has potential applications in the production of bioethanol.

Exchange coupled CoPt/FePtC media for heat assisted magnetic recording

NASA Astrophysics Data System (ADS)

Dutta, Tanmay; Piramanayagam, S. N.; Ru, Tan Hui; Saifullah, M. S. M.; Bhatia, C. S.; Yang, Hyunsoo

2018-04-01

L10 FePtC granular media are being studied as potential future magnetic recording media and are set to be used in conjunction with heat assisted magnetic recording (HAMR) to enable recording at write fields within the range of current day recording heads. Media structures based on a FePtC storage layer and a capping layer can alleviate the switching field distribution (SFD) requirements of HAMR and reduce the noise originating from the writing process. However, the current designs suffer from SFD issues due to high temperature writing. To overcome this problem, we study a CoPt/FePtC exchange coupled composite structure, where FePtC serves as the storage layer and CoPt (with higher Curie temperature, Tc) as the capping layer. CoPt remains ferromagnetic at near Tc of FePtC. Consequently, the counter exchange energy from CoPt would reduce the noise resulting from the adjacent grain interactions during the writing process. CoPt/FePtC bilayer samples with different thicknesses of CoPt were investigated. Our studies found that CoPt forms a continuous layer at a thickness of 6 nm and leads to considerable reduction in the saturation field and its distribution.

Efficient one-pot sonochemical synthesis of thickness-controlled silica-coated superparamagnetic iron oxide (Fe3O4/SiO2) nanospheres

NASA Astrophysics Data System (ADS)

Abbas, Mohamed; Abdel-Hamed, M. O.; Chen, Jiangang

2017-12-01

A facile and eco-friendly efficient sonochemical approach was designed for the synthesis of highly crystalline Fe3O4 and Fe3O4/SiO2 core/shell nanospheres in single reaction. The generated physical properties (shock waves, microjets, and turbulent flows) from ultrasonication as a consequence of the collapse of microbubbles and polyvinylpyrrolidone (PVP) as a chemical linker were found to play a crucial role in the successful formation of the core/shell NPs within short time than the previously reported methods. Transmission electron microscopy revealed that a uniform SiO2 shell is successfully coated over Fe3O4 nanospheres, and the thickness of the silica shell could be easily controlled in the range from 5 to 15 nm by adjusting the reaction parameters. X-ray diffraction data were employed to confirm the formation of highly crystalline and pure phase of a cubic inverse spinel structure for magnetite (Fe3O4) nanospheres. The magnetic properties of the as-synthesized Fe3O4 and Fe3O4/SiO2 core/shell nanospheres were measured at room temperature using vibrating sample magnetometer, and the results demonstrated a high magnetic moment values with superparamagnetic properties.

Enhanced magnetic moment in ultrathin Fe-doped CoFe2O4 films

NASA Astrophysics Data System (ADS)

Moyer, J. A.; Vaz, C. A. F.; Kumah, D. P.; Arena, D. A.; Henrich, V. E.

2012-11-01

The effect of film thickness on the magnetic properties of ultrathin Fe-doped cobalt ferrite (Co1-xFe2+xO4) grown on MgO (001) substrates is investigated by superconducting quantum interference device magnetometry and x-ray magnetic linear dichroism, while the distribution of the Co2+ cations between the octahedral and tetrahedral lattice sites is studied with x-ray absorption spectroscopy. For films thinner than 10 nm, there is a large enhancement of the magnetic moment; conversely, the remanent magnetization and coercive fields both decrease, while the magnetic spin axes of all the cations become less aligned with the [001] crystal direction. In particular, at 300 K the coercive fields of the thinnest films vanish. The spectroscopy data show that no changes occur in the cation distribution as a function of film thickness, ruling this out as the origin of the enhanced magnetic moment. However, the magnetic measurements all support the possibility that these ultrathin Fe-doped CoFe2O4 films are transitioning into a superparamagnetic state, as has been seen in ultrathin Fe3O4. A weakening of the magnetic interactions at the antiphase boundaries, leading to magnetically independent domains within the film, could explain the enhanced magnetic moment in ultrathin Fe-doped CoFe2O4 and the onset of superparamagnetism at room temperature.

Tailoring of Perpendicular Magnetic Anisotropy in Dy13Fe87 Thin Films with Hexagonal Antidot Lattice Nanostructure

PubMed Central

Vega, Victor; Ibabe, Angel; Jaafar, Miriam; Asenjo, Agustina

2018-01-01

In this article, the magnetic properties of hexagonally ordered antidot arrays made of Dy13Fe87 alloy are studied and compared with corresponding ones of continuous thin films with the same compositions and thicknesses, varying between 20 nm and 50 nm. Both samples, the continuous thin films and antidot arrays, were prepared by high vacuum e-beam evaporation of the alloy on the top-surface of glass and hexagonally self-ordered nanoporous alumina templates, which serve as substrates, respectively. By using a highly sensitive magneto-optical Kerr effect (MOKE) and vibrating sample magnetometer (VSM) measurements an interesting phenomenon has been observed, consisting in the easy magnetization axis transfer from a purely in-plane (INP) magnetic anisotropy to out-of-plane (OOP) magnetization. For the 30 nm film thickness we have measured the volume hysteresis loops by VSM with the easy magnetization axis lying along the OOP direction. Using magnetic force microscopy measurements (MFM), there is strong evidence to suggest that the formation of magnetic domains with OOP magnetization occurs in this sample. This phenomenon can be of high interest for the development of novel magnetic and magneto-optic perpendicular recording patterned media based on template-assisted deposition techniques. PMID:29642476

Tailoring of Perpendicular Magnetic Anisotropy in Dy13Fe87 Thin Films with Hexagonal Antidot Lattice Nanostructure.

PubMed

Salaheldeen, Mohamed; Vega, Victor; Ibabe, Angel; Jaafar, Miriam; Asenjo, Agustina; Fernandez, Agustin; Prida, Victor M

2018-04-08

In this article, the magnetic properties of hexagonally ordered antidot arrays made of Dy 13 Fe 87 alloy are studied and compared with corresponding ones of continuous thin films with the same compositions and thicknesses, varying between 20 nm and 50 nm. Both samples, the continuous thin films and antidot arrays, were prepared by high vacuum e-beam evaporation of the alloy on the top-surface of glass and hexagonally self-ordered nanoporous alumina templates, which serve as substrates, respectively. By using a highly sensitive magneto-optical Kerr effect (MOKE) and vibrating sample magnetometer (VSM) measurements an interesting phenomenon has been observed, consisting in the easy magnetization axis transfer from a purely in-plane (INP) magnetic anisotropy to out-of-plane (OOP) magnetization. For the 30 nm film thickness we have measured the volume hysteresis loops by VSM with the easy magnetization axis lying along the OOP direction. Using magnetic force microscopy measurements (MFM), there is strong evidence to suggest that the formation of magnetic domains with OOP magnetization occurs in this sample. This phenomenon can be of high interest for the development of novel magnetic and magneto-optic perpendicular recording patterned media based on template-assisted deposition techniques.

Thickness dependence of voltage-driven magnetization switching in FeCo/PI/piezoelectric actuator heterostructures

NASA Astrophysics Data System (ADS)

Cui, B. S.; Guo, X. B.; Wu, K.; Li, D.; Zuo, Y. L.; Xi, L.

2016-03-01

Strain mediated magnetization switching of ferromagnetic/substrate/piezoelectric actuator heterostructures has become a hot issue due to the advantage of low-power consumption. In this work, Fe65Co35 thin films were deposited on a flexible polyamides (PI) substrate, which has quite low Young’s module (~4 GPa for PI as compared to ~180 GPa for Si) and benefits from complete transfer of the strain from the piezoelectric actuator to magnetic thin films. A complete 90° transition of the magnetic easy axis was realized in 50 nm thick FeCo films under the voltage of 70 V, while a less than 90° rotation angle of the magnetic easy axis direction was observed in other samples, which was ascribed to the distribution of the anisotropy field and/or the orthogonal misalignment between stress induced anisotropy and original uniaxial anisotropy. A model considering two uniaxial anisotropies with orthogonal arrangement was used to quantitatively understand the observed results and the linear-like voltage dependent anisotropy field, especially for 10 nm FeCo films, in which the switching mechanism along the easy axis direction can be explained by the domain wall depinning model. It indicates that the magnetic domain-wall movement velocity may be controlled by strain through tuning the energy barrier of the pinning in heterostructures. Moreover, voltage-driven 90° magnetization switching with low-power consumption was achieved in this work.

Role of spin polarization in FM/Al/FM trilayer film at low temperature

NASA Astrophysics Data System (ADS)

Lu, Ning; Webb, Richard

2014-03-01

Measurements of electronic transport in diffusive FM/normal metal/FM trilayer film are performed at temperature ranging from 2K to 300K to determine the behavior of the spin polarized current in normal metal under the influence of quantum phase coherence and spin-orbital interaction. Ten samples of Hall bar with length of 200 micron and width of 20 micron are fabricated through e-beam lithography followed by e-gun evaporation of Ni0.8Fe0.2, aluminum and Ni0.8Fe0.2 with different thickness (5nm to 45nm) in vacuum. At low temperature of 4.2K, coherent backscattering, Rashba spin-orbital interaction and spin flip scattering of conduction electrons contribute to magnetoresistance at low field. Quantitative analysis of magnetoresistance shows transition between weak localization and weak anti-localization for samples with different thickness ratio, which indicates the spin polarization actually affects the phase coherence length and spin-orbital scattering length. However, at temperature between 50K and 300K, only the spin polarization dominates the magnetoresistance.

Downscaling ferroelectric field effect transistors by using ferroelectric Si-doped HfO2

NASA Astrophysics Data System (ADS)

Martin, Dominik; Yurchuk, Ekaterina; Müller, Stefan; Müller, Johannes; Paul, Jan; Sundquist, Jonas; Slesazeck, Stefan; Schlösser, Till; van Bentum, Ralf; Trentzsch, Martin; Schröder, Uwe; Mikolajick, Thomas

2013-10-01

Throughout the 22 nm technology node HfO2 is established as a reliable gate dielectric in contemporary complementary metal oxide semiconductor (CMOS) technology. The working principle of ferroelectric field effect transistors FeFET has also been demonstrated for some time for dielectric materials like Pb[ZrxTi1-x]O3 and SrBi2Ta2O9. However, integrating these into contemporary downscaled CMOS technology nodes is not trivial due to the necessity of an extremely thick gate stack. Recent developments have shown HfO2 to have ferroelectric properties, given the proper doping. Moreover, these doped HfO2 thin films only require layer thicknesses similar to the ones already in use in CMOS technology. This work will show how the incorporation of Si induces ferroelectricity in HfO2 based capacitor structures and finally demonstrate non-volatile storage in nFeFETs down to a gate length of 100 nm. A memory window of 0.41 V can be retained after 20,000 switching cycles. Retention can be extrapolated to 10 years.

Magnetic and Transport Properties of Heterostructured Films of Prussian Blue Analogues and Manganites

NASA Astrophysics Data System (ADS)

Quintero, P. A.; Jeen, H.; Knowles, E. S.; Biswas, A.; Meisel, M. W.; Andrus, M. J.; Talham, D. R.

2011-03-01

The magnetic and transport properties of heterostructured films consisting of Prussian blue analogues, Aj M' k [M(CN)6 ]l . n H2 O (M' M-PBA), where A is an alkali ion and M' ,M are transition metals, and manganites have been studied. Specifically, NiCr-PBA and CoFe-PBA films of ~ 100 ~nm thickness have been deposited on perovskite (La 1-y Pr y)0.67 Ca 0.33 Mn O3 (LPCMO) manganese films of ~ 30 ~nm thickness. The effect of the ferromagnetic NiCr-PBA, Tc ~ 70 ~K, and the photo-controllable ferrimagnetic CoFe-PBA, Tc ~ 20 ~K, on the I-V properties of the LPCMO will be reported, where special attention will be given to the changes of the transition temperatures of the ferromagnetic metallic (FMM) and the charge-ordered insulating (COI) phases in the LPCMO substrate. ** Supported by NSF DMR-0701400 (MWM), DMR-0804452 (AB), DMR-1005581 (DRT), DMR-0654118 (NHMFL), and by scholarship from the Organization of American States (PAQ). D.M.~Pajerowski et al., J.~Am.~Chem. Soc. 132 (2010) 4058.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Cheng-Cheng; Wang, Ru-Zhi, E-mail: wrz@bjut.edu.cn; Zhu, Man-Kang

GaN nanofilms (NFs) with different structures are grown on SiC substrates by pulsed laser deposition under different conditions. The synthesized GaN NFs are studied by X-ray diffraction, field-emission (FE) scanning electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. The GaN NFs are composed of diversified GaN nanoparticles with a diameter of 9–38 nm, thickness of 10–50 nm, and roughness of 0.22–13.03 nm. FE from the GaN NFs is structure dependent, which is explained by stress changing the band gap of the NFs. By structure modulation, the turn-on field of GaN NFs can be as low as 0.66 V/μm at a current density ofmore » 1 μA/cm{sup 2}, with a current density of up to 1.1 mA/cm{sup 2} at a field of 4.18 V/μm. Fowler-Nordheim curves of some samples contain multiple straight lines, which originate from the structural change and diversification of GaN nanoparticles under an applied field. Overall, our results suggest that GaN NFs with excellent FE properties can be prepared on SiC substrates, which provides a new route to fabricate high-efficiency FE nanodevices.« less

Dependence of the optical constants and the performance in the SPREE gas measurement on the thickness of doped tin oxide over coatings

NASA Astrophysics Data System (ADS)

Fischer, D.; Hertwig, A.; Beck, U.; Negendank, D.; Lohse, V.; Kormunda, M.; Esser, N.

2017-11-01

In this study, thickness related changes of the optical properties of doped tin oxide were studied. Two different sets of samples were prepared. The first set was doped with iron or nickel on silicon substrate with thicknesses of 29-56 nm, the second was iron doped on gold/glass substrate with 1.6-6.3 nm. The optical constants were determined by using spectral ellipsometry (SE) followed by modelling of the dielectric function with an oscillator model using Gaussian peaks. The analysis of the optical constants shows a dependence of the refraction and the absorption on the thickness of the doped tin oxide coating. In addition to the tin oxide absorption in the UV, one additional absorption peak was found in the near-IR/red which is related to plasmonic effects due to the doping. This peak shifts from the near-IR to the red part of the visible spectrum and becomes stronger by reducing the thickness, probably due to the formation of metal nanoparticles in this layer. These results were found for two different sets of samples by using the same optical model. Afterwards the second sample set was tested in the Surface Plasmon Resonance Enhanced Ellipsometric (SPREE) gas measurement with CO gas. It was found that the thickness has significant influence on the sensitivity and thus the adsorption of the CO gas. By increasing the thickness from 1.6 nm to 5.1 nm, the sensing ability is enhanced due to a higher coverage of the surface with the over coating. This is explained by the high affinity of CO molecules to the incorporated Fe-nanoparticles in the tin oxide coating. By increasing the thickness further to 6.3 nm, the sensing ability drops because the layer disturbs the SPR sensing effect too much.

Perpendicular magnetic anisotropy in Ta|Co{sub 40}Fe{sub 40}B{sub 20}|MgAl{sub 2}O{sub 4} structures and perpendicular CoFeB|MgAl{sub 2}O{sub 4}|CoFeB magnetic tunnel junction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tao, B. S.; Li, D. L.; Yuan, Z. H.

2014-09-08

Magnetic properties of Co{sub 40}Fe{sub 40}B{sub 20} (CoFeB) thin films sandwiched between Ta and MgAl{sub 2}O{sub 4} layers have been systematically studied. For as-grown state, Ta/CoFeB/MgAl{sub 2}O{sub 4} structures exhibit good perpendicular magnetic anisotropy (PMA) with interface anisotropy K{sub i} = 1.22 erg/cm{sup 2}, which further increases to 1.30 erg/cm{sup 2} after annealing, while MgAl{sub 2}O{sub 4}/CoFeB/Ta multilayer shows in-plane magnetic anisotropy and must be annealed in order to achieve PMA. For bottom CoFeB layer, the thickness window for PMA is from 0.6 to 1.0 nm, while that for top CoFeB layer is between 0.8 and 1.4 nm. Perpendicular magnetic tunnel junctions (p-MTJs) with a coremore » structure of CoFeB/MgAl{sub 2}O{sub 4}/CoFeB have also been fabricated and tunneling magnetoresistance ratio of about 36% at room temperature and 63% at low temperature have been obtained. The intrinsic excitations in the p-MTJs have been identified by inelastic electron-tunneling spectroscopy.« less

Unusual enhancement of effective magnetic anisotropy with decreasing particle size in maghemite nanoparticles

NASA Astrophysics Data System (ADS)

Pisane, K. L.; Singh, Sobhit; Seehra, M. S.

2017-05-01

In magnetic nanoparticles (NPs), the observed increase in the effective magnetic anisotropy Keff with the decrease in particle size D is often interpreted, sometimes unsuccessfully, using the equation Keff = Kb + (6KS/D), where Kb is the bulk-like anisotropy of the core spins and KS is the anisotropy of spins in the surface layer. Here, we test the validity of this relation in γ-Fe2O3 NPs for sizes D from 15 nm to 2.5 nm. The samples include oleic acid-coated NPs with D = 2.5, 3.4, 6.3, and 7.0 nm investigated here, with results on 14 other sizes taken from literature. Keff is determined from the analysis of the frequency dependence of the blocking temperature TB after considering the effects of interparticle interactions on TB. For the γ-Fe2O3 NPs with D < 5 nm, an unusual enhancement of Keff with decreasing D, well above the magnitudes predicted by the above equation, is observed. Instead the variation of Keff vs. D is best described by an extension of the above equation by including Ksh term from spins in a shell of thickness d. Based on this core-shell-surface layer model, the data are fit to the equation Keff = Kb + (6KS/D) + Ksh{[1-(2d/D)]-3-1} with Kb = 1.9 × 105 ergs/cm3, KS = 0.035 ergs/cm2, and Ksh = 1.057 × 104 ergs/cm3 as the contribution of spins in the shell of thickness d = 1.1 nm. Significance of this result is discussed.

Sharp transition from ripple patterns to a flat surface for ion beam erosion of Si with simultaneous co-deposition of iron

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, K.; Broetzmann, M.; Hofsaess, H.

We investigate pattern formation on Si by sputter erosion under simultaneous co-deposition of Fe atoms, both at off-normal incidence, as function of the Fe surface coverage. The patterns obtained for 5 keV Xe ion irradiation at 30 Degree-Sign incidence angle are analyzed with atomic force microscopy. Rutherford backscattering spectroscopy of the local steady state Fe content of the Fe-Si surface layer allows a quantitative correlation between pattern type and Fe coverage. With increasing Fe coverage the patterns change, starting from a flat surface at low coverage (< 2 Multiplication-Sign 10{sup 15} Fe/cm{sup 2}) over dot patterns (2-8 Multiplication-Sign 10{sup 15}more » Fe/cm{sup 2}), ripples patterns (8-17 Multiplication-Sign 10{sup 15} Fe/cm{sup 2}), pill bug structures (1.8 Multiplication-Sign 10{sup 16} Fe/cm{sup 2}) and a rather flat surface with randomly distributed weak pits at high Fe coverage (>1.8 Multiplication-Sign 10{sup 16} Fe/cm{sup 2}). Our results confirm the observations by Macko et al. for 2 keV Kr ion irradiation of Si with Fe co-deposition. In particular, we also find a sharp transition from pronounced ripple patterns with large amplitude (rms roughness {approx} 18 nm) to a rather flat surface (rms roughness {approx} 0.5 nm). Within this transition regime, we also observe the formation of pill bug structures, i.e. individual small hillocks with a rippled structure on an otherwise rather flat surface. The transition occurs within a very narrow regime of the steady state Fe surface coverage between 1.7 and 1.8 Multiplication-Sign 10{sup 16} Fe/cm{sup 2}, where the composition of the mixed Fe-Si surface layer of about 10 nm thickness reaches the stoichiometry of FeSi{sub 2}. Phase separation towards amorphous iron silicide is assumed as the major contribution for the pattern formation at lower Fe coverage and the sharp transition from ripple patterns to a flat surface.« less

Achieving the broader frequency electromagnetic absorber by development of magnetic core-shell composite with tunable shell/core sizes

NASA Astrophysics Data System (ADS)

Cheng, Ye; Guo, Yuhang; Zhang, Zhenya; Dong, Songtao; Liu, Suwei; Wang, Hongying

2018-03-01

Magnetic absorber has been regarded as the advanced electromagnetic energy transfer material to solve the increasingly high frequency electromagnetic interference issue. Even so, the pure magnetic material, in particular magnetic metal nanoparticle, suffering from the poor chemical stability and strong eddy current effect, thus limits it further application. To overcome this shortage, surrounded the magnetic metal nanoparticle (MPs) with insulated oxide shell has been considered to be an efficient route to suppress such an eddy current effect. Meanwhile, the combined insulated shell with good impedance matching feature, shows a positive role on the electromagnetic energy transfer intensity. In this regard, the binary Fe@α-Fe2O3 composite with the average size of ∼ 20 nm was prepared by a facile self-oxidation reaction. Interestingly, both the core diameter and shell thickness is controllable by controlling the oxide degree. The electromagnetic energy transfer performance revealed the maximum absorption frequency bandwidth of the optimal Fe@α-Fe2O3 composite is up to 5.3 G(8.2-13.5 GHz)under a small coating thickness of 1.5 mm.

High-resolution x-ray diffraction and transmission electron microscopy of multiferroic BiFeO3 films

NASA Astrophysics Data System (ADS)

Qi, Xiaoding; Wei, Ming; Lin, Yuan; Jia, Quanxi; Zhi, Dan; Dho, Joonghoe; Blamire, Mark G.; MacManus-Driscoll, Judith L.

2005-02-01

High-resolution x-ray diffraction and transmission electron microscopy (TEM) have been used to study BiFeO3 thin films grown on the bare and SrRuO3 buffered (001) SrTiO3 substrates. Reciprocal space mapping (RSM) around (002) and (103) reflections revealed that BFO films with a thickness of about 200 nm were almost fully relaxed and had a rhombohedral structure. Cross-sectional, high-resolution TEM showed that the films started to relax at a very early stage of growth, which was consistent with the RSM results. A thin intermediate layer of about 2 nm was observed at the interface, which had a smaller lattice than the overgrown film. Twist distortions about the c axis to release the shear strain introduced by the growth of rhombic (001) BiFeO3 on cubic (001) SrTiO3 were also observed. The results indicate that a strained, coherent BiFeO3 film on (001) SrTiO3 is very difficult to maintain and (111) STO substrates are preferable.

Enhanced and broadband microwave absorption of flake-shaped Fe and FeNi composite with Ba ferrites

NASA Astrophysics Data System (ADS)

Li, Wangchang; Lv, Junjun; Zhou, Xiang; Zheng, Jingwu; Ying, Yao; Qiao, Liang; Yu, Jing; Che, Shenglei

2017-03-01

In order to achieve a broad bandwidth absorber at high frequency, the composites of M-type ferrite BaCo1.0Ti1.0Fe10O19 (BaM) with flaked carbonyl iron powders (CIP) and flaked Fe50Ni50 were prepared to optimize the surface impedance in broadband frequency, respectively. The diameter of the flaked carbonyl iron powders (CIP) and Fe50Ni50 is in the range of 5-10 μm and 10-20 μm and the thickness of the CIP and Fe50Ni50 is close to 200 nm and 400 nm, respectively. The complex permeability and permittivity show that the addition of BaM obviously reduces the values of real part of permittivity and imaginary part of the permeability which can enhance the matched-wave-impedance. The absorption bands less than -10 dB of CIP-BaM and FeNi-BaM absorber approach to 5.5 GHz (5.7-11.2 GHz) and 7 GHz (11-18 GHz) at 1.5 mm. However, the bands of CIP and FeNi are only 1.9 GHz (4.7-6.6 GHz) and 2.1 GHz (4.0-6.1 GHz). Hence, the electromagnetic match property is greatly improved by BaM ferrites, and this composite shows a broaden absorption band.

Elemental moment variation of bcc FexMn1-x on MgO(001)

NASA Astrophysics Data System (ADS)

Bhatkar, H.; Snow, R. J.; Arenholz, E.; Idzerda, Y. U.

2017-02-01

We report the growth, structural characterization, and electronic structure evolution of epitaxially grown bcc FexMn1-x on MgO(001). It is observed that the 20 nm thick FexMn1-x alloy films remained bcc from 0.65≤x≤1, much beyond the bulk stability range of 0.88≤x≤1. X-ray absorption spectroscopy and X-ray magnetic circular dichroism show that both the Fe and Mn L3 binding energies slightly increase with Mn incorporation and that the elemental moment of Fe in the 20 nm crystalline bcc alloy film remain nearly constant, then shows a dramatic collapse near x 0.84. The Mn MCD intensity is found to be small at all compositions that exhibit ferromagnetism

Determining the spin dependent mean free path in Co90Fe10 using giant magnetoresistance

NASA Astrophysics Data System (ADS)

Shakespear, K. F.; Perdue, K. L.; Moyerman, S. M.; Checkelsky, J. G.; Harberger, S. S.; Tamboli, A. C.; Carey, M. J.; Sparks, P. D.; Eckert, J. C.

2005-05-01

The spin dependent mean free path in Co90Fe10 is determined as a function of temperature down to 5K using two different spin valve structures. At 5K the spin dependent mean free path for one structure was measured to be 9.4±1.4nm, decreasing by a factor of 3 by 350K. For the other structure, it is 7.5±0.5nm at 5K and decreased by a factor of 1.5 by 350K. In both cases, the spin dependent mean free path approaches the typical thickness of ferromagnetic layers in spin valves at room temperature and, thus, has an impact on the choice of design parameters for the development of new spintronic devices.

Magnetic behaviour of multisegmented FeCoCu/Cu electrodeposited nanowires

NASA Astrophysics Data System (ADS)

Núñez, A.; Pérez, L.; Abuín, M.; Araujo, J. P.; Proenca, M. P.

2017-04-01

Understanding the magnetic behaviour of multisegmented nanowires (NWs) is a major key for the application of such structures in future devices. In this work, magnetic/non-magnetic arrays of FeCoCu/Cu multilayered NWs electrodeposited in nanoporous alumina templates are studied. Contrarily to most reports on multilayered NWs, the magnetic layer thickness was kept constant (30 nm) and only the non-magnetic layer thickness was changed (0 to 80 nm). This allowed us to tune the interwire and intrawire interactions between the magnetic layers in the NW array creating a three-dimensional (3D) magnetic system without the need to change the template characteristics. Magnetic hysteresis loops, measured with the applied field parallel and perpendicular to the NWs’ long axis, showed the effect of the non-magnetic Cu layer on the overall magnetic properties of the NW arrays. In particular, introducing Cu layers along the magnetic NW axis creates domain wall nucleation sites that facilitate the magnetization reversal of the wires, as seen by the decrease in the parallel coercivity and the reduction of the perpendicular saturation field. By further increasing the Cu layer thickness, the interactions between the magnetic segments, both along the NW axis and of neighbouring NWs, decrease, thus rising again the parallel coercivity and the perpendicular saturation field. This work shows how one can easily tune the parallel and perpendicular magnetic properties of a 3D magnetic layer system by adjusting the non-magnetic layer thickness.

An ultra-small NiFe2O4 hollow particle/graphene hybrid: fabrication and electromagnetic wave absorption property.

PubMed

Yan, Feng; Guo, Dong; Zhang, Shen; Li, Chunyan; Zhu, Chunling; Zhang, Xitian; Chen, Yujin

2018-02-08

Herein, ultra-small NiFe 2 O 4 hollow particles, with the diameter and wall thickness of only 6 and 1.8 nm, respectively, were anchored on a graphene surface based on the nanoscale Kirkendall effect. The hybrid exhibits an excellent electromagnetic wave absorption property, comparable or superior to that of most reported absorbers. Our strategy may open a way to grow ultra-small hollow particles on graphene for applications in many fields such as eletromagnetic wave absorption and energy storage and conversion.

Investigation of structural and magnetic properties of rapidly-solidified iron-silicon alloys at ambient and elevated temperatures

DOE PAGES

Jayaraman, T. V.; Meka, V. M.; Jiang, X.; ...

2018-01-09

Here we investigated the ambient temperature structural properties (thickness, width, microstructure, and lattice parameter), and the ambient and high temperature (up to 900 K) direct current (DC) magnetic properties—saturation magnetization (M S) and intrinsic coercivity (H CI)—of rapidly-solidified (melt-spun) Fe-x wt.% Si (x = 3, 5, & 8) alloys. The wheel surface speeds selected for the study were 30 m/s and 40 m/s. The ribbons produced at the lower wheel surface speed (30 m/s) were continuous having relatively uniform edges compared to the ribbons produced at the higher wheel surface speed. The thickness and the width of the melt-spun ribbonsmore » ranged between ~15 and 60 μm and 500–800 μm, respectively. The x-ray diffraction spectra of the melt-spun ribbons indicated the presence of disordered α-phase, irrespective of the composition, and the wheel surface speed. The lattice parameter decreased gradually as a function of increasing silicon content from ~0.2862 nm (Fe-3 wt.% Si) to ~0.2847 nm (Fe-8 wt.% Si). The wheel surface speed showed an insignificant effect on M S while increased silicon content resulted in a decreasing trend in M S. Elevated temperature evaluation of the magnetization (M-T curves at ~7.96 kA/m) in the case of Fe-3 & 5 wt.% Si alloy ribbons was distinctly different from that of the Fe-8 wt.% Si alloy ribbons. The curves of the as-prepared Fe-3 wt.% Si and Fe-5 wt.% Si alloy ribbons were irreversible while that of Fe-8 wt.% Si was reversible. The M S for any of the combinations of wheel surface speed and composition decreased monotonically with the increase in temperature (from 300 to 900 K). While H CI increased with the increase in temperature for all the wheel surface speed and composition combination, its nature of increase is distinct for Fe-8 wt.% Si alloy ribbons compared to Fe-3 & 5 wt.% Si alloys ribbons. Finally, it appears that rapidly-solidified Fe-3 wt.% Si and Fe-5 wt.% Si alloys ribbons are primarily comprised of the α phase (disordered phase) while the Fe-8 wt.% Si alloy ribbons are comprised primarily of disordered phase along with minor constituents of an ordered phase.« less

Investigation of structural and magnetic properties of rapidly-solidified iron-silicon alloys at ambient and elevated temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jayaraman, T. V.; Meka, V. M.; Jiang, X.

Here we investigated the ambient temperature structural properties (thickness, width, microstructure, and lattice parameter), and the ambient and high temperature (up to 900 K) direct current (DC) magnetic properties—saturation magnetization (M S) and intrinsic coercivity (H CI)—of rapidly-solidified (melt-spun) Fe-x wt.% Si (x = 3, 5, & 8) alloys. The wheel surface speeds selected for the study were 30 m/s and 40 m/s. The ribbons produced at the lower wheel surface speed (30 m/s) were continuous having relatively uniform edges compared to the ribbons produced at the higher wheel surface speed. The thickness and the width of the melt-spun ribbonsmore » ranged between ~15 and 60 μm and 500–800 μm, respectively. The x-ray diffraction spectra of the melt-spun ribbons indicated the presence of disordered α-phase, irrespective of the composition, and the wheel surface speed. The lattice parameter decreased gradually as a function of increasing silicon content from ~0.2862 nm (Fe-3 wt.% Si) to ~0.2847 nm (Fe-8 wt.% Si). The wheel surface speed showed an insignificant effect on M S while increased silicon content resulted in a decreasing trend in M S. Elevated temperature evaluation of the magnetization (M-T curves at ~7.96 kA/m) in the case of Fe-3 & 5 wt.% Si alloy ribbons was distinctly different from that of the Fe-8 wt.% Si alloy ribbons. The curves of the as-prepared Fe-3 wt.% Si and Fe-5 wt.% Si alloy ribbons were irreversible while that of Fe-8 wt.% Si was reversible. The M S for any of the combinations of wheel surface speed and composition decreased monotonically with the increase in temperature (from 300 to 900 K). While H CI increased with the increase in temperature for all the wheel surface speed and composition combination, its nature of increase is distinct for Fe-8 wt.% Si alloy ribbons compared to Fe-3 & 5 wt.% Si alloys ribbons. Finally, it appears that rapidly-solidified Fe-3 wt.% Si and Fe-5 wt.% Si alloys ribbons are primarily comprised of the α phase (disordered phase) while the Fe-8 wt.% Si alloy ribbons are comprised primarily of disordered phase along with minor constituents of an ordered phase.« less

Alternating stacking of ferromagnetic nanosheet and nanoparticle films: heteroassembly and magneto-optical Kerr effect

NASA Astrophysics Data System (ADS)

Jia, Baoping; Zhang, Wei; Liu, Hui; Lin, Bencai; Ding, Jianning

2016-09-01

Heterostructured multilayer films of two different nanocrystals have been successfully fabricated by layer-by-layer stacking of Ti0.8Co0.2O2 nanosheet and Fe3O4 nanoparticle films. UV-Vis spectroscopy and AFM observation confirmed the successful alternating deposition in the multilayer buildup process. The average thickness of both Ti0.8Co0.2O2 nanosheet and Fe3O4 nanoparticle layers was determined to be about 1.4-1.7 and 5 nm, which was in good agreement with TEM results. Magneto-optical Kerr effect measurements demonstrated that the heteroassemblies exhibit gigantic magnetic circular dichroism (MCD) (2 × 104 deg/cm) at 320-360 nm, deriving from strong interlayer [Co2+]t2g-[Fe3+]eg d-d charge transfer which was further confirmed by X-ray photoelectron spectroscopy. Their structure-dependent MCD showed high potential in rational design and construction of high-efficiency magneto-optical devices.

Fabrication of bifunctional core-shell Fe3O4 particles coated with ultrathin phosphor layer

PubMed Central

2013-01-01

Bifunctional monodispersed Fe3O4 particles coated with an ultrathin Y2O3:Tb3+ shell layer were fabricated using a facile urea-based homogeneous precipitation method. The obtained composite particles were characterized by powder X-ray diffraction, transmission electron microscopy (TEM), quantum design vibrating sample magnetometry, and photoluminescence (PL) spectroscopy. TEM revealed uniform spherical core-shell-structured composites ranging in size from 306 to 330 nm with a shell thickness of approximately 25 nm. PL spectroscopy confirmed that the synthesized composites displayed a strong eye-visible green light emission. Magnetic measurements indicated that the composite particles obtained also exhibited strong superparamagnetic behavior at room temperature. Therefore, the inner Fe3O4 core and outer Y2O3:Tb3+ shell layer endow the composites with both robust magnetic properties and strong eye-visible luminescent properties. These composite materials have potential use in magnetic targeting and bioseparation, simultaneously coupled with luminescent imaging. PMID:23962025

Fabrication of bifunctional core-shell Fe3O4 particles coated with ultrathin phosphor layer

NASA Astrophysics Data System (ADS)

Atabaev, Timur Sh; Kim, Hyung-Kook; Hwang, Yoon-Hwae

2013-08-01

Bifunctional monodispersed Fe3O4 particles coated with an ultrathin Y2O3:Tb3+ shell layer were fabricated using a facile urea-based homogeneous precipitation method. The obtained composite particles were characterized by powder X-ray diffraction, transmission electron microscopy (TEM), quantum design vibrating sample magnetometry, and photoluminescence (PL) spectroscopy. TEM revealed uniform spherical core-shell-structured composites ranging in size from 306 to 330 nm with a shell thickness of approximately 25 nm. PL spectroscopy confirmed that the synthesized composites displayed a strong eye-visible green light emission. Magnetic measurements indicated that the composite particles obtained also exhibited strong superparamagnetic behavior at room temperature. Therefore, the inner Fe3O4 core and outer Y2O3:Tb3+ shell layer endow the composites with both robust magnetic properties and strong eye-visible luminescent properties. These composite materials have potential use in magnetic targeting and bioseparation, simultaneously coupled with luminescent imaging.

Effect of heavy metal layer thickness on spin-orbit torque and current-induced switching in Hf|CoFeB|MgO structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akyol, Mustafa; Jiang, Wanjun; Yu, Guoqiang

We study the heavy metal layer thickness dependence of the current-induced spin-orbit torque (SOT) in perpendicularly magnetized Hf broken vertical bar CoFeB broken vertical bar MgO multilayer structures. The damping-like (DL) current-induced SOT is determined by vector anomalous Hall effect measurements. A non-monotonic behavior in the DL-SOT is found as a function of the thickness of the heavy-metal layer. The sign of the DL-SOT changes with increasing the thickness of the Hf layer in the trilayer structure. As a result, in the current-driven magnetization switching, the preferred direction of switching for a given current direction changes when the Hf thicknessmore » is increased above similar to 7 nm. Although there might be a couple of reasons for this unexpected behavior in DL-SOT, such as the roughness in the interfaces and/or impurity based electric potential in the heavy metal, one can deduce a roughness dependence sign reversal in DL-SOT in our trilayer structure.« less

Carbon Nanotube Microarrays Grown on Nanoflake Substrates

NASA Technical Reports Server (NTRS)

Schmidt, Howard K.; Hauge, Robert H.; Pint, Cary; Pheasant, Sean

2013-01-01

This innovation consists of a new composition of matter where single-walled carbon nanotubes (SWNTs) are grown in aligned arrays from nanostructured flakes that are coated in Fe catalyst. This method of growth of aligned SWNTs, which can yield well over 400 percent SWNT mass per unit substrate mass, exceeds current yields for entangled SWNT growth. In addition, processing can be performed with minimal wet etching treatments, leaving aligned SWNTs with superior properties over those that exist in entangled mats. The alignment of the nanotubes is similar to that achieved in vertically aligned nanotubes, which are called "carpets. " Because these flakes are grown in a state where they are airborne in a reactor, these flakes, after growing SWNTs, are termed "flying carpets. " These flakes are created in a roll-to-roll evaporator system, where three subsequent evaporations are performed on a 100-ft (approx. =30-m) roll of Mylar. The first layer is composed of a water-soluble "release layer, " which can be a material such as NaCl. After depositing NaCl, the second layer involves 40 nm of supporting layer material . either Al2O3 or MgO. The thickness of the layer can be tuned to synthesize flakes that are larger or smaller than those obtained with a 40-nm deposition. Finally, the third layer consists of a thin Fe catalyst layer with a thickness of 0.5 nm. The thickness of this layer ultimately determines the diameter of SWNT growth, and a layer that is too thick will result in the growth of multiwalled carbon nanotubes instead of single-wall nanotubes. However, between a thickness of 0.5 nm to 1 nm, single-walled carbon nanotubes are known to be the primary constituent. After this three-layer deposition process, the Mylar is rolled through a bath of water, which allows catalyst-coated flakes to detach from the Mylar. The flakes are then collected and dried. The method described here for making such flakes is analogous to that which is used to make birefringent ink that is coated on U.S. currency. After deposition, the growth is carried out in a hot-filament chemical vapor deposition apparatus. A tungsten hot filament placed in the flow of H2 at a temperature greater than 1,600 C creates atomic hydrogen, which serves to reduce the Fe catalyst into a metallic state. The catalyst can now precipitate SWNTs in the presence of growth gases. The gases used for the experiments reported are C2H2, H2O, and H2, at rates of 2, 2, and 400 standard cubic centimeters per minute (sccm), respectively. In order to retain the flakes, a cage is constructed by spot welding stainless steel or copper mesh to form an enclosed area, in which the flakes are placed prior to growth. This allows growth gases and atomic hydrogen to reach the flakes, but does not allow the flakes, which rapidly nucleate SWNTs, to escape from the cage.

Interface perpendicular magnetic anisotropy in ultrathin Ta/NiFe/Pt layered structures

NASA Astrophysics Data System (ADS)

Hirayama, Shigeyuki; Kasai, Shinya; Mitani, Seiji

2018-01-01

Interface perpendicular magnetic anisotropy (PMA) in ultrathin Ta/NiFe/Pt layered structures was investigated through magnetization measurements. Ta/NiFe/Pt films with NiFe layer thickness (t) values of 2 nm or more showed typical in-plane magnetization curves, which was presumably due to the dominant contribution of the shape magnetic anisotropy. The thickness dependence of the saturation magnetization of the entire NiFe layer (M s) was well analyzed using the so-called dead-layer model, showing that the magnetically active part of the NiFe layer has saturation magnetization (M\\text{s}\\text{act}) independent of t and comparable to the bulk value. In the perpendicular direction, the saturation field H k was found to clearly decrease with decreasing t, while the effective field of shape magnetic anisotropy due to the active NiFe saturation magnetization M\\text{s}\\text{act} should be independent of t. These observations show that there exists interface PMA in the layered structures. The interface PMA energy density was determined to be ∼0.17 erg/cm2 using the dead-layer model. Motivated by the correlation observed between M s and H k, we also attempted to interpret the experimental results using an alternative approach beyond the dead-layer model; however, it gives only implications on the incomplete validity of the dead-layer model and no better understanding.

Characterization of novel microstructures in Al-Fe-V-Si and Al-Fe-V-Si-Y alloys processed at intermediate cooling rates

NASA Astrophysics Data System (ADS)

Marshall, Ryan

Samples of an Al-Fe-V-Si alloy with and without small Y additions were prepared by copper wedge-mold casting. Analysis of the microstructures developed at intermediate cooling rates revealed the formation of an atypical morphology of the cubic alpha-Al12(Fe/V)3Si phase (Im 3 space group with a = 1.26 nm) in the form of a microeutectic with alpha-Al that forms in relatively thick sections. This structure was determined to exhibit promising hardness and thermal stability when compared to the commercial rapidly solidified and processed Al-Fe-V-Si (RS8009) alloy. In addition, convergent beam electron diffraction (CBED) and selected area electron diffraction (SAD) were used to characterize a competing intermetallic phase, namely, a hexagonal phase identified as h-AlFeSi (P6/mmm space group with a = 2.45 nm c = 1.25 nm) with evidence of a structural relationship to the icosahedral quasicrystalline (QC) phase (it is a QC approximant) and a further relationship to the more desirable alpha-Al12(Fe/V) 3Si phase, which is also a QC approximant. The analysis confirmed the findings of earlier studies in this system, which suggested the same structural relationships using different methods. As will be shown, both phases form across a range of cooling rates and appear to have good thermal stabilities. Additions of Y to the alloy were also studied and found to cause the formation of primary YV2Al20 particles on the order of 1 microm in diameter distributed throughout the microstructure, which otherwise appeared essentially identical to that of the Y-free 8009 alloy. The implications of these results on the possible development of these structures will be discussed in some detail.

Synthesis and properties MFe2O4 (M = Fe, Co) nanoparticles and core-shell structures

NASA Astrophysics Data System (ADS)

Yelenich, O. V.; Solopan, S. O.; Greneche, J. M.; Belous, A. G.

2015-08-01

Individual Fe3-xO4 and CoFe2O4 nanoparticles, as well as Fe3-xO4/CoFe2O4 core/shell structures were synthesized by the method of co-precipitation from diethylene glycol solutions. Core/shell structure were synthesized with CoFe2O4-shell thickness of 1.0, 2.5 and 3.5 nm. X-ray diffraction patterns of individual nanoparticles and core/shell are similar and indicate that all synthesized samples have a cubic spinel structure. Compares Mössbauer studies of CoFe2O4, Fe3-xO4 nanoparticles indicate superparamagnetic properties at 300 K. It was shown that individual magnetite nanoparticles are transformed into maghemite through oxidation during the synthesis procedure, wherein the smallest nanoparticles are completely oxidized while a magnetite core does occur in the case of the largest nanoparticles. The Mössbauer spectra of core/shell nanoparticles with increasing CoFe2O4-shell thickness show a gradual decrease in the relative intensity of the quadrupole doublet and significant decrease of the mean isomer shift value at both RT and 77 K indicating a decrease of the superparamagnetic relaxation phenomena. Specific loss power for the prepared ferrofluids was experimentally calculated and it was determined that under influence of ac-magnetic field magnetic fluid based on individual CoFe2O4 and Fe3-xO4 particles are characterized by very low heating temperature, when magnetic fluids based on core/shell nanoparticles demonstrate higher heating effect.

Microstructure and magnetic properties of (001) textured L1(0) FePt films on amorphous glass substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Speliotis, T; Varvaro, G; Testa, AM

2015-05-15

L1(0) FePt thin films with an island-like morphology and magnetic perpendicular anisotropy were grown at low temperature (300 < T-dep< 375 degrees C) by magnetron sputtering on Hoya glass substrates using a 30-nm thick Cr (2 0 0) underlayer. An MgO buffer layer with a thickness of 2 nm was used to inhibit the diffusion from the Cr underlayer and promote the growth of (0 0 1) oriented L1(0) FePt films by inducing an in-plane lattice distortion. By varying the substrate temperature and the Ar sputter pressure (3.5 < P-Ar< 15 mTorr) during the deposition, the degree of chemical order,more » the microstructure and the magnetic properties were tuned and the best properties in term of squareness ratio (M-r/M-s similar to 0.95) and coercive field (H-c similar to 14 kOe) were observed for films deposited at T-dep = 350 degrees C and P-Ar= 5 mTorr, due to the appearance of a tensile strain, which favors the perpendicular anisotropy. The analysis of the angular dependence of remanent magnetization curves on the optimized sample suggests that the magnetization reversal is highly incoherent due to the inter-island interactions. Our results provide useful information on the low temperature growth of FePt films with perpendicular anisotropy onto glass substrates, which are relevant for a variety of technological applications, such as magnetic recording and spintronic devices. (C) 2015 Elsevier B.V. All rights reserved.« less

Spin injection into silicon in three-terminal vertical and four-terminal lateral devices with Fe/Mg/MgO/Si tunnel junctions having an ultrathin Mg insertion layer

NASA Astrophysics Data System (ADS)

Sato, Shoichi; Nakane, Ryosho; Hada, Takato; Tanaka, Masaaki

2017-12-01

We demonstrate that the spin injection/extraction efficiency is enhanced by an ultrathin Mg insertion layer (⩽2 nm) in Fe /Mg /MgO /n+-Si tunnel junctions. In diode-type vertical three-terminal devices fabricated on a Si substrate, we observe the narrower three-terminal Hanle (N-3TH) signals indicating true spin injection into Si and estimate the spin polarization in Si to be 16% when the thickness of the Mg insertion layer is 1 nm, whereas no N-3TH signal is observed without the Mg insertion. This means that the spin injection/extraction efficiency is enhanced by suppressing the formation of a magnetically dead layer at the Fe/MgO interface. We also observe clear spin transport signals, such as nonlocal Hanle signals and spin-valve signals, in a lateral four-terminal device with the same Fe /Mg /MgO /n+-Si tunnel junctions fabricated on a Si-on-insulator substrate. It is found that both the intensity and linewidth of the spin signals are affected by the geometrical effects (device geometry and size). We have derived analytical functions taking into account the device structures, including channel thickness and electrode size, and estimated important parameters: spin lifetime and spin polarization. Our analytical functions explain the experimental results very well. Our study shows the importance of suppressing a magnetically dead layer and provides a unified understanding of spin injection/detection signals in different device geometries.

Structural properties of ultrafine Ba-hexaferrite nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Makovec, Darko, E-mail: Darko.Makovec@ijs.si; Primc, Darinka; Sturm, Saso

2012-12-15

Crystal structure of ultrafine Ba-hexaferrite (BaFe{sub 12}O{sub 19}) nanoparticles was studied using X-ray diffractometry (XRD), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDXS), X-ray absorption fine structure (XAFS), and Moessbauer spectroscopy (MS), to be compared to the structure of larger nanoparticles and the bulk. The nanoparticles were synthesized with hydrothermal treatment of an appropriate suspension of Ba and Fe hydroxides in the presence of a large excess of OH{sup -}. The ultrafine nanoparticles were formed in a discoid shape, {approx}10 nm wide and only {approx}3 nm thick, comparable to the size of the hexagonal unit cell in the c-direction.more » The HRTEM image analysis confirmed the hexaferrite structure, whereas EDXS showed the composition matching the BaFe{sub 12}O{sub 19} formula. XAFS and MS analyses showed considerable disorder of the structure, most probably responsible for the low magnetization. - Graphical abstract: Left: HREM image of an ultrafine Ba-hexaferrite nanoparticle (inset: TEM image of the nanoparticles); Right: the experimental HRTEM image is compared with calculated image and corresponding atomic model. Highlights: Black-Right-Pointing-Pointer Crystal structure of ultrafine Ba-hexaferrite (BaFe{sub 12}O{sub 19}) nanoparticles was compared to the structure of the bulk. Black-Right-Pointing-Pointer Thickness the discoid nanoparticles was comparable to the size of the hexagonal unit cell in the c-direction. Black-Right-Pointing-Pointer Considerable disorder of the nanoparticles' structure is most probably responsible for their low magnetization.« less

Influence of surface topography on RBS measurements: case studies of (Cu/Fe/Pd) multilayers and FePdCu alloys nanopatterned by self-assembly

NASA Astrophysics Data System (ADS)

Krupinski, M.; Perzanowski, M.; Zabila, Y.; Zarzycki, A.; Marszałek, M.

2017-03-01

In this paper the influence of surface topography on Rutherford backscattering spectrometry (RBS) is discussed. (Cu/Fe/Pd) multilayers with total thickness of about 10 nm were deposited by physical vapor deposition on self-organized array of SiO2 nanoparticles with the size of 50 nm and 100 nm. As a reference, the multilayered systems were also prepared on flat substrates under the same conditions. After the deposition, morphology of the systems was studied by scanning electron microscopy (SEM), while chemical analysis was performed using Rutherford backscattering spectrometry. It was found that the RBS spectra and determined compositions for flat and patterned multilayers differ. The difference is discussed by taking into account the effect of additional inelastic scattering and energy straggling occurring due to developed topography of patterned systems. Then, the multilayers were annealed in 600 °C in order to obtain FePdCu alloy. The phenomenon of solid-state dewetting resulted in the formation of isolated alloy islands on the top of SiO2 nanoparticles. The SEM and RBS analysis were repeated showing correlation between the size distribution of obtained alloy islands and broadening of peaks appearing in RBS spectra. Invited talk at 8th International Workshop on Advanced Materials Science and Nanotechnology (IWAMSN2016), 8-12 November 2016, Ha Long City, Vietnam.

Effect of exchange coupling on magnetic property in Sm-Co/α-Fe layered system

NASA Astrophysics Data System (ADS)

C, X. Sang; G, P. Zhao; W, X. Xia; X, L. Wan; F, J. Morvan; X, C. Zhang; L, H. Xie; J, Zhang; J, Du; A, R. Yan; P, Liu

2016-03-01

The hysteresis loops as well as the spin distributions of Sm-Co/α-Fe bilayers have been investigated by both three-dimensional (3D) and one-dimensional (1D) micromagnetic calculations, focusing on the effect of the interface exchange coupling under various soft layer thicknesses ts. The exchange coupling coefficient Ahs between the hard and soft layers varies from 1.8 × 10-6 erg/cm to 0.45 × 10-6 erg/cm, while the soft layer thickness increases from 2 nm to 10 nm. As the exchange coupling decreases, the squareness of the loop gradually deteriorates, both pinning and coercive fields rise up monotonically, and the nucleation field goes down. On the other hand, an increment of the soft layer thickness leads to a significant drop of the nucleation field, the deterioration of the hysteresis loop squareness, and an increase of the remanence. The simulated loops based on the 3D and 1D methods are consistent with each other and in good agreement with the measured loops for Sm-Co/α-Fe multilayers. Project supported by the National Natural Science Foundation of China (Grant Nos. 11074179 and 10747007), the National Basic Research Program of China (Grant No. 2014CB643702), the Zhejiang Provincial Natural Science Foundation of China (Grant No. LY14E010006), the Construction Plan for Scientific Research Innovation Teams of Universities in Sichuan Province, China (Grant No. 12TD008), the Scientific Research Foundation for the Returned Overseas Chinese Scholars of the Education Ministry, China, and the Program for Key Science and Technology Innovation Team of Zhejiang Province, China (Grant No. 2013TD08).

Spin transport and spin accumulation signals in Si studied in tunnel junctions with a Fe/Mg ferromagnetic multilayer and an amorphous SiOxNy tunnel barrier

NASA Astrophysics Data System (ADS)

Nakane, Ryosho; Hada, Takato; Sato, Shoichi; Tanaka, Masaaki

2018-04-01

We studied the spin accumulation signals in phosphorus-doped n+-Si (8 × 1019 cm-3) by measuring the spin transport in three-terminal vertical devices with Fe(3 nm)/Mg(0 and 1 nm)/SiOxNy(1 nm)/n+-Si(001) tunnel junctions, where the amorphous SiOxNy layer was formed by oxnitridation of the Si substrate with radio frequency plasma. Obvious spin accumulation signals were observed at 4-300 K in the spin extraction geometry when the thickness of the Mg insertion layer was 1 nm. We found that by inserting a thin (1 nm) Mg layer, intermixing of Fe and SiOxNy is suppressed, leading to the appearance of the spin accumulation signals, and this result is consistent with the dead layer model recently proposed by our group [S. Sato et al., Appl. Phys. Lett. 107, 032407 (2015)]. We obtained relatively high spin polarization (PS) of electrons tunneling through the junction and long spin lifetime (τS): PS = 16% and τS = 5.6 ns at 4 K and PS = 7.5% and τS = 2.7 ns at 300 K. Tunnel junctions with an amorphous SiOxNy tunnel barrier are very promising for Si-based spintronic devices, since they can be formed by the method compatible with the silicon complementary metal-oxide-semiconductor technology.

Thickness Dependence of the Dzyaloshinskii-Moriya Interaction in Co2 FeAl Ultrathin Films: Effects of Annealing Temperature and Heavy-Metal Material

NASA Astrophysics Data System (ADS)

Belmeguenai, M.; Roussigné, Y.; Bouloussa, H.; Chérif, S. M.; Stashkevich, A.; Nasui, M.; Gabor, M. S.; Mora-Hernández, A.; Nicholson, B.; Inyang, O.-O.; Hindmarch, A. T.; Bouchenoire, L.

2018-04-01

The interfacial Dzyaloshinskii-Moriya interaction (IDMI) is investigated in Co2FeAl (CFA) ultrathin films of various thicknesses (0.8 nm ≤tCFA≤2 nm ) grown by sputtering on Si substrates, using Pt, W, Ir, and MgO buffer or/and capping layers. Vibrating sample magnetometry reveals that the magnetization at saturation (Ms ) for the Pt- and Ir-buffered films is higher than the usual Ms of CFA due to the proximity-induced magnetization (PIM) in Ir and Pt estimated to be 19% and 27%, respectively. The presence of PIM in these materials is confirmed using x-ray resonant magnetic reflectivity. Moreover, while no PIM is induced in W, higher PIM is obtained with Pt when it is used as a buffer layer rather than a capping layer. Brillouin light scattering in the Damon-Eshbach geometry is used to investigate the thickness dependences of the IDMI constants from the spin-wave nonreciprocity and the perpendicular anisotropy field versus the annealing temperature. The IDMI sign is found to be negative for Pt /CFA and Ir /CFA , while it is positive for W /CFA . The thickness dependence of the effective IDMI constant for stacks involving Pt and W shows the existence of two regimes similar to that of the perpendicular anisotropy constant due to the degradation of the interfaces as the CFA thickness approaches a critical thickness. The surface IDMI and anisotropy constants of each stack are determined for the thickest samples where a linear thickness dependence of the effective IDMI constant and the effective magnetization are observed. The interface anisotropy and IDMI constants investigated for the Pt /CFA /MgO system show different trends with the annealing temperature. The decrease of the IDMI constant with increasing annealing temperature is probably due to the electronic structure changes at the interfaces, while the increase of the interface anisotropy constant is coherent with the interface quality and disorder enhancement.

Textured Nd2Fe14B flakes with enhanced coercivity

NASA Astrophysics Data System (ADS)

Cui, B. Z.; Zheng, L. Y.; Marinescu, M.; Liu, J. F.; Hadjipanayis, G. C.

2012-04-01

Morphology, structure, and magnetic properties of the [001] textured Nd2Fe14B nanocrystalline flakes prepared by surfactant-assisted high energy ball milling (HEBM) and subsequent annealing were studied. These flakes have a thickness of 80-200 nm, a length of 0.5-10 μm, and an average grain size of 10-14 nm. The addition of some amount of Dy, Nd70Cu30 alloy, and an appropriate post annealing increased the coercivity iHc of the Nd2Fe14B flakes. iHc was 3.7, 4.3, and 5.7 kOe for the Nd15.5Fe78.5B6, Nd14Dy1.5Fe78.5B6 and 83.3 wt.% Nd14Dy1.5Fe78.5B6 + 16.7 wt.% Nd70Cu30 flakes prepared by HEBM for 5 h in heptane with 20 wt.% oleylamine, respectively. After annealing at 450 °C for 0.5 h, their iHc increased to 5.1, 6.2, and 7.0 kOe, respectively. Anisotropic magnetic behavior was found in all of the as-milled and annealed flakes. Both, the thickening of Nd-rich phase at grain boundaries via diffusion of Nd70Cu30 and the surface modification of the Nd2Fe14B flake could be the main reasons for the coercivity enhancement in the as-milled and annealed Nd70Cu30-added Nd2Fe14B flakes.

Effects of Fragmented Fe Intermetallic Compounds on Ductility in Al-Si-Mg Alloys.

PubMed

Kim, JaeHwang; Kim, DaeHwan

2018-03-01

Fe is intentionally added in order to form the Fe intermetallic compounds (Fe-IMCs) during casting. Field emission scanning electron microscope with energy dispersive spectrometer (EDS) was conducted to understand microstructural changes and chemical composition analyses. The needlelike Fe-IMCs based on two dimensional observation with hundreds of micro size are modified to fragmented particles with the minimum size of 300 nm through clod rolling with 80% thickness reduction. The ratio of Fe:Si on the fragmented Fe-IMCs after 80% reduction is close to 1:1, representing the β-Al5FeSi. The yield and tensile strengths are increased with increasing reduction rate. On the other hand, the elongation is decreased with the 40% reduction, but slightly increased with the 60% reduction. The elongation is dramatically increased over two times for the specimen of 80% reduction compared with that of the as-cast. Fracture behavior is strongly affected by the morphology and size of Fe-IMCs. The fracture mode is changed from brittle to ductile with the microstructure modification of Fe-IMCs.

MnFe2O4 as a gas sensor towards SO2 and NO2 gases

NASA Astrophysics Data System (ADS)

Rathore, Deepshikha; Mitra, Supratim

2016-05-01

The chemical co-precipitation method was used to synthesize MnFe2O4 nanoparticles. Single cubic phase formation of nanoparticles was confirmed by X-ray diffraction technique. The average particle size of MnFe2O4 nanoparticles was found to be 10.7 nm using Scherrer formula. The ultrafine powder of MnFe2O4 nanoparticles was pressed to design pellet of 10 mm diameter and 1mm thickness. Copper electrodes have been deposited on the surface of pellet using silver paste in the form of capacitor. Fabricated gas sensing device of MnFe2O4 nanoparticles was tested towards SO2 and NO2 gases. Cole-Cole plot of MnFe2O4 was investigated with the help of electrochemical workstation. The performance of the sensors including sensitivity, response and recovery time was also determined. It was observed that the MnFe2O4 nanoparticles are more sensible for NO2 gas as compared to SO2 gas.

Fundamental limits in heat-assisted magnetic recording and methods to overcome it with exchange spring structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suess, D.; Abert, C.; Bruckner, F.

2015-04-28

The switching probability of magnetic elements for heat-assisted recording with pulsed laser heating was investigated. It was found that FePt elements with a diameter of 5 nm and a height of 10 nm show, at a field of 0.5 T, thermally written-in errors of 12%, which is significantly too large for bit-patterned magnetic recording. Thermally written-in errors can be decreased if larger-head fields are applied. However, larger fields lead to an increase in the fundamental thermal jitter. This leads to a dilemma between thermally written-in errors and fundamental thermal jitter. This dilemma can be partly relaxed by increasing the thickness of the FePtmore » film up to 30 nm. For realistic head fields, it is found that the fundamental thermal jitter is in the same order of magnitude of the fundamental thermal jitter in conventional recording, which is about 0.5–0.8 nm. Composite structures consisting of high Curie top layer and FePt as a hard magnetic storage layer can reduce the thermally written-in errors to be smaller than 10{sup −4} if the damping constant is increased in the soft layer. Large damping may be realized by doping with rare earth elements. Similar to single FePt grains in composite structure, an increase of switching probability is sacrificed by an increase of thermal jitter. Structures utilizing first-order phase transitions breaking the thermal jitter and writability dilemma are discussed.« less

Magnetic response of hybrid ferromagnetic and antiferromagnetic core-shell nanostructures.

PubMed

Khan, U; Li, W J; Adeela, N; Irfan, M; Javed, K; Wan, C H; Riaz, S; Han, X F

2016-03-21

The synthesis of FeTiO3-Ni(Ni80Fe20) core-shell nanostructures by a two-step method (sol-gel and DC electrodeposition) has been demonstrated. XRD analysis confirms the rhombohedral crystal structure of FeTiO3(FTO) with space group R3[combining macron]. Transmission electron microscopy clearly depicts better morphology of nanostructures with shell thicknesses of ∼25 nm. Room temperature magnetic measurements showed significant enhancement of magnetic anisotropy for the permalloy (Ni80Fe20)-FTO over Ni-FTO core-shell nanostructures. Low temperature magnetic measurements of permalloy-FeTiO3 core-shell structure indicated a strong exchange bias mechanism with magnetic coercivity below the antiferromagnetic Neel temperature (TN = 59 K). The exchange bias is attributed to the alignment of magnetic moments in the antiferromagnetic material at low temperature. Our scheme opens a path towards optimum automotive systems and wireless communications wherein broader bandwidths and smaller sizes are required.

Manipulation of competing ferromagnetic and antiferromagnetic domains in exchange-biased nanostructures

DOE PAGES

Fraile Rodríguez, Arantxa; Basaran, Ali C.; Morales, Rafael; ...

2015-11-20

In this work, using photoemission electron microscopy combined with x-ray magnetic circular dichroism we show that a progressive spatial confinement of a ferromagnet (FM), either through thickness variation or laterally via patterning, actively controls the domains of uncompensated spins in the antiferromagnet (AF) in exchange-biased systems. Direct observations of the spin structure in both sides of the FM/AF interface in a model system, Ni/FeF 2, show that the spin structure is determined by the balance between the competing FM and AF magnetic energies. Coexistence of exchange bias domains, with opposite directions, can be established in Ni/FeF 2 bilayers for Nimore » thicknesses below 10 nm. Patterning the Ni/FeF 2 heterostructures with antidots destabilizes the FM state, enhancing the formation of opposite exchange bias domains below a critical antidot separation of the order of a few FeF 2 crystal domains. The results suggest that dimensional confinement of the FM may be used to manipulate the AF spin structure in spintronic devices and ultrahigh-density information storage media. Lastly, the underlying mechanism of the uncompensated AF domain formation in Ni/FeF 2 may be generic to other magnetic systems with complex noncollinear FM/AF spin structures.« less

Magnetic anisotropy modulation of epitaxial Fe3O4 films on MgO substrates

NASA Astrophysics Data System (ADS)

Chichvarina, O.; Herng, T. S.; Xiao, W.; Hong, X.; Ding, J.

2015-05-01

Fe3O4 has been widely studied because of its great potential in spintronics and other applications. As a magnetic electrode, it is highly desired if magnetic anisotropy can be controlled. Here, we report the results from our systematic study on the magnetic properties of magnetite (Fe3O4) thin films epitaxially grown on various MgO substrates. Strikingly, we observed a prominent perpendicular magnetic anisotropy in Fe3O4 film deposited on MgO (111) substrate. When measured in out-of-plane direction, the film (40 nm thick) exhibits a well-defined square hysteresis loop with coercivity (Hc) above 1 kOe, while much lower coercivity was obtained in the in-plane orientation. In sharp contrast, the films deposited onto MgO (100) and MgO (110) substrates show in-plane magnetic anisotropy. These films exhibit a typical soft magnet characteristic—Hc lies within the range of 200-400 Oe. All the films showed a clear Verwey transition near 120 K—a characteristic of Fe3O4 material. In addition, a series of magnetoresistance (MR) measurements is performed and the MR results are in good agreement with the magnetic observations. The role of the substrate orientation and film thickness dependency is also investigated.

Effect of processing parameters and pore structure of nanostructured silica aerogel on the physical properties of aerogel blankets

NASA Astrophysics Data System (ADS)

Latifi, Fatemeh; Talebi, Zahra; Khalili, Haleh; Zarrebini, Mohammad

2018-05-01

This work investigates the influence of processing parameters and aerogel pore structure on the physical properties and hydrophobicity of aerogel blankets. Aerogel blankets were produced by in situ synthesis of nanostructured silica aerogel on a polyester nonwoven substrate. Nitrogen adsorption-desorption analysis, contact angle test and FE-SEM images were used to characterize both the aerogel particles and the blankets. The results showed that the weight and thickness of the blanket were reduced when the low amount of catalyst was used. A decrease in the aerogel pore size from 22 to 11 nm increased the weight and thickness of the blankets. The xerogel particles with high density and pore size of 5 nm reduced the blanket weight. Also, the blanket weight and thickness were increased due to increasing the sol volume. It was found that the hydrophobicity of aerogel blankets is not influenced by sol volume and pore structure of silica aerogel.

Textured Pr{sub 2}Fe{sub 14}B flakes with submicron or nanosize thickness prepared by surfactant-assisted ball milling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zuo, Wen-Liang, E-mail: wlzuo@iphy.ac.cn, E-mail: shenbg@aphy.iphy.ac.cn; Liu, Rong-Ming; Zheng, Xin-Qi

2014-05-07

The textured Pr{sub 2}Fe{sub 14}B nanoflakes were produced by surfactant-assisted ball milling (SABM). Single phase tetragonal structure was characterized for the samples before and after SABM by X-ray diffraction (XRD). The thickness and length of the as-milled flakes are mainly in the range of 50–150 nm and 0.5–2 μm, respectively. For the field-aligned Pr{sub 2}Fe{sub 14}B nanoflakes, the out-of-plane texture (the easy magnetization direction (EMD) along the c-axis) is indicated from the increasing (00l) peaks in the XRD patterns. SEM image demonstrates that the EMD is parallel to flaky surface, which is different from the RCo{sub 5} (R = rare earth) system with EMDmore » perpendicular to the surface. We propose a hypothesis that the easy glide planes are related with the area of crystal planes. In addition, a large coercivity H{sub c} = 3.9 kOe is observed in the Pr{sub 2}Fe{sub 14}B flakes with strong texture.« less

Superb electromagnetic wave-absorbing composites based on large-scale graphene and carbon nanotube films.

PubMed

Li, Jinsong; Lu, Weibang; Suhr, Jonghwan; Chen, Hang; Xiao, John Q; Chou, Tsu-Wei

2017-05-24

Graphene has sparked extensive research interest for its excellent physical properties and its unique potential for application in absorption of electromagnetic waves. However, the processing of stable large-scale graphene and magnetic particles on a micrometer-thick conductive support is a formidable challenge for achieving high reflection loss and impedance matching between the absorber and free space. Herein, a novel and simple approach for the processing of a CNT film-Fe 3 O 4 -large scale graphene composite is studied. The Fe 3 O 4 particles with size in the range of 20-200 nm are uniformly aligned along the axial direction of the CNTs. The composite exhibits exceptionally high wave absorption capacity even at a very low thickness. Minimum reflection loss of -44.7 dB and absorbing bandwidth of 4.7 GHz at -10 dB are achieved in composites with one-layer graphene in six-layer CNT film-Fe 3 O 4 prepared from 0.04 M FeCl 3 . Microstructural and theoretical studies of the wave-absorbing mechanism reveal a unique Debye dipolar relaxation with an Eddy current effect in the absorbing bandwidth.

Structural and Magnetic Response in Bimetallic Core/Shell Magnetic Nanoparticles

PubMed Central

Nairan, Adeela; Khan, Usman; Iqbal, Munawar; Khan, Maaz; Javed, Khalid; Riaz, Saira; Naseem, Shahzad; Han, Xiufeng

2016-01-01

Bimagnetic monodisperse CoFe2O4/Fe3O4 core/shell nanoparticles have been prepared by solution evaporation route. To demonstrate preferential coating of iron oxide onto the surface of ferrite nanoparticles X-ray diffraction (XRD), High resolution transmission electron microscope (HR-TEM) and Raman spectroscopy have been performed. XRD analysis using Rietveld refinement technique confirms single phase nanoparticles with average seed size of about 18 nm and thickness of shell is 3 nm, which corroborates with transmission electron microscopy (TEM) analysis. Low temperature magnetic hysteresis loops showed interesting behavior. We have observed large coercivity 15.8 kOe at T = 5 K, whereas maximum saturation magnetization (125 emu/g) is attained at T = 100 K for CoFe2O4/Fe3O4 core/shell nanoparticles. Saturation magnetization decreases due to structural distortions at the surface of shell below 100 K. Zero field cooled (ZFC) and Field cooled (FC) plots show that synthesized nanoparticles are ferromagnetic till room temperature and it has been noticed that core/shell sample possess high blocking temperature than Cobalt Ferrite. Results indicate that presence of iron oxide shell significantly increases magnetic parameters as compared to the simple cobalt ferrite. PMID:28335200

Recycling bacteria for the synthesis of LiMPO4 (M = Fe, Mn) nanostructures for high-power lithium batteries.

PubMed

Zhou, Yanping; Yang, Dan; Zeng, Yi; Zhou, Yan; Ng, Wun Jern; Yan, Qingyu; Fong, Eileen

2014-10-15

In this work, a novel waste-to-resource strategy to convert waste bacteria into a useful class of cathode materials, lithium metal phosphate (LiMPO4; M = Fe, Mn), is presented. Escherichia coli (E. coli) bacteria used for removing phosphorus contamination from wastewater are harvested and used as precursors for the synthesis of LiMPO4. After annealing, LiFePO4 and LiMnPO4 nanoparticles with dimensions around 20 nm are obtained. These particles are found to be enveloped in a carbon layer with a thickness around 3-5 nm, generated through the decomposition of the organic matter from the bacterial cell cytoplasm. The battery performance for the LiFePO4 is evaluated. A high discharge capacity of 140 mAh g(-1) at 0.1 C with a flat plateau located at around 3.5 V is obtained. In addition, the synthesized particles display excellent stability and rate capabilities. Even under a high C rate of 10 C, a stable discharge capacity of 75.4 mAh g(-1) can still be achieved. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Structure and soft magnetic properties of Fe-Si-B-P-Cu nanocrystalline alloys with minor Mn addition

NASA Astrophysics Data System (ADS)

Jia, Xingjie; Li, Yanhui; Wu, Licheng; Zhang, Wei

2018-05-01

Addition of minor Mn effectively improves the amorphous-forming ability and thermal stability of the Fe85Si2B8P4Cu1 alloy. With increasing the Mn content from 0 to 3 at.%, the critical thickness for amorphous formation and onset temperature of the primary crystallization increase from 14 μm and 659 K to 27 μm and 668 K, respectively. The fine nanocrystalline structure with α-Fe grains in size (D) of < 20 nm was obtained for the annealed amorphous alloys, which show excellent soft magnetic properties. The alloying of Mn reduces the coercivity (Hc) by decreasing the D value and widens the optimum annealing temperature range for obtaining low Hc, although the saturation magnetic flux density (Bs) is decreased slightly. The Fe83Mn2Si2B8P4Cu1 nanocrystalline alloy possesses fine structure with a D of ˜17.5 nm, and exhibits a high Bs of ˜1.75 T and a low Hc of ˜5.9 A/m. The mechanism related to the alloying effects on the structure and magnetic properties was discussed in term of the crystallization activation energy.

Spin-Coating and Characterization of Multiferroic MFe2O4 (M=Co, Ni) / BaTiO3 Bilayers

NASA Astrophysics Data System (ADS)

Quandt, Norman; Roth, Robert; Syrowatka, Frank; Steimecke, Matthias; Ebbinghaus, Stefan G.

2016-01-01

Bilayer films of MFe2O4 (M=Co, Ni) and BaTiO3 were prepared by spin coating of N,N-dimethylformamide/acetic acid solutions on platinum coated silicon wafers. Five coating steps were applied to get the desired thickness of 150 nm for both the ferrite and perovskite layer. XRD, IR and Raman spectroscopy revealed the formation of phase-pure ferrite spinels and BaTiO3. Smooth surfaces with roughnesses in the order of 3 to 5 nm were found in AFM investigations. Saturation magnetization of 347 emu cm-3 for the CoFe2O4/BaTiO3 and 188 emu cm-3 for the NiFe2O4/BaTiO3 bilayer, respectively were found. For the CoFe2O4/BaTiO3 bilayer a strong magnetic anisotropy was observed with coercivity fields of 5.1 kOe and 3.3 kOe (applied magnetic field perpendicular and parallel to film surface), while for the NiFe2O4/BaTiO3 bilayer this effect is less pronounced. Saturated polarization hysteresis loops prove the presence of ferroelectricity in both systems.

Enhanced interlayer exchange coupling in antiferromagnetically coupled ultrathin (Co70Fe30/Pd) multilayers

NASA Astrophysics Data System (ADS)

Meng, Zhaoliang; Qiu, Jinjun; Han, Guchang; Teo, Kie Leong

2015-12-01

We report the studies of magnetization reversal and magnetic interlayer coupling in synthetic antiferromagnetic (SAF) [Pd/Co70Fe30]9/Ru(tRu)/Pd(tPd)/[Co70Fe30/Pd]9 structure as functions of inserted Pd layer (tPd) and Ru layer (tRu) thicknesses. We found the exchange coupling field (Hex) and perpendicular magnetic anisotropy (PMA) can be controlled by both the tPd and tRu, The Hex shows a Ruderman-Kittel-Kasuya-Yosida-type oscillatory decay dependence on tRu and a maximum interlayer coupling strength Jex = 0.522 erg/cm2 is achieved at tPd + tRu ≈ 0.8 nm in the as-deposited sample. As it is known that a high post-annealing stability of SAF structure is required for magnetic random access memory applications, the dependence of Hex and PMA on the post-annealing temperature (Ta) is also investigated. We found that both high PMA of the top Co70Fe30/Pd multilayer is maintained and Hex is enhanced with increasing Ta up to 350 °C for tRu > 0.7 nm in our SAF structure.

Functional magnetic porous silica for T 1-T 2 dual-modal magnetic resonance imaging and pH-responsive drug delivery of basic drugs

NASA Astrophysics Data System (ADS)

Li, Ling; Zhang, Run; Guo, Yi; Zhang, Cheng; Zhao, Wei; Xu, Zhiping; Whittaker, Andrew K.

2016-12-01

A smart magnetic-targeting drug carrier γ-Fe2O3@p-silica comprising a γ-Fe2O3 core and porous shell has been prepared and characterized. The particles have a uniform size of about 60 nm, and a porous shell of thickness 3 nm. Abundant hydroxyl groups and a large surface area enabled the γ-Fe2O3@p-silica to be readily loaded with a large payload of the basic model drug rhodamine B (RB) (up to 73 mg g-1). Cytotoxicity assays of the γ-Fe2O3@p-silica particles indicated that the particles were biocompatible and suitable for carrying drugs. It was found that the RB was released rapidly at pH 5.5 but at pH 7.4 the rate and extent of release was greatly attenuated. The particles therefore demonstrate an excellent pH-triggered drug release. In addition, the γ-Fe2O3@p-silica particles could be tracked by magnetic resonance imaging (MRI). A clear dose-dependent contrast enhancement in both T 1-weighted and T 2-weighted MR images indicated the potential of the γ-Fe2O3@p-silica particles to act as dual-mode T 1 and T 2 MRI contrast agents.

Investigation of structural and magnetic properties of rapidly-solidified iron-silicon alloys at ambient and elevated temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jayaraman, T. V.; Meka, V. M.; Jiang, X.

In this work, we investigated the ambient temperature structural properties (~300 K) and the ambient and high temperature (up to 900 K) direct current (DC) magnetic properties of melt-spun Fe-x wt.% Si (x = 3, 5, & 8) alloys. The wheel surface speeds selected for the study were 30 m/s and 40 m/s. The thickness, width, lattice parameter, saturation magnetization (MS), and intrinsic coercivity (HCI) of the melt spun ribbons are presented and compared with data in the literature. The ribbons produced at the lower wheel surface speed (30 m/s) were continuous having relatively uniform edges compared to the ribbonsmore » produced at the higher wheel surface speed. The thickness and the width of the melt-spun ribbons ranged between ~15-60 μm and 500-800 μm, respectively. The x-ray diffraction spectra of the melt-spun ribbons indicated the presence of disordered α-phase, irrespective of the composition, and the wheel-surface speed. The lattice parameter decreased gradually as a function of increasing silicon content from ~0.2862 nm (Fe-3 wt.% Si) to ~0.2847 nm (Fe-8 wt.% Si). Wheel surface speed was not shown to have a significant effect on the magnetization, but primarily impacted the ribbon structure. A decreasing trend in the saturation magnetization was observed as a function of increased silicon content. The intrinsic coercivity of the melt-spun alloys ranged between ~50 to 200 A/m. Elevated temperature evaluation of the magnetization in the case of Fe-3 & 5 wt.% Si alloy ribbons was distinctly different from the Fe-8 wt.% Si alloy ribbons. The curves of the as-prepared Fe-3 wt.% Si and Fe-5 wt.% Si alloy ribbons were irreversible while that of Fe-8 wt.% Si was reversible. The MS for any of the combinations of wheel surface speed and composition decreased monotonically with the increase in temperature (from 300 – 900 K). The percentage decrease in MS from 300 K to 900 K for the Fe-3 wt.% Si and Fe-5 wt.% Si alloys was ~19-22 %, while the percentage decrease in the same temperature range for Fe-8 wt.% Si alloy was ~26-30 %. It appears that Fe-3 wt.% Si and Fe-5 wt.% Si alloys ribbons are primarily comprised of the α phase (disordered phase) with any minor constituents being beyond the detection limits of the studies performed, while the Fe-8 wt.% Si alloy ribbons are comprised of disordered and regions of short-range ordering.« less

TEM and AES investigations of the natural surface nano-oxide layer of an AISI 316L stainless steel microfibre.

PubMed

Ramachandran, Dhanya; Egoavil, Ricardo; Crabbe, Amandine; Hauffman, Tom; Abakumov, Artem; Verbeeck, Johan; Vandendael, Isabelle; Terryn, Herman; Schryvers, Dominique

2016-11-01

The chemical composition, nanostructure and electronic structure of nanosized oxide scales naturally formed on the surface of AISI 316L stainless steel microfibres used for strengthening of composite materials have been characterised using a combination of scanning and transmission electron microscopy with energy-dispersive X-ray, electron energy loss and Auger spectroscopy. The analysis reveals the presence of three sublayers within the total surface oxide scale of 5.0-6.7 nm thick: an outer oxide layer rich in a mixture of FeO.Fe 2 O 3 , an intermediate layer rich in Cr 2 O 3 with a mixture of FeO.Fe 2 O 3 and an inner oxide layer rich in nickel. © 2016 The Authors Journal of Microscopy © 2016 Royal Microscopical Society.

Fabrication of nano-Fe3O4 3D structure on carbon fibers as a microwave absorber and EMI shielding composite by modified EPD method

NASA Astrophysics Data System (ADS)

Gholampoor, Mahdi; Movassagh-Alanagh, Farid; Salimkhani, Hamed

2017-02-01

Recently, electromagnetic interference (EMI) shielding materials have absorbed a lot of attention due to a growing need for application in the area of electronic and wireless devices. In this study, a carbon-based EMI shielding composite was fabricated by electrophoretic deposition of Fe3O4 nano-particles on carbon fibers (CFs) as a 3D structure incorporated with an epoxy resin. Co-precipitation method was employed to synthesize Fe3O4 nano-particles. This as-synthesized Fe3O4 nano-powder was then successfully deposited on CFs using a modified multi-step electrophoretic deposition (EPD) method. The results of structural studies showed that the Fe3O4 nano-particles (25 nm) were successfully and uniformly deposited on CFs. The measured magnetic properties of as-synthesized Fe3O4 nano-powder and nano-Fe3O4/CFs composite showed that the saturation magnetization of bare Fe3O4 was decreased from Ms = 72.3 emu/g to Ms = 33.1 emu/g for nano-Fe3O4/CFs composite and also corecivity of Fe3O4 was increased from Hc = 4.9 Oe to Hc = 168 Oe for composite. The results of microwave absorption tests revealed that the reflection loss (RL) of an epoxy-based nano-Fe3O4/CFs composite are significantly influenced by layer thickness. The maximum RL value of -10.21 dB at 10.12 GHz with an effective absorption bandwidth about 2 GHz was obtained for the sample with the thickness of 2 mm. It also exhibited an EMI shielding performance of -23 dB for whole the frequency range of 8.2-12.4 GHz.

Spin Seebeck effect and thermal spin galvanic effect in Ni80Fe20/p-Si bilayers

NASA Astrophysics Data System (ADS)

Bhardwaj, Ravindra G.; Lou, Paul C.; Kumar, Sandeep

2018-01-01

The development of spintronics and spin-caloritronics devices needs efficient generation, detection, and manipulation of spin current. The thermal spin current from the spin-Seebeck effect has been reported to be more energy efficient than the electrical spin injection methods. However, spin detection has been the one of the bottlenecks since metals with large spin-orbit coupling is an essential requirement. In this work, we report an efficient thermal generation and interfacial detection of spin current. We measured a spin-Seebeck effect in Ni80Fe20 (25 nm)/p-Si (50 nm) (polycrystalline) bilayers without a heavy metal spin detector. p-Si, having a centrosymmetric crystal structure, has insignificant intrinsic spin-orbit coupling, leading to negligible spin-charge conversion. We report a giant inverse spin-Hall effect, essential for the detection of spin-Seebeck effects, in the Ni80Fe20/p-Si bilayer structure, which originates from Rashba spin orbit coupling due to structure inversion asymmetry at the interface. In addition, the thermal spin pumping in p-Si leads to spin current from p-Si to the Ni80Fe20 layer due to the thermal spin galvanic effect and the spin-Hall effect, causing spin-orbit torques. The thermal spin-orbit torques lead to collapse of magnetic hysteresis of the 25 nm thick Ni80Fe20 layer. The thermal spin-orbit torques can be used for efficient magnetic switching for memory applications. These scientific breakthroughs may give impetus to the silicon spintronics and spin-caloritronics devices.

One-dimensional magnetic nanocomposites with attapulgites as templates: Growth, formation mechanism and magnetic alignment

NASA Astrophysics Data System (ADS)

Fu, Meng; Li, Xiangming; Jiang, Rui; Zhang, Zepeng

2018-05-01

Magnetic nanocomposite composed of attapulgite and Fe3O4 was synthesized by a simple and facile co-precipitation method. Its structure and morphology was verified using X-ray diffraction, transmission electron microscopy, scanning electron microscopy and Fourier transform infrared spectroscopy. Although the difficulty of forming uniform Fe3O4 on the attapulgite surface was discussed in detail in this study, one-dimensional magnetic nanorod with attapulgites as core and Fe3O4 as uniform shell was implemented for the first time using a cationic polymer surfactant, polyethylenimine. Polyethylenimine concentration, Fe3+/Fe2+ concentration and temperature were controlled to investigate the morphological evolutions of this nanocomposite. It was found that a uniform shell could be available with thickness tuning from 10 nm to 40 nm when Fe3+ concentration ranged from 0.01 mol/L to 0.03 mol/L meanwhile the polyethylenimine concentration was kept at 0.2 mg/mL and the temperature was kept at 60-80 °C. Finally, a possible mechanism for the formation of the Fe3O4 shell was suggested. The polyethylenimine on the surface of the attapulgites first adsorbed Fe3+/Fe2+ and then released under the action of alkali. It acted as a linker for the Fe3O4 nanoparticles nucleation in situ. The synthesized one-dimensional nanocomposites exhibit the superparamagnetism and fast response to an external magnetic field. The alignment of attapulgite-Fe3O4 one-dimensional nanocomposite along the external magnetic field was demonstrated. It provides promising candidates for building blocks and functional devices, which are low cost, non-toxic and eco-friendly, and opens the door for the application of attapulgite as one-dimensional nanomaterials.

Symmetry of Highly-Strained BiFeO3 Films in the Ultrathin Regime

NASA Astrophysics Data System (ADS)

Yang, Yongsoo; Senabulya, Nancy; Clarke, Roy; Schlepütz, Christian M.; Beekman, Christianne; Siemons, Wolter; Christen, Hans M.

2014-03-01

At room temperature, highly-strained BiFeO3 (BFO) films grown on LaAlO3 substrates exhibit a monoclinic structure with a giant c/a ratio (~1.3) when the films are thicker than 4 nm. Their structural symmetry can be controlled by adjusting the temperature [Appl. Phys. Express 4, 095801 (2011), Adv. Mater. 25, 5561 (2013)], with a high-temperature tetragonal phase being observed. We report that a structural phase transition can also be achieved by controlling the film thickness: synchrotron x-ray diffraction data shows that the Bragg peak splitting associated with the monoclinic phase disappears as the film thickness decreases below 3 nm, indicating a tetragonal symmetry, but still maintaining the giant c/a ratio. Unlike a similar transition reported for moderately strained BFO grown on SrTiO3 [APL Mater. 1, 052102 (2013)], the half-order Bragg peaks indicate that this transition does not involve a significant change in the octahedral tilt pattern of the film. This suggests that the structural evolution of highly-strained BFO films should be understood in terms of the unique (non-octahedral) oxygen coordination of the Fe ion in this highly-strained BFO, not the corner-connectivity of the oxygen octahedra between the film and the substrate. Funding: U.S. Department of Energy, BES-MSED (U. Michigan: DE-FG02-06ER46273, and at ORNL). Measurements: 13-BMC, 33-IDD, 33-BMC of the Advanced Photon Source, ANL (DE-AC02-06CH11357).

Enhanced annealing stability and perpendicular magnetic anisotropy in perpendicular magnetic tunnel junctions using W layer

NASA Astrophysics Data System (ADS)

Chatterjee, Jyotirmoy; Sousa, Ricardo C.; Perrissin, Nicolas; Auffret, Stéphane; Ducruet, Clarisse; Dieny, Bernard

2017-05-01

The magnetic properties of the perpendicular storage electrode (buffer/MgO/FeCoB/Cap) were studied as a function of annealing temperature by replacing Ta with W and W/Ta cap layers with variable thicknesses. W in the cap boosts up the annealing stability and increases the effective perpendicular anisotropy by 30% compared to the Ta cap. Correspondingly, an increase in the FeCoB critical thickness characterizing the transition from perpendicular to in-plane anisotropy was observed. Thicker W layer in the W(t)/Ta 1 nm cap layer makes the storage electrode highly robust against annealing up to 570 °C. The stiffening of the overall stack resulting from the W insertion due to its very high melting temperature seems to be the key mechanism behind the extremely high thermal robustness. The Gilbert damping constant of FeCoB with the W/Ta cap was found to be lower when compared with the Ta cap and stable with annealing. The evolution of the magnetic properties of bottom pinned perpendicular magnetic tunnel junctions (p-MTJ) stack with the W2/Ta1 nm cap layer shows back-end-of-line compatibility with increasing tunnel magnetoresistance up to the annealing temperature of 425 °C. The pMTJ thermal budget is limited by the synthetic antiferromagnetic hard layer which is stable up to 425 °C annealing temperature while the storage layer is stable up to 455 °C.

Magnetostriction Increase of Polycrystalline Fe-Al-B Thin Sheets after Thermomechanical Process

NASA Astrophysics Data System (ADS)

Dias, M. B. S.; Fulop, G. O.; Baldan, C. A.; Bormio-Nunes, C.

2017-12-01

Magnetostrictive materials are applied in several types of sensors, actuators, and energy harvesting. In particular, for AC devices, thin materials are desired to reduce eddy current losses. It is well known that the magnetostriction of single crystals and textured materials is higher than in polycrystalline ones, however, the cost and manufacture speed are crucial to be used as parts of commercial devices. Therefore, polycrystalline samples are strong candidates for common applications. In this work, (Fe x Al100- x )98.4B1.6 ( x = 86.6, 82 and 79.4) alloys were rolled down to 0.7 mm of thickness and annealed at 1473 K (1200 °C) for 2 hours aiming to reduce the thickness of the samples without deteriorating the magnetic properties. The alloys, even with higher contents of Al, were easily deformed to the thickness of 0.7 mm and this ability is attributed to the presence of the Fe2B phase. After the thermomechanical process, new isotropic recrystallized grains emerged and the longitudinal magnetostriction increased to 75.8, 16.9, and 3.2 pct, achieving 28.3, 28.4, and 28.8 ppm, respectively, for x = 86.6, 82, and 79.4. The piezomagnetic coefficient obtained of 4 nm/A is a suitable actuating sensitivity.

In-plane magnetic anisotropy and coercive field dependence upon thickness of CoFeB

NASA Astrophysics Data System (ADS)

Kipgen, Lalminthang; Fulara, Himanshu; Raju, M.; Chaudhary, Sujeet

2012-09-01

The structural and magnetic properties of as-grown 5-50 nm thin ion-beam sputter deposited transition metal-metalloid Co20Fe60B20 (CFB) films are reported in this communication. A broad peak observed at 2θ∼45° in the glancing angle X-ray diffraction pattern revealed the formation of very fine nano-sized grains embedded in majority amorphous CFB matrix. Although no magnetic field is applied during deposition, the longitudinal magneto-optic Kerr effect measurements performed at 300 K in these as-grown films clearly established the presence of in-plane uniaxial magnetic anisotropy (Ku). It is argued that this observed anisotropy is strain-induced. This is supported by the observed dependence of direction of Ku on the angle between applied magnetic field and crystallographic orientation of the underlying Si(100) substrate, and increase in the coercivity with the increase of the film thickness.

Spin-orbit torque in a bulk perpendicular magnetic anisotropy Pd/FePd/MgO system

PubMed Central

Lee, Hwang-Rae; Lee, Kyujoon; Cho, Jaehun; Choi, Young-Ha; You, Chun-Yeol; Jung, Myung-Hwa; Bonell, Frédéric; Shiota, Yoichi; Miwa, Shinji; Suzuki, Yoshishige

2014-01-01

Spin-orbit torques, including the Rashba and spin Hall effects, have been widely observed and investigated in various systems. Since interesting spin-orbit torque (SOT) arises at the interface between heavy nonmagnetic metals and ferromagnetic metals, most studies have focused on the ultra-thin ferromagnetic layer with interface perpendicular magnetic anisotropy. Here, we measured the effective longitudinal and transverse fields of bulk perpendicular magnetic anisotropy Pd/FePd (1.54 to 2.43 nm)/MgO systems using harmonic methods with careful correction procedures. We found that in our range of thicknesses, the effective longitudinal and transverse fields are five to ten times larger than those reported in interface perpendicular magnetic anisotropy systems. The observed magnitude and thickness dependence of the effective fields suggest that the SOT do not have a purely interfacial origin in our samples. PMID:25293693

Enhanced exchange bias in MnN/CoFe bilayers after high-temperature annealing

NASA Astrophysics Data System (ADS)

Dunz, M.; Schmalhorst, J.; Meinert, M.

2018-05-01

We report an exchange bias of more than 2700 Oe at room temperature in MnN/CoFe bilayers after high-temperature annealing. We studied the dependence of exchange bias on the annealing temperature for different MnN thicknesses in detail and found that samples with tMnN > 32nm show an increase of exchange bias for annealing temperatures higher than TA = 400 °C. Maximum exchange bias values exceeding 2000 Oe with reasonably small coercive fields around 600 Oe are achieved for tMnN = 42, 48 nm. The median blocking temperature of those systems is determined to be 180 °C after initial annealing at TA = 525 °C. X-ray diffraction measurements and Auger depth profiling show that the large increase of exchange bias after high-temperature annealing is accompanied by strong nitrogen diffusion into the Ta buffer layer of the stacks.

One-pot template-free synthesis of uniform-sized fullerene-like magnetite hollow spheres

NASA Astrophysics Data System (ADS)

Zhu, Qing; Zhang, Yue; Liu, Zheng; Zhou, Xinrui; Zhang, Xinmei; Zeng, Lintao

2015-11-01

Uniform-sized Fe3O4 hollow spheres with average diameter of 250 nm and shell thickness of ∼50 nm have been successfully synthesized through a simple hydrothermal route with the presence of di-n-propylamine (DPA) as a weak-base. The reaction time and DPA amount play important roles in the formation of the magnetite hollow spheres. The structures of the products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectra, scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. The results show that the single-crystalline Fe3O4 hollow spheres are composed of well-aligned magnetite nanoparticles (NPs). The magnetic property investigation shows that these hollow spheres have a higher saturation magnetization (Ms) than the solid spheres. Furthermore, a possible mechanism for the formation of magnetite hollow spheres is proposed based on the experimental observations.

Synthesis of Co/MFe(2)O(4) (M = Fe, Mn) Core/Shell Nanocomposite Particles.

PubMed

Peng, Sheng; Xie, Jin; Sun, Shouheng

2008-01-01

Monodispersed cobalt nanoparticles (NPs) with controllable size (8-14 nm) have been synthesized using thermal decomposition of dicobaltoctacarbonyl in organic solvent. The as-synthesized high magnetic moment (125 emu/g) Co NPs are dispersible in various organic solvents, and can be easily transferred into aqueous phase by surface modification using phospholipids. However, the modified hydrophilic Co NPs are not stable as they are quickly oxidized, agglomerated in buffer. Co NPs are stabilized by coating the MFe(2)O(4) (M = Fe, Mn) ferrite shell. Core/shell structured bimagnetic Co/MFe(2)O(4) nanocomposites are prepared with tunable shell thickness (1-5 nm). The Co/MFe(2)O(4) nanocomposites retain the high magnetic moment density from the Co core, while gaining chemical and magnetic stability from the ferrite shell. Comparing to Co NPs, the nanocomposites show much enhanced stability in buffer solution at elevated temperatures, making them promising for biomedical applications.

Enhancement of superconducting transition temperature in FeSe electric-double-layer transistor with multivalent ionic liquids

NASA Astrophysics Data System (ADS)

Miyakawa, Tomoki; Shiogai, Junichi; Shimizu, Sunao; Matsumoto, Michio; Ito, Yukihiro; Harada, Takayuki; Fujiwara, Kohei; Nojima, Tsutomu; Itoh, Yoshimitsu; Aida, Takuzo; Iwasa, Yoshihiro; Tsukazaki, Atsushi

2018-03-01

We report on an enhancement of the superconducting transition temperature (Tc) of the FeSe-based electric-double-layer transistor (FeSe-EDLT) by applying the multivalent oligomeric ionic liquids (ILs). The IL composed of dimeric cation (divalent IL) enables a large amount of charge accumulation on the surface of the FeSe ultrathin film, resulting in inducing electron-rich conduction even in a rather thick 10 nm FeSe channel. The onset Tc in FeSe-EDLT with the divalent IL is enhanced to be approaching about 50 K at the thin limit, which is about 7 K higher than that in EDLT with conventional monovalent ILs. The enhancement of Tc is a pronounced effect of the application of the divalent IL, in addition to the large capacitance, supposing preferable interface formation of ILs driven by geometric and/or Coulombic effect. The present finding strongly indicates that multivalent ILs are powerful tools for controlling and improving physical properties of materials.

Preparation and electrical properties of Cr 2O 3 gate insulator embedded with Fe dot

NASA Astrophysics Data System (ADS)

Yokota, Takeshi; Kuribayashi, Takaaki; Murata, Shotaro; Gomi, Manabu

2008-09-01

We investigated the electrical properties of a metal (Au)/insulator (magneto-electric materials: Cr 2O 3)/magnetic materials (Fe)/tunnel layer (Cr 2O 3)/semiconductor (Si) capacitor. This capacitor shows the typical capacitance-voltage ( C- V) properties of an Si-MIS capacitor with hysteresis depending on the Fe dispersibility which is determined by the deposition condition. The C- V curve of the only sample having a 0.5 nm Fe layer was seen to have a hysteresis window with a clockwise trace, indicating that electrons have been injected into the ultra-thin Fe layer. The samples having Fe layers of other thicknesses show a counterclockwise trace, which indicates that the film has mobile ionic charges due to the dispersed Fe. These results indicated that the charge-injection site, which works as a memory, in the Cr 2O 3 can be prepared by Fe insertion, which is deposited using well-controlled conditions. The results also revealed the possibility of an MIS capacitor containing both ferromagnetic materials and an ME insulating layer in a single system.

TEM/STEM study of Zircaloy-2 with protective FeAl(Cr) layers under simulated BWR environment and high-temperature steam exposure

NASA Astrophysics Data System (ADS)

Park, Donghee; Mouche, Peter A.; Zhong, Weicheng; Mandapaka, Kiran K.; Was, Gary S.; Heuser, Brent J.

2018-04-01

FeAl(Cr) thin-film depositions on Zircaloy-2 were studied using transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) with respect to oxidation behavior under simulated boiling water reactor (BWR) conditions and high-temperature steam. Columnar grains of FeAl with Cr in solid solution were formed on Zircaloy-2 coupons using magnetron sputtering. NiFe2O4 precipitates on the surface of the FeAl(Cr) coatings were observed after the sample was exposed to the simulated BWR environment. High-temperature steam exposure resulted in grain growth and consumption of the FeAl(Cr) layer, but no delamination at the interface. Outward Al diffusion from the FeAl(Cr) layer occurred during high-temperature steam exposure (700 °C for 3.6 h) to form a 100-nm-thick alumina oxide layer, which was effective in mitigating oxidation of the Zircaloy-2 coupons. Zr intermetallic precipitates formed near the FeAl(Cr) layer due to the inward diffusion of Fe and Al. The counterflow of vacancies in response to the Al and Fe diffusion led to porosity within the FeAl(Cr) layer.

Orthorhombic MoO3 nanobelts based NO2 gas sensor

NASA Astrophysics Data System (ADS)

Mane, A. A.; Moholkar, A. V.

2017-05-01

Molybdenum trioxide (MoO3) nanobelts have been deposited onto the glass substrates using chemical spray pyrolysis (CSP) deposition method. The XRD patterns reveal that films are polycrystalline having an orthorhombic crystal structure. Raman spectra confirm that the films are orthorhombic in phase. The XPS study shows the presence of two well resolved spectral lines of Mo-3d core levels appearing at the binding energy values of 232.82 eV and 235.95 eV corresponding to Mo-3d5/2 and Mo-3d3/2, respectively. These binding energy values are assigned to Mo6+ oxidation state of fully oxidized MoO3. The FE-SEM micrographs show the formation of nanobelts-like morphology. The AFM micrographs reveal that the RMS surface roughness increases from 16.5 nm to 17.5 nm with increase in film thickness from 470 nm to 612 nm and then decreases to 16 nm for 633 nm film thickness. The band gap energy is found to be decreased from 3.40 eV to 3.38 eV. To understand the electronic transport phenomenon in MoO3 thin films, dielectric properties are studied. For 612 nm film thickness, the highest NO2 gas response of 68% is obtained at an operating temperature of 200 °C for 100 ppm concentration with response and recovery times of 15 s and 150 s, respectively. The lower detection limit is found to be 10 ppm which is half of the immediately dangerous to life or health (IDLH) value of 20 ppm. Finally, NO2 gas sensing mechanism in an orthorhombic MoO3 crystal structure is discussed in detail.

One-pot synthesis of in-situ carbon-coated Fe3O4 as a long-life lithium-ion battery anode

NASA Astrophysics Data System (ADS)

Liu, Min; Jin, Hongyun; Uchaker, Evan; Xie, Zhiqiang; Wang, Ying; Cao, Guozhong; Hou, Shuen; Li, Jiangyu

2017-04-01

Fe3O4 has been regarded as a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity, low cost, and environmental friendliness. In this work, we present a one-pot reducing-composite-hydroxide-mediated (R-CHM) method to synthesize in situ carbon-coated Fe3O4 (Fe3O4@C) at 280 °C using Fe(NO3)3 · 9H2O and PEG800 as raw materials and NaOH/KOH as the medium. The as-prepared Fe3O4 octahedron has an average size of 100 nm in diameter, covered by a carbon layer with a thickness of 3 nm, as revealed by FESEM and HRTEM images. When used as anode materials in LIBs, Fe3O4@C exhibited an outstanding rate capability (1006, 918, 825, 737, 622, 455 and 317 mAh g-1 at 0.1, 0.2, 0.5, 0.8, 1.0, 1.5 and 2.0 A g-1). Moreover, it presented an excellent cycling stability, with a retained capacity of 261 mAh g-1 after 800 cycles under an extremely high specific current density of 2.0 A g-1. Such results indicate that Fe3O4@C can provide a new route into the development of long-life electrodes for future rechargeable LIBs. Importantly, the R-CHM developed in our work can be extended for the synthesis of other carbon-coated electrodes for LIBs and functional nanostructures for broader applications.

Textured Nd2Fe14B flakes with enhanced coercivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cui, BZ; Zheng, LY; Marinescu, M

2012-04-01

Morphology, structure, and magnetic properties of the [001] textured Nd2Fe14B nanocrystalline flakes prepared by surfactant-assisted high energy ball milling (HEBM) and subsequent annealing were studied. These flakes have a thickness of 80-200 nm, a length of 0.5-10 mu m, and an average grain size of 10-14nm. The addition of some amount of Dy, Nd70Cu30 alloy, and an appropriate post annealing increased the coercivity H-i(c) of the Nd2Fe14B flakes. iHc was 3.7, 4.3, and 5.7 kOe for the Nd15.5Fe78.5B6, Nd14Dy1.5Fe78.5B6 and 83.3wt.% Nd14Dy1.5Fe78.5B6+16.7 wt.% Nd70Cu30 flakes prepared by HEBM for 5 h in heptane with 20 wt.% oleylamine, respectively. After annealingmore » at 450 degrees C for 0.5h, their iHc increased to 5.1, 6.2, and 7.0 kOe, respectively. Anisotropic magnetic behavior was found in all of the as-milled and annealed flakes. Both, the thickening of Nd-rich phase at grain boundaries via diffusion of Nd70Cu30 and the surface modification of the Nd2Fe14B flake could be the main reasons for the coercivity enhancement in the as-milled and annealed Nd70Cu30-added Nd2Fe14B flakes. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3679425]« less

Multifunctional Au-Fe3O4@MOF core-shell nanocomposite catalysts with controllable reactivity and magnetic recyclability

NASA Astrophysics Data System (ADS)

Ke, Fei; Wang, Luhuan; Zhu, Junfa

2014-12-01

The recovery and reuse of expensive catalysts are important in both heterogeneous and homogeneous catalysis due to economic and environmental reasons. This work reports a novel multifunctional magnetic core-shell gold catalyst which can be easily prepared and shows remarkable catalytic properties in the reduction of 4-nitrophenol. The novel Au-Fe3O4@metal-organic framework (MOF) catalyst consists of a superparamagnetic Au-Fe3O4 core and a porous MOF shell with controllable thickness. Small Au nanoparticles (NPs) of 3-5 nm are mainly sandwiched between the Fe3O4 core and the porous MOF shell. Catalytic studies show that the core-shell structured Au-Fe3O4@MOF catalyst has a much higher catalytic activity than other reported Au-based catalysts toward the reduction of 4-nitrophenol. Moreover, this catalyst can be easily recycled due to the presence of the superparamagnetic core. Therefore, compared to conventional catalysts used in the reduction of 4-nitrophenol, this porous MOF-based magnetic catalyst is green, cheap and promising for industrial applications.The recovery and reuse of expensive catalysts are important in both heterogeneous and homogeneous catalysis due to economic and environmental reasons. This work reports a novel multifunctional magnetic core-shell gold catalyst which can be easily prepared and shows remarkable catalytic properties in the reduction of 4-nitrophenol. The novel Au-Fe3O4@metal-organic framework (MOF) catalyst consists of a superparamagnetic Au-Fe3O4 core and a porous MOF shell with controllable thickness. Small Au nanoparticles (NPs) of 3-5 nm are mainly sandwiched between the Fe3O4 core and the porous MOF shell. Catalytic studies show that the core-shell structured Au-Fe3O4@MOF catalyst has a much higher catalytic activity than other reported Au-based catalysts toward the reduction of 4-nitrophenol. Moreover, this catalyst can be easily recycled due to the presence of the superparamagnetic core. Therefore, compared to conventional catalysts used in the reduction of 4-nitrophenol, this porous MOF-based magnetic catalyst is green, cheap and promising for industrial applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05421k

The Ultrathin Limit and Dead-layer Effects in Local Polarization Switching of BiFeO3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maksymovych, Petro; Huijben, Mark; Pan, Minghu

Using piezoresponse force microscopy in ultra-high vacuum, polarization switching has been detected and quantified in epitaxial BiFeO3 films from 200 down to ~ 4 unit cells. Local remnant piezoresponse was used to infer the applied electric field inside the ferroelectric volume, and account for the elusive effect of dead-layers in ultrathin films. The dead-layer manifested itself in the slower than anticipated decrease of the switching bias with film thickness, yielding apparent Kay-Dunn scaling of the switching field, while the statistical analysis of hysteresis loops revealed lateral variation of the dead-layer with sub-10 nm resolution.

Observation of spin-polarized electron transport in Alq3 by using a low work function metal

NASA Astrophysics Data System (ADS)

Jang, Hyuk-Jae; Pernstich, Kurt P.; Gundlach, David J.; Jurchescu, Oana D.; Richter, Curt. A.

2012-09-01

We present the observation of magnetoresistance in Co/Ca/Alq3/Ca/NiFe spin-valve devices. Thin Ca layers contacting 150 nm thick Alq3 enable the injection of spin-polarized electrons into Alq3 due to the engineering of the band alignment. The devices exhibit symmetric current-voltage (I-V) characteristics indicating identical metal contacts on Alq3, and up to 4% of positive magnetoresistance was observed at 4.5 K. In contrast, simultaneously fabricated Co/Alq3/NiFe devices displayed asymmetric I-V curves due to the different metal electrodes, and spin-valve effects were not observed.

Pt thickness dependence of spin Hall effect switching of in-plane magnetized CoFeB free layers studied by differential planar Hall effect

NASA Astrophysics Data System (ADS)

Mihajlović, G.; Mosendz, O.; Wan, L.; Smith, N.; Choi, Y.; Wang, Y.; Katine, J. A.

2016-11-01

We introduce a differential planar Hall effect method that enables the experimental study of spin orbit torque switching of in-plane magnetized free layers in a simple Hall bar device geometry. Using this method, we study the Pt thickness dependence of switching currents and show that they decrease monotonically down to the minimum experimental thickness of ˜5 nm, while the critical current and power densities are very weakly thickness dependent, exhibiting the minimum values of Jc0 = 1.1 × 108 A/cm2 and ρJc0 2=0.6 ×1012 W/cm 3 at this minimum thickness. Our results suggest that a significant reduction of the critical parameters could be achieved by optimizing the free layer magnetics, which makes this technology a viable candidate for fast, high endurance and low-error rate applications such as cache memories.

A comparative study of the influence of nickel oxide layer on the FTO surface of organic light emitting diode

NASA Astrophysics Data System (ADS)

Saikia, Dhrubajyoti; Sarma, Ranjit

2018-03-01

The influence of thin layer of nickel oxide (NiO) over the fluorine-doped tin oxide (FTO) surface on the performance of Organic light-emitting diode (OLED) is reported. With an optimal thickness of NiO (10 nm), the luminance efficiency is found to be increased as compared to the single FTO OLED. The performance of OLED is studied by depositing NiO films at different thicknesses on the FTO surface and analyzed their J-V and L-V characteristics. Further analysis is carried out by measuring sheet resistance and optical transmittance. The surface morphology is studied with the help of FE-SEM images. Our results indicate that NiO (10 nm) buffer layer is an excellent choice to increase the efficiency of FTO based OLED devices within the charge tunneling region. The maximum value of current efficiency is found to be 7.32 Cd/A.

Giant Spin Hall Effect and Switching Induced by Spin-Transfer Torque in a W /Co40Fe40B20/MgO Structure with Perpendicular Magnetic Anisotropy

NASA Astrophysics Data System (ADS)

Hao, Qiang; Xiao, Gang

2015-03-01

We obtain robust perpendicular magnetic anisotropy in a β -W /Co40Fe40B20/MgO structure without the need of any insertion layer between W and Co40Fe40B20 . This is achieved within a broad range of W thicknesses (3.0-9.0 nm), using a simple fabrication technique. We determine the spin Hall angle (0.40) and spin-diffusion length for the bulk β form of tungsten with a large spin-orbit coupling. As a result of the giant spin Hall effect in β -W and careful magnetic annealing, we significantly reduce the critical current density for the spin-transfer-torque-induced magnetic switching in Co40Fe40B20 . The elemental β -W is a superior candidate for magnetic memory and spin-logic applications.

Aluminium alloyed iron-silicide/silicon solar cells: A simple approach for low cost environmental-friendly photovoltaic technology.

PubMed

Kumar Dalapati, Goutam; Masudy-Panah, Saeid; Kumar, Avishek; Cheh Tan, Cheng; Ru Tan, Hui; Chi, Dongzhi

2015-12-03

This work demonstrates the fabrication of silicide/silicon based solar cell towards the development of low cost and environmental friendly photovoltaic technology. A heterostructure solar cells using metallic alpha phase (α-phase) aluminum alloyed iron silicide (FeSi(Al)) on n-type silicon is fabricated with an efficiency of 0.8%. The fabricated device has an open circuit voltage and fill-factor of 240 mV and 60%, respectively. Performance of the device was improved by about 7 fold to 5.1% through the interface engineering. The α-phase FeSi(Al)/silicon solar cell devices have promising photovoltaic characteristic with an open circuit voltage, short-circuit current and a fill factor (FF) of 425 mV, 18.5 mA/cm(2), and 64%, respectively. The significant improvement of α-phase FeSi(Al)/n-Si solar cells is due to the formation p(+-)n homojunction through the formation of re-grown crystalline silicon layer (~5-10 nm) at the silicide/silicon interface. Thickness of the regrown silicon layer is crucial for the silicide/silicon based photovoltaic devices. Performance of the α-FeSi(Al)/n-Si solar cells significantly depends on the thickness of α-FeSi(Al) layer and process temperature during the device fabrication. This study will open up new opportunities for the Si based photovoltaic technology using a simple, sustainable, and los cost method.

Electrodeposited Nanolaminated CoNiFe Cores for Ultracompact DC-DC Power Conversion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, J; Kim, M; Herrault, F

2015-09-01

Laminated metallic alloy cores (i.e., alternating layers of thin film metallic alloy and insulating material) of appropriate lamination thickness enable suppression of eddy current losses at high frequencies. Magnetic cores comprised of many such laminations yield substantial overall magnetic volume, thereby enabling high-power operation. Previously, we reported nanolaminated permalloy (Ni-80 Fe-20) cores based on a sequential electrodeposition technique, demonstrating negligible eddy current losses at peak flux densities up to 0.5 T and operating at megahertz frequencies. This paper demonstrates improved performance of nanolaminated cores comprising tens to hundreds of layers of 300-500-nm-thick CoNiFe films that exhibit superior magnetic properties (e.g.,more » higher saturation flux density and lower coercivity) than permalloy. Nanolaminated CoNiFe cores can be operated up to a peak flux density of 0.9 T, demonstrating improved power handling capacity and exhibiting 30% reduced volumetric core loss, attributed to lowered hysteresis losses compared to the nanolaminated permalloy core of the same geometry. Operating these cores in a buck dc-dc power converter at a switching frequency of 1 MHz, the nanolaminated CoNiFe cores achieved a conversion efficiency exceeding 90% at output power levels up to 7 W, compared to an achieved permalloy core conversion efficiency below 86% at 6 W.« less

Growth, structure, and properties of epitaxial thin films of first-principles predicted multiferroic Bi2FeCrO6

NASA Astrophysics Data System (ADS)

Nechache, Riad; Harnagea, Catalin; Pignolet, Alain; Normandin, François; Veres, Teodor; Carignan, Louis-Philippe; Ménard, David

2006-09-01

The authors report the structural and physical properties of epitaxial Bi2FeCrO6 thin films on epitaxial SrRuO3 grown on (100)-oriented SrTiO3 substrates by pulsed laser ablation. The 300nm thick films exhibit both ferroelectricity and magnetism at room temperature with a maximum dielectric polarization of 2.8μC /cm2 at Emax=82kV/cm and a saturated magnetization of 20emu/cm3 (corresponding to ˜0.26μB per rhombohedral unit cell), with coercive fields below 100Oe. The results confirm the predictions made using ab initio calculations about the existence of multiferroic properties in Bi2FeCrO6.

Magnetostriction and complex permeability of [Fe62Co19Ga19/Py]5/glass multilayered films

NASA Astrophysics Data System (ADS)

Liu, Chi-Ching; Jen, Shien-Uang; Lin, Yu-Cha; Lai, Chih-Huang; Liao, Sheng-Chieh; Chien, Chia-Hua

2015-07-01

[Fe62Co19Ga19(x)/Py(40-x)]5/glass multilayered films, where x=0, 5, 10, 15, 20 nm, y=x(nm)/40(nm), and 0≤y≤1, were made by the magnetron sputtering method at room temperature. The total number of combined [Fe-Co-Ga/Py] unit-layers was five. The total film thickness (tf) was fixed at 200 nm. We have performed two kinds of experiments on these films: (i) the saturation magnetostriction (λS) measurement, and (ii) the complex permeability (μ=μR-jμI) experiment to find the resonance frequency (fR) as a function of external magnetic field (HE). By definition, the microwave power absorption Pabs at ferromagnetic resonance (FMR) for a metallic conductor is written as Pabs = [(μR2+ μI2)1/2 +μI ]1/2 . We define the half-width of the absorption peak Δf as Δf ≣ ΔfS+ΔfA, where ΔfS and ΔfA are the symmetric and asymmetric parts in Δf. The degree of asymmetry, ΔfA/Δf, of each absorption peak is associated with the structural and/or magnetic inhomogeneity in the film. The main findings from this study are summarized as follows: (A) maximum λS occurs in the y=1 film, and as y increases, λS increases; (B) biasing field for magnetostriction decreases greatly by adding Py layers; (C) the magnetostriction sensitivity remains almost constant in the range 0.4

Surface passivation of Fe{sub 3}O{sub 4} nanoparticles with Al{sub 2}O{sub 3} via atomic layer deposition in a rotating fluidized bed reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duan, Chen-Long; Deng, Zhang; Cao, Kun

2016-07-15

Iron(II,III) oxide (Fe{sub 3}O{sub 4}) nanoparticles have shown great promise in many magnetic-related applications such as magnetic resonance imaging, hyperthermia treatment, and targeted drug delivery. Nevertheless, these nanoparticles are vulnerable to oxidation and magnetization loss under ambient conditions, and passivation is usually required for practical applications. In this work, a home-built rotating fluidized bed (RFB) atomic layer deposition (ALD) reactor was employed to form dense and uniform nanoscale Al{sub 2}O{sub 3} passivation layers on Fe{sub 3}O{sub 4} nanoparticles. The RFB reactor facilitated the precursor diffusion in the particle bed and intensified the dynamic dismantling of soft agglomerates, exposing every surfacemore » reactive site to precursor gases. With the aid of in situ mass spectroscopy, it was found that a thicker fluidization bed formed by larger amount of particles increased the residence time of precursors. The prolonged residence time allowed more thorough interactions between the particle surfaces and the precursor gas, resulting in an improvement of the precursor utilization from 78% to nearly 100%, even under a high precursor feeding rate. Uniform passivation layers around the magnetic cores were demonstrated by both transmission electron microscopy and the statistical analysis of Al mass concentrations. Individual particles were coated instead of the soft agglomerates, as was validated by the specific surface area analysis and particle size distribution. The results of thermogravimetric analysis suggested that 5 nm-thick ultrathin Al{sub 2}O{sub 3} coatings could effectively protect the Fe{sub 3}O{sub 4} nanoparticles from oxidation. The x-ray diffraction patterns also showed that the magnetic core crystallinity of such passivated nanoparticles could be well preserved under accelerated oxidation conditions. The precise thickness control via ALD maintained the saturation magnetization at 66.7 emu/g with a 5 nm-thick Al{sub 2}O{sub 3} passivation layer. This good preservation of the magnetic properties with superior oxidation resistance will be beneficial for practical magnetic-based applications.« less

Does the conductivity of interconnect coatings matter for solid oxide fuel cell applications?

NASA Astrophysics Data System (ADS)

Goebel, Claudia; Fefekos, Alexander G.; Svensson, Jan-Erik; Froitzheim, Jan

2018-04-01

The present work aims to quantify the influence of typical interconnect coatings used for solid oxide fuel cells (SOFC) on area specific resistance (ASR). To quantify the effect of the coating, the dependency of coating thickness on the ASR is examined on Crofer 22 APU at 600 °C. Three different Co coating thicknesses are investigated, 600 nm, 1500 nm, and 3000 nm. Except for the reference samples, the material is pre-oxidized prior to coating to mitigate the outward diffusion of iron and consequent formation of poorly conducting (Co,Fe)3O4 spinel. Exposures are carried out at 600 °C in stagnant laboratory air for 500 h and subsequent ASR measurements are performed. Additionally the microstructure is investigated with scanning electron microscopy (SEM). On all pre-oxidized samples, a homogenous dense Co3O4 top layer is observed beneath which a thin layer of Cr2O3 is present. As the ASR values range between 7 and 12 mΩcm2 for all pre-oxidized samples, even though different Co3O4 thicknesses are observed, the results strongly suggest that for most applicable cases the impact of the coating on ASR is negligible and the main contributor is Cr2O3.

Investigation of magnetic properties of Fe{sub 3}O{sub 4} nanoparticles using temperature dependent magnetic hyperthermia in ferrofluids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nemala, H.; Thakur, J. S.; Lawes, G.

2014-07-21

Rate of heat generated by magnetic nanoparticles in a ferrofluid is affected by their magnetic properties, temperature, and viscosity of the carrier liquid. We have investigated temperature dependent magnetic hyperthermia in ferrofluids, consisting of dextran coated superparamagnetic Fe{sub 3}O{sub 4} nanoparticles, subjected to external magnetic fields of various frequencies (188–375 kHz) and amplitudes (140–235 Oe). Transmission electron microscopy measurements show that the nanoparticles are polydispersed with a mean diameter of 13.8 ± 3.1 nm. The fitting of experimental dc magnetization data to a standard Langevin function incorporating particle size distribution yields a mean diameter of 10.6 ± 1.2 nm, and a reduced saturation magnetization (∼65 emu/g) comparedmore » to the bulk value of Fe{sub 3}O{sub 4} (∼95 emu/g). This is due to the presence of a finite surface layer (∼1 nm thickness) of non-aligned spins surrounding the ferromagnetically aligned Fe{sub 3}O{sub 4} core. We found the specific absorption rate, measured as power absorbed per gram of iron oxide nanoparticles, decreases monotonically with increasing temperature for all values of magnetic field and frequency. Using the size distribution of magnetic nanoparticles estimated from the magnetization measurements, we have fitted the specific absorption rate versus temperature data using a linear response theory and relaxation dissipation mechanisms to determine the value of magnetic anisotropy constant (28 ± 2 kJ/m{sup 3}) of Fe{sub 3}O{sub 4} nanoparticles.« less

Fast electrosynthesis of Fe-containing layered double hydroxide arrays toward highly efficient electrocatalytic oxidation reactions† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5sc02417j

PubMed Central

Li, Zhenhua; An, Hongli; Wang, Zixuan; Xu, Simin; Evans, David G.; Duan, Xue

2015-01-01

A new electrochemical synthesis route was developed for the fabrication of Fe-containing layered double hydroxide (MFe-LDHs, M = Ni, Co and Li) hierarchical nanoarrays, which exhibit highly-efficient electrocatalytic performances for the oxidation reactions of several small molecules (water, hydrazine, methanol and ethanol). Ultrathin MFe-LDH nanoplatelets (200–300 nm in lateral length; 8–12 nm in thickness) perpendicular to the substrate surface are directly prepared within hundreds of seconds (<300 s) under cathodic potential. The as-obtained NiFe-LDH nanoplatelet arrays display promising behavior in the oxygen evolution reaction (OER), giving rise to a rather low overpotential (0.224 V) at 10.0 mA cm–2 with largely enhanced stability, much superior to previously reported electro-oxidation catalysts as well as the state-of-the-art Ir/C catalyst. Furthermore, the MFe-LDH nanoplatelet arrays can also efficiently catalyze several other fuel molecules’ oxidation (e.g., hydrazine, methanol and ethanol), delivering a satisfactory electrocatalytic activity and a high operation stability. In particular, this preparation method of Fe-containing LDHs is amenable to fast, effective and large-scale production, and shows promising applications in water splitting, fuel cells and other clean energy devices. PMID:29435211

Synthesis of green Fe3+/glucose/rGO electrode for supercapacitor application assisted by chemical exfoliation process from burning coconut shell

NASA Astrophysics Data System (ADS)

Putra, Gilang B. A.; Pradana, Herdy Y.; Soenaryo, Dimas E. T.; Baqiya, Malik A.; Darminto

2018-04-01

For the goal of large, environmental - friendly, renewable, and inexpensive energy storage, the development of supercapacitor electrodes is needed, by anchoring transition metal oxide (Fe3+ ion) as pseudo capacitor electrode material with reduced graphene oxide (rGO) from an old coconut shell as electrochemical double layer capacitor (EDLC). This porous electrode composite is prepared by sonication and chemical exfoliation assisted by acid. Synthesis of supercapacitor is also added by glucose, which acts as a spacer between layers of rGO to increase the capacitance, also as binder between the materials used. Combining Fe3+ with old coconut shell rGO give high specific capacitance of up to 99 F/g at a potential window of -1 V to 1 V. The Fe3+/glucose/rGO electrode has thickness of up to 57 nm (from PSA result) and give a uniform distribution from EDX mapping with disperse Fe domains and not bonding with rGO.

Investigation of porosity and heterojunction effects of a mesoporous hematite electrode on photoelectrochemical water splitting.

PubMed

Liu, Jingling; Shahid, Muhammad; Ko, Young-Seon; Kim, Eunchul; Ahn, Tae Kyu; Park, Jong Hyeok; Kwon, Young-Uk

2013-06-28

In this paper, we report the porosity and heterojunction effects of hematite (α-Fe2O3) on the photoelectrochemical (PEC) water splitting properties. The worm-like mesoporous hematite thin films (MHFs) with a pore size of ~9 nm and a wall thickness of ~5 nm were successfully obtained through the self-assembly process. MHFs formed on FTO showed much better PEC properties than those of nonporous hematite thin films (NP-HF) owing to the suppression of charge recombination. The PEC data of MHFs under front and back illumination conditions indicated that the porous structure allows the diffusion of electrolyte deep inside the MHF increasing the number of holes to be utilized in the water oxidation reaction. A heterojunction structure was formed by introducing a thin layer of SnO2 (~15 nm in thickness) between the MHF and FTO for a dramatically enhanced PEC response, which is attributed to the efficient electron transfer. Our spectroscopic and electrochemical data show that the SnO2 layer functions as an efficient electron transmitter, but does not affect the recombination kinetics of MHFs.

Novel self-organization mechanism in ultrathin liquid films: theory and experiment.

PubMed

Trice, Justin; Favazza, Christopher; Thomas, Dennis; Garcia, Hernando; Kalyanaraman, Ramki; Sureshkumar, Radhakrishna

2008-07-04

When an ultrathin metal film of thickness h (<20 nm) is melted by a nanosecond pulsed laser, the film temperature is a nonmonotonic function of h and achieves its maximum at a certain thickness h*. This is a consequence of the h and time dependence of energy absorption and heat flow. Linear stability analysis and nonlinear dynamical simulations that incorporate such intrinsic interfacial thermal gradients predict a characteristic pattern length scale Lambda that decreases for h>h*, in contrast to the classical spinodal dewetting behavior where Lambda increases monotonically as h2. These predictions agree well with experimental observations for Co and Fe films on SiO2.

Effect of catalyst film thickness on carbon nanotube growth by selective area chemical vapor deposition

NASA Astrophysics Data System (ADS)

Wei, Y. Y.; Eres, Gyula; Merkulov, V. I.; Lowndes, D. H.

2001-03-01

The correlation between prepatterned catalyst film thickness and carbon nanotube (CNT) growth by selective area chemical vapor deposition (CVD) was studied using Fe and Ni as catalyst. To eliminate sample-to-sample variations and create a growth environment in which the film thickness is the sole variable, samples with continuously changing catalyst film thickness from 0 to 60 nm were fabricated by electron-gun evaporation. Using thermal CVD CNTs preferentially grow as a dense mat on the thin regions of the catalyst film. Moreover, beyond a certain critical film thickness no tubes were observed. The critical film thickness for CNT growth was found to increase with substrate temperature. There appears to be no strong correlation between the film thickness and the diameter of the tubes. In contrast, using plasma enhanced CVD with Ni as catalyst, vertically oriented CNTs grow in the entire range of catalyst film thickness. The diameter of these CNTs shows a strong correlation with the catalyst film thickness. The significance of these experimental trends is discussed within the framework of the diffusion model for CNT growth.

Ferroelectric FET for nonvolatile memory application with two-dimensional MoSe2 channels

NASA Astrophysics Data System (ADS)

Wang, Xudong; Liu, Chunsen; Chen, Yan; Wu, Guangjian; Yan, Xiao; Huang, Hai; Wang, Peng; Tian, Bobo; Hong, Zhenchen; Wang, Yutao; Sun, Shuo; Shen, Hong; Lin, Tie; Hu, Weida; Tang, Minghua; Zhou, Peng; Wang, Jianlu; Sun, Jinglan; Meng, Xiangjian; Chu, Junhao; Li, Zheng

2017-06-01

Graphene and other two-dimensional materials have received considerable attention regarding their potential applications in nano-electronics. Here, we report top-gate nonvolatile memory field-effect transistors (FETs) with different layers of MoSe2 nanosheets channel gated by ferroelectric film. The conventional gate dielectric of FETs was replaced by a ferroelectric thin film that provides a ferroelectric polarization electric field, and therefore defined as an Fe-FET where the poly (vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) was used as the gate dielectric. Among the devices with MoSe2 channels of different thicknesses, the device with a single layer of MoSe2 exhibited a large hysteresis of electronic transport with an over 105 write/erase ratio, and displayed excellent retention and endurance performance. The possible mechanism of the device’s good properties was qualitatively analyzed using band theory. Additionally, a comprehensive study comparing the memory properties of MoSe2 channels of different thicknesses is presented. Increasing the numbers of MoSe2 layers was found to cause a reduced memory window. However, MoSe2 thickness of 5 nm yielded a write/erase ratio of more than 103. The results indicate that, based on a Fe-FET structure, the combination of two-dimensional semiconductors and organic ferroelectric gate dielectrics shows good promise for future applications in nonvolatile ferroelectric memory.

Correlative cellular ptychography with functionalized nanoparticles at the Fe L-edge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gallagher-Jones, Marcus; Dias, Carlos Sato Baraldi; Pryor, Alan

Precise localization of nanoparticles within a cell is crucial to the understanding of cell-particle interactions and has broad applications in nanomedicine. Here in this paper, we report a proof-of-principle experiment for imaging individual functionalized nanoparticles within a mammalian cell by correlative microscopy. Using a chemically-fixed HeLa cell labeled with fluorescent core-shell nanoparticles as a model system, we implemented a graphene-oxide layer as a substrate to significantly reduce background scattering. We identified cellular features of interest by fluorescence microscopy, followed by scanning transmission X-ray tomography to localize the particles in 3D, and ptychographic coherent diffractive imaging of the fine features inmore » the region at high resolution. By tuning the X-ray energy to the Fe L-edge, we demonstrated sensitive detection of nanoparticles composed of a 22 nm magnetic Fe 3O 4 core encased by a 25-nm-thick fluorescent silica (SiO 2) shell. These fluorescent core-shell nanoparticles act as landmarks and offer clarity in a cellular context. Our correlative microscopy results confirmed a subset of particles to be fully internalized, and high-contrast ptychographic images showed two oxidation states of individual nanoparticles with a resolution of ~16.5 nm. The ability to precisely localize individual fluorescent nanoparticles within mammalian cells will expand our understanding of the structure/function relationships for functionalized nanoparticles.« less

Preparation and Application of Hollow Silica/magnetic Nanocomposite Particle

NASA Astrophysics Data System (ADS)

Wang, Cheng-Chien; Lin, Jing-Mo; Lin, Chun-Rong; Wang, Sheng-Chang

The hollow silica/cobalt ferrite (CoFe2O4) magnetic microsphere with amino-groups were successfully prepared via several steps, including preparing the chelating copolymer microparticles as template by soap-free emulsion polymerization, manufacturing the hollow cobalt ferrite magnetic microsphere by in-situ chemical co-precipitation following calcinations, and surface modifying of the hollow magnetic microsphere by 3-aminopropyltrime- thoxysilane via the sol-gel method. The average diameter of polymer microspheres was ca. 200 nm from transmission electron microscope (TEM) measurement. The structure of the hollow magnetic microsphere was characterized by using TEM and scanning electron microscope (SEM). The spinel-type lattice of CoFe2O4 shell layer was identified by using XRD measurement. The diameter of CoFe2O4 crystalline grains ranged from 54.1 nm to 8.5 nm which was estimated by Scherrer's equation. Additionally, the hollow silica/cobalt ferrite microsphere possesses superparamagnetic property after VSM measurement. The result of BET measurement reveals the hollow magnetic microsphere which has large surface areas (123.4m2/g). After glutaraldehyde modified, the maximum value of BSA immobilization capacity of the hollow magnetic microsphere was 33.8 mg/g at pH 5.0 buffer solution. For microwave absorption, when the hollow magnetic microsphere was compounded within epoxy resin, the maximum reflection loss of epoxy resins could reach -35dB at 5.4 GHz with 1.9 mm thickness.

Correlative cellular ptychography with functionalized nanoparticles at the Fe L-edge

DOE PAGES

Gallagher-Jones, Marcus; Dias, Carlos Sato Baraldi; Pryor, Alan; ...

2017-07-06

Precise localization of nanoparticles within a cell is crucial to the understanding of cell-particle interactions and has broad applications in nanomedicine. Here in this paper, we report a proof-of-principle experiment for imaging individual functionalized nanoparticles within a mammalian cell by correlative microscopy. Using a chemically-fixed HeLa cell labeled with fluorescent core-shell nanoparticles as a model system, we implemented a graphene-oxide layer as a substrate to significantly reduce background scattering. We identified cellular features of interest by fluorescence microscopy, followed by scanning transmission X-ray tomography to localize the particles in 3D, and ptychographic coherent diffractive imaging of the fine features inmore » the region at high resolution. By tuning the X-ray energy to the Fe L-edge, we demonstrated sensitive detection of nanoparticles composed of a 22 nm magnetic Fe 3O 4 core encased by a 25-nm-thick fluorescent silica (SiO 2) shell. These fluorescent core-shell nanoparticles act as landmarks and offer clarity in a cellular context. Our correlative microscopy results confirmed a subset of particles to be fully internalized, and high-contrast ptychographic images showed two oxidation states of individual nanoparticles with a resolution of ~16.5 nm. The ability to precisely localize individual fluorescent nanoparticles within mammalian cells will expand our understanding of the structure/function relationships for functionalized nanoparticles.« less

Transmission Electron Microscopy of Itokawa Regolith Grains

NASA Technical Reports Server (NTRS)

Keller, Lindsay P.; Berger, E. L.

2013-01-01

Introduction: In a remarkable engineering achievement, the JAXA space agency successfully recovered the Hayabusa space-craft in June 2010, following a non-optimal encounter and sur-face sampling mission to asteroid 25143 Itokawa. These are the first direct samples ever obtained and returned from the surface of an asteroid. The Hayabusa samples thus present a special op-portunity to directly investigate the evolution of asteroidal sur-faces, from the development of the regolith to the study of the effects of space weathering. Here we report on our preliminary TEM measurements on two Itokawa samples. Methods: We were allocated particles RA-QD02-0125 and RA-QD02-0211. Both particles were embedded in low viscosity epoxy and thin sections were prepared using ultramicrotomy. High resolution images and electron diffraction data were ob-tained using a JEOL 2500SE 200 kV field-emission scanning-transmission electron microscope. Quantitative maps and anal-yses were obtained using a Thermo thin-window energy-dispersive x-ray (EDX) spectrometer. Results: Both particles are olivine-rich (Fo70) with µm-sized inclusions of FeS and have microstructurally complex rims. Par-ticle RA-QD02-0125 is rounded and has numerous sub-µm grains attached to its surface including FeS, albite, olivine, and rare melt droplets. Solar flare tracks have not been observed, but the particle is surrounded by a continuous 50 nm thick, stuctur-ally disordered rim that is compositionally similar to the core of the grain. One of the surface adhering grains is pyrrhotite show-ing a S-depleted rim (8-10 nm thick) with nanophase Fe metal grains (<5 nm) decorating the outermost surface. The pyrrhotite displays a complex superstructure in its core that is absent in the S-depleted rim. Particle RA-QD02-0211 contains solar flare particle tracks (2x109 cm-2) and shows a structurally disordered rim 100 nm thick. The track density corresponds to a surface exposure of 103-104 years based on the track production rate of [1]. The dis-ordered rim is nanocrystalline with minor amorphous material between crystalline domains. Quantitative element maps show the outermost 10 nm of the disordered rim is Si-rich. Discussion and Conclusions: Both particles record the ef-fects of space weathering processes on Itokawa. Noguchi et al. [2] proposed that the disordered rims they observed on Itokawa particles largely result from solar wind radiation damage and we arrive at a similar conclusion for the two particles we analyzed. The microstructure of the S-depleted layer on the pyrrhotite grain in RA-QD02-0125 is similar to that observed in troilite irradiated with 1018 4 kV He+ [3, 4]. Prolonged irradiation has also been shown to disorder pyrrhotite such that the superstructure reflec-tions are lost [5].

Plasmonic detection of possible defects in multilayer nanohole array consisting of essential materials in simplified STT-RAM cell

NASA Astrophysics Data System (ADS)

Sadri-Moshkenani, Parinaz; Khan, Mohammad Wahiduzzaman; Zhao, Qiancheng; Krivorotov, Ilya; Nilsson, Mikael; Bagherzadeh, Nader; Boyraz, Ozdal

2017-08-01

Plasmonic nanostructures are highly used for sensing purposes since they support plasmonic modes which make them highly sensitive to the refractive index change of their surrounding medium. Therefore, they can also be used to detect changes in optical properties of ultrathin layer films in a multilayer plasmonic structure. Here, we investigate the changes in optical properties of ultrathin films of macro structures consisting of STT-RAM layers. Among the highest sensitive plasmonic structures, nanohole array has attracted many research interest because of its ease of fabrication, small footprint, and simplified optical alignment. Hence it is more suitable for defect detection in STT-RAM geometries. Moreover, the periodic nanohole pattern in the nanohole array structure makes it possible to couple the light to the surface plasmon polariton (SPP) mode supported by the structure. To assess the radiation damages and defects in STT-RAM cells we have designed a multilayer nanohole array based on the layers used in STT-RAM structure, consisting 4nm- Ta/1.5nm-CoFeB/2nm-MgO/1.5nm-CoFeB/4nm-Ta layers, all on a 300nm silver layer on top of a PEC boundary. The nanoholes go through all the layers and become closed by the PEC boundary on one side. The dimensions of the designed nanoholes are 313nm depth, 350nm diameter, and 700nm period. Here, we consider the normal incidence of light and investigate zeroth-order reflection coefficient to observe the resonance. Our simulation results show that a 10% change in refractive index of the 2nm-thick MgO layer leads to about 122GHz shift in SPP resonance in reflection pattern.

Core and shell size dependences on strain in core@shell Prussian blue analogue (PBA) nanoparticles and the effect on photomagnetism.

NASA Astrophysics Data System (ADS)

Cain, J. M.; Ferreira, C. F.; Felts, A. C.; Locicero, S. A.; Liang, J.; Talham, D. R.; Meisel, M. W.

RbxCo[Fe(CN)6]y@Ka Ni[Cr(CN)6]b core@shell heterostructures have been shown to exhibit a photoinduced decrease in magnetization that persists up to the Tc = 70 K of the KNiCr-PBA component, which is not photoactive as a single-phase material. A magnetomechanical effect can explain how the strain in the shell evolves from thermal and photoinduced changes in the volume of the core. Moreover, a simple model has been used to estimate the depth of the strained region of the shell, but only one size of core (347 +/- 35 nm) has been studied. Since the strain depth in the shell is expected to be dependent on the size of the core, three distinct RbCoFe-PBA core sizes were synthesized, and on each, three different KNiCr-PBA shell thicknesses were grown. The magnetization of each core-shell combination was measured before and after irradiation with white light. Our results suggest the strain depth, as expected, increases from 56 nm in heterostructures with a core size of 328 +/- 29 nm to more than 90 nm in heterostructures with a core size of 575 +/- 113 nm. The data from the smallest core size also shows features indicating the model may be too simple. Supported by NSF DMR-1405439 (DRT) and DMR-1202033 (MWM).

Impedance spectroscopy and microstructural characterization of the corrosion behavior of FeCrAl alloy in lead-bismuth eutectic

NASA Astrophysics Data System (ADS)

Chen, Xiang; Haasch, Rick; Stubbins, James F.

2012-12-01

The corrosion behavior of FeCrAl alloy in Lead-Bismuth Eutectic (LBE) saturated with oxygen at 550 °C was investigated. Impedance Spectroscopy (IS) measurement was made continuously on one specimen during the entire LBE exposure test to characterize the corrosion kinetics. Various microanalysis techniques, including SEM, EDS, XRD, AES, and XPS were used to analyze the corrosion products of post-exposure specimens. It was found that a very thin, adherent alumina oxide layer formed on the specimen surface and was able to protect the alloy from the corrosion attack in LBE. The thickness of the alumina surface layer increased very slowly with time reaching about 837 nm in average thickness after exposure for 3600-h in LBE. The IS measurements match the microanalysis results in three respects: first, a non-zero impedance measurement agrees with the existence of a continuous surface oxide layer; second, a general increase of the impedance was observed during the real-time IS measurement which means that the IS measurements reflect the growth rate of the oxide layer; and third, the oxide film thickness derived from the IS data compares favorably with the SEM film thickness measurements which establishes the validity of using IS to monitor the real-time corrosion kinetics of alloys in LBE.

Stable Fe/ZSM-5 Nanosheet Zeolite Catalysts for the Oxidation of Benzene to Phenol

PubMed Central

2017-01-01

Fe/ZSM-5 nanosheet zeolites of varying thickness were synthesized with di- and tetraquaternary ammonium structure directing agents and extensively characterized for their textural, structural, and catalytic properties. Introduction of Fe3+ ions in the framework of nanosheet zeolites was slightly less effective than in bulk ZSM-5 zeolite. Steaming was necessary to activate all catalysts for N2O decomposition and benzene oxidation. The higher the Fe content, the higher the degree of Fe aggregation was after catalyst activation. The degree of Fe aggregation was lower when the crystal domain size of the zeolite or the Fe content was decreased. These two parameters had a substantial influence on the catalytic performance. Decreasing the number of Fe sites along the b-direction strongly suppressed secondary reactions of phenol and, accordingly, catalyst deactivation. This together with the absence of diffusional limitations in nanosheet zeolites explains the much higher phenol productivity obtainable with nanostructured Fe/ZSM-5. Steamed Fe/ZSM-5 zeolite nanosheet synthesized using C22-6-3·Br2 (domain size in b-direction ∼3 nm) and containing 0.24 wt % Fe exhibited the highest catalytic performance. During the first 24 h on stream, this catalyst produced 185 mmolphenol g–1. Calcination to remove the coke deposits completely restored the initial activity. PMID:28413693

The effect of FeF2 on the magneto-optic response in FeF2/Fe/FeF2 sandwiches

NASA Astrophysics Data System (ADS)

Pištora, J.; Lesňák, M.; Lišková, E.; Višňovský, Š.; Harward, I.; Maslankiewicz, P.; Balin, K.; Celinski, Z.; Mistrík, J.; Yamaguchi, T.; Lopusnik, R.; Vlček, J.

2010-04-01

The room temperature optical constants n and k of MBE grown FeF2 films are reported. Because of poor chemical stability, FeF2 had to be coated with a protective Au layer. Reflection spectral ellipsometry in the photon energy range between 1.3 and 5.2 eV was performed on structures with a typical profile Au(0.5 nm)/FeF2(120 nm)/Au(30 nm)/Ag(20 nm)/Fe(0.6 nm) grown on GaAs(0 0 1) substrate. The spectra of n and k in FeF2 were subsequently employed in the design of FeF2/Fe/FeF2 sandwiches considered as magneto-optic (MO) sensors for weak microwave currents. Their MO response was evaluated using reflection MO (Kerr) spectroscopy at polar magnetization. The present results may be of interest in MO studies of magnetic nanostructures with Fe/FeF2/Fe, including MO magnetometry and MO magnetic domain imaging.

Tailoring the soft magnetic properties of sputtered multilayers by microstructure engineering for high frequency applications

NASA Astrophysics Data System (ADS)

Falub, Claudiu V.; Rohrmann, Hartmut; Bless, Martin; Meduňa, Mojmír; Marioni, Miguel; Schneider, Daniel; Richter, Jan H.; Padrun, Marco

2017-05-01

Soft magnetic Ni78.5Fe21.5, Co91.5Ta4.5Zr4 and Fe52Co28B20 thin films laminated with SiO2, Al2O3, AlN, and Ta2O5 dielectric interlayers were deposited on 8" Si wafers using DC, pulsed DC and RF cathodes in the industrial, high-throughput Evatec LLS-EVO-II magnetron sputtering system. A typical multilayer consists of a bilayer stack up to 50 periods, with alternating (50-100) nm thick magnetic layers and (2-20) nm thick dielectric interlayers. We introduced the in-plane magnetic anisotropy in these films during sputtering by a combination of a linear magnetic field, seed layer texturing by means of linear collimators, and the oblique incidence inherent to the geometry of the sputter system. Depending on the magnetic material, the anisotropy field for these films was tuned in the range of ˜(7-120) Oe by choosing the appropriate interlayer thickness, the aspect ratios of the linear collimators in front of the targets, and the sputter process parameters (e.g. pressure, power, DC pulse frequency), while the coercivity was kept low, ˜(0.05-0.9) Oe. The alignment of the easy axis (EA) on the 8" wafers was typically between ±1.5° and ±4°. We discuss the interdependence of structure and magnetic properties in these films, as revealed by atomic force microscopy (AFM), X-ray reflectivity (XRR) with reciprocal space mapping (RSM) and magneto-optical Kerr effect (MOKE) measurements.

Structural and electronic properties of ultrathin FeSe films grown on Bi2Se3(0 0 0 1) studied by STM/STS

NASA Astrophysics Data System (ADS)

Singh, Udai Raj; Warmuth, Jonas; Markmann, Verena; Wiebe, Jens; Wiesendanger, Roland

2017-01-01

We report scanning tunnelling microscopy and spectroscopy (STM/STS) studies on one and two unit cell (UC) high FeSe thin films grown on Bi2Se3(0 0 0 1). In our thin films, we find the tetragonal phase of FeSe and dumb-bell shaped defects oriented along Se-Se bond directions. In addition, we observe striped moiré patterns with a periodicity of (7.3  ±  0.1) nm generated by the mismatch between the FeSe lattice and the Bi2Se3 lattice. We could not find any signature of a superconducting gap in the tunneling spectra measured on the surface of one and two UC thick islands of FeSe down to 6.5 K. The spectra rather show an asymmetric behavior across and a finite density of states at the Fermi level (E F) resembling those taken in the normal state of bulk FeSe.

FAST TRACK COMMUNICATION: Gyration mode splitting in magnetostatically coupled magnetic vortices in an array

NASA Astrophysics Data System (ADS)

Barman, Anjan; Barman, Saswati; Kimura, T.; Fukuma, Y.; Otani, Y.

2010-10-01

We present the experimental observation of gyration mode splitting by the time-resolved magneto-optical Kerr effect in an array consisting of magnetostatically coupled Ni81Fe19 discs of 1 µm diameter, 50 nm thickness and inter-disc separations varying between 150 and 270 nm. A splitting of the vortex core gyration mode is observed when the inter-disc separation is 200 nm or less and the splitting is controllable by a bias magnetic field. The observed mode splitting is interpreted by micromagnetic simulations as the normal modes of the vortex cores analogous to the coupled classical oscillators. The splitting depends upon the strength of the inter-disc magnetostatic coupling mediated by magnetic side charges, which depends strongly on the magnetic ground states of the samples.

Quantitative analysis of the protein corona on FePt nanoparticles formed by transferrin binding

PubMed Central

Jiang, Xiue; Weise, Stefan; Hafner, Margit; Röcker, Carlheinz; Zhang, Feng; Parak, Wolfgang J.; Nienhaus, G. Ulrich

2010-01-01

Nanoparticles are finding a rapidly expanding range of applications in research and technology, finally entering our daily life in medical, cosmetic or food products. Their ability to invade all regions of an organism including cells and cellular organelles offers new strategies for medical diagnosis and therapy (nanomedicine), but their safe use requires a deep knowledge about their interactions with biological systems at the molecular level. Upon incorporation, nanoparticles are exposed to biological fluids from which they adsorb proteins and other biomolecules to form a ‘protein corona’. These nanoparticle–protein interactions are still poorly understood and quantitative studies to characterize them remain scarce. Here we have quantitatively analysed the adsorption of human transferrin onto small (radius approx. 5 nm) polymer-coated FePt nanoparticles by using fluorescence correlation spectroscopy. Transferrin binds to the negatively charged nanoparticles with an affinity of approximately 26 µM in a cooperative fashion and forms a monolayer with a thickness of 7 nm. By using confocal fluorescence microscopy, we have observed that the uptake of FePt nanoparticles by HeLa cells is suppressed by the protein corona compared with the bare nanoparticles. PMID:19776149

A new method for the preparation of a Fe{sub 3}O{sub 4}/graphene hybrid material and its applications in electromagnetic wave absorption

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Tsung-Yung; Lu, Kai-Tai; Peng, Cheng-Hsiung

2015-10-15

Graphical abstract: A microwave-assisted solvothermal process was used to prepare Fe{sub 3}O{sub 4} nanoparticles/graphene hybrids, which could be applied as an electromagnetic (EM) radiation absorbent. The absorber, composed of 20 wt% Fe{sub 3}O{sub 4}/graphene–epoxy, exhibited a dual-frequency reflection characteristic covering the C and Ku bands with maximum reflection losses of less than −20 dB at thicknesses of 4 and 5 mm. - Highlights: • Fe{sub 3}O{sub 4}/graphene composites were prepared by a microwave-assisted solvothermal route. • Uniform loading of Fe{sub 3}O{sub 4} nanoparticles on graphene was obtained. • The products as-synthesized show great promise as a microwave absorption material. •more » Synergistic effects of Fe{sub 3}O{sub 4} and graphene caused improved absorption efficiency. • The Fe{sub 3}O{sub 4}/graphene product possessed a dual-frequency reflection characteristic. - Abstract: A rapid, simple, and inexpensive process combining a microwave-assisted technique and a solvothermal method has been developed using graphene sheets and FeCl{sub 3}·6H{sub 2}O as the reactant to prepare graphene/Fe{sub 3}O{sub 4} nanoparticle hybrids, which can be applied as an electromagnetic radiation absorbent. The experimental factors (i.e., composition ratio, microwave power, and irradiation time) on the products’ characteristics were examined. Under optimal conditions, the morphological analysis revealed that the graphene sheet was homogeneously covered with Fe{sub 3}O{sub 4} nanoparticles (∼50 nm). The electromagnetic parameters of the composites made from 20 wt% Fe{sub 3}O{sub 4}/graphene–epoxy were measured by a vector network analyzer. It was found that the 4- and 5 mm-thick composites could attain a reflection loss below −20 dB in the dual-ranges of 4–8 and 12–18 GHz.« less

Ferroelectric and electrical characterization of multiferroic BiFeO3 at the single nanoparticle level

NASA Astrophysics Data System (ADS)

Vasudevan, R. K.; Bogle, K. A.; Kumar, A.; Jesse, S.; Magaraggia, R.; Stamps, R.; Ogale, S. B.; Potdar, H. S.; Nagarajan, V.

2011-12-01

Ferroelectric BiFeO3 (BFO) nanoparticles deposited on epitaxial substrates of SrRuO3 (SRO) and La1-xSrxMnO3 (LSMO) were studied using band excitation piezoresponse spectroscopy (BEPS), piezoresponse force microscopy (PFM), and ferromagnetic resonance (FMR). BEPS confirms that the nanoparticles are ferroelectric in nature. Switching behavior of nanoparticle clusters were studied and showed evidence for inhomogeneous switching. The dimensionality of domains within nanoparticles was found to be fractal in nature, with a dimensionality constant of ˜1.4, on par with ferroelectric BFO thin-films under 100 nm in thickness. Ferromagnetic resonance studies indicate BFO nanoparticles only weakly affect the magnetic response of LSMO.

Control of the permeability loss-peak frequency of Ni81Fe19 thin films through laser ablation of triangular and square cluster geometries

NASA Technical Reports Server (NTRS)

Grimes, C. A.; Lumpp, J. K.

2000-01-01

Laser ablation arrays of triangular and square shaped clusters, comprised of 23 micrometers diam circular holes, are defined upon 100 nm thick Ni81Fe19 films used to control the rf permeability spectra. Cluster-to-cluster spacing is varied from 200 to 600 micrometers. For each geometry it is found that the loss peak frequency and permeability magnitude shift lower, in a step-wise fashion, at a cluster-to-cluster spacing between 275 and 300 micrometers. The nonlinear shift in the behavior of the permeability spectra correlates with a dramatic increase in domain wall density. c2000 American Institute of Physics.

Parameter-free determination of the exchange constant in thin films using magnonic patterning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Langer, M.; Wagner, K.; Fassbender, J.

2016-03-07

An all-electrical method is presented to determine the exchange constant of magnetic thin films using ferromagnetic resonance. For films of 20 nm thickness and below, the determination of the exchange constant A, a fundamental magnetic quantity, is anything but straightforward. Among others, the most common methods are based on the characterization of perpendicular standing spin-waves. These approaches are however challenging, due to (i) very high energies and (ii) rather small intensities in this thickness regime. In the presented approach, surface patterning is applied to a permalloy (Ni{sub 80}Fe{sub 20}) film and a Co{sub 2}Fe{sub 0.4}Mn{sub 0.6}Si Heusler compound. Acting as amore » magnonic crystal, such structures enable the coupling of backward volume spin-waves to the uniform mode. Subsequent ferromagnetic resonance measurements give access to the spin-wave spectra free of unquantifiable parameters and, thus, to the exchange constant A with high accuracy.« less

Simultaneous laser excitation of backward volume and perpendicular standing spin waves in full-Heusler Co2FeAl0.5Si0.5 films

PubMed Central

Chen, Zhifeng; Yan, Yong; Li, Shufa; Xu, Xiaoguang; Jiang, Yong; Lai, Tianshu

2017-01-01

Spin-wave dynamics in full-Heusler Co2FeAl0.5Si0.5 films are studied using all-optical pump-probe magneto-optical polar Kerr spectroscopy. Backward volume magnetostatic spin-wave (BVMSW) mode is observed in films with thickness ranging from 20 to 100 nm besides perpendicular standing spin-wave (PSSW) mode, and found to be excited more efficiently than the PSSW mode. The field dependence of the effective Gilbert damping parameter appears especial extrinsic origin. The relationship between the lifetime and the group velocity of BVMSW mode is revealed. The frequency of BVMSW mode does not obviously depend on the film thickness, but the lifetime and the effective damping appear to do so. The simultaneous excitation of BVMSW and PSSW in Heusler alloy films as well as the characterization of their dynamic behaviors may be of interest for magnonic and spintronic applications. PMID:28195160

Aluminium alloyed iron-silicide/silicon solar cells: A simple approach for low cost environmental-friendly photovoltaic technology

PubMed Central

Kumar Dalapati, Goutam; Masudy-Panah, Saeid; Kumar, Avishek; Cheh Tan, Cheng; Ru Tan, Hui; Chi, Dongzhi

2015-01-01

This work demonstrates the fabrication of silicide/silicon based solar cell towards the development of low cost and environmental friendly photovoltaic technology. A heterostructure solar cells using metallic alpha phase (α-phase) aluminum alloyed iron silicide (FeSi(Al)) on n-type silicon is fabricated with an efficiency of 0.8%. The fabricated device has an open circuit voltage and fill-factor of 240 mV and 60%, respectively. Performance of the device was improved by about 7 fold to 5.1% through the interface engineering. The α-phase FeSi(Al)/silicon solar cell devices have promising photovoltaic characteristic with an open circuit voltage, short-circuit current and a fill factor (FF) of 425 mV, 18.5 mA/cm2, and 64%, respectively. The significant improvement of α-phase FeSi(Al)/n-Si solar cells is due to the formation p+−n homojunction through the formation of re-grown crystalline silicon layer (~5–10 nm) at the silicide/silicon interface. Thickness of the regrown silicon layer is crucial for the silicide/silicon based photovoltaic devices. Performance of the α-FeSi(Al)/n-Si solar cells significantly depends on the thickness of α-FeSi(Al) layer and process temperature during the device fabrication. This study will open up new opportunities for the Si based photovoltaic technology using a simple, sustainable, and los cost method. PMID:26632759

Perpendicular magnetic anisotropy in CoXPd100-X alloys for magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

Clark, B. D.; Natarajarathinam, A.; Tadisina, Z. R.; Chen, P. J.; Shull, R. D.; Gupta, S.

2017-08-01

CoFeB/MgO-based perpendicular magnetic tunnel junctions (p-MTJ's) with high anisotropy and low damping are critical for spin-torque transfer random access memory (STT-RAM). Most schemes of making the pinned CoFeB fully perpendicular require ferrimagnets with high damping constants, a high temperature-grown L10 alloy, or an overly complex multilayered synthetic antiferromagnet (SyAF). We report a compositional study of perpendicular CoxPd alloy-pinned Co20Fe60B20/MgO based MTJ stacks, grown at moderate temperatures in a planetary deposition system. The perpendicular anisotropy of the CoxPd alloy films can be tuned based on the layer thickness and composition. The films were characterized by alternating gradient magnetometry (AGM), energy-dispersive X-rays (EDX), and X-ray diffraction (XRD). Current-in-plane tunneling (CIPT) measurements have also been performed on the compositionally varied CoxPd MTJ stacks. The CoxPd alloy becomes fully perpendicular at approximately x = 30% (atomic fraction) Co. Full-film MTJ stacks of Si/SiO2/MgO (13)/CoXPd100-x (50)/Ta (0.3)/CoFeB (1)/MgO (1.6)/CoFeB (1)/Ta (5)/Ru (10), with the numbers enclosed in parentheses being the layer thicknesses in nm, were sputtered onto thermally oxidized silicon substrates and in-situ lamp annealed at 400 °C for 5 min. CIPT measurements indicate that the highest TMR is observed for the CoPd composition with the highest perpendicular magnetic anisotropy.

High-rate and ultralong cycle-life LiFePO4 nanocrystals coated by boron-doped carbon as positive electrode for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Feng, Jinpeng; Wang, Youlan

2016-12-01

An evolutionary modification approach, boron-doped carbon coating, has been used to improve the electrochemical performances of positive electrodes for lithium-ion batteries, and demonstrates apparent and significant modification effects. In this study, the boron-doped carbon coating is firstly adopted and used to decorate the performance of LiFePO4. The obtained composite exhibits a unique core-shell structure with an average diameter of 140 nm and a 4 nm thick boron-doped carbon shell that uniformly encapsulates the core. Owing to the boron element which could induce high amount of defects in the carbon, the electronic conductivity of LiFePO4 is greatly ameliorated. Thus, the boron-doped composite shows superior rate capability and cycle stability than the undoped sample. For instance, the reversible specific capacity of LiFePO4@B0.4-C can reach 164.1 mAh g-1 at 0.1C, which is approximately 96.5% of the theoretical capacity (170 mAh g-1). Even at high rate of 10C, it still shows a high specific capacity of 126.8 mAh g-1 and can be maintained at 124.5 mAh g-1 after 100 cycles with capacity retention ratio of about 98.2%. This outstanding Li-storage property enable the present design strategy to open up the possibility of fabricating the LiFePO4@B-C composite for high-performance lithium-ion batteries.

A study of the properties and microstructure of Ni 81Fe 19 ultrathin films with MgO

NASA Astrophysics Data System (ADS)

Li, Minghua; Han, Gan; Ding, Lei; Wang, Xiaocui; Liu, Yang; Feng, Chun; Wang, Haicheng; Yu, Guanghua

2012-01-01

The anisotropic magnetoresistance (AMR) of a Ta (5 nm)/MgO (3 nm)/Ni81Fe19 (10 nm)/MgO (2 nm)/Ta (3 nm) film with MgO-Nano Oxide Layer (NOL) increases dramatically from 1.05% to 3.24% compared with a Ta (5 nm)/Ni81Fe19 (10 nm)/Ta (3 nm) film without the MgO-NOL layer after annealing at 380 °C for 2 h. Although the MgO destroys the NiFe (1 1 1) texture, it enhances the specular electron scattering of the conduction electrons at the NOL interface and suppresses the interface reactions and diffusion at the Ta/NiFe and NiFe/Ta interfaces. The NiFe (1 1 1) texture was formed after the annealing, resulting in a higher AMR ratio. X-ray photoelectron spectroscope results show that Mg and Mg2+ were present in the MgOx films.

Magnetic and Mössbauer spectroscopy studies of hollow microcapsules made of silica-coated CoFe2O4 nanoparticles

NASA Astrophysics Data System (ADS)

Lyubutin, I. S.; Gervits, N. E.; Starchikov, S. S.; Lin, Chun-Rong; Tseng, Yaw-Teng; Shih, Kun-Yauh; Wang, Cheng-Chien; Chen, I.-Han; Ogarkova, Yu L.; Korotkov, N. Yu

2016-01-01

The hollow microcapsules made of silica-coated CoFe2O4 nanoparticles were synthesized using chemical co-precipitation, followed by the sol-gel method. Poly(MMA-co-MAA) microspheres were used as a core template which can be completely removed after annealing at 450 °C. The microcapsules are monodisperse with the outer diameter of about 450 nm and the thickness of the shell is about 50 nm. The nanoparticles of Co-ferrite are single crystalline. The size of the nanoparticles and magnetic properties of CoFe2O4/SiO2 hollow spheres can be tuned with high accuracy at the annealing stage. The Mössbauer data indicate that CoFe2O4 ferrite is an inverse spinel, in which Fe3+ and Co2+ ions are distributed in both octahedral and tetrahedral sites with the inversion degree close to the bulk ferrite value. At low temperature the CoFe2O4/SiO2 nanoparticles are in antiferromagnetic (AFM) state due to the canted or triangular magnetic structure. Under heating in the applied field, AFM structure transforms to the ferrimagnetic (FM) structure, that increases the magnetization. The Mössbauer data revealed that the small size CoFe2O4/SiO2 particles do not show superparamagnetic behavior, but they transit to the paramagnetic state by the jump-like first order magnetic transition (JMT). This effect is a specific property of the magnetic nanoparticles isolated by inert material. The suggested method of synthesis can be modified with various bio-ligands on the silane surface, and such materials can find many applications in diagnostics and bio-separation.

Magnetoelectricity in CoFe2O4 nanocrystal-P(VDF-HFP) thin films

PubMed Central

2013-01-01

Transition metal ferrites such as CoFe2O4, possessing a large magnetostriction coefficient and high Curie temperature (Tc > 600 K), are excellent candidates for creating magnetic order at the nanoscale and provide a pathway to the fabrication of uniform particle-matrix films with optimized potential for magnetoelectric coupling. Here, a series of 0–3 type nanocomposite thin films composed of ferrimagnetic cobalt ferrite nanocrystals (8 to 18 nm) and a ferroelectric/piezoelectric polymer poly(vinylidene fluoride-co-hexafluoropropene), P(VDF-HFP), were prepared by multiple spin coating and cast coating over a thickness range of 200 nm to 1.6 μm. We describe the synthesis and structural characterization of the nanocrystals and composite films by XRD, TEM, HRTEM, STEM, and SEM, as well as dielectric and magnetic properties, in order to identify evidence of cooperative interactions between the two phases. The CoFe2O4 polymer nanocomposite thin films exhibit composition-dependent effective permittivity, loss tangent, and specific saturation magnetization (Ms). An enhancement of the effective permittivity and saturation magnetization of the CoFe2O4-P(VDF-HFP) films was observed and directly compared with CoFe2O4-polyvinylpyrrolidone, a non-ferroelectric polymer-based nanocomposite prepared by the same method. The comparison provided evidence for the observation of a magnetoelectric effect in the case of CoFe2O4-P(VDF-HFP), attributed to a magnetostrictive/piezoelectric interaction. An enhancement of Ms up to +20.7% was observed at room temperature in the case of the 10 wt.% CoFe2O4-P(VDF-HFP) sample. PMID:24004499

UV absorption investigation of ferromagnetically filled ultra-thick carbon onions, carriers of the 217.5 nm Interstellar Absorption Feature

NASA Astrophysics Data System (ADS)

Boi, Filippo S.; Zhang, Xiaotian; Ivaturi, Sameera; Liu, Qianyang; Wen, Jiqiu; Wang, Shanling

2017-12-01

Carbon nano-onions (CNOs) are fullerene-like structures which consist of quasi-spherical closed carbon shells. These structures have become a subject of great interest thanks to their characteristic absorption feature of interstellar origin (at 217.5 nm, 4.6 μm-1). An additional extinction peak at 3.8 μm-1 has also been reported and attributed to absorption by graphitic residues between the as-grown CNOs. Here, we report the ultraviolet absorption properties of ultra-thick CNOs filled with FePt3 crystals, which also exhibit two main absorption peaks—features located at 4.58 μm-1 and 3.44 μm-1. The presence of this additional feature is surprising and is attributed to nonmagnetic graphite flakes produced as a by-product in the pyrolysis experiment (as confirmed by magnetic separation methods). Instead, the feature at 4.58 μm-1 is associated with the π-plasmonic resonance of the CNOs structures. The FePt3 filled CNOs were fabricated in situ by an advanced one-step fast process consisting in the direct sublimation and pyrolysis of two molecular precursors, namely, ferrocene and dichloro-cyclooctadiene-platinum in a chemical vapour deposition system. The morphological, structural, and magnetic properties of the as-grown filled CNOs were characterized by a means of scanning and transmission electron microscopy, X-ray diffraction, and magnetometry.

Temperature dependence of exchange anisotropy for (0 0 1) oriented Mn 89Pt 11/ferromagnetic bilayers

NASA Astrophysics Data System (ADS)

Yamato, T.; Kume, T.; Kato, T.; Tsunashima, S.; Iwata, S.

Temperature dependence of the exchange anisotropy was investigated for (0 0 1)-oriented top-type Mn 89Pt 11 ( tAF nm)/Ni 80Fe 20 (5 nm) and bottom-type Ni 80Fe 20 (3 nm)/Mn 89Pt 11 (30 nm) and Co 90Fe 10 (3 nm)/Mn 89Pt 11 (30 nm) bilayers. The top-type MnPt/NiFe bilayers exhibited both 1 and 4-fold anisotropies in their in-plane torque curves at 80 K. For tAF=3 nm, rapid decrease of 1-fold component and gradual decrease of 4-fold component were observed with increasing temperature. While for tAF=30 nm, the 1 and 4-fold anisotropies decreased similarly with temperature. In the bottom-type bilayers, by using CoFe ferromagnetic layer, the 4-fold anisotropy was found to become twice as that of the NiFe/MnPt bilayer.

MnFe{sub 2}O{sub 4} as a gas sensor towards SO{sub 2} and NO{sub 2} gases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rathore, Deepshikha, E-mail: deep.nano@gmail.com; Mitra, Supratim

2016-05-06

The chemical co-precipitation method was used to synthesize MnFe{sub 2}O{sub 4} nanoparticles. Single cubic phase formation of nanoparticles was confirmed by X-ray diffraction technique. The average particle size of MnFe{sub 2}O{sub 4} nanoparticles was found to be 10.7 nm using Scherrer formula. The ultrafine powder of MnFe{sub 2}O{sub 4} nanoparticles was pressed to design pellet of 10 mm diameter and 1mm thickness. Copper electrodes have been deposited on the surface of pellet using silver paste in the form of capacitor. Fabricated gas sensing device of MnFe{sub 2}O{sub 4} nanoparticles was tested towards SO{sub 2} and NO{sub 2} gases. Cole-Cole plot of MnFe{submore » 2}O{sub 4} was investigated with the help of electrochemical workstation. The performance of the sensors including sensitivity, response and recovery time was also determined. It was observed that the MnFe{sub 2}O{sub 4} nanoparticles are more sensible for NO{sub 2} gas as compared to SO{sub 2} gas.« less

X-ray magneto-optic KERR effect studies of spring magnet heterostructures.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kortright, J. B.; Kim, S.-K.; Fullerton, E. E.

2000-11-01

The complex 3-dimensional magnetization reversal behavior of Sin-Co/Fe exchange spring films is used to test the sensitivity of different resonant soft x-ray magneto-optical Kerr effect (MOKE) measurements to changes in longitudinal and transverse moments within the SOIIFe layer and to changes in these moments in depth within the Fe layer. As in the visible MOKE, changes in longitudinal and net transverse moments are resolved by measuring both Kerr rotation and intensity loops in the near the Fe 2p core resonance. These x-ray MOKE signals measured using linear incident polarization are more directly interpreted in terms of longitudinal and transverse momentsmore » than are the same signals measured using elliptical polarization. Varying photon energy near the Fe L3line is shown to be an effective means of resolving distinctly different reversal behavior at the top and bottom of the 20 nm thick Fe layer resulting from the strong exchange coupling at the Sin-Co/Fe interface. Measured x-ray MOKE spectra and signals are in qualitative agreement with those calculated using standard magneto-optical formalisms incorporating interference between different layers and measured helicity-dependent magneto-optical constants for Fe.« less

Sonochemical approach to the synthesis of Fe(3)O(4)@SiO(2) core-shell nanoparticles with tunable properties.

PubMed

Morel, Anne-Laure; Nikitenko, Sergei I; Gionnet, Karine; Wattiaux, Alain; Lai-Kee-Him, Josephine; Labrugere, Christine; Chevalier, Bernard; Deleris, Gerard; Petibois, Cyril; Brisson, Alain; Simonoff, Monique

2008-05-01

In this study, we report a rapid sonochemical synthesis of monodisperse nonaggregated Fe(3)O(4)@SiO(2) magnetic nanoparticles (NPs). We found that coprecipitation of Fe(II) and Fe(III) in aqueous solutions under the effect of power ultrasound yields smaller Fe(3)O(4) NPs with a narrow size distribution (4-8 nm) compared to the silent reaction. Moreover, the coating of Fe(3)O(4) NPs with silica using an alkaline hydrolysis of tetraethyl orthosilicate in ethanol-water mixture is accelerated many-fold in the presence of a 20 kHz ultrasonic field. The thickness of the silica shell can be easily controlled in the range of several nanometers during sonication. Mossbauer spectra revealed that nonsuperparamagnetic behavior of obtained core-shell NPs is mostly related to the dipole-dipole interactions of magnetic cores and not to the particle size effect. Core-shell Fe(3)O(4)@SiO(2) NPs prepared with sonochemistry exhibit a higher magnetization value than that for NPs obtained under silent conditions owing to better control of the deposited silica quantities as well as to the high speed of sonochemical coating, which prevents the magnetite from oxidizing.

Modern applications of terahertz emission spectroscopy

NASA Astrophysics Data System (ADS)

Harrel, Shayne Matthew

Terahertz (THz) emission spectroscopy (TES) is newly developed experimental technique capable of measuring ultrafast dynamics in a variety of systems. Unlike pump-probe spectroscopies where the signals are obtained indirectly, the THz waveform emitted by the dynamical process serves as the signal field. Information about processes involving a time-dependent magnetization, polarization or current is obtained using TES. The detection scheme is polarization sensitive and allows the direction of the dynamical event to be recovered. The role of solvation on intramolecular charge transfer in DMANS (4-(dimethylamino)-4'-nitrostilbene) is studied using TES in three solvents: benzene, toluene, and 1,3-dichlorobenzene. These solvents have similar molecular structures but different polarities and dielectric constants. The charge transfer dynamics are found to depend on the solvent. A secondary feature in the THz emission appearing 4-6 Ps after the main pulse provides evidence that DMANS may undergo a twisted intramolecular charge transfer state (TICT) upon photoexcitation. The ultrafast magnetization dynamics of polycrystalline Ni and single Fe films ranging in thickness from 5 nm to 60 nm are reported using TES. For samples thicker than the visible optical skin depth, (˜10 nm for Ni and ˜27 nm for Fe), the emission is easily interpreted using Lenz's law. For films thinner than visible optical skin depth, the emission patterns are qualitatively different. These results suggest that there are two generation mechanisms at work: one that arises purely from bulk demagnetization in the thick sample limit and another that is the result of difference frequency generation enhanced by the magnetized surface. A comparative study of the magnetization dynamics of a 40 nm Ni and 40 Fe film shows that the magnetization recovers faster in Fe than in Ni. The dependence of optical rectification and shift currents in unbiased GaAs (111) is reported using TES. It is found that the dependence of the emission with respect to linear excitation polarization is well described by theory. The emission with respect to elliptical polarization also agrees well with theory when exciting below and far above the bandgap. However, the THz emission when exciting slightly above the bandgap is strongly influenced by spin-polarized electrons. The magnetic field generated by these spin-polarized electrons is responsible for altering their own trajectories via the self-induced Hall effect. The dependence of THz generation mechanisms in ZnTe (110) on excitation intensity is investigated using TES. Optical rectification is found to be the dominant generation mechanism only at the lowest excitation powers (<5 mW). A model of second harmonic induced shift currents generating THz radiation is unable to explain the emissions at higher excitation powers.

Double Carbon Nano Coating of LiFePO4 Cathode Material for High Performance of Lithium Ion Batteries.

PubMed

Ding, Yan-Hong; Huang, Guo-Long; Li, Huan-Huan; Xie, Hai-Ming; Sun, Hai-Zhu; Zhang, Jing-Ping

2015-12-01

Double carbon-coated LiFePO4 (D-LiFePO4/C) composite with sphere-like structure was synthesized through combination of co-precipitation and solid-state methods. Cetyl-trimethyl-ammonium bromide (CTAB) and citric acid served as two kinds of carbon sources in sequence. SEM images demonstrated that double carbon coating had certain influence on the morphology. The thickness of carbon coating on D-LiFePO4/C was about 1.7 nm and the content of carbon was 2.48 wt%, according to HRTEM and TG analysis. The electrochemical impedance spectroscopy analysis indicated that the D-LiFePO4/C composite presented the charge-transfer resistance of 68 Ω and Li ion diffusion coefficient of 2.68 x 10(-13) cm2 S(-1), while the single carbon-coated LiFePO4 (S-LiFePO4/C) exhibited 135.5Ω and 4.03 x 10(-14) cm2 S(-1). Especially, the prepared D-LiFePO4/C electrode showed discharge capacities of 102.9 (10C) and 87.1 (20C) mA h g(-1), respectively, with almost no capacity lost after 400 cycles at 10C, which were much better than those of S-LiFePO4/C composite.

Molecular Beam Epitaxial Growth of Iron Nitrides on Zinc-Blende Gallium Nitride(001)

NASA Astrophysics Data System (ADS)

Pak, Jeongihm; Lin, Wenzhi; Chinchore, Abhijit; Wang, Kangkang; Smith, Arthur R.

2008-03-01

Iron nitrides are attractive materials for their high magnetic moments, corrosion, and oxidation resistance. We present the successful epitaxial growth of iron nitride on zinc-blende gallium nitride (c-GaN) in order to develop a novel magnetic transition metal nitride/semiconductor system. First, GaN is grown on magnesium oxide (MgO) substrates having (001) orientation using rf N2-plasma molecular beam epitaxy. Then we grow FeN at substrate temperature of ˜ 210 ^oC up to a thickness of ˜ 10.5 nm. In-situ reflection high-energy electron diffraction (RHEED) is used to monitor the surface during growth. Initial results suggest that the epitaxial relationship is FeN[001] || GaN[001] and FeN[100] || GaN[100]. Work in progress is to investigate the surface using in-situ scanning tunneling microscopy (STM) to reveal the surface structure at atomic scale, as well as to explore more Fe-rich magnetic phases.

Synthesis and gas sensing properties of α-Fe(2)O(3)@ZnO core-shell nanospindles.

PubMed

Zhang, Jun; Liu, Xianghong; Wang, Liwei; Yang, Taili; Guo, Xianzhi; Wu, Shihua; Wang, Shurong; Zhang, Shoumin

2011-05-06

α-Fe(2)O(3)@ZnO core-shell nanospindles were synthesized via a two-step hydrothermal approach, and characterized by means of SEM/TEM/XRD/XPS. The ZnO shell coated on the nanospindles has a thickness of 10-15 nm. Considering that both α-Fe(2)O(3) and ZnO are good sensing materials, we have investigated the gas sensing performances of the core-shell nanocomposite using ethanol as the main probe gas. It is interesting to find that the gas sensor properties of the core-shell nanospindles are significantly enhanced compared with pristine α-Fe(2)O(3). The enhanced sensor properties are attributed to the unique core-shell nanostructure. The detailed sensing mechanism is discussed with respect to the energy band structure and the electron depletion theory. The core-shell nanostructure reported in this work provides a new path to fabricate highly sensitive materials for gas sensing applications.

Effect of L1{sub 2} ordering in antiferromagnetic Ir-Mn epitaxial layer on exchange bias of FePd films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Y. C.; Duh, J. G., E-mail: pmami.hsiao@gmail.com, E-mail: lin.yg@nsrrc.org.tw, E-mail: jgd@mx.nthu.edu.tw; Hsiao, S. N., E-mail: pmami.hsiao@gmail.com, E-mail: lin.yg@nsrrc.org.tw, E-mail: jgd@mx.nthu.edu.tw

2015-05-07

Two series of samples of single-layer IrMn and IrMn/FePd bilayer films, deposited on a single-crystal MgO substrate at different IrMn deposition temperatures (T{sub s} = 300–700 °C), were investigated using magnetron sputtering. L1{sub 2} ordering was revealed for the 30 nm-thick IrMn epitaxial (001) films with T{sub s} ≥ 400 °C, determined by synchrotron radiation x-ray diffractometry (XRD). XRD results also provide evidence of the epitaxial growth of the IrMn films on MgO substrate. Increasing T{sub s} from 400 to 700 °C monotonically increases the ordering parameter of L1{sub 2} phases from 0.17 to 0.81. An in-plane exchange bias field (H{sub eb}) of 22 Oe is obtained in amore » 10 nm-thick FePd film that is deposited on the disordered IrMn films. As the L1{sub 2} ordering of the IrMn layers increases, the H{sub eb} gradually decreases to 0 Oe, meaning that the exchange bias behavior vanishes. The increased surface roughness, revealed by atomic force microscopy, of the epitaxial IrMn layers with increasing T{sub s} cannot be the main cause of the decrease in H{sub eb} due to the compensated surface spins regardless of the disordered and ordered (001) IrMn layers. The change of antiferromagnetic structure from the A1 to the L1{sub 2} phase was correlated with the evolution of H{sub eb}.« less

Scaling behavior of fully spin-coated TFT

NASA Astrophysics Data System (ADS)

Mondal, Sandip; Kumar, Arvind; Rao, K. S. R. Koteswara; Venkataraman, V.

2017-05-01

We studied channel scaling behavior of fully spin coated, low temperature solution processed thin film transistor (TFT) fabricated on p++ - Si (˜1021 cm-3) as bottom gate. The solution processed, spin coated 40 nm thick amorphous Indium Gallium Zinc Oxide (a-IGZO) and 50 nm thick amorphous zirconium di-oxide (a-ZrO2) has been used as channel and low leakage dielectric at 350°C respectively. The channel scaling effect of the TFT with different width/length ratio (W/L= 2.5, 5 and 15) for same channel length (L = 10 μm) has been demonstrated. The lowest threshold voltage (Vth) is 6.25 V for the W/L=50/10. The maximum field effect mobility (μFE) has been found to be 0.123 cm2/Vs from W/L of 50/10 with the drain to source voltage (VD) of 10V and 20V gate to source voltage (VG). We also demonstrated that there is no contact resistance effect on the mobility of the fully sol-gel spin coated TFT.

Effect of IrMn inserted layer on anomalous-Hall resistance and spin-Hall magnetoresistance in Pt/IrMn/YIG heterostructures

NASA Astrophysics Data System (ADS)

Shang, T.; Yang, H. L.; Zhan, Q. F.; Zuo, Z. H.; Xie, Y. L.; Liu, L. P.; Zhang, S. L.; Zhang, Y.; Li, H. H.; Wang, B. M.; Wu, Y. H.; Zhang, S.; Li, Run-Wei

2016-10-01

We report an investigation of anomalous-Hall resistance (AHR) and spin-Hall magnetoresistance (SMR) in Pt/Ir20Mn80/Y3Fe5O12 (Pt/IrMn/YIG) heterostructures. The AHR of Pt/IrMn/YIG heterostructures with an antiferromagnetic inserted layer is dramatically enhanced as compared to that of the Pt/YIG bilayer. The temperature dependent AHR behavior is nontrivial, while the IrMn thickness dependent AHR displays a peak at an IrMn thickness of 3 nm. The observed SMR in the temperature range of 10-300 K indicates that the spin current generated in the Pt layer can penetrate the IrMn layer (≤3 nm) to interact with the ferromagnetic YIG layer. The lack of conventional anisotropic magnetoresistance (AMR) implies that the insertion of the IrMn layer between Pt and YIG could efficiently suppress the magnetic proximity effect (MPE) on induced Pt moments by YIG.

Improved performance of organic light-emitting diode with vanadium pentoxide layer on the FTO surface

NASA Astrophysics Data System (ADS)

Saikia, D.; Sarma, R.

2017-06-01

Vanadium pentoxide layer deposited on the fluorine-doped tin oxide (FTO) anode by vacuum deposition has been investigated in organic light-emitting diode (OLED). With 12 nm optimal thickness of V2O5, the luminance efficiency is increased by 1.66 times compared to the single FTO-based OLED. The improvement of current efficiency implies that there is a better charge injection and better controlling of hole current. To investigate the performance of OLED by the buffer layer, V2O5 films of different thicknesses were deposited on the FTO anode and their J- V and L- V characteristics were studied. Further analysis was carried out by measuring sheet resistance, optical transmittance and surface morphology with the FE-SEM images. This result indicates that the V2O5 (12 nm) buffer layer is a good choice for increasing the efficiency of FTO-based OLED devices within the tunnelling region. Here the maximum value of current efficiency is found to be 2.83 cd / A.

Unveiling structural, chemical and magnetic interfacial peculiarities in ε-Fe2O3/GaN (0001) epitaxial films.

PubMed

Ukleev, Victor; Suturin, Sergey; Nakajima, Taro; Arima, Taka-Hisa; Saerbeck, Thomas; Hanashima, Takayasu; Sitnikova, Alla; Kirilenko, Demid; Yakovlev, Nikolai; Sokolov, Nikolai

2018-06-07

The metastable ε-Fe 2 O 3 is known to be the most intriguing ferrimagnetic and multiferroic iron oxide phase exhibiting a bunch of exciting physical properties both below and above room temperature. The present paper unveils the structural and magnetic peculiarities of a few nm thick interface layer discovered in these films by a number of techniques. The polarized neutron reflectometry data suggests that the interface layer resembles GaFeO 3 in composition and density and is magnetically softer than the rest of the ε-Fe 2 O 3 film. While the in-depth density variation is in agreement with the transmission electron microscopy measurements, the layer-resolved magnetization profiles are qualitatively consistent with the unusual wasp-waist magnetization curves observed by superconducting quantum interference device magnetometry. Interestingly a noticeable Ga diffusion into the ε-Fe 2 O 3 films has been detected by secondary ion mass spectroscopy providing a clue to the mechanisms guiding the nucleation of exotic metastable epsilon ferrite phase on GaN at high growth temperature and influencing the interfacial properties of the studied films.

Preparation and characterization of core-shell structured LiFePO4/C composite using a novel carbon source for lithium-ion battery cathode

NASA Astrophysics Data System (ADS)

Huang, Zan; Luo, Peifang; Wang, Daxiang

2017-03-01

Core-shell structured LiFePO4/C1 cathode material is synthesized via a rapid microwave irradiation route using ethylene diamine tetraacetic acid (EDTA) as the novel carbon source. XRD results reveal that all the patterns can be indexed as the olivine-type structured LiFePO4 with the space group of Pnma. TEM images show that the obtained carbon is an amorphous layer with a thickness of about 3-4 nm. When the LiFePO4/C1 used as cathode material for lithium-ion battery, it delivers an initial discharge capacity of 163.1 mAh g-1 at 0.1 C which is about 96% of the theoretical capacity. Moreover, it also shows excellent rate performance and good cycle stability due to the enhanced electronic conductivity as proved by the electrochemical impedance spectroscopy (EIS). Thus, this carbon decorated LiFePO4 composite synthesized via the rapid microwave irradiation method is a promising cathode material for high-performance lithium-ion battery.

Study of interlayer coupling between FePt and FeCoB thin films through MgO spacer layer

NASA Astrophysics Data System (ADS)

Singh, Sadhana; Kumar, Dileep; Gupta, Mukul; Reddy, V. Raghvendra

2017-05-01

Interlayer exchange coupling between hard-FePt and soft-FeCoB magnetic layers has been studied with increasing thickness of insulator MgO spacer layer in FePt/MgO/FeCoB sandwiched structure. A series of the samples were prepared in identical condition using ion beam sputtering method and characterized for their magnetic and structural properties using magneto-optical Kerr effect (MOKE) and X-ray reflectivity measurements. The nature of coupling between FePt and FeCoB was found to be ferromagnetic which decreases exponentially with increasing thickness of MgO layer. At very low thickness of MgO layer, both layers were found strongly coupled thus exhibiting coherent magnetization reversal. At higher thickness, both layers were found decoupled and magnetization reversal occurred at different switching fields. Strong coupling at very low thickness is attributed to pin holes in MgO layer which lead to direct coupling whereas on increasing thickness, coupling may arise due to magneto-static interactions.

In situ investigations of phase transformations in Fe-sheathed MgB2 wires

NASA Astrophysics Data System (ADS)

Grivel, J.-C.; Pinholt, R.; Andersen, N. H.; Kovác, P.; Husek, I.; Homeyer, J.

2006-01-01

The phase evolution inside Fe-sheathed wires containing precursor powders consisting of a mixture of Mg and B has been studied in situ by means of x-ray diffraction with hard synchrotron radiation (90 keV). Mg was found to disappear progressively during the heating stage. At 500 °C, the intensity of the Mg diffraction lines is reduced by about 20%. This effect is partly attributable to MgO formation. The MgB2 phase was detected from 575 °C. Fe2B was forming at the interface between the sheath and the ceramic core at sintering temperatures of 780 and 700 °C, but not at 650 °C. The formation rate of this phase is strongly dependent on the heat treatment temperature. Its presence can be readily detected as soon as the average interface reaction thickness exceeds 150-200 nm.

The magnetoresistance of sub-micron Fe wires

NASA Astrophysics Data System (ADS)

Blundell, S. J.; Shearwood, C.; Gester, M.; Baird, M. J.; Bland, J. A. C.; Ahmed, H.

1994-07-01

A novel combination of electron- and ion-beam lithography has been used to prepare Fe gratings with wire widths of 0.5 μm and wire separations in the range 0.5-4 μm from an Fe/GaAs (001) film of thickness 25 nm. With an in-plane magnetic field applied perpendicular to the length of the wires, a harder magnetisation loop is observed using the magneto-optic Kerr effect (MOKE), compared with that observed in the unprocessed film. We observe a strong effect in the magnetoresistance (MR) when the magnetic field is applied transverse to the wires. It is believed that this effect originates from the highly non-uniform demagnetising field in each wire of the grating. These results demonstrate that the combination of MOKE and MR measurements can provide important information about the magnetisation reversal processes in magnetic gratings and can be used to understand the effect of shape anisotropy on magnetic properties.

Femtosecond laser excitation of multiple spin waves and composition dependence of Gilbert damping in full-Heusler Co{sub 2}Fe{sub 1−x}Mn{sub x}Al films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Chuyuan; Li, Shufa; Lai, Tianshu, E-mail: stslts@mail.sysu.edu.cn, E-mail: jhzhao@red.semi.ac.cn

2013-12-02

Spin-wave dynamics in 30 nm thick Co{sub 2}Fe{sub 1−x}Mn{sub x}Al full-Heusler films is investigated using time-resolved magneto-optical polar Kerr spectroscopy under an external field perpendicular to films. Damon-Eshbach (DE) and the first-order perpendicular standing spin-wave (PSSW) modes are observed simultaneously in four samples with x = 0, 0.3, 0.7, and 1. The frequency of DE and PSSW modes does not apparently depend on composition x, but damping of DE mode significantly on x and reaches the minimum as x = 0.7. The efficient coherent excitation of DE spin wave exhibits the promising application of Co{sub 2}Fe{sub 0.3}Mn{sub 0.7}Al films in magnonic devices.

Structural, magnetic, and ferroelectric properties of T-like cobalt-doped BiFeO3 thin films

NASA Astrophysics Data System (ADS)

Young, T.; Sharma, P.; Kim, D. H.; Ha, Thai Duy; Juang, Jenh-Yih; Chu, Y.-H.; Seidel, J.; Nagarajan, V.; Yasui, S.; Itoh, M.; Sando, D.

2018-02-01

We present a comprehensive study of the physical properties of epitaxial cobalt-doped BiFeO3 films ˜50 nm thick grown on (001) LaAlO3 substrates. X-ray diffraction and magnetic characterization demonstrate high quality purely tetragonal-like (T') phase films with no parasitic impurities. Remarkably, the step-and-terrace film surface morphology can be fully recovered following a local electric-field-induced rhombohedral-like to T' phase transformation. Local switching spectroscopy experiments confirm the ferroelectric switching to follow previously reported transition pathways. Critically, we show unequivocal evidence for conduction at domain walls between polarization variants in T'-like BFO, making this material system an attractive candidate for domain wall-based nanoelectronics.

Space Weathering of Olivine in Lunar Soils: A Comparison to Itokawa Regolith Samples

NASA Technical Reports Server (NTRS)

Keller, L. P.; Berger, E. L.

2014-01-01

Regolith particles from airless bodies preserve a record of the space weathering processes that occurred during their surface exposure history. These processes have major implications for interpreting remote-sensing data from airless bodies. Solar wind irradiation effects occur in the rims of exposed grains, and impact processes result in the accumulation of vapordeposited elements and other surface-adhering materials. The grains returned from the surface of Itokawa by the Hayabusa mission allow the space weathering "style" of a chondritic, asteroidal "soil" to be compared to the lunar case. Here, we present new studies of space-weathered olivine grains from lunar soils, and compare these results to olivine grains from Itokawa. Samples and Methods: We analyzed microtome thin sections of olivine grains from the 20-45 micron fractions of three lunar soils: 71061, 71501 and 10084 (immature, submature and mature, respectively). Imaging and analytical data were obtained using a JEOL 2500SE 200kV field-emission scanning-transmission electron microscope equipped with a thin-window energy-dispersive x-ray spectrometer. Similar analyses were obtained from three Hayabusa olivine grains. Results and Discussion: We observed lunar grains showing a range of solar flare track densities (from <10(exp 9) to approx.10(exp 12)/sq cm). The lunar olivines all show disordered, highly strained, nanocrystalline rims up to 150-nm thick. The disordered rim thickness is positively correlated with solar flare track density. All of the disordered rims are overlain by a Si-rich amorphous layer, ranging up to 50-nm thick, enriched in elements that are not derived from the host olivine (e.g., Ca, Al, and Ti). The outmost layer represents impact-generated vapor deposits typically observed on other lunar soil grains. The Hayabusa olivine grains show track densities <10(exp 10)/sq cm and display disordered rims 50- to 100-nm thick. The track densities are intermediate to those observed in olivines in immature and submature lunar soils and indicate surface exposures of approx. 10(exp 5) years. The outermost few nanometers of the disordered rims on Hayabusa olivines are more Si-rich and Mg- and Fe-depleted relative to the cores of the grains and likely represent a minor accumulation of impact-generated vapors or sputter deposits. Nanophase Fe metal particles are less abundant in the Hayabusa rims compared to the rims on lunar grains. Conclusions: The Hayabusa and lunar olivine grain rims have widths and microstructures consistent with formation from atomic displacement damage from solar wind ions. The space weathering features in the Hayabusa grains are similar to those observed in olivines from immature to submature lunar soils. A major difference, however, is that the Hayabusa grains appear to lack the hypervelocity impact products (melt spherules, thick vapor deposits, and abundant nanophase Fe metal particles) that are common in lunar soil grains with a similar exposure history.

High performance top-gated ferroelectric field effect transistors based on two-dimensional ZnO nanosheets

NASA Astrophysics Data System (ADS)

Tian, Hongzheng; Wang, Xudong; Zhu, Yuankun; Liao, Lei; Wang, Xianying; Wang, Jianlu; Hu, Weida

2017-01-01

High quality ultrathin two-dimensional zinc oxide (ZnO) nanosheets (NSs) are synthesized, and the ZnO NS ferroelectric field effect transistors (FeFETs) are demonstrated based on the P(VDF-TrFE) polymer film used as the top gate insulating layer. The ZnO NSs exhibit a maximum field effect mobility of 588.9 cm2/Vs and a large transconductance of 2.5 μS due to their high crystalline quality and ultrathin two-dimensional structure. The polarization property of the P(VDF-TrFE) film is studied, and a remnant polarization of >100 μC/cm2 is achieved with a P(VDF-TrFE) thickness of 300 nm. Because of the ultrahigh remnant polarization field generated in the P(VDF-TrFE) film, the FeFETs show a large memory window of 16.9 V and a high source-drain on/off current ratio of more than 107 at zero gate voltage and a source-drain bias of 0.1 V. Furthermore, a retention time of >3000 s of the polarization state is obtained, inspiring a promising candidate for applications in data storage with non-volatile features.

Preparation of c-axis perpendicularly oriented ultra-thin L10-FePt films on MgO and VN underlayers

NASA Astrophysics Data System (ADS)

Futamoto, Masaaki; Shimizu, Tomoki; Ohtake, Mitsuru

2018-05-01

Ultra-thin L10-FePt films of 2 nm average thickness are prepared on (001) oriented MgO and VN underlayers epitaxially grown on base substrate of SrTiO3(001) single crystal. Detailed cross-sectional structures are observed by high-resolution transmission electron microscopy. Continuous L10-FePt(001) thin films with very flat surface are prepared on VN(001) underlayer whereas the films prepared on MgO(001) underlayer consist of isolated L10-FePt(001) crystal islands. Presence of misfit dislocation and lattice bending in L10-FePt material is reducing the effective lattice mismatch with respect to the underlayer to be less than 0.5 %. Formation of very flat and continuous FePt layer on VN underlayer is due to the large surface energy of VN material where de-wetting of FePt material at high temperature annealing process is suppressed under a force balance between the surface and interface energies of FePt and VN materials. An employment of underlayer or substrate material with the lattice constant and the surface energy larger than those of L10-FePt is important for the preparation of very thin FePt epitaxial thin continuous film with the c-axis controlled to be perpendicular to the substrate surface.

Thickness-dependent electrocaloric effect in mixed-phase Pb0.87Ba0.1 La0.02(Zr0.6Sn0.33Ti0.07)O3 thin films

PubMed Central

Correia, T. M.

2016-01-01

Full-perovskite Pb0.87Ba0.1La0.02(Zr0.6Sn0.33Ti0.07)O3 (PBLZST) thin films were fabricated by a sol–gel method. These revealed both rhombohedral and tetragonal phases, as opposed to the full-tetragonal phase previously reported in ceramics. The fractions of tetragonal and rhombohedral phases are found to be strongly dependent on film thickness. The fraction of tetragonal grains increases with increasing film thickness, as the substrate constraint throughout the film decreases with film thickness. The maximum of the dielectric constant (εm) and the corresponding temperature (Tm) are thickness-dependent and dictated by the fraction of rhombohedral and tetragonal phase, with εm reaching a minimum at 400 nm and Tm shifting to higher temperature with increasing thickness. With the thickness increase, the breakdown field decreases, but field-induced antiferroelectric–ferroelectric (EAFE−FE) and ferroelectric–antiferroelectric (EFE−AFE) switch fields increase. The electrocaloric effect increases with increasing film thickness. This article is part of the themed issue ‘Taking the temperature of phase transitions in cool materials’. PMID:27402937

Current-perpendicular-to-the-plane magnetoresistance from large interfacial spin-dependent scattering between Co{sub 50}Fe{sub 50} magnetic layer and In-Zn-O conductive oxide spacer layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakatani, T. M., E-mail: Tomoya.Nakatani@hgst.com; Childress, J. R.

2015-06-28

We have investigated electrically conductive indium-zinc-oxide (IZO) deposited by magnetron sputtering as spacer layer for current-perpendicular-to-the-plane giant magnetoresistance sensor devices. Spin-valves with a Co{sub 50}Fe{sub 50}/IZO/Co{sub 50}Fe{sub 50} trilayer showed resistance-area product (RA) ranging from 110 to 250 mΩ μm{sup 2}, significantly larger than all-metal structures with Ag or Cu spacers (∼40 mΩ μm{sup 2}). Magnetoresistance ratios (ΔR/R) of 2.5% to 5.5% depending on the IZO spacer thickness (1.5–6.0 nm), corresponding to ΔRA values from 3 to 13 mΩ μm{sup 2}, were obtained. The values of ΔRA with the IZO spacers and Co{sub 50}Fe{sub 50} magnetic layers were significantly larger than thosemore » with conventional metal spacers and Co{sub 50}Fe{sub 50} magnetic layers (∼1–2 mΩ μm{sup 2}). The dependence of ΔRA on the magnetic layer thickness suggests that the larger ΔRA obtained with IZO spacer is due to a large interfacial spin-dependent scattering caused by the large specific resistance at the Co{sub 50}Fe{sub 50}/IZO interface. From structural characterization by TEM and the observed dependence of the RA dispersion on device size, the electric current flowing through the IZO spacer is thought to be laterally uniform, similar to normal metal spacers.« less

360° deterministic magnetization rotation in a three-ellipse magnetoelectric heterostructure

NASA Astrophysics Data System (ADS)

Kundu, Auni A.; Chavez, Andres C.; Keller, Scott M.; Carman, Gregory P.; Lynch, Christopher S.

2018-03-01

A magnetic dipole-coupled magnetoelectric heterostructure comprised of three closely spaced ellipse shapes was designed and shown to be capable of achieving deterministic in-plane magnetization rotation. The design approach used a combination of conventional micromagnetic simulations to obtain preliminary configurations followed by simulations using a fully strain-coupled, time domain micromagnetic code for a detailed assessment of performance. The conventional micromagnetic code has short run times and was used to refine the ellipse shape and orientation, but it does not accurately capture the effects of the strain gradients present in the piezoelectric and magnetostrictive layers that contribute to magnetization reorientation. The fully coupled code was used to assess the effects of strain and magnetic field gradients on precessional switching in the side ellipses and on the resulting dipole-field driven magnetization reorientation in the center ellipse. The work led to a geometry with a CoFeB ellipse (125 nm × 95 nm × 4 nm) positioned between two smaller CoFeB ellipses (75 nm × 50 nm × 4 nm) on a 500 nm PZT-5H film substrate clamped at its bottom surface. The smaller ellipses were oriented at 45° and positioned at 70° and 250° about the central ellipse due to the film deposition on a thick substrate. A 7.3 V pulse applied to the PZT for 0.22 ns produced 180° switching of the magnetization in the outer ellipses that then drove switching in the center ellipse through dipole-dipole coupling. Full 360° deterministic rotation was achieved with a second pulse. The temporal response of the resulting design is discussed.

High surface stability of magnetite on bi-layer Fe3O4/Fe/MgO(0 0 1) films under 1 MeV Kr+ ion irradiation

NASA Astrophysics Data System (ADS)

Kim-Ngan, N.-T. H.; Krupska, M.; Balogh, A. G.; Malinsky, P.; Mackova, A.

2017-12-01

We investigate the stability of the bi-layer Fe3O4/Fe(0 0 1) films grown epitaxially on MgO(0 0 1) substrates with the layer thickness in the range of 25-100 nm upon 1 MeV Kr+ ion irradiation. The layer structure and layer composition of the films before and after ion irradiation were studied by XRR, RBS and RBS-C techniques. The interdiffusion and intermixing was analyzed. No visible change in the RBS spectra was observed upon irradiation with ion fluence below 1015 Kr cm-2. The bi-layer structure and the stoichiometric Fe3O4 layer on the surface were well preserved after Kr+ ion irradiation at low damage levels, although the strong intermixing implied a large interfacial (Fe x O y ) and (Fe, Mg)O y layer respective at Fe3O4-Fe and Fe-MgO interface. The high ion fluence of 3.8  ×  1016 Kr cm-2 has induced a complete oxidization of the buffer Fe layer. Under such Kr fluence, the stoichiometry of the Fe3O4 surface layer was still preserved indicating its high stability. The entire film contains Fe x O y -type composition at ion fluence large than 5.0  ×  1016 Kr cm-2.

Capture Efficiency of Biocompatible Magnetic Nanoparticles in Arterial Flow: A Computer Simulation for Magnetic Drug Targeting.

PubMed

Lunnoo, Thodsaphon; Puangmali, Theerapong

2015-12-01

The primary limitation of magnetic drug targeting (MDT) relates to the strength of an external magnetic field which decreases with increasing distance. Small nanoparticles (NPs) displaying superparamagnetic behaviour are also required in order to reduce embolization in the blood vessel. The small NPs, however, make it difficult to vector NPs and keep them in the desired location. The aims of this work were to investigate parameters influencing the capture efficiency of the drug carriers in mimicked arterial flow. In this work, we computationally modelled and evaluated capture efficiency in MDT with COMSOL Multiphysics 4.4. The studied parameters were (i) magnetic nanoparticle size, (ii) three classes of magnetic cores (Fe3O4, Fe2O3, and Fe), and (iii) the thickness of biocompatible coating materials (Au, SiO2, and PEG). It was found that the capture efficiency of small particles decreased with decreasing size and was less than 5 % for magnetic particles in the superparamagnetic regime. The thickness of non-magnetic coating materials did not significantly influence the capture efficiency of MDT. It was difficult to capture small drug carriers (D<200 nm) in the arterial flow. We suggest that the MDT with high-capture efficiency can be obtained in small vessels and low-blood velocities such as micro-capillary vessels.

Determination of band gap in epitaxial delafossite Cu oxide using optical techniques

NASA Astrophysics Data System (ADS)

Cabrera, Alejandro; Wheatley, R.; Seifert, B.; Wallentowitz, S.; Joshi, T.; Lederman, D.

Highly epitaxial delafossite CuFeO2 and CuFe1-xGaxO2 films were grown using Pulsed Laser Deposition techniques. The sample thicknesses were estimated to be 21 nm, 75 nm.The estimated gallium fraction of substituted ferric atoms was x =0.25 for the composite sample. We present the study of the fundamental band gap(s) for each sample via observation of their respective optical absorption properties in the NIR-VIS region using transmittance and diffuse reflection spectroscopy. Predominant absorption edges measured were between 1.1eV and 3.1eV from transmittance spectra. The sample of CuFe1-xGaxO2 showed measurable absorption features located at 2.4eV and 2.8eV. This study also found evidence of changes between apparent absorption edges between transmittance and diffuse reflectance spectroscopies of each sample and it may be resultant from absorption channels via surface states. Future photoluminescence experiments are planned to determine the photo-induced semiconductor behavior of these materials. ACNOWLEDGEMENTS: This work was supported by FONDECyT 1130372 and Proyecto Anillo ACT1409 at PUC and supported in part by the WV Higher Education Policy Commission (Grant HEPC.dsr.12.29) and by FAME sponsored by MARCO and DARPA (contract # 2013-MA-2382).

Magnetic and microwave absorbing properties of magnetite-thermoplastic natural rubber nanocomposites

NASA Astrophysics Data System (ADS)

Kong, Ing; Hj Ahmad, Sahrim; Hj Abdullah, Mustaffa; Hui, David; Nazlim Yusoff, Ahmad; Puryanti, Dwi

2010-11-01

Magnetic and microwave absorbing properties of thermoplastic natural rubber (TPNR) filled magnetite (Fe 3O 4) nanocomposites were investigated. The TPNR matrix was prepared from polypropylene (PP), natural rubber (NR) and liquid natural rubber (LNR) in the ratio of 70:20:10 with the LNR as the compatibilizer. TPNR-Fe 3O 4 nanocomposites with 4-12 wt% Fe 3O 4 as filler were prepared via a Thermo Haake internal mixer using a melt-blending method. XRD reveals the presence of cubic spinel structure of Fe 3O 4 with the lattice parameter of a=8.395 Å. TEM micrograph shows that the Fe 3O 4 nanoparticles are almost spherical with the size ranging 20-50 nm. The values of saturation magnetization ( MS), remanence ( MR), initial magnetic susceptibility ( χi) and initial permeability ( μi) increase, while the coercivity ( HC) decreases with increasing filler content for all compositions. For nanocomposites, the values of the real ( ɛr') and imaginary permittivity ( ɛr'') and imaginary permeability ( μr'') increase, while the value of real permeability ( μr') decreases as the filler content increases. The absorption or minimum reflection loss ( RL) continuously increases and the dip shifts to a lower frequency region with the increasing of both filler content in nanocomposites and the sample thickness. The RL is -25.51 dB at 12.65 GHz and the absorbing bandwidth in which the RL is less than -10 dB is 2.7 GHz when the filler content is 12 wt% at 9 mm sample thickness.

High Resolution Quantitative Microbeam Analysis of Ir-coated Geological Specimens Using Conventionally Coated Standards

NASA Astrophysics Data System (ADS)

Armstrong, J. T.; Crispin, K. L.

2012-12-01

Traditionally, quantitative electron microbeam analyses of insulating specimens are performed after coating the materials with thin conducting layers of carbon. For x-ray lines greater than 1 keV in energy and beam voltages in excess of 10 keV, the results are insensitive to the exact thickness of the carbon coat. High resolution imaging, low voltage analysis, and analysis of specimens containing low levels of carbon require the use of substitute conductive coats. Typical substitutes for carbon coats (e.g., Au, Au-Pd, Cr, Al) require either using similarly coated standards or substantial corrections to be applied. Even when using modern multi-layer correction algorithms or Monte Carlo calculations, significant errors can result (e.g., Armstrong 2009, Armstrong and Crispin, 2012). We propose the use of ultra-thin layers of Ir as a substitute for C in the analysis of insulating geological specimens. Ir has been found to be an excellent coating material for high resolution imaging (e.g., Echlin, 2009). Sputtered layers as thin as 0.5 nm are found to be conductive, and layers of just a few nm provide good protection against beam damage with sub-nm grain size (Sebring et al., 1999). We have analyzed a series of geological materials with Ir coats between 1 - 8 nm and found similar levels of effects on emitted x-ray intensities as produced with typical carbon coat thicknesses (10-25 nm). E.g., for Ir thicknesses less than 5 nm, the reduction of intensity for x-ray lines between 1 and 7 keV are between 1-3% for a beam energy of 15 keV. The reduction in intensity for higher-energy lines such as Fe-K is actually less than produced by typical C-coats. We will present the results of these experiments and propose simple algorithmic equations which fit these data.

Structural changes of macula and optic disk of the fellow eye in patients with nonarteritic anterior ischemic optic neuropathy.

PubMed

Duman, R; Yavas, G F; Veliyev, I; Dogan, M; Duman, R

2018-05-10

The aim was to assess the ganglion cell complex (GCC) thickness, retinal nerve fiber layer (RNFL) thickness and optic disk features in the affected eyes (AE) and unaffected fellow eyes (FE) of subjects with unilateral nonarteritic anterior ischemic optic neuropathy (NAION) and to compare with healthy control eyes (CE) using spectral domain-optical coherence tomography (SD-OCT). This study included 28 patients and age, sex and refraction-matched 28 control subjects. Mean GCC thickness and peripapillary RNFL thickness in four quadrants measured by cirrus SD-OCT were evaluated in both AE and FE of patients and CE. In addition, optic disk measurements obtained with OCT were evaluated. Mean GCC thickness was significantly lower in AE compared with both FE and CE (P < 0.001), and mean GCC thickness in FE was significantly lower than CE (P = 0.022). In addition, mean RNFL thickness in superior and nasal quadrants significantly decreased in FE compared with CE (P = 0.020 and 0.010, respectively). Furthermore, AE had significantly greater optic disk cupping compared with both FE and CE (P < 0.001). GCC and RNFL thickness decreased significantly at late stages of NAION, in both AE and FE compared with CE, suggesting that some subclinical structural changes may occur in FE despite lack of obvious visual symptoms. In addition, there was no significant difference in optic disk features between the CE and FE. And significantly greater optic disk cupping in the AE compared with both FE and CE supports the acquired enlargement of cupping after the onset of NAION.

Characterization and corrosion behavior of F6NM stainless steel treated in high temperature water

NASA Astrophysics Data System (ADS)

Li, Zheng-yang; Cai, Zhen-bing; Yang, Wen-jin; Shen, Xiao-yao; Xue, Guo-hong; Zhu, Min-hao

2018-03-01

F6NM martensitic stainless steel was exposed to 350 °C water condition for 500, 1500, and 2500 h to simulate pressurized water reactor (PWR) condition. The characterization and corrosion behavior of the oxide film were investigated. Results indicate that the exposed steel surface formed a double-layer oxide film. The outer oxide film is Fe-rich and contains two type oxide particles. However, the inner oxide film is Cr-rich, and two oxide films, whose thicknesses increase with increasing exposure time. The oxide film reduces the corrosion behavior because the outer oxide film has many crack and pores. Finally, the mechanism and factors affecting the formation of the oxide film were investigated.

Magnetic and electrical properties of FeSi/FeSi-ZrO 2 multilayers prepared by EB-PVD

NASA Astrophysics Data System (ADS)

Bi, Xiaofang; Lan, Weihua; Ou, Shengquan; Gong, Shengkai; Xu, Huibin

2003-04-01

FeSi/FeSi-ZrO 2 and FeSi/ZrO 2 multilayer materials were prepared by electron beam physical vapor deposition with the FeSi-ZrO 2 layer thickness about 0.6 μm, and their magnetic and electrical properties were studied as a function of FeSi layer thickness. With increasing FeSi layer thickness from 0.3 to 3 μm, the coercivity decreased from 0.92 to 0.31 kA/m and the saturation magnetization changed from 164 to 186 emu/g. The effect of the layer number on the magnetic properties was discussed in terms of interfacial mixing and oxidation. It was also discovered that the magnetic properties of the multilayer materials were affected by the spacer material, exhibiting higher saturation magnetization and lower coercivity for the FeSi/FeSi-ZrO 2 than those for the FeSi/ZrO 2 with the same individual layer thicknesses. This behavior could be explained by the weaker magnetic interaction between FeSi layers separated by the non-magnetic ZrO 2 layer. Furthermore, the electrical resistivity changed from 1850 to 1250 μΩ cm for the multilayer materials for the FeSi thickness increasing from 0.30 to 3 μm.

Polypeptide multilayer films on colloidal particles: an in situ electro-optical study.

PubMed

Radeva, Tsetska; Kamburova, Kamelia

2007-04-15

The buildup of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) multilayers on beta-FeOOH colloidal particles was investigated by means of electro-optics and electrophoresis. The films were built at different (acidic) pH in the absence of salt. We found that the thickness of the film grows linearly when the fully charged PLL (at pH 5.5) is combined with almost fully charged PGA (at pH 6.5), with a thickness of about 2 nm per single layer. When the fully charged PLL is combined with weakly charged PGA (at pH 4.5), the film thickness increases exponentially with the number of deposited layers. The thickness of the exponentially growing film increases to 300 nm after deposition of 16 layers. The exponential film growth is attributed to the ability of the PLL to diffuse "in" and "out" of the film bulk at each deposition step. The variation in the electrical polarizability of the film-coated particles was also monitored as a function of the number of adsorbed layers. The result reveals that the PLL chains, which can diffuse into the film bulk, have no measurable contribution to the electro-optical effect of the films terminated with PLL. It is only due to the polarization of counterions of the PLL adsorbed on the film surface.

Structure and magnetic properties of Fe-Co-B alloy thin films prepared on cubic (001) single-crystal substrates

NASA Astrophysics Data System (ADS)

Ohtake, Mitsuru; Serizawa, Kana; Futamoto, Masaaki; Kirino, Fumiyoshi; Inaba, Nobuyuki

2018-04-01

Fe70Co30 and (Fe70Co30)0.95B5 (at. %) alloy films of 5 nm thickness are prepared by sputtering on cubic (001) oxide substrates at 200 °C. The lattice mismatch between film and substrate is varied from -4.2%, 0%, to +3.5% by employing MgO, MgAl2O4, and SrTiO3 substrates, respectively. Fe70Co30 and (Fe70Co30)0.95B5 single-crystal films with bcc structure grow epitaxially on all the substrates in the orientation relationship of (001)[110]film || (001)[100]substrate. The in-plane and out-of-plane lattice constants, a and c, are in agreement within small differences ranging between +1.1% and -0.9% with the value of bulk bcc-Fe70Co30 crystal, even though there exist the lattice mismatches of -4.2% and +3.5%. The result indicates that misfit dislocations are introduced around the film/substrate interface when films are deposited on MgO and SrTiO3 substrates. The single-crystal films show in-plane magnetic anisotropies with the easy magnetization direction of bcc[100], which are reflecting the magnetocrystalline anisotropy of bulk Fe70Co30 crystal.

Atomic structures of B20 FeGe thin films grown on the Si(111) surface

NASA Astrophysics Data System (ADS)

Kim, Wondong; Noh, Seungkyun; Yoon, Jisoo; Kim, Young Heon; Lee, Inho; Kim, Jae-Sung; Hwang, Chanyong

We investigated the growth and atomic structures of FeGe thin films on the Si (111) surface by using scanning tunneling microscopy (STM) and transmission electron microscopy (TEM). The 2 5nm- thick FeGe thin films were prepared on the clean Si(111) 7x7 surface by co-deposition of Fe and Ge from separated electron-beam evaporators. With direct deposition on the substrate at the temperature above 550 K, the surface of FeGe films was not smooth and consisted of coarse grains. By the combination of room-temperature annealing and post-annealing process around 800 K, the structure of FeGe thin films evolved into the well crystalized structures. Atom-resolved STM images revealed that there are at least four different surface terminations. We constructed atomic models for each surface terminations based on the bulk atomic arrangement of a B20 chiral structure and confirmed that the observed STM images are successfully reproduced by using computational simulations employing Vienna Ab Initio Simulation package (VASP) with a B20 chiral structure model. TEM cross-sectional images also support our atomic models by revealing clearly the characteristic zigzag features of B20 structures of FeGe(111) thin films.

Evidence of a reduction reaction of oxidized iron/cobalt by boron atoms diffused toward naturally oxidized surface of CoFeB layer during annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sato, Soshi, E-mail: sato.soshi@cies.tohoku.ac.jp; Honjo, Hiroaki; Niwa, Masaaki

2015-04-06

We have investigated the redox reaction on the surface of Ta/CoFeB/MgO/CoFeB magnetic tunnel junction stack samples after annealing at 300, 350, and 400 °C for 1 h using angle-resolved X-ray photoelectron spectroscopy for precise analysis of the chemical bonding states. At a capping tantalum layer thickness of 1 nm, both the capping tantalum layer and the surface of the underneath CoFeB layer in the as-deposited stack sample were naturally oxidized. By comparison of the Co 2p and Fe 2p spectra among the as-deposited and annealed samples, reduction of the naturally oxidized cobalt and iron atoms occurred on the surface of the CoFeB layer.more » The reduction reaction was more significant at higher annealing temperature. Oxidized cobalt and iron were reduced by boron atoms that diffused toward the surface of the top CoFeB layer. A single CoFeB layer was prepared on SiO{sub 2}, and a confirmatory evidence of the redox reaction with boron diffusion was obtained by angle-resolved X-ray photoelectron spectroscopy analysis of the naturally oxidized surface of the CoFeB single layer after annealing. The redox reaction is theoretically reasonable based on the Ellingham diagram.« less

Regulation of the forming process and the set voltage distribution of unipolar resistance switching in spin-coated CoFe2O4 thin films.

PubMed

Mustaqima, Millaty; Yoo, Pilsun; Huang, Wei; Lee, Bo Wha; Liu, Chunli

2015-01-01

We report the preparation of (111) preferentially oriented CoFe2O4 thin films on Pt(111)/TiO2/SiO2/Si substrates using a spin-coating process. The post-annealing conditions and film thickness were varied for cobalt ferrite (CFO) thin films, and Pt/CFO/Pt structures were prepared to investigate the resistance switching behaviors. Our results showed that resistance switching without a forming process is preferred to obtain less fluctuation in the set voltage, which can be regulated directly from the preparation conditions of the CFO thin films. Therefore, instead of thicker film, CFO thin films deposited by two times spin-coating with a thickness about 100 nm gave stable resistance switching with the most stable set voltage. Since the forming process and the large variation in set voltage have been considered as serious obstacles for the practical application of resistance switching for non-volatile memory devices, our results could provide meaningful insights in improving the performance of ferrite material-based resistance switching memory devices.

Pulsed laser deposition of epitaxial yttrium iron garnet films with low Gilbert damping and bulk-like magnetization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Onbasli, M. C., E-mail: onbasli@mit.edu; Kim, D. H.; Ross, C. A.

2014-10-01

Yttrium iron garnet (YIG, Y {sub 3}Fe{sub 5}O{sub 12}) films have been epitaxially grown on Gadolinium Gallium Garnet (GGG, Gd{sub 3}Ga{sub 5}O{sub 12}) substrates with (100) orientation using pulsed laser deposition. The films were single-phase, epitaxial with the GGG substrate, and the root-mean-square surface roughness varied between 0.14 nm and 0.2 nm. Films with thicknesses ranging from 17 to 200 nm exhibited low coercivity (<2 Oe), near-bulk room temperature saturation moments (∼135 emu cm{sup −3}), in-plane easy axis, and damping parameters as low as 2.2 × 10{sup −4}. These high quality YIG thin films are useful in the investigation ofmore » the origins of novel magnetic phenomena and magnetization dynamics.« less

Synthesis and characterization of Eu{sup 3+}:Gd{sub 2}O{sub 3} hollow spheres for biomedical applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumari, Manisha, E-mail: guptamanisha69@yahoo.co.in; Sharma, Prashant K., E-mail: prashantnac@gmail.com

Multifunctional magnetic Nanoparticles (MFMNPs) are potentially applicable in both drug delivery systems (DDS) and hyperthermia treatment. Structural, surface morphology and optical property were investigated by X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM) and photoluminescence (PL) measurement. Uniform Eu{sup 3+}:Gd{sub 2}O{sub 3} hollow microspheres of 1.8-2.0 μm diameters were synthesized by template based approach. We found that synthesized Hollow spheres are 100 nm in thickness. FE-SEM images revealed that the synthesized material are hollow in structure with good porous structure and these pores work as pathway for releasing drugs from the hollow particle inside. Luminescent properties of material were studiedmore » by room temperature photoluminescence emission spectra under the excitation of 275 nm. Material exhibit bright red emission corresponding to the {sup 5}D{sub 0}-{sup 7}F{sub 2} transition of the activator ions under ultraviolet light excitation, which might find potential applications in fields such as drug delivery or biological labeling because of their excellent luminescence properties.« less

Photoluminescence and doping mechanism of theranostic Eu3+/Fe3+ dual-doped hydroxyapatite nanoparticles.

PubMed

Chen, Min-Hua; Yoshioka, Tomohiko; Ikoma, Toshiyuki; Hanagata, Nobutaka; Lin, Feng-Huei; Tanaka, Junzo

2014-10-01

Theranostic nanoparticles currently have been regarded as an emerging concept of 'personalized medicine' with diagnostic and therapeutic dual-functions. Eu 3+ doped hydroxyapatite (HAp) has been regarded as a promising fluorescent probe for in vivo imaging applications. Additionally, substitution of Ca 2+ with Fe 3+ in HAp crystal may endow the capability of producing heat upon exposure to a magnetic field. Here we report a preliminary study of doping mechanism and photoluminescence of Eu 3+ and Fe 3+ doped HAp nanoparticles (Eu/Fe:HAp). HAp with varied concentration of Eu 3+ and Fe 3+ doping are presented as Eu(10 mol%):HAp, Eu(7 mol%)-Fe(3 mol%):HAp, Eu(5 mol%)-Fe(5 mol%):HAp, Eu(3 mol%)-Fe(7 mol%):HAp, and Fe(10 mol%):HAp in the study. The results showed that the HAp particles, in nano-size with rod-like morphology, were successfully doped with Eu 3+ and Fe 3+ , and the particles can be well suspended in cell culture medium. Photoluminescence analysis revealed that particles have prominent emissions at 536 nm, 590 nm, 615 nm, 650 nm and 695 nm upon excitation at a wavelength of 397 nm. Moreover, these Eu/Fe:HAp nanoparticles belonged to B-type carbonated HAp, which has been considered an effective biodegradable and biocompatible drug/gene carrier in biological applications.

Photoluminescence and doping mechanism of theranostic Eu3+/Fe3+ dual-doped hydroxyapatite nanoparticles

NASA Astrophysics Data System (ADS)

Chen, Min-Hua; Yoshioka, Tomohiko; Ikoma, Toshiyuki; Hanagata, Nobutaka; Lin, Feng-Huei; Tanaka, Junzo

2014-10-01

Theranostic nanoparticles currently have been regarded as an emerging concept of ‘personalized medicine’ with diagnostic and therapeutic dual-functions. Eu3+ doped hydroxyapatite (HAp) has been regarded as a promising fluorescent probe for in vivo imaging applications. Additionally, substitution of Ca2+ with Fe3+ in HAp crystal may endow the capability of producing heat upon exposure to a magnetic field. Here we report a preliminary study of doping mechanism and photoluminescence of Eu3+ and Fe3+ doped HAp nanoparticles (Eu/Fe:HAp). HAp with varied concentration of Eu3+ and Fe3+ doping are presented as Eu(10 mol%):HAp, Eu(7 mol%)-Fe(3 mol%):HAp, Eu(5 mol%)-Fe(5 mol%):HAp, Eu(3 mol%)-Fe(7 mol%):HAp, and Fe(10 mol%):HAp in the study. The results showed that the HAp particles, in nano-size with rod-like morphology, were successfully doped with Eu3+ and Fe3+, and the particles can be well suspended in cell culture medium. Photoluminescence analysis revealed that particles have prominent emissions at 536 nm, 590 nm, 615 nm, 650 nm and 695 nm upon excitation at a wavelength of 397 nm. Moreover, these Eu/Fe:HAp nanoparticles belonged to B-type carbonated HAp, which has been considered an effective biodegradable and biocompatible drug/gene carrier in biological applications.

Strain-tuning of the magnetocaloric transition temperature in model FeRh films

NASA Astrophysics Data System (ADS)

Loving, M. G.; Barua, R.; Le Graët, C.; Kinane, C. J.; Heiman, D.; Langridge, S.; Marrows, C. H.; Lewis, L. H.

2018-01-01

The chemically ordered B2 phase of equiatomic FeRh is known to absorb or evolve a significant latent heat as it traverses its first-order phase transition in response to thermal, magnetic, and mechanical drivers. This attribute makes FeRh an ideal magnetocaloric material testbed for investigation of relationships between the crystalline lattice and the magnetic spins, which are especially experimentally accessible in thin films. In this work, epitaxial FeRh films of nominal 30 nm and 50 nm thicknesses with out-of-plane c-axis orientation were sputter-deposited at high temperature onto (0 0 1)-MgO or (0 0 0 1)-Al2O3 substrates and capped with Al, Au, Cr, or W after in situ annealing at 973 K to promote CsCl-type chemical order. In this manner a controlled strain state was invoked. Experimental results derived from laboratory and synchrotron x-ray diffraction combined with magnetometry indicate that the antiferromagnetic (AF)—ferromagnetic (FM) magnetostructural phase transformation in these films may be tuned over an ~50° range (373 K-425 K) through variation in the c/a ratio derived from lattice strain delivered by the substrate and the capping layers. These results supply fundamental information that might be used to engineer the magnetocaloric working material in new system designs by introducing targeted values of passive strain to the system.

DOE Office of Scientific and Technical Information (OSTI.GOV)

John, Melanie, E-mail: melanie.john@min.uni-muenchen.de; Heuss-Aßbichler, Soraya; Park, So-Hyun

This study presents a new low temperature synthesis method to obtain pure delafossite (Cu{sup 1+}Fe{sup 3+}O{sub 2}) at a temperature of 70 °C within 24 h. For the first time delafossite is synthesized solely by precipitation and subsequent ageing process and without usage of any additives controlling the oxidation state of copper. The synthesized material, called LT-delafossite, consists of pure Cu{sup 1+}Fe{sup 3+}O{sub 2} exclusive of any side products. Rietveld analysis confirms the presence of both 3R (space group (SG): R-3m) and 2H (SG: P6{sub 3}/mmc) polytypes in LT-delafossite. Electron microscopy images show nanometer-sized hexagonal plates with a diameter <500more » nm and a thickness of <30 nm. Measurements of the magnetic susceptibility from 2 K to 350 K in zero-field show one peak ∼18.5 K, which is attributed to an AFM phase transition. Zero-field-cooled magnetization data between −14 T and +14 T at 2 K revealed an s-shape form around the origin having no remanent magnetization. - Highlights: • New process: low temperature synthesis of pure CuFeO{sub 2} nanoparticles. • Synthesis at 70 °C within 24 h solely by precipitation and ageing. • Nanoparticle characterization by XRD, FTIR, SEM, ICP–OES, TEM and Mößbauer. • Special magnetic properties of nano-sized CuFeO{sub 2} synthesized at low temperatures.« less

Spin-filter specular spin valves

NASA Astrophysics Data System (ADS)

Lu, Z. Q.; Pan, G.; Jibouri, A. A.; Zheng, Yaunkai

2002-01-01

Both a thin free layer and high magnetoresistance (MR) ratio are required in spin valves for high magnetic density recording heads. In traditional spin valve structures, reducing the free layer normally results in a reduction in MR. We report here on a spin-filter specular spin valve with structure Ta 3.5 nm/NiFe 2 nm/IrMn 6 nm/CoFe 1.5 nm/Nol/CoFe 2 nm/Cu 2.2 nm/CoFe tF/Cu tSF/Nol2/Ta 3 nm, which is demonstrated to maintain MR ratio higher than 12% even when the CoFe free layer is reduced to 1 nm. The semiclassical Boltzmann transport equation was used to simulate MR ratio. An optimized MR ratio of ˜14.5% was obtained when tF was about 1.5 nm and tSF about 1.0 nm as a result of the balance between the increase in electron mean free path difference and current shunting through conducting layer. It is found that the Cu enhancing layer not only enhances the MR ratio but also improves soft magnetic properties of CoFe free layer due to the low atomic intermixing observed between Co and Cu. The CoFe free layer of 1-4 nm exhibits a low coercivity of ˜3 Oe even after annealing at 270 °C for 7 h in a field of 1 kOe. Furthermore, the interlayer coupling field Hint between free layer and pinned layer can be controlled by balancing the Rudermann-Kittel-(Kasuya)-Yosida and magnetostatic coupling. Such a thin soft CoFe free layer is particularly attractive for high density read sensor application.

[Influence of C-Fe Lines Interference Correction on Laser-Induced Breakdown Spectroscopy Measurement of Unburned Carbon in Fly Ash].

PubMed

Yao, Shun-chun; Chen, Jian-chao; Lu, Ji-dong; Shen, Yue-liang; Pan, Gang

2015-06-01

In coal-fired plants, Unburned carbon (UC) in fly ash is the major determinant of combustion efficiency in coal-fired boiler. The balance between unburned carbon and NO(x) emissions stresses the need for rapid and accurate methods for the measurement of unburned carbon. Laser-induced breakdown spectroscopy (LIBS) is employed to measure the unburned carbon content in fly ash. In this case, it is found that the C line interference with Fe line at about 248 nm. The interference leads to C could not be quantified independently from Fe. A correction approach for extracting C integrated intensity from the overlapping peak is proposed. The Fe 248.33 nm, Fe 254.60 nm and Fe 272.36 nm lines are used to correct the Fe 247.98 nm line which interference with C 247.86 nm, respectively. Then, the corrected C integrated intensity is compared with the uncorrected C integrated intensity for constructing calibration curves of unburned carbon, and also for the precision and accuracy of repeat measurements. The analysis results show that the regression coefficients of the calibration curves and the precision and accuracy of repeat measurements are improved by correcting C-Fe interference, especially for the fly ash samples with low level unburned carbon content. However, the choice of the Fe line need to avoid a over-correction for C line. Obviously, Fe 254.60 nm is the best

Magnetically recyclable Bi/Fe-based hierarchical nanostructures via self-assembly for environmental decontamination

NASA Astrophysics Data System (ADS)

Hu, Zhong-Ting; Chen, Zhong; Goei, Ronn; Wu, Weiyi; Lim, Teik-Thye

2016-06-01

Pristine bismuth ferrite usually possesses weak magnetic properties (e.g., saturation magnetization Ms < 3 emu g-1) for practical magnetic separation applications. Herein, a superparamagnetic bismuth ferrite with coral-like hierarchical morphology (BFO-M) was fabricated through methanol solvothermal treatment of the as-prepared Bi2Fe4O9 nanoclusters (P-BFO). The BFO-M shows a higher Ms of ~31 emu g-1 compared to that of P-BFO treated in water (BFO-A), in ethanol (BFO-E) and in ethylene glycol (BFO-G). Compared to single-crystalline Bi2Fe4O9 (PS) and Bi2Fe4O9 clusters (NSP), BFO-M shows an excellent organic pollutant removal rate by virtue of its high adsorption capacity and catalytic activity when methyl orange (MO) is used as the model organic pollutant. BFO-M also exhibits good visible light photo-Fenton oxidation rates for pharmaceuticals and pesticides. Even at a low catalyst loading of 0.12 g L-1, the removal rate of organic pollutants (e.g., 5-fluorouracil, isoproturon) can be ~99% in 100 min under visible light irradiation. Besides, BFO-M is also a good adsorbent for different kinds of heavy metal ions (Pb(ii), Cr(iii), Cu(ii), As(v), etc.). For example, its maximal adsorption capacity for Pb(ii) is 214.5 mg g-1. The used BFO-M can be recovered via magnetic separation. The outstanding performances of BFO-M can be ascribed to its coral-like hierarchical morphology which consists of the self-assembly of 1D nanowires (~6 nm in diameter) and 2D ultrathin nanoflakes (~4.5 nm in thickness). A schematic illustration of its morphology formation is proposed.Pristine bismuth ferrite usually possesses weak magnetic properties (e.g., saturation magnetization Ms < 3 emu g-1) for practical magnetic separation applications. Herein, a superparamagnetic bismuth ferrite with coral-like hierarchical morphology (BFO-M) was fabricated through methanol solvothermal treatment of the as-prepared Bi2Fe4O9 nanoclusters (P-BFO). The BFO-M shows a higher Ms of ~31 emu g-1 compared to that of P-BFO treated in water (BFO-A), in ethanol (BFO-E) and in ethylene glycol (BFO-G). Compared to single-crystalline Bi2Fe4O9 (PS) and Bi2Fe4O9 clusters (NSP), BFO-M shows an excellent organic pollutant removal rate by virtue of its high adsorption capacity and catalytic activity when methyl orange (MO) is used as the model organic pollutant. BFO-M also exhibits good visible light photo-Fenton oxidation rates for pharmaceuticals and pesticides. Even at a low catalyst loading of 0.12 g L-1, the removal rate of organic pollutants (e.g., 5-fluorouracil, isoproturon) can be ~99% in 100 min under visible light irradiation. Besides, BFO-M is also a good adsorbent for different kinds of heavy metal ions (Pb(ii), Cr(iii), Cu(ii), As(v), etc.). For example, its maximal adsorption capacity for Pb(ii) is 214.5 mg g-1. The used BFO-M can be recovered via magnetic separation. The outstanding performances of BFO-M can be ascribed to its coral-like hierarchical morphology which consists of the self-assembly of 1D nanowires (~6 nm in diameter) and 2D ultrathin nanoflakes (~4.5 nm in thickness). A schematic illustration of its morphology formation is proposed. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr03677e

Magnetic and superconducting phase diagram of Nb/Gd/Nb trilayers

NASA Astrophysics Data System (ADS)

Khaydukov, Yu. N.; Vasenko, A. S.; Kravtsov, E. A.; Progliado, V. V.; Zhaketov, V. D.; Csik, A.; Nikitenko, Yu. V.; Petrenko, A. V.; Keller, T.; Golubov, A. A.; Kupriyanov, M. Yu.; Ustinov, V. V.; Aksenov, V. L.; Keimer, B.

2018-04-01

We report on a study of the structural, magnetic, and superconducting properties of Nb (25 nm ) /Gd (df) /Nb (25 nm ) hybrid structures of a superconductor/ ferromagnet (S/F) type. The structural characterization of the samples, including careful determination of the layer thickness, was performed using neutron and x-ray scattering with the aid of depth-sensitive mass spectrometry. The magnetization of the samples was determined by superconducting quantum interference device magnetometry and polarized neutron reflectometry, and the presence of magnetic ordering for all samples down to the thinnest Gd(0.8 nm) layer was shown. The analysis of the neutron spin asymmetry allowed us to prove the absence of magnetically dead layers in junctions with Gd interlayer thickness larger than one monolayer. The measured dependence of the superconducting transition temperature Tc(df) has a damped oscillatory behavior with well-defined positions of the minimum at df=3 nm and the following maximum at df=4 nm, in qualitative agreement with prior work [J. S. Jiang et al., Phys. Rev. B 54, 6119 (1996), 10.1103/PhysRevB.54.6119]. We use a theoretical approach based on the Usadel equations to analyze the experimental Tc(df) dependence. The analysis shows that the observed minimum at df=3 nm can be described by the so-called zero to π phase transitions of highly transparent S/F interfaces with a superconducting correlation length ξf≈4 nm in Gd. This penetration length is several times higher than for strong ferromagnets like Fe, Co, and Ni, thus simplifying the preparation of S/F structures with df˜ξf which are of topical interest in superconducting spintronics.

Spin and orbital magnetic moments of Fe and Co in Co/Fe and Fe/Co multilayers on Si from L2,3 edge X-ray Magnetic Circular Dichroism Spectroscopy

NASA Astrophysics Data System (ADS)

Vemuru, Krishnamurthy; Rosenberg, Richard; Mankey, Gary

Nanostructured FeCo thin films are interesting for magnetic recording applications due to their high saturation magnetization, high Curie temperature and low magnetocrystalline anisotropy. It is desirable to know how the magnetism is modified by the nanostructrure. We report Fe L 2 , 3 edge and Co L2 , 3 edge x-ray magnetic circular dichroism (XMCD) investigations of element specific spin and orbital magnetism of Fe and Co in two multilayer samples: (S1) Si/SiO2/[Co 0.8 nm/Fe 1.6 nm]x32/W (2nm) and (S2) Si/SiO2/[Co 1.6 nm/Fe 0.8 nm]x32/W (2nm) thin films at room temperature. Sum rule analysis of XMCD at Fe L2 , 3 edge in sample S1 shows that the orbital moment of Fe is strongly enhanced and the spin moment is strongly reduced as compared to the values found in bulk Fe. Details of sum rule analysis will be presented to compare and contrast spin magnetic moments and orbital magnetic moments of Fe and Co in the two multilayer samples. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

Novel nano materials for high performance logic and memory devices

NASA Astrophysics Data System (ADS)

Das, Saptarshi

After decades of relentless progress, the silicon CMOS industry is approaching a stall in device performance for both logic and memory devices due to fundamental scaling limitations. In order to reinforce the accelerating pace, novel materials with unique properties are being proposed on an urgent basis. This list includes one dimensional nanotubes, quasi one dimensional nanowires, two dimensional atomistically thin layered materials like graphene, hexagonal boron nitride and the more recently the rich family of transition metal di-chalcogenides comprising of MoS2, WSe2, WS2 and many more for logic applications and organic and inorganic ferroelectrics, phase change materials and magnetic materials for memory applications. Only time will tell who will win, but exploring these novel materials allow us to revisit the fundamentals and strengthen our understanding which will ultimately be beneficial for high performance device design. While there has been growing interest in two-dimensional (2D) crystals other than graphene, evaluating their potential usefulness for electronic applications is still in its infancies due to the lack of a complete picture of their performance potential. The fact that the 2-D layered semiconducting di-chalcogenides need to be connected to the "outside" world in order to capitalize on their ultimate potential immediately emphasizes the importance of a thorough understanding of the contacts. This thesis demonstrate that through a proper understanding and design of source/drain contacts and the right choice of number of MoS2 layers the excellent intrinsic properties of this 2D material can be harvested. A comprehensive experimental study on the dependence of carrier mobility on the layer thickness of back gated multilayer MoS 2 field effect transistors is also provided. A resistor network model that comprises of Thomas-Fermi charge screening and interlayer coupling is used to explain the non-monotonic trend in the extracted field effect mobility with the layer thickness. The non-monotonic trend suggests that in order to harvest the maximum potential of MoS2 for high performance device applications, a layer thickness in the range of 6-12 nm would be ideal. Finally using scandium contacts on 10nm thick exfoliated MoS2 flakes that are covered by a 15nm ALD grown Al2O3 film, record high mobility of 700cm2/Vs is achieved at room-temperature which is extremely encouraging for the design of high performance logic devices. The destructive nature of the readout process in Ferroelectric Random Access Memories (FeRAMs) is one of the major limiting factors for their wide scale commercialization. Utilizing Ferroelectric Field-Effect Transistor RAM (FeTRAM) instead solves the destructive read out problem, but at the expense of introducing crystalline ferroelectrics that are hard to integrate into CMOS. In order to address these challenges a novel, fully functional, CMOS compatible, One-Transistor-One-Transistor (1T1T) memory cell architecture using an organic ferroelectric -- PVDF-TrFE -- as the memory storage unit (gate oxide) and a silicon nanowire as the memory read out unit (channel material) is proposed and experimentally demonstrated. While evaluating the scaling potential of the above mentioned organic FeTRAM, it is found that the switching time and switching voltage of this organic copolymer PVDF-TrFE exhibits an unexpected scaling behavior as a function of the lateral device dimensions. The phenomenological theory, that explains this abnormal scaling trend, involves in-plane interchain and intrachain interaction of the copolymer - resulting in a power-law dependence of the switching field on the device area (ESW alpha ACH0.1) that is ultimately responsible for the decrease in the switching time and switching voltage. These findings are encouraging since they indicate that scaling the switching voltage and switching time without aggressively scaling the copolymer thickness occurs naturally while scaling the device area -- in this way ultimately improving the packing density and leading towards high performance memory devices.

The Chemical Composition of the Galactic Bulge and Implications for its Evolution

NASA Astrophysics Data System (ADS)

McWilliam, Andrew

2016-08-01

At a bulge latitude of b = -4°, the average [Fe/H] and [Mg/H] values are +0.06 and +0.17 dex, roughly 0.2 and 0.7 dex higher than the local thin and thick disk values, respectively, suggesting a large bulge effective yield, perhaps due to efficient retention of supernova ejecta. The bulge vertical [Fe/H] gradient, at ∼0.5 dex/kpc, appears to be due to a changing mixture of sub-populations (near +0.3 dex and -0.3 dex and one possibly near -0.7 dex) with latitude. At solar [Fe/H], the bulge [Al/Fe] and [α/Fe] ratios are ∼ +0.15 dex. Below [Fe/H] ∼ -0.5 dex, the bulge and local thick disk compositions are very similar; but the measured [Mg/Fe], [/Fe], [La/Eu] and dramatic [Cu/Fe] ratios suggest higher SFR in the bulge. However, these composition differences with the thick disk could be due to measurement errors and non-LTE effects. Unusual zig-zag trends of [Cu/Fe] and [Na/Fe] suggest metallicity-dependent nucleosynthesis by core-collapse supernovae in the Type Ia supernova time-delay scenario. The bulge sub-population compositions resemble the local thin and thick disks, but at higher [Fe/H], suggesting a radial [Fe/H] gradient of -0.04 to -0.05 dex/kpc for both the thin and thick disks. If the bulge formed through accretion of inner thin and thick disk stars, it appears that these stars retained vertical scale heights characteristic of their kinematic origin, resulting in the vertical [Fe/H] gradient and [α/Fe] trends seen today.

78 FR 35954 - Notice of Availability of the Final Environmental Impact Statement for the SunZia Southwest...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-06-14

... Manager, BLM New Mexico State Office, 301 Dinosaur Trail, Santa Fe, NM 87508-1560. Interested persons may...; address BLM, New Mexico State Office, 301 Dinosaur Trail, Santa Fe, NM 87508-1560; email [email protected] State Office, 301 Dinosaur Trail, Santa Fe, NM 87508-1560 New Mexico State Land Office, 310 Old Santa Fe...

Tuning Superconductivity in FeSe Thin Films via Magnesium Doping.

PubMed

Qiu, Wenbin; Ma, Zongqing; Liu, Yongchang; Shahriar Al Hossain, Mohammed; Wang, Xiaolin; Cai, Chuanbing; Dou, Shi Xue

2016-03-01

In contrast to its bulk crystal, the FeSe thin film or layer exhibits better superconductivity performance, which recently attracted much interest in its fundamental research as well as in potential applications around the world. In the present work, tuning superconductivity in FeSe thin films was achieved by magnesium-doping technique. Tc is significantly enhanced from 10.7 K in pure FeSe films to 13.4 K in optimized Mg-doped ones, which is approximately 1.5 times higher than that of bulk crystals. This is the first time achieving the enhancement of superconducting transition temperature in FeSe thin films with practical thickness (120 nm) via a simple Mg-doping process. Moreover, these Mg-doped FeSe films are quite stable in atmosphere with Hc2 up to 32.7 T and Tc(zero) up to 12 K, respectively, implying their outstanding potential for practical applications in high magnetic fields. It was found that Mg enters the matrix of FeSe lattice, and does not react with FeSe forming any other secondary phase. Actually, Mg first occupies Fe-vacancies, and then substitutes for some Fe in the FeSe crystal lattices when Fe-vacancies are fully filled. Simultaneously, external Mg-doping introduces sufficient electron doping and induces the variation of electron carrier concentration according to Hall coefficient measurements. This is responsible for the evolution of superconducting performance in FeSe thin films. Our results provide a new strategy to improve the superconductivity of 11 type Fe-based superconductors and will help us to understand the intrinsic mechanism of this unconventional superconducting system.

Large ferroelectric polarization of TiN/Hf0.5Zr0.5O2/TiN capacitors due to stress-induced crystallization at low thermal budget

NASA Astrophysics Data System (ADS)

Kim, Si Joon; Narayan, Dushyant; Lee, Jae-Gil; Mohan, Jaidah; Lee, Joy S.; Lee, Jaebeom; Kim, Harrison S.; Byun, Young-Chul; Lucero, Antonio T.; Young, Chadwin D.; Summerfelt, Scott R.; San, Tamer; Colombo, Luigi; Kim, Jiyoung

2017-12-01

We report on atomic layer deposited Hf0.5Zr0.5O2 (HZO)-based capacitors which exhibit excellent ferroelectric (FE) characteristics featuring a large switching polarization (45 μC/cm2) and a low FE saturation voltage (˜1.5 V) as extracted from pulse write/read measurements. The large FE polarization in HZO is achieved by the formation of a non-centrosymmetric orthorhombic phase, which is enabled by the TiN top electrode (TE) having a thickness of at least 90 nm. The TiN films are deposited at room temperature and annealed at 400 °C in an inert environment for at least 1 min in a rapid thermal annealing system. The room-temperature deposited TiN TE acts as a tensile stressor on the HZO film during the annealing process. The stress-inducing TiN TE is shown to inhibit the formation of the monoclinic phase during HZO crystallization, forming an orthorhombic phase that generates a large FE polarization, even at low process temperatures.

Orientation of FePt nanoparticles on top of a-SiO2/Si(001), MgO(001) and sapphire(0001): effect of thermal treatments and influence of substrate and particle size.

PubMed

Schilling, Martin; Ziemann, Paul; Zhang, Zaoli; Biskupek, Johannes; Kaiser, Ute; Wiedwald, Ulf

2016-01-01

Texture formation and epitaxy of thin metal films and oriented growth of nanoparticles (NPs) on single crystal supports are of general interest for improved physical and chemical properties especially of anisotropic materials. In the case of FePt, the main focus lies on its highly anisotropic magnetic behavior and its catalytic activity, both due to the chemically ordered face-centered tetragonal (fct) L10 phase. If the c-axis of the tetragonal system can be aligned normal to the substrate plane, perpendicular magnetic recording could be achieved. Here, we study the orientation of FePt NPs and films on a-SiO2/Si(001), i.e., Si(001) with an amorphous (a-) native oxide layer on top, on MgO(001), and on sapphire(0001) substrates. For the NPs of an approximately equiatomic composition, two different sizes were chosen: "small" NPs with diameters in the range of 2-3 nm and "large" ones in the range of 5-8 nm. The 3 nm thick FePt films, deposited by pulsed laser deposition (PLD), served as reference samples. The structural properties were probed in situ, particularly texture formation and epitaxy of the specimens by reflection high-energy electron diffraction (RHEED) and, in case of 3 nm nanoparticles, additionally by high-resolution transmission electron microscopy (HRTEM) after different annealing steps between 200 and 650 °C. The L10 phase is obtained at annealing temperatures above 550 °C for films and 600 °C for nanoparticles in accordance with previous reports. On the amorphous surface of a-SiO2/Si substrates we find no preferential orientation neither for FePt films nor nanoparticles even after annealing at 630 °C. On sapphire(0001) supports, however, FePt nanoparticles exhibit a clearly preferred (111) orientation even in the as-prepared state, which can be slightly improved by annealing at 600-650 °C. This improvement depends on the size of NPs: Only the smaller NPs approach a fully developed (111) orientation. On top of MgO(001) the effect of annealing on particle orientation was found to be strongest. From a random orientation in the as-prepared state observed for both, small and large FePt NPs, annealing at 650 °C for 30 min reorients the small particles towards a cube-on-cube epitaxial orientation with a minor fraction of (111)-oriented particles. In contrast, large FePt NPs keep their as-prepared random orientation even after doubling the annealing period at 650 °C to 60 min.

Orientation of FePt nanoparticles on top of a-SiO2/Si(001), MgO(001) and sapphire(0001): effect of thermal treatments and influence of substrate and particle size

PubMed Central

Schilling, Martin; Ziemann, Paul; Zhang, Zaoli; Biskupek, Johannes; Kaiser, Ute

2016-01-01

Summary Texture formation and epitaxy of thin metal films and oriented growth of nanoparticles (NPs) on single crystal supports are of general interest for improved physical and chemical properties especially of anisotropic materials. In the case of FePt, the main focus lies on its highly anisotropic magnetic behavior and its catalytic activity, both due to the chemically ordered face-centered tetragonal (fct) L10 phase. If the c-axis of the tetragonal system can be aligned normal to the substrate plane, perpendicular magnetic recording could be achieved. Here, we study the orientation of FePt NPs and films on a-SiO2/Si(001), i.e., Si(001) with an amorphous (a-) native oxide layer on top, on MgO(001), and on sapphire(0001) substrates. For the NPs of an approximately equiatomic composition, two different sizes were chosen: “small” NPs with diameters in the range of 2–3 nm and “large” ones in the range of 5–8 nm. The 3 nm thick FePt films, deposited by pulsed laser deposition (PLD), served as reference samples. The structural properties were probed in situ, particularly texture formation and epitaxy of the specimens by reflection high-energy electron diffraction (RHEED) and, in case of 3 nm nanoparticles, additionally by high-resolution transmission electron microscopy (HRTEM) after different annealing steps between 200 and 650 °C. The L10 phase is obtained at annealing temperatures above 550 °C for films and 600 °C for nanoparticles in accordance with previous reports. On the amorphous surface of a-SiO2/Si substrates we find no preferential orientation neither for FePt films nor nanoparticles even after annealing at 630 °C. On sapphire(0001) supports, however, FePt nanoparticles exhibit a clearly preferred (111) orientation even in the as-prepared state, which can be slightly improved by annealing at 600–650 °C. This improvement depends on the size of NPs: Only the smaller NPs approach a fully developed (111) orientation. On top of MgO(001) the effect of annealing on particle orientation was found to be strongest. From a random orientation in the as-prepared state observed for both, small and large FePt NPs, annealing at 650 °C for 30 min reorients the small particles towards a cube-on-cube epitaxial orientation with a minor fraction of (111)-oriented particles. In contrast, large FePt NPs keep their as-prepared random orientation even after doubling the annealing period at 650 °C to 60 min. PMID:27335749

Exchange-coupled Fe3O4/CoFe2O4 nanoparticles for advanced magnetic hyperthermia

NASA Astrophysics Data System (ADS)

Glassell, M.; Robles, J.; Das, R.; Phan, M. H.; Srikanth, H.

Iron oxide nanoparticles especially Fe3O4, γ-Fe2O3 have been extensively studied for magnetic hyperthermia because of their tunable magnetic properties and stable suspension in superparamagnetic regime. However, their relatively low heating capacity hindered practical application. Recently, a large improvement in heating efficiency has been reported in exchange-coupled nanoparticles with exchange coupling between soft and hard magnetic phases. Here, we systematically studied the effect of core and shell size on the heating efficiency of the Fe3O4/CoFe2O4 core/shell nanoparticles. The nanoparticles were synthesized using thermal decomposition of organometallic precursors. Transmission electron microscopy (TEM) showed formation of spherical shaped Fe3O4 and Fe3O-/CoFe2O4 nanoparticles. Magnetic measurements showed high magnetization (≅70 emu/g) and superparamagnetic behavior for the nanoparticles at room temperature. Magnetic hyperthermia results showed a large increase in specific absorption rate (SAR) for 8nm Fe3O4/CoFe2O4 compared to Fe3O4 nanoparticles of the same size. The heating efficiency of the Fe3O4/CoFe2O4 with 1 nm CoFe2O4 (shell) increased from 207 to 220 W/g (for 800 Oe) with increase in core size from 6 to 8 nm. The heating efficiency of the Fe3O4/CoFe2O4 with 2 nm CoFe2O4 (shell) and core size of 8 nm increased from 220 to 460 W/g (for 800 Oe). These exchange-coupled Fe3O4/CoFe2O4 core/shell nanoparticles can be a good candidate for advanced hyperthermia application.

High-performance field emission device utilizing vertically aligned carbon nanotubes-based pillar architectures

NASA Astrophysics Data System (ADS)

Gupta, Bipin Kumar; Kedawat, Garima; Gangwar, Amit Kumar; Nagpal, Kanika; Kashyap, Pradeep Kumar; Srivastava, Shubhda; Singh, Satbir; Kumar, Pawan; Suryawanshi, Sachin R.; Seo, Deok Min; Tripathi, Prashant; More, Mahendra A.; Srivastava, O. N.; Hahm, Myung Gwan; Late, Dattatray J.

2018-01-01

The vertical aligned carbon nanotubes (CNTs)-based pillar architectures were created on laminated silicon oxide/silicon (SiO2/Si) wafer substrate at 775 °C by using water-assisted chemical vapor deposition under low pressure process condition. The lamination was carried out by aluminum (Al, 10.0 nm thickness) as a barrier layer and iron (Fe, 1.5 nm thickness) as a catalyst precursor layer sequentially on a silicon wafer substrate. Scanning electron microscope (SEM) images show that synthesized CNTs are vertically aligned and uniformly distributed with a high density. The CNTs have approximately 2-30 walls with an inner diameter of 3-8 nm. Raman spectrum analysis shows G-band at 1580 cm-1 and D-band at 1340 cm-1. The G-band is higher than D-band, which indicates that CNTs are highly graphitized. The field emission analysis of the CNTs revealed high field emission current density (4mA/cm2 at 1.2V/μm), low turn-on field (0.6 V/μm) and field enhancement factor (6917) with better stability and longer lifetime. Emitter morphology resulting in improved promising field emission performances, which is a crucial factor for the fabrication of pillared shaped vertical aligned CNTs bundles as practical electron sources.

Optimization of one-dimensional photonic crystals with double layer magneto-active defect

NASA Astrophysics Data System (ADS)

Mikhailova, T. V.; Berzhansky, V. N.; Shaposhnikov, A. N.; Karavainikov, A. V.; Prokopov, A. R.; Kharchenko, Yu. M.; Lukienko, I. M.; Miloslavskaya, O. V.; Kharchenko, M. F.

2018-04-01

Success of practical implementation of one-dimensional photonic crystals with magneto-active layers is evaluated in high values of magneto-optical (MO) quality factor Q and figure of merit F. The article relates to optimization of one-dimensional photonic crystals with double layer magneto-active (MA) defect of composition Bi1.0Y0.5Gd1.5Fe4.2Al0.8O12/Bi2.8Y0.2Fe5O12 located between the nongarnet dielectric Bragg mirrors. The structure design was performed by changing the number of layer pairs in Bragg mirrors m and the optical thickness of MA defect lM to achieve high values of MO characteristics. Theoretical predictions were confirmed by experimental investigation of eight synthesized configurations with m = 4 and m = 7. We have demonstrated the maximum Q = 15.1 deg and F = 7.5% at 624 nm for structure with m = 4 and lM = (2.5·λ0/2), where λ0 = 690 nm is the photonic band gap center. Configurations with m = 3 can also provide their effectiveness in realization. Maximum MO activity was achieved for configurations with m = 7. The structures with lM = (0.8·λ0/2) and lM = (2.5·λ0/2) showed respectively the specific Faraday rotation -113 deg/μm (that exceeds in 62 times the Faraday rotation of MA double layer film) at 654 nm and absolute Faraday rotation -20.6 deg at 626 nm.

Aggregation state and magnetic properties of magnetite nanoparticles controlled by an optimized silica coating

NASA Astrophysics Data System (ADS)

Pérez, Nicolás; Moya, C.; Tartaj, P.; Labarta, A.; Batlle, X.

2017-01-01

The control of magnetic interactions is becoming essential to expand/improve the applicability of magnetic nanoparticles (NPs). Here, we show that an optimized microemulsion method can be used to obtain homogenous silica coatings on even single magnetic nuclei of highly crystalline Fe3-xO4 NPs (7 and 16 nm) derived from a high-temperature method. We show that the thickness of this coating is controlled almost at will allowing much higher average separation among particles as compared to the oleic acid coating present on pristine NPs. Magnetic susceptibility studies show that the thickness of the silica coating allows the control of magnetic interactions. Specifically, as this effect is better displayed for the smallest particles, we show that dipole-dipole interparticle interactions can be tuned progressively for the 7 nm NPs, from almost non-interacting to strongly interacting particles at room temperature. The quantitative analysis of the magnetic properties unambiguously suggests that dipolar interactions significantly broaden the effective distribution of energy barriers by spreading the distribution of activation magnetic volumes.

Tribological properties and surface structures of ion implanted 9Cr18Mo stainless steels

NASA Astrophysics Data System (ADS)

Fengbin, Liu; Guohao, Fu; Yan, Cui; Qiguo, Sun; Min, Qu; Yi, Sun

2013-07-01

The polished quenched-and-tempered 9Cr18Mo steels were implanted with N ions and Ti ions respectively at a fluence of 2 × 1017 ions/cm2. The mechanical properties of the samples were investigated by using nanoindenter and tribometer. The results showed that the ion implantations would improve the nanohardness and tribological property, especially N ion implantation. The surface analysis of the implanted samples was carried out by using XRD, XPS and AES. It indicated that the surface exhibits graded layers after ion implantation. For N ion implantation, the surface about 20 nm thickness is mainly composed of supersaturated interstitial N solid solution, oxynitrides, CrxCy phase and metal nitrides. In the subsurface region, the metal nitrides dominate and the other phases disappear. For Ti ion implantation, the surface of about 20 nm thickness is mainly composed of titanium oxides and carbon amorphous phase, the interstitial solid solution of Ti in Fe is abundant in the subsurface region. The surface components and structures have significant contributions to the improved mechanical properties.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mufti, Nandang, E-mail: nandangmufti@gmail.com; Atma, T., E-mail: nandangmufti@gmail.com; Fuad, A., E-mail: nandangmufti@gmail.com

The aim of this research is to synthesize nanoparticles of black pigment of Magnetite (Fe{sub 3}O{sub 4}), red pigment of hematite (α-Fe{sub 2}O{sub 3}), and yellow pigment of ghoetite (α-FeOOH) from the iron sand. The black pigment of Fe{sub 3}O{sub 4} and the yellow pigment α-FeOOH nanoparticles were synthesized by coprecipitation method with variation of pH. Whereas, the red pigment Fe{sub 2}O{sub 3} was synthesized by sintering Fe{sub 3}O{sub 4} nanoparticles at temperature between 400 °C and 700 7°C for 1 hour. All the pigments has been characterized using X-ray diffraction and SEM. The XRD results shown that the particlemore » size of the black pigmen Fe{sub 3}O{sub 4}, red pigment Fe{sub 3}O{sub 4} and yellow pigment α-FeOOH are around 12, 32, and 30 nm respectively. The particle size of Fe{sub 2}O{sub 3} nanoparticles increase by increasing sintering temperature from 32 nm at 400 °C to 39 nm at 700 °C. For yellow pigment of α-FeOOH, the particle size increase by increasing pH from 30,54 nm at pH 4 to 48,60 nm at pH 7. The SEM results shown that the morphologies of black, yellow and red pigments are aglomarated.« less

Atomic mixing induced by swift heavy ion irradiation of Fe/Zr multilayers

NASA Astrophysics Data System (ADS)

Jaouen, C.; Michel, A.; Pacaud, J.; Dufour, C.; Bauer, Ph.; Gervais, B.

1999-01-01

The mechanism of ion induced mixing and phase change was studied for Fe/Zr multilayers, and specifically for the case of swift heavy ions giving rise to a very large electronic excitation of the target. The multilayers had a modulation of 7.6 nm and an overall composition Fe 69Zr 31. The Zr layers were amorphous whereas the Fe ones were crystalline (bcc) with a very strong (1 1 0) texture in the growth direction. The phase transformation and the composition changes were analysed using the structural and magnetic properties of the Fe component by means of a detailed analysis of the X-ray diffraction profiles and with the aid of backscattering Mössbauer spectroscopy. A complete mixing was observed at a fluence of 10 13 U/cm 2. Both phenomena, the dose dependence of the ion beam mixed amorphous non-magnetic phase and the quantitative evolution of the crystalline iron layer thickness, suggest that mixing occurs in a two-stage process. At an initial stage, an anisotropic diffusion of iron atoms in the amorphous zirconium layers takes place along the interface, while subsequent ion bombardment leads to a generalised transformation through the whole of the Fe layer. Finally, the implications of these observations are discussed in comparison to the plastic deformation phenomena reported for amorphous alloys.

Magnetic field-induced modification of selection rules for Rb D 2 line monitored by selective reflection from a vapor nanocell

NASA Astrophysics Data System (ADS)

Klinger, Emmanuel; Sargsyan, Armen; Tonoyan, Ara; Hakhumyan, Grant; Papoyan, Aram; Leroy, Claude; Sarkisyan, David

2017-08-01

Magnetic field-induced giant modification of the probabilities of five transitions of 5S1 / 2,Fg = 2 → 5P3 / 2,Fe = 4 of 85Rb and three transitions of 5S1 / 2,Fg = 1 → 5P3 / 2,Fe = 3 of 87Rb forbidden by selection rules for zero magnetic field has been observed experimentally and described theoretically for the first time. For the case of excitation with circularly-polarized (σ+) laser radiation, the probability of Fg = 2,mF = - 2 → Fe = 4,mF = - 1 transition becomes the largest among the seventeen transitions of 85Rb Fg = 2 → Fe = 1,2,3,4 group, and the probability of Fg = 1, mF = - 1 → Fe = 3,mF = 0 transition becomes the largest among the nine transitions of 87Rb Fg = 1 → Fe = 0,1,2,3 group, in a wide range of magnetic field 200-1000 G. Complete frequency separation of individual Zeeman components was obtained by implementation of derivative selective reflection technique with a 300 nm-thick nanocell filled with Rb, allowing formation of narrow optical resonances. Possible applications are addressed. The theoretical model is well consistent with the experimental results.

Characterization of Fe-TiO2 films synthesized by sol-gel method for application in energy conversion devices

NASA Astrophysics Data System (ADS)

da Silva Santos, Reginaldo; de Oliveira, Haroldo G.; Longo, Claudia

2009-08-01

Fe-TiO2 particles were synthesized by sol-gel process from hydrolysis of titanium tetra-isopropoxide with nitric acid and ferric nitrate aqueous solutions (relative Fe:Ti molar ratio ranging from 1 to 6 at %) followed by hydrothermal treatment. Thin films were deposited onto conducting glass electrodes from a suspension with polyethylene glycol and heating at 450 °C for 30 min, which resulted in 1.5 μm thick transparent porous films. Crystalline samples, 93 % anatase and 7 % brookite, were obtained. Increasing the iron amount, the crystallite size estimated from XRD patterns ranged from 18 to 11 nm and the color varied from slightly yellow to brown. The optical properties have also changed; the absorption edge shifted towards longer wavelengths, with band gap energy decreasing from 3.0 to 2.7 eV. The films exhibited photocatalytic activity for phenol degradation that indicates promising applications in solar energy conversion.

Sub-nanosecond time-resolved near-field scanning magneto-optical microscope.

PubMed

Rudge, J; Xu, H; Kolthammer, J; Hong, Y K; Choi, B C

2015-02-01

We report on the development of a new magnetic microscope, time-resolved near-field scanning magneto-optical microscope, which combines a near-field scanning optical microscope and magneto-optical contrast. By taking advantage of the high temporal resolution of time-resolved Kerr microscope and the sub-wavelength spatial resolution of a near-field microscope, we achieved a temporal resolution of ∼50 ps and a spatial resolution of <100 nm. In order to demonstrate the spatiotemporal magnetic imaging capability of this microscope, the magnetic field pulse induced gyrotropic vortex dynamics occurring in 1 μm diameter, 20 nm thick CoFeB circular disks has been investigated. The microscope provides sub-wavelength resolution magnetic images of the gyrotropic motion of the vortex core at a resonance frequency of ∼240 MHz.

Spectroscopic and magnetic studies of highly dispersible superparamagnetic silica coated magnetite nanoparticles

NASA Astrophysics Data System (ADS)

Tadyszak, Krzysztof; Kertmen, Ahmet; Coy, Emerson; Andruszkiewicz, Ryszard; Milewski, Sławomir; Kardava, Irakli; Scheibe, Błażej; Jurga, Stefan; Chybczyńska, Katarzyna

2017-07-01

Superparamagnetic behavior in aqueously well dispersible magnetite core-shell Fe3O4@SiO2 nanoparticles is presented. The magnetic properties of core-shell nanoparticles were measured with use of the DC, AC magnetometry and EPR spectroscopy. Particles where characterized by HR-TEM and Raman spectroscopy, showing a crystalline magnetic core of 11.5 ± 0.12 nm and an amorphous silica shell of 22 ± 1.5 nm in thickness. The DC, AC magnetic measurements confirmed the superparamagnetic nature of nanoparticles, additionally the EPR studies performed at much higher frequency than DC, AC magnetometry (9 GHz) have confirmed the paramagnetic nature of the nanoparticles. Our results show the excellent magnetic behavior of the particles with a clear magnetite structure, which are desirable properties for environmental remediation and biomedical applications.

A proposed new type of arsenian pyrite: Composition, nanostructure and geological significance

NASA Astrophysics Data System (ADS)

Deditius, Artur P.; Utsunomiya, Satoshi; Renock, Devon; Ewing, Rodney C.; Ramana, Chintalapalle V.; Becker, Udo; Kesler, Stephen E.

2008-06-01

This report describes a new form of arsenian pyrite, called As3+-pyrite, in which As substitutes for Fe [(Fe,As)S2], in contrast to the more common form of arsenian pyrite, As1--pyrite, in which As1- substitutes for S [Fe(As,S)2]. As3+-pyrite has been observed as colloformic overgrowths on As-free pyrite in a hydrothermal gold deposit at Yanacocha, Peru. XPS analyses of the As3+-pyrite confirm that As is present largely as As3+. EMPA analyses show that As3+-pyrite incorporates up to 3.05 at % of As and 0.53 at. %, 0.1 at. %, 0.27 at. %, 0.22 at. %, 0.08 at. % and 0.04 at. % of Pb, Au, Cu, Zn, Ni, and Co, respectively. Incorporation of As3+ in the pyrite could be written like: As+yAu+1-y(□)⇔2Fe; where Au+ and vacancy (□) help to maintain the excess charge. HRTEM observations reveal a sharp boundary between As-free pyrite and the first overgrowth of As3+-pyrite (20-40 nm thick) and co-linear lattice fringes indicating epitaxial growth of As3+-pyrite on As-free pyrite. Overgrowths of As3+-pyrite onto As-free pyrite can be divided into three groups on the basis of crystal size, 8-20 nm, 100-300 nm and 400-900 nm, and the smaller the crystal size the higher the concentration of toxic arsenic and trace metals. The Yanacocha deposit, in which As3+-pyrite was found, formed under relatively oxidizing conditions in which the dominant form of dissolved As in the stability field of pyrite is As3+; in contrast, reducing conditions are typical of most environments that host As1--pyrite. As3+-pyrite will likely be found in other oxidizing hydrothermal and diagenetic environments, including high-sulfidation epithermal deposits and shallow groundwater systems, where probably kinetically controlled formation of nanoscale crystals such as observed here would be a major control on incorporation and release of As3+ and toxic heavy metals in oxidizing natural systems.

Origin of Lamellar Magnetism (Invited)

NASA Astrophysics Data System (ADS)

McEnroe, S. A.; Robinson, P.; Fabian, K.; Harrison, R. J.

2010-12-01

The theory of lamellar magnetism arose through search for the origin of the strong and extremely stable remanent magnetization (MDF>100 mT) recorded in igneous and metamorphic rocks containing ilmenite with exsolution lamellae of hematite, or hematite with exsolution lamellae of ilmenite. Properties of rocks producing major remanent magnetic anomalies could not be explained by PM ilmenite or CAF hematite alone. Monte Carlo modeling of chemical and magnetic interactions in such intergrowths at high temperature indicated the presence of "contact layers" one cation layer thick at (001) interfaces of the two phases. Contact layers, with chemical composition different from layers in the adjacent phases, provide partial relief of ionic charge imbalance at interfaces, and can be common, not only in magnetic minerals. In rhombohedral Fe-Ti oxides, magnetic moments of 2 Fe2+Fe3+ contact layers (2 x 4.5µB) on both sides of a lamella, are balanced by the unbalanced magnetic moment of 1 Fe3+ hematite layer (1 x 5µB), to produce a net uncompensated ferrimagnetic "lamellar moment" of 4µB. Bulk lamellar moment is not proportional to the amount of magnetic oxide, but to the quantity of magnetically "in-phase" lamellar interfaces, with greater abundance and smaller thickness of lamellae, extending down to 1-2 nm. The proportion of "magnetically in-phase" lamellae relates to the orientation of (001) interfaces to the magnetizing field during exsolution, hence highest in samples with a strong lattice-preferred orientation of (001) parallel to the field during exsolution. The nature of contact layers, ~0.23 nm thick, with Fe2+Fe3+ charge ordering postulated by the Monte Carlo models, was confirmed by bond-valence and DFT calculations, and, their presence confirmed by Mössbauer measurements. Hysteresis experiments on hematite with nanoscale ilmenite at temperatures below 57 K, where ilmenite becomes AF, demonstrate magnetic exchange bias produced by strong coupling across phase interfaces. Interface coupling, with nominal magnetic moments perpendicular and parallel to (001), is facilitated by magnetic moments in hematite near interfaces that are a few degrees out of the (001) plane, proved by neutron diffraction experiments. When a ~b.y.-old sample, with a highly stable NRM, is ZF cooled below 57 K, it shows bimodal exchange bias, indicating the presence of two lamellar populations that are magnetically "out-of-phase", and incidentally proving the existence of lamellar magnetism. Lamellar magnetism may enhance the strength and stability of remanence in samples with magnetite or maghemite lamellae in pure hematite, or magnetite lamellae in ilmenite, where coarse magnetite or maghemite alone would be multi-domain. Here the "contact layers" should be a complex hybrid of 2/3-filled rhombohedral layers parallel to (001) and 3/4-filled cubic octahedral layers parallel to (111), with a common octahedral orientation confirmed by TEM observations. Here, because of different layer populations, the calculated lamellar moment may be higher than in the purely rhombohedral example.

Magnetic properties of the surface layer and its magnetic interaction with the interior of Nd-Fe-B sintered magnets

NASA Astrophysics Data System (ADS)

Kobayashi, Kurima; Nakamura, Michi-hide; Urushibata, Kimiko

2015-05-01

The magnetization and demagnetization mechanisms in the mechanically polished surface layers (SL) of the c-plane and a-b plane of Nd-Fe-B sintered magnets were investigated. The magnetic interaction between the SL and the interior of the magnet was clarified by using vibrating sample magnetometer measurements of a whole sample and magneto-force microscopy observations of the domain structure of the SL layer. The polishing eliminated the Nd-rich grain boundary phases, which was only about 2 nm thick, from the SL crystal grains in the sintered magnets. The a-b plane polishing caused the independent magnetic reversal of the a-b plane SL, which was about 5.5 μm thick, as in the platy samples. The coercivities (μ0Hc) of the SL were less than 0.3 T. In contrast, the c-plane polishing did not produce independent magnetic reversal of the SL, although the coercivity of bulk samples was clearly decreased by the formation of the c-plane SL. The grains in the SL should form clusters that alter the demagnetizing factors, depending on the shape of cluster as a magnetic unit. The magnetic interaction among the SL crystal grains is expected to play an important role in the coercivity mechanism of Nd-Fe-B sintered magnets.

Efficient charge-spin conversion and magnetization switching through the Rashba effect at topological-insulator/Ag interfaces

NASA Astrophysics Data System (ADS)

Shi, Shuyuan; Wang, Aizhu; Wang, Yi; Ramaswamy, Rajagopalan; Shen, Lei; Moon, Jisoo; Zhu, Dapeng; Yu, Jiawei; Oh, Seongshik; Feng, Yuanping; Yang, Hyunsoo

2018-01-01

We report the observation of efficient charge-to-spin conversion in the three-dimensional topological insulator (TI) B i2S e3 and Ag bilayer by the spin-torque ferromagnetic resonance technique. The spin-orbit-torque ratio in the B i2S e3/Ag /CoFeB heterostructure shows a significant enhancement as the Ag thickness increases to ˜2 nm and reaches a value of 0.5 for 5 nm Ag, which is ˜3 times higher than that of B i2S e3/CoFeB at room temperature. The observation reveals the interfacial effect of B i2S e3/Ag exceeds that of the topological surface states (TSSs) in the B i2S e3 layer and plays a dominant role in the charge-to-spin conversion in the B i2S e3/Ag /CoFeB system. Based on first-principles calculations, we attribute our observation to the large Rashba splitting bands which wrap the TSS band and have the same net spin polarization direction as the TSS of B i2S e3 . Subsequently, we demonstrate Rashba-induced magnetization switching in B i2S e3/Ag /Py with a low current density of 5.8 ×105A /c m2 .

Characterization of Bi and Fe co-doped PZT capacitors for FeRAM.

PubMed

Cross, Jeffrey S; Kim, Seung-Hyun; Wada, Satoshi; Chatterjee, Abhijit

2010-08-01

Ferroelectric random access memory (FeRAM) has been in mass production for over 15 years. Higher polarization ferroelectric materials are needed for future devices which can operate above about 100 °C. With this goal in mind, co-doping of thin Pb(Zr 40 ,Ti 60 )O 3 (PZT) films with 1 at.% Bi and 1 at.% Fe was examined in order to enhance the ferroelectric properties as well as characterize the doped material. The XRD patterns of PZT-5% BiFeO 3 (BF) and PZT 140-nm thick films showed (111) orientation on (111) platinized Si wafers and a 30 °C increase in the tetragonal to cubic phase transition temperature, often called the Curie temperature, from 350 to 380 °C with co-doping, indicating that Bi and Fe are substituting into the PZT lattice. Raman spectra revealed decreased band intensity with Bi and Fe co-doping of PZT compared to PZT. Polarization hysteresis loops show similar values of remanent polarization, but square-shaped voltage pulse-measured net polarization values of PZT-BF were higher and showed higher endurance to repeated cycling up to 10 10 cycles. It is proposed that Bi and Fe are both in the +3 oxidation state and substituting into the perovskite A and B sites, respectively. Substitution of Bi and Fe into the PZT lattice likely creates defect dipoles, which increase the net polarization when measured by the short voltage pulse positive-up-negative-down (PUND) method.

Facile One-pot Transformation of Iron Oxides from Fe2O3 Nanoparticles to Nanostructured Fe3O4@C Core-Shell Composites via Combustion Waves

PubMed Central

Shin, Jungho; Lee, Kang Yeol; Yeo, Taehan; Choi, Wonjoon

2016-01-01

The development of a low-cost, fast, and large-scale process for the synthesis and manipulation of nanostructured metal oxides is essential for incorporating materials with diverse practical applications. Herein, we present a facile one-pot synthesis method using combustion waves that simultaneously achieves fast reduction and direct formation of carbon coating layers on metal oxide nanostructures. Hybrid composites of Fe2O3 nanoparticles and nitrocellulose on the cm scale were fabricated by a wet impregnation process. We demonstrated that self-propagating combustion waves along interfacial boundaries between the surface of the metal oxide and the chemical fuels enabled the release of oxygen from Fe2O3. This accelerated reaction directly transformed Fe2O3 into Fe3O4 nanostructures. The distinctive color change from reddish-brown Fe2O3 to dark-gray Fe3O4 confirmed the transition of oxidation states and the change in the fundamental properties of the material. Furthermore, it simultaneously formed carbon layers of 5–20 nm thickness coating the surfaces of the resulting Fe3O4 nanoparticles, which may aid in maintaining the nanostructures and improving the conductivity of the composites. This newly developed use of combustion waves in hybridized nanostructures may permit the precise manipulation of the chemical compositions of other metal oxide nanostructures, as well as the formation of organic/inorganic hybrid nanostructures. PMID:26902260

Characterization of Bi and Fe co-doped PZT capacitors for FeRAM

PubMed Central

Cross, Jeffrey S; Kim, Seung-Hyun; Wada, Satoshi; Chatterjee, Abhijit

2010-01-01

Ferroelectric random access memory (FeRAM) has been in mass production for over 15 years. Higher polarization ferroelectric materials are needed for future devices which can operate above about 100 °C. With this goal in mind, co-doping of thin Pb(Zr40,Ti60)O3 (PZT) films with 1 at.% Bi and 1 at.% Fe was examined in order to enhance the ferroelectric properties as well as characterize the doped material. The XRD patterns of PZT-5% BiFeO3 (BF) and PZT 140-nm thick films showed (111) orientation on (111) platinized Si wafers and a 30 °C increase in the tetragonal to cubic phase transition temperature, often called the Curie temperature, from 350 to 380 °C with co-doping, indicating that Bi and Fe are substituting into the PZT lattice. Raman spectra revealed decreased band intensity with Bi and Fe co-doping of PZT compared to PZT. Polarization hysteresis loops show similar values of remanent polarization, but square-shaped voltage pulse-measured net polarization values of PZT-BF were higher and showed higher endurance to repeated cycling up to 1010 cycles. It is proposed that Bi and Fe are both in the +3 oxidation state and substituting into the perovskite A and B sites, respectively. Substitution of Bi and Fe into the PZT lattice likely creates defect dipoles, which increase the net polarization when measured by the short voltage pulse positive-up-negative-down (PUND) method. PMID:27877349

Nanometer-Thick Yttrium Iron Garnet Film Development and Spintronics-Related Study

NASA Astrophysics Data System (ADS)

Chang, Houchen

In the last decade, there has been a considerable interest in using yttrium iron garnet (Y3Fe5O12, YIG) materials for magnetic insulator-based spintronics studies. This interest derives from the fact that YIG materials have very low intrinsic damping. The development of YIG-based spintronics demands YIG films that have a thickness in the nanometer (nm) range and at the same time exhibit low damping similar to single-crystal YIG bulk materials. This dissertation reports comprehensive experimental studies on nm-thick YIG films by magnetron sputtering techniques. Optimization of sputtering control parameters and post-deposition annealing processes are discussed in detail. The feasibility of low-damping YIG nm-thick film growth via sputtering is demonstrated. A 22.3-nm-thick YIG film, for example, shows a Gilbert damping constant of less than 1.0 x 10-4. The demonstration is of great technological significance because sputtering is a thin film growth technique most widely used in industry. The spin Seebeck effect (SSE) refers to the generation of spin voltage in a ferromagnet (FM) due to a temperature gradient. The spin voltage can produce a pure spin current into a normal metal (NM) that is in contact with the FM. Various theoretical models have been proposed to interpret the SSE, although a complete understanding of the effect has not been realized yet. In this dissertation the study of the role of damping on the SSE in YIG thin films is conducted for the first time. With the thin film development method mentioned in the last paragraph, a series of YIG thin films showing very similar structural and static magnetic properties but rather different Gilbert damping values were prepared. A Pt capping layer was grown on each YIG film to probe the strength of the SSE. The experimental data show that the YIG films with a smaller intrinsic Gilbert damping shows a stronger SSE. The majority of the previous studies on YIG spintronics utilized YIG films that were grown on single-crystal Gd3Ga5O 12 (GGG) substrates first and then capped with either a thin NM layer or a thin topological insulator (TI) layer. The use of the GGG substrates is crucial in terms of realizing high-quality YIG films, because GGG not only has a crystalline structure almost perfectly matching that of YIG but is also extremely stable at high temperature in oxygen that is the condition needed for YIG crystallization. The feasibility of growing high-quality YIG thin films on Pt thin films is explored in this dissertation. This work is of great significance because it enables the fabrication of sandwich-like NM/YIG/NM or NM/YIG/TI structures. Such tri-layered structures will facilitate various interesting fundamental studies as well as device developments. The demonstration of a magnon-mediated electric current drag phenomenon is presented as an example for such tri-layered structures.

Synchrotron X-ray studies of epitaxial ferroelectric thin films and nanostructures

NASA Astrophysics Data System (ADS)

Klug, Jeffrey A.

The study of ferroelectric thin films is a field of considerable scientific and technological interest. In this dissertation synchrotron x-ray techniques were applied to examine the effects of lateral confinement and epitaxial strain in ferroelectric thin films and nanostructures. Three materials systems were investigated: laterally confined epitaxial BiFeO3 nanostructures on SrTiO3 (001), ultra-thin commensurate SrTiO 3 films on Si (001), and coherently strained films of BaTiO3 on DyScO3 (110). Epitaxial films of BiFeO3 were deposited by radio frequency magnetron sputtering on SrRuO3 coated SrTiO 3 (001) substrates. Laterally confined nanostructures were fabricated using focused ion-beam processing and subsequently characterized with focused beam x-ray nanodiffraction measurements with unprecedented spatial resolution. Results from a series of rectangular nanostructures with lateral dimensions between 500 nm and 1 mum and a comparably-sized region of the unpatterned BiFeO3 film revealed qualitatively similar distributions of local strain and lattice rotation with a 2-3 times larger magnitude of variation observed in those of the nanostructures compared to the unpatterned film. This indicates that lateral confinement leads to enhanced variation in the local strain and lattice rotation fields in epitaxial BiFeO3 nanostructures. A commensurate 2 nm thick film of SrTiO3 on Si was characterized by the x-ray standing wave (XSW) technique to determine the Sr and Ti cation positions in the strained unit cell in order to verify strain-induced ferroelectricity in SrTiO3/Si. A Si (004) XSW measurement at 10°C indicated that the average Ti displacement from the midpoint between Sr planes was consistent in magnitude to that predicted by a density functional theory (DFT) calculated ferroelectric structure. The Ti displacement determined from a 35°C measurement better matched a DFT-predicted nonpolar structure. The thin film extension of the XSW technique was employed to measure the polar displacement of the Ba cations in a 50 nm thick coherently strained BaTiO3 film on DyScO3 (110). An analysis assuming a bulk-like ratio between the Ti and Ba displacements found that the polar shift of Ba cations was larger than in bulk BaTiO3, which was consistent with strain-induced enhancement of ferroelectric polarization in BaTiO3/DyScO3 (110).

Lightweight NiFe2O4 with controllable 3D network structure and enhanced microwave absorbing properties

NASA Astrophysics Data System (ADS)

Wang, Fen; Wang, Xing; Zhu, Jianfeng; Yang, Haibo; Kong, Xingang; Liu, Xiao

2016-11-01

3D network structure NiFe2O4 was successfully synthesized by a templated salt precipitation method using PMMA colloid crystal as templates. The morphology, phase composition and microwave absorbing properties of as-prepared samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), vector network analyzer (VNA), and so on. The results revealed that the 3D network structure was configurated with smooth spherical walls composed of NiFe2O4 nanocrystals and their pore diameters being in the range of 80-250 nm. The microwave absorption properties of the 3D network structure NiFe2O4 were crucially determined by the special structure. The synergy of intrinsic magnetic loss of magnetic NiFe2O4 and the interfacial polarization enhanced by 3D network structure and the interaction of multiple mechanisms endowed the sample with the feature of strong absorption, broad bandwidth and lightweight. There is more than one valley in the reflection loss curves and the maximum reflection loss is 27.5 dB with a bandwidth of 4 GHz. Moreover, the 3D network structure NiFe2O4 show a greater reflection loss with the same thickness comparing to the ordinary NiFe2O4 nanoparticles, which could achieve the feature of lightweight of the microwave absorbing materials.

Lightweight NiFe2O4 with controllable 3D network structure and enhanced microwave absorbing properties

PubMed Central

Wang, Fen; Wang, Xing; Zhu, Jianfeng; Yang, Haibo; Kong, Xingang; Liu, Xiao

2016-01-01

3D network structure NiFe2O4 was successfully synthesized by a templated salt precipitation method using PMMA colloid crystal as templates. The morphology, phase composition and microwave absorbing properties of as-prepared samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), vector network analyzer (VNA), and so on. The results revealed that the 3D network structure was configurated with smooth spherical walls composed of NiFe2O4 nanocrystals and their pore diameters being in the range of 80–250 nm. The microwave absorption properties of the 3D network structure NiFe2O4 were crucially determined by the special structure. The synergy of intrinsic magnetic loss of magnetic NiFe2O4 and the interfacial polarization enhanced by 3D network structure and the interaction of multiple mechanisms endowed the sample with the feature of strong absorption, broad bandwidth and lightweight. There is more than one valley in the reflection loss curves and the maximum reflection loss is 27.5 dB with a bandwidth of 4 GHz. Moreover, the 3D network structure NiFe2O4 show a greater reflection loss with the same thickness comparing to the ordinary NiFe2O4 nanoparticles, which could achieve the feature of lightweight of the microwave absorbing materials. PMID:27897209

Surface molecular imprinting onto fluorescein-coated magnetic nanoparticlesvia reversible addition fragmentation chain transfer polymerization: A facile three-in-one system for recognition and separation of endocrine disrupting chemicals

NASA Astrophysics Data System (ADS)

Li, Ying; Dong, Cunku; Chu, Jia; Qi, Jingyao; Li, Xin

2011-01-01

In this study, we present a general protocol for the making of surface-imprinted magnetic fluorescence beads viareversible addition-fragmentation chain transfer polymerization. The resulting composites were characterized by X-ray diffraction analysis, transmission electron microscopy, scanning electron microscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy, and energy dispersive spectroscopy. The as-synthesized beads exhibited homogeneous polymer films (thickness of about 5.7 nm), spherical shape, high fluorescence intensity and magnetic property (Magnetization (Ms) = 3.67 emu g-1). The hybrids bind the original template 17β-estradiol with an appreciable selectivity over structurally related compounds. In addition, the resulting hybrids performed without obvious deterioration after five repeated cycles. This study therefore demonstrates the potential of molecularly imprinted polymers for the recognition and separation of endocrine disrupting chemicals.In this study, we present a general protocol for the making of surface-imprinted magnetic fluorescence beads viareversible addition-fragmentation chain transfer polymerization. The resulting composites were characterized by X-ray diffraction analysis, transmission electron microscopy, scanning electron microscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy, and energy dispersive spectroscopy. The as-synthesized beads exhibited homogeneous polymer films (thickness of about 5.7 nm), spherical shape, high fluorescence intensity and magnetic property (Magnetization (Ms) = 3.67 emu g-1). The hybrids bind the original template 17β-estradiol with an appreciable selectivity over structurally related compounds. In addition, the resulting hybrids performed without obvious deterioration after five repeated cycles. This study therefore demonstrates the potential of molecularly imprinted polymers for the recognition and separation of endocrine disrupting chemicals. Electronic supplementary information (ESI) available: Supplementary figure S1. The hysteresis loop of Fe3O4 (a), Fe3O4@SiO2 (b), and Fe3O4@SiO2-Dye-SiO2 (c). See DOI: 10.1039/c0nr00614a

Effect of annealing temperature on surface morphology and ultralow ferromagnetic resonance linewidth of yttrium iron garnet thin film grown by rf sputtering

NASA Astrophysics Data System (ADS)

Cao Van, Phuoc; Surabhi, Srivathsava; Dongquoc, Viet; Kuchi, Rambabu; Yoon, Soon-Gil; Jeong, Jong-Ryul

2018-03-01

We report high-quality yttrium-iron-garnet (YIG; Y3Fe5O12) ultrathin films grown on {111} gadolinium-gallium-garnet (GGG; Gd3Ga5O12) substrates using RF sputtering deposition on an off-stoichiometric target and optimized thermal treatments. We measured a narrow peak-to-peak ferromagnetic resonance linewidth (ΔH) whose minimum value was 1.9 Oe at 9.43 GHz for a 60-nm-thick YIG film. This value is comparable to the most recently published value for a YIG thin film grown by pulsed laser deposition. The temperature dependence of the ΔH was investigated systematically, the optimal annealing condition for our growing condition was 875 °C. Structural analysis revealed that surface roughness and crystallinity played an important role in the observed ΔH broadening. Furthermore, the thickness dependence of the ΔH, which indicated that 60 nm thickness was optimal to obtain narrow ΔH YIG films, was also investigated. The thickness dependence of ΔH was understood on the basis of contributions of surface-associated magnon scattering and magnetic inhomogeneities to the ΔH broadening. Other techniques such as transmission electron microscopy, scanning electron microscopy, and X-ray diffraction were used to study the crystalline structure of the YIG films. The high quality of the films in terms of their magnetic properties was expressed through a very low coercivity and high saturation magnetization measured using a vibration sample magnetometer.

Anomalously large ferromagnetic resonance linewidth in the Gd/Cr/Fe film plane

NASA Astrophysics Data System (ADS)

Sun, Li; Zhang, Wen; Wong, Ping Kwan Johnny; Yin, Yuli; Jiang, Sheng; Huang, Zhaocong; Zhai, Ya; Yao, Zhongyu; Du, Jun; Sui, Yunxia; Zhai, Hongru

2018-04-01

As an important parameter for characterizing the magnetization dynamics, Gilbert damping constant α in a thin film or a multilayer is generally extracted from the linear fitting of the frequency-dependence of the ferromagnetic resonance linewidth, sometimes accompanied with a tiny deviation of the linewidth to a smaller value at the low-frequency or high-frequency region due to the two-magnon scattering with an in-plane-field configuration, in which an in-plane magnetic field H perpendicular to a microwave field h was applied in film plane during measurement. In contrast, here we report, in ultrathin Gd/Cr/Fe multilayers, an anomalously large linewidth in the film plane at the low-frequency region. For the first time, we have successfully extracted the Gilbert damping constant from perfect theoretical fitting to the experimental data, by considering the effective direction of the magnetization around in precession staying out of the film plane when the in-pane H at which the precession starts is below the saturation field. This magnetization deviation from the film plane is found to have an obvious contribution to the enhanced linewidth caused by two magnon scattering, while slightly reduce the intrinsic linewidth. Under the same resonance frequency, the deviation angle reaches the maximum values at tCr = 1.0 nm while decreases when tCr increases to 1.5 nm, which coincides with the trend of the surface perpendicular anisotropy constant K⊥. A reduced intrinsic damping constant α is obtained as the introduction of Gd layer and Cr layer as a result of the competition between the spin pumping effect and the interfacial effects at the Fe/Gd and Fe/Cr interfaces. While the decreasing α for film with Cr layer thickness increasing to 1.5 nm might means the contribution of the electron density of states at the Fermi energy n(EF). This study offers an effective way to accurately obtain the intrinsic damping constant of spintronic materials/devices, which is essential for broad applications in spintronics.

Enhancement of magnetoresistance by inserting thin NiAl layers at the interfaces in Co{sub 2}FeGa{sub 0.5}Ge{sub 0.5}/Ag/Co{sub 2}FeGa{sub 0.5}Ge{sub 0.5} current-perpendicular-to-plane pseudo spin valves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jung, J. W.; Sakuraba, Y., E-mail: Sakuraba.Yuya@nims.go.jp; Sasaki, T. T.

2016-03-07

We have investigated the effects of insertion of a thin NiAl layer (≤0.63 nm) into a Co{sub 2}FeGa{sub 0.5}Ge{sub 0.5} (CFGG)/Ag interface on the magnetoresistive properties in CFGG/Ag/CFGG current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo spin valves (PSVs). First-principles calculations of ballistic transmittance clarified that the interfacial band matching at the (001)-oriented NiAl/CFGG interface is better than that at the (001)-Ag/CFGG interface. The insertion of 0.21-nm-thick NiAl layers at the Co{sub 2}FeGa{sub 0.5}Ge{sub 0.5}/Ag interfaces effectively improved the magnetoresistance (MR) output; the observed average and the highest MR ratio (ΔRA) are 62% (25 mΩ μm{sup 2}) and 77% (31 mΩ μm{sup 2}) atmore » room temperature, respectively, which are much higher than those without NiAl insertion. Microstructural analysis using scanning transmission electron microscopy confirmed the existence of thin NiAl layers at the Ag interfaces with only modest interdiffusion even after annealing at 550 °C. The improvement of the interfacial spin-dependent scattering by very thin NiAl insertion can be a predominant reason for the enhancement of the MR output.« less

Changes in size of nano phase iron inclusions with temperature: Experimental simulation of space weathering effects at high temperature

NASA Astrophysics Data System (ADS)

Rout, S. S.; Moroz, L. V.; Stockhoff, T.; Baither, D.; Bischoff, A.; Hiesinger, H.

2011-10-01

The mean size of nano phase iron inclusions (npFe0), produced during the space weathering of iron-rich regolith of airless solar system bodies, significantly affects visible and near-infrared (VNIR) spectra. To experimentally simulate the change in the size of npFe0 inclusions with increasing temperature, we produced sputter film deposits on a silicon dioxide substrate by sputtering a pressed pellet prepared from fine olivine powder using 600V Ar+ ions. This silicon dioxide substrate covered with the deposit was later heated to 450°C for 24 hours in an oven under argon atmosphere. Initial TEM analysis of the unheated silicon dioxide substrate showed the presence of a ~ 50 nm-thick layer of an amorphous deposit with nano clusters that has not yet been identified.

Bioconjugated iron oxide nanocubes: synthesis, functionalization, and vectorization.

PubMed

Wortmann, Laura; Ilyas, Shaista; Niznansky, Daniel; Valldor, Martin; Arroub, Karim; Berger, Nadja; Rahme, Kamil; Holmes, Justin; Mathur, Sanjay

2014-10-08

A facile bottom-up approach for the synthesis of inorganic/organic bioconjugated nanoprobes based on iron oxide nanocubes as the core with a nanometric silica shell is demonstrated. Surface coating and functionalization protocols developed in this work offered good control over the shell thickness (8-40 nm) and enabled biovectorization of SiO2@Fe3O4 core-shell structures by covalent attachment of folic acid (FA) as a targeting unit for cellular uptake. The successful immobilization of folic acid was investigated both quantitatively (TGA, EA, XPS) and qualitatively (AT-IR, UV-vis, ζ-potential). Additionally, the magnetic behavior of the nanocomposites was monitored after each functionalization step. Cell viability studies confirmed low cytotoxicity of FA@SiO2@Fe3O4 conjugates, which makes them promising nanoprobes for targeted internalization by cells and their imaging.

Probing the magnetic moment of FePt micromagnets prepared by focused ion beam milling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Overweg, H. C.; Haan, A. M. J. den; Eerkens, H. J.

2015-08-17

We investigate the degradation of the magnetic moment of a 300 nm thick FePt film induced by Focused Ion Beam (FIB) milling. A 1 μm × 8 μm rod is milled out of a film by a FIB process and is attached to a cantilever by electron beam induced deposition. Its magnetic moment is determined by frequency-shift cantilever magnetometry. We find that the magnetic moment of the rod is μ = 1.1 ± 0.1 × 10{sup −12} Am{sup 2}, which implies that 70% of the magnetic moment is preserved during the FIB milling process. This result has important implications for atom trapping and magnetic resonance force microscopy, which are addressed inmore » this paper.« less

Unconventional spin distributions in thick Ni{sub 80}Fe{sub 20} nanodisks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, D.; Lupo, P.; Haldar, A.

2016-05-09

We study the spin distributions in permalloy (Py: Ni{sub 80}Fe{sub 20}) nanodisks as a function of diameter D (300 nm ≤ D ≤ 1 μm) and thickness L (30 nm ≤ L ≤ 100 nm). We observed that beyond a certain thickness, for a fixed disk diameter, an unconventional spin topology precipitates which is marked by the presence of a divergence field within the magnetic vortex curl. The strength of this divergence changes anti-symmetrically from negative to positive—depending on the core polarity—along the axis of the cylindrical nanodisk. This is also accompanied by a skyrmion-like out-of-plane bending of the spin vectors farther away from the disk center. Additionally, the vortex core dilatesmore » significantly when compared to its typical size. This has been directly observed using magnetic force microscopy. We determined from the ferromagnetic resonance spectroscopy measurements that the unconventional topology in the thicker nanodisks gyrated at a frequency, which is significantly lower than what is predicted by a magnetic vortex based analytical model. Micromagnetic simulations involving dipolar and exchange interactions appear to satisfactorily reproduce the experimentally observed static and dynamic behaviors. Besides providing a physical example of an unconventional topology, these results can also aid the design of topologically protected memory elements.« less

A transmission electron microscopy study of CoFe2O4 ferrite nanoparticles in silica aerogel matrix using HREM and STEM imaging and EDX spectroscopy and EELS.

PubMed

Falqui, Andrea; Corrias, Anna; Wang, Peng; Snoeck, Etienne; Mountjoy, Gavin

2010-04-01

Magnetic nanocomposite materials consisting of 5 and 10 wt% CoFe2O4 nanoparticles in a silica aerogel matrix have been synthesized by the sol-gel method. For the CoFe2O4-10wt% sample, bright-field scanning transmission electron microscopy (BF STEM) and high-resolution transmission electron microscopy (HREM) images showed distinct, rounded CoFe2O4 nanoparticles, with typical diameters of roughly 8 nm. For the CoFe2O4-5wt% sample, BF STEM images and energy dispersive X-ray (EDX) measurements showed CoFe2O4 nanoparticles with diameters of roughly 3 +/- 1 nm. EDX measurements indicate that all nanoparticles consist of stoichiometric CoFe2O4, and electron energy-loss spectroscopy measurements from lines crossing nanoparticles in the CoFe2O4-10wt% sample show a uniform composition within nanoparticles, with a precision of at best than +/-0.5 nm in analysis position. BF STEM images obtained for the CoFe2O4-10wt% sample showed many "needle-like" nanostructures that typically have a length of 10 nm and a width of 1 nm, and frequently appear to be attached to nanoparticles. These needle-like nanostructures are observed to contain layers with interlayer spacing 0.33 +/- 0.1 nm, which could be consistent with Co silicate hydroxide, a known precursor phase in these nanocomposite materials.

UV-vis spectral property of a multi-hydroxyl Schiff-base derivative and its colorimetric response to some special metal ions.

PubMed

Xing, Lin; Zheng, Xiaoyu; Sun, Wenyu; Yuan, Hua; Hu, Lei; Yan, Zhengquan

2018-06-05

A multi-hydroxyl Schiff-base derivative, N-2'-hydroxyl-1'-naphthyl methylene-2-amino phenol (HNMAP), was synthesized and characterized by FTIR, 1 H NMR and UV-vis spectroscopy. It was noted to find there was great effect for solvent and pH on the UV-vis spectroscopy of HNMAP. Especially, some metal ions could make its UV-vis spectra changed regularly with different time-resolved effects. For example, a real-time and multi-wavelength response to Fe 2+ at 520 nm, 466 nm and 447 nm and a quite slow one about 26 min to Fe 3+ at 447 nm and 466 nm, respectively. Under the optimized conditions, the changes in the corresponding absorption intensities at above wavelengths were in proportion to c Fe 2+ or c Fe 3+ during respectively partitioned linear ranges, which realized to quantitatively detect Fe 2+ or Fe 3+ with a large linear range more than two orders of magnitude. A 1:1 complex mode for HNMAP-Fe 2+ and 1:2 for HNMAP-Fe 3+ were proposed from UV-vis spectral titration and Job's plot. HNMAP would be a potential sensor for colorimetric detection of Fe 2+ and Fe 3+ in practice. Copyright © 2018 Elsevier B.V. All rights reserved.

Effect of the spin-twist structure on the spin-wave dynamics in Fe{sub 55}Pt{sub 45}/Ni{sub 80}Fe{sub 20} exchange coupled bi-layers with varying Ni{sub 80}Fe{sub 20} thickness

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pal, Semanti; Barman, Saswati, E-mail: saswati@bose.res.in; Barman, Anjan, E-mail: abarman@bose.res.in

2014-05-07

We have investigated optically induced ultrafast magnetization dynamics of a series of Fe{sub 55}Pt{sub 45}/Ni{sub 80}Fe{sub 20} exchange spring bi-layers with varying Ni{sub 80}Fe{sub 20} thickness. Rich spin-wave spectra are observed; whose frequency shows a strong dependence on the Ni{sub 80}Fe{sub 20} layer thickness. Micromagnetic simulations based on a simplified magnetic microstructure were able to reproduce the experimental data qualitatively. The spin twist structure introduced in the Ni{sub 80}Fe{sub 20} layer gives rise to new modes in the composite system as opposed to the bare Ni{sub 80}Fe{sub 20} films.

In situ growth of capping-free magnetic iron oxide nanoparticles on liquid-phase exfoliated graphene

NASA Astrophysics Data System (ADS)

Tsoufis, T.; Syrgiannis, Z.; Akhtar, N.; Prato, M.; Katsaros, F.; Sideratou, Z.; Kouloumpis, A.; Gournis, D.; Rudolf, P.

2015-05-01

We report a facile approach for the in situ synthesis of very small iron oxide nanoparticles on the surface of high-quality graphene sheets. Our synthetic strategy involved the direct, liquid-phase exfoliation of highly crystalline graphite (avoiding any oxidation treatment) and the subsequent chemical functionalization of the graphene sheets via the well-established 1,3-dipolar cycloaddition reaction. The resulting graphene derivatives were employed for the immobilization of the nanoparticle precursor (Fe cations) at the introduced organic groups by a modified wet-impregnation method, followed by interaction with acetic acid vapours. The final graphene-iron oxide hybrid material was achieved by heating (calcination) in an inert atmosphere. Characterization by X-ray diffraction, transmission electron and atomic force microscopy, Raman and X-ray photoelectron spectroscopy gave evidence for the formation of rather small (<12 nm), spherical, magnetite-rich nanoparticles which were evenly distributed on the surface of few-layer (<1.2 nm thick) graphene. Due to the presence of the iron oxide nanoparticles, the hybrid material showed a superparamagnetic behaviour at room temperature.We report a facile approach for the in situ synthesis of very small iron oxide nanoparticles on the surface of high-quality graphene sheets. Our synthetic strategy involved the direct, liquid-phase exfoliation of highly crystalline graphite (avoiding any oxidation treatment) and the subsequent chemical functionalization of the graphene sheets via the well-established 1,3-dipolar cycloaddition reaction. The resulting graphene derivatives were employed for the immobilization of the nanoparticle precursor (Fe cations) at the introduced organic groups by a modified wet-impregnation method, followed by interaction with acetic acid vapours. The final graphene-iron oxide hybrid material was achieved by heating (calcination) in an inert atmosphere. Characterization by X-ray diffraction, transmission electron and atomic force microscopy, Raman and X-ray photoelectron spectroscopy gave evidence for the formation of rather small (<12 nm), spherical, magnetite-rich nanoparticles which were evenly distributed on the surface of few-layer (<1.2 nm thick) graphene. Due to the presence of the iron oxide nanoparticles, the hybrid material showed a superparamagnetic behaviour at room temperature. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00765h

Training effect of the exchange bias in sputter deposited Fe3O4 thin films with varying thickness

NASA Astrophysics Data System (ADS)

Muhammed Shameem, P. V.; Senthil Kumar, M.

2018-07-01

The training effect property of the exchange bias in the reactively sputtered polycrystalline Fe3O4 thin films of varying thicknesses in the range 25-200 nm are studied. Structural studies by X-ray diffraction, X-ray photoelectron spectroscopy and selected area electron diffraction confirm the formation of single phase Fe3O4. The scanning electron spectroscopy images show that the grains are uniformly distributed. All the samples show clear and consistent exchange bias training behaviour due to the dynamics of the spins at the interface of the ferrimagnetic core and the spin glass-like surface of the grains. The analysis of the training effect data of the exchange bias field HE measured at 2 K by using three different models show that the model based on the relaxation of the frozen and rotatable spin components at the interface gives the best description for all the samples. From this model, it is found that the reversible interface spins relax around 7 times faster than the frozen interface spins at 2 K for all the samples and that their relative relaxation rates are independent of the sample thickness. This constancy show that the relative relaxation rates of the interfacial frozen and rotatable spin components is a material dependent property. The frozen component of the interfacial spins of each sample is found to be dominated at the initial stage of the training. A direct equivalence between the HE and remanence asymmetry ME is observed. Above the spin freezing temperature, the training effect measurements at 75 K show that the HE decreases sharply with successive field cycling as compared to the measurements made at 2 K and the HE vanishes after first few cycles.

New developments in magneto-optical imaging applied to rock magnetism: a case study on meteorites (Invited)

NASA Astrophysics Data System (ADS)

Uehara, M.; Gattacceca, J.; van der Beek, C. J.; Leroux, H.; Jacob, D.

2010-12-01

We present results of an integrated study of metallic grains in meteorites, combining magneto-optical imaging (MOI), petrography, FE-SEM, TEM, and microprobe analyses. Indeed, metallic Fe-Ni grains in meteorites have inner structures due to Ni diffusion during slow cooling subsequent to metamorphism on their parent body. Previous magnetic studies suggested that tetrataenite (ordered FeNi) is the stable magnetic carriers in these meteorites. On the other hand, mineralogical studies showed that tetrataenite is intimately mixed with other Fe-Ni phases (kamacite and taenite, that contain less than 10 wt.% and around 30 wt.% Ni, respectively), and forms complex microstructures (see below). However, due to the typical spatial resolution of classical bulk magnetic measurements (~1 mm), it has been so far difficult to isolate the contribution of these different Fe-Ni minerals. The MOI technique measures the magnetic flux threading a magneto-optically active film directly placed on the sample. This film rotates the polarization direction of transmitted light (Faraday rotation). Through the analyzer of a reflected light microscope, the vertical component of surface magnetic field of the sample is observed with a spatial resolution of a few µm, which allows direct comparison between mineralogical and magnetic microstructures of metal grains. We studied Agen (H5) and Ausson (L5) ordinary chondrites. Optical and electron microscopies showed two types of micron- to submicron-scaled tetrataenite-bearing microstructures: (1) Zoned taenite particles that consist of a taenite core, surrounded by a "cloudy zone" (20-150 nm large tetrataenite granules embedded in taenite matrix), and a 1-10 µm thick tetrataenite rim. (2) Zoneless plessite particles that consist of < 10 µm large tetrataenite grains embedded in a kamacite matrix. MOI of saturation remanence showed that only the nm-sized tetrataenite granules in cloudy zone carry very strong remanence. Micron-scale mapping of coercivity of remanence (Bcr), by means of DC demagnetization coupled with MOI, combined with FE-SEM and TEM study showed that this cloudy zone has zoning in Ni composition, tetrataenite grain size, and Bcr. The center part has finer tetrataenite (20 nm), lower bulk Ni composition (30 wt.%) and higher Bcr values (up to 1 T) than the outer part (150 nm, 55 wt.%, and 400 mT respectively). Therefore, tetrataenite in the cloudy zone is a potential very stable carrier of extraterrestrial remanence. Moreover, magnetically soft minerals (e.g. kamacite) are occasionally inversely magnetized by stray fields from adjacent cloudy zone. This implies that bulk measurements of FeNi-bearing meteorites may be misleading because of microscopic-scale interactions between magnetically hard tetrataenite and other soft minerals.

Characterization of the thin layer photocatalysts TiO2 and V2O5- and Fe2O3- doped TiO2 prepared by the sol-gel method

NASA Astrophysics Data System (ADS)

Loc Luu, Cam; Nguyen, Quoc Tuan; Thoang Ho, Si; Nguyen, Tri

2013-09-01

The catalysts TiO2 and TiO2 doped with Fe and V were prepared using the sol-gel method. TiO2-modified samples were obtained in the form of a thick film on pyrex glass sticks and tubes and were used as catalysts in the gas phase photo-oxidation of p-xylene. The physico-chemical characteristics of the catalysts were determined using the methods of Brunauer-Emmett-Teller adsorption, x-ray diffraction, and infrared, ultraviolet and visible and Raman spectroscopies. The experimental results show that the introduction of V did not expand the region of light absorption, but slightly reduced the size of the TiO2 particles, and reduced the number of OH-groups, which should decrease the photocatalytic activity and efficiency of the obtained catalysts compared to those of pure TiO2. The Fe-doped TiO2 samples, in contrast, are characterized by an extension of the spectrum of photon absorption to the visible region with wavenumbers λ up to 464 nm and the values of their band gap energy decreased to lower quantities (up to 2.67 eV), therefore they should have higher catalytic activity and conversion efficiency of p-xylene in the visible region than the original sample. For these catalysts, a combined utilization of radiation by ultraviolet (λ = 365 nm) and visible (λ = 470 nm) light increased the activity and the yield in p-xylene conversion by a factor of around 2-3, as well as making these quantities more stable in comparison with those of TiO2-P25 Degussa.

Annealing temperature and thickness dependencies of structural and magnetic properties of Co2FeAl thin films

NASA Astrophysics Data System (ADS)

Belmeguenai, M.; Gabor, M. S.; Zighem, F.; Roussigné, Y.; Faurie, D.; Tiusan, C.

2016-09-01

Co2FeAl (CFA) thin films, of various thicknesses (3 nm≤t ≤50 nm ), have been grown by sputtering on (001) MgO single-crystal substrates and annealed at different temperatures (RT≤Ta≤600 ∘C , where RT is the room temperature). The influence of the CFA thickness (t ), as well as ex situ annealing temperature (Ta), on the magnetic and structural properties has been investigated by x-ray diffraction (XRD), vibrating sample magnetometry, and broadband microstrip ferromagnetic resonance (MS-FMR). The XRD revealed an epitaxial growth of the films with the cubic [001] CFA axis normal to the substrate plane and that the chemical order varies from the B 2 phase to the A 2 phase when decreasing t or Ta. The deduced lattice parameters showed an in-plane tetragonal distortion and in-plane and out-plane strains that increase with Ta and 1 /t . For all Ta values, the variation of the effective magnetization, deduced from the fit of MS-FMR measurements, shows two different regimes separated by a critical thickness, which is Ta dependent. It decreases (increases) linearly with the inverse thickness (1 /t ) in the first (second) regime due to the contribution of the magnetoelastic anisotropy to surface (to volume) anisotropy. The observed behavior has been analyzed through a model allowing for the separation of the magnetocrystalline, magnetoelastic, and Néel-type interface anisotropy constants to the surface and the volume anisotropies. Similar behavior has been observed for the effective fourfold anisotropy field which governs the in-plane anisotropy present in all the samples. Finally, the MS-FMR data also allow one to conclude that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with Ta.

Structure and corrosion behavior of sputter deposited cerium oxide based coatings with various thickness on Al 2024-T3 alloy substrates

NASA Astrophysics Data System (ADS)

Liu, Yuanyuan; Huang, Jiamu; Claypool, James B.; Castano, Carlos E.; O'Keefe, Matthew J.

2015-11-01

Cerium oxide based coatings from ∼100 to ∼1400 nm in thickness were deposited onto Al 2024-T3 alloy substrates by magnetron sputtering of a 99.99% pure CeO2 target. The crystallite size of CeO2 coatings increased from 15 nm to 46 nm as the coating thickness increased from ∼100 nm to ∼1400 nm. The inhomogeneous lattice strain increased from 0.36% to 0.91% for the ∼100 nm to ∼900 nm thick coatings and slightly decreased to 0.89% for the ∼1400 nm thick coating. The highest adhesion strength to Al alloy substrates was for the ∼210 nm thick coating, due to a continuous film coverage and low internal stress. Electrochemical measurements indicated that sputter deposited crystalline CeO2 coatings acted as physical barriers that provide good cathodic inhibition for Al alloys in saline solution. The ∼900 nm thick CeO2 coated sample had the best corrosion performance that increased the corrosion resistance by two orders magnitude and lowered the cathodic current density 30 times compared to bare Al 2024-T3 substrates. The reduced defects and exposed surface, along with suppressed charge mobility, likely accounts for the improved corrosion performance as coating thickness increased from ∼100 nm to ∼900 nm. The corrosion performance decreased for ∼1400 nm thick coatings due in part to an increase in coating defects and porosity along with a decrease in adhesion strength.

Studies of electrochemical oxidation of Zircaloy nuclear reactor fuel cladding using time-of-flight-energy elastic recoil detection analysis

NASA Astrophysics Data System (ADS)

Whitlow, H. J.; Zhang, Y.; Wang, Y.; Winzell, T.; Simic, N.; Ahlberg, E.; Limbäck, M.; Wikmark, G.

2000-03-01

The trend towards increased fuel burn-up and higher operating temperatures in order to achieve more economic operation of nuclear power plants places demands on a better understanding of oxidative corrosion of Zircaloy (Zry) fuel rod cladding. As part of a programme to study these processes we have applied time-of-flight-energy elastic recoil detection (ToF-E ERD), electrochemical impedance measurements and scanning electron microscopy to quantitatively characterise thin-oxide films corresponding to the pre-transition oxidation regime. Oxide films of different nominal thickness in the 9-300 nm range were grown on a series of rolled Zr and Zry-2 plates by anodisation in dilute H 2SO 4 with applied voltages. The dielectric thickness of the oxide layer was determined from the electrochemical impedance measurements and the surface topography characterised by scanning electron microscopy. ToF-E ERD with a 60 MeV 127I 11+ ion beam was used to determine the oxygen content and chemical composition of the oxide layer. In the Zr samples, the oxygen content (O atom cm -2) that was determined by ERD was closely similar to the O content derived from impedance measurements from the dielectric film. The absolute agreement was well within the uncertainty associated with the stopping powers. Moreover, the measured composition of the thick oxide layers corresponded to ZrO 2 for the films thicker than 65 nm where the oxide layer was resolved in the ERD depth profile. Zry-2 samples exhibited a similar behaviour for small thickness ( ⩽130 nm) but had an enhanced O content at larger thicknesses that could be associated either with enhanced rough surface topography or porous oxide formation that was correlated with the presence of Second Phase Particles (SPP) in Zry-2. The concentration of SPP elements (Fe, Cr, Ni) in relation to Zr was the same in the outer 9×10 17 atom cm -2 of oxide as in the same thickness of metal. The results also revealed the presence of about 1 at.% 32S in the oxides on the Zr and Zry-2 samples which presumably originates from the electrolyte.

Role of CoFeB thickness in electric field controlled sub-100 nm sized magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

Lourembam, James; Huang, Jiancheng; Lim, Sze Ter; Gerard, Ernult Franck

2018-05-01

We report a comprehensive study on the role of the free layer thickness (tF) in electric-field controlled nanoscale perpendicular magnetic tunnel junctions (MTJs), comprising of free layer structure Ta/Co40Fe40B20/MgO, by using dc magnetoresistance and ultra-short magnetization switching measurements. Focusing on MTJs that exhibits positive effective device anisotropy (Keff), we observe that both the voltage-controlled magnetic anisotropy (ξ) and voltage modulation of coercivity show strong dependence on tF. We found that ξ varies dramatically and unexpectedly from ˜-3 fJ/V-m to ˜-41 fJ/V-m with increasing tF. We discuss the possibilities of electric-field tuning of the effective surface anisotropy term, KS as well as an additional interfacial magnetoelastic anisotropy term, K3 that scales with 1 /tF2. Voltage pulse induced 180° magnetization reversal is also demonstrated in our MTJs. Unipolar switching and oscillatory function of switching probability vs. pulse duration can be observed at higher tF, and agrees well with the two key device parameters — Keff and ξ.

Synthesis and electrochemical studies on Al 2O 3 coated LiNi 0.5Co 0.44Fe 0.06VO 4 for lithium ion batteries

NASA Astrophysics Data System (ADS)

Fey, George Ting-Kuo; Muralidharan, Pandurangan; Cho, Yung-Da

LiNi 0.5Co 0.44Fe 0.06VO 4 cathode material has been synthesized by a citric acid:polyethylene glycol polymeric method at 723 K for 5 h in air. The surface of the LiNi 0.5Co 0.44Fe 0.06VO 4 was coated with various wt.% of Al 2O 3 by a wet chemical procedure and heat treated 873 K for 2 h in air. The samples were characterized by XRD, FTIR, SEM, and TEM techniques. XRD patterns expose that the complete crystalline phase occurred at 723 K and there was no indication of new peaks for the coated samples. FTIR spectra show that the complete removal of organic residues and the formation of LiNi 0.5Co 0.44Fe 0.06VO 4. TG/DTGA results reveal that the formation of LiNi 0.5Co 0.44Fe 0.06VO 4 occurred between 480 and 670 K and the complete crystalline occurred at 723 K. SEM micrographs show the various morphological stages of the polymeric intermediates. TEM micrographs of the pristine LiNi 0.5Co 0.44Fe 0.06VO 4 reveal that the particle size ranged from 130 to 150 nm and Al 2O 3 coating on the fine particles was compact and had an average thickness of about 15 nm. The charge-discharge experiments were carried out between 2.8 and 4.9 V (versus Li) at a current rate of 0.15 C. The 1.0 wt.% Al 2O 3 coated sample had the best electrochemical performance, with an initial capacity of 65 mAh g -1 and capacity retention of 60% after 50 cycles. The electrochemical impedance behavior suggests that the failure of pristine cathode performance is associated with an increase in the impedance growth on the surface of the cathode material upon continuous cycling.

A silicon dioxide modified magnetic nanoparticles-labeled lateral flow strips for HBs antigen.

PubMed

Zhang, Xueqing; Jiang, Lin; Zhang, Chunlei; Li, Ding; Wang, Can; Gao, Feng; Cui, Daxiang

2011-12-01

Herein we reported a new type of silicon dioxide wrapped magnetic nanoparticles-labeled lateral flow strip for detection of HBs antigen in sera. The SiO2 wrapped Fe3O4 nanocomposites were prepared and characterized by HR-TEM, FTIR and magnetometer. As-prepared nanocomposites were used to label anti-HBV surface monoclonal antibody, the lateral flow strips were constructed, and 100 specimens of sera were collected and tested. Results showed that the prepared SiO2 wrapped Fe3O4 nanocomposites were shell/core structure, well dispersed, with the size of 25 nm in diameter, the thickness of the shell was about 3 nm, their magnetic saturation intensity was 44.3 meu g(-1). Clinical sera specimens test results showed that the prepared lateral flow strips were with the detection limitation of 5 pg/mL by naked eye observation, and 0.1 pg/mL by CCD reader or MAR Analyzer, specificity was 100%. In conclusion, one kind of silicon dioxide wrapped magnetic nanoparticles-labeled lateral flow strip for ultrasensitive detection of HBs antigen was successfully developed, its ease of use, sensitiveness and low-cost make it well-suited for population-based on-the-site hepatitis B screening.

Ferroelectric domain switching dynamics and memristive behaviors in BiFeO3-based magnetoelectric heterojunctions

NASA Astrophysics Data System (ADS)

Huang, Weichuan; Liu, Yukuai; Luo, Zhen; Hou, Chuangming; Zhao, Wenbo; Yin, Yuewei; Li, Xiaoguang

2018-06-01

The ferroelectric domain reversal dynamics and the corresponding resistance switching as well as the memristive behaviors in epitaxial BiFeO3 (BFO, ~150 nm) based multiferroic heterojunctions were systematically investigated. The ferroelectric domain reversal dynamics could be described by the nucleation-limited-switching model with the Lorentzian distribution of logarithmic domain-switching times. By engineering the domain states, multi and even continuously tunable resistances states, i.e. memristive states, could be non-volatilely achieved. The resistance switching speed can be as fast as 30 ns in the BFO-based multiferroic heterojunctions with a write voltage of ~20 V. By reducing the thickness of BFO, the La0.6Sr0.4MnO3/BFO (~5 nm)/La0.6Sr0.4MnO3 multiferroic tunnel junction (MFTJ) shows an even a quicker switching speed (20 ns) with a much lower operation voltage (~4 V). Importantly, the MFTJ exhibits a tunable interfacial magnetoelectric coupling related to the ferroelectric domain switching dynamics. These findings enrich the potential applications of multiferroic BFO based devices in high-speed, low-power, and high-density memories as well as future neuromorphic computational architectures.

Growth of L1{sub 0}-ordered crystal in FePt and FePd thin films on MgO(001) substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Futamoto, Masaaki, E-mail: futamoto@elect.chuo-u.ac.jp; Nakamura, Masahiro; Ohtake, Mitsuru

2016-08-15

Formation of L1{sub 0}-oredered structure from disordered A1 phase has been investigated for FePt and FePd films on MgO(001) substrates employing a two-step method consisting of low temperature deposition at 200 °C followed by high-temperature annealing at 600 °C. L1{sub 0}-(001) variant crystal with the c-axis perpendicular to the substrate grows preferentially in FePd films whereas L1{sub 0}-(100), (010) variants tend to be mixed with the L1{sub 0}-(001) variant in FePt films. The structure analysis by X-ray diffraction indicates that a difference in A1 lattice strain is the influential factor that determines the resulting L1{sub 0}-variant structure in ordered thinmore » films. Misfit dislocations and anti-phase boundaries are observed in high-resolution transmission electron micrographs of 10 nm-thick Fe(Pt, Pd) film consisting of L1{sub 0}-(001) variants which are formed through atomic diffusion at 600 °C in a laterally strained FePt/PeFd epitaxial thin film. Based on the experimental results, a nucleation and growth model for explaining L1{sub 0}-variant formation is proposed, which suggests a possibility in tailoring the L1{sub 0} variant structure in ordered magnetic thin films by controlling the alloy composition, the layer structure, and the substrate material.« less

Structural, magnetic, dielectric, and electrical properties of NiFe2O4 spinel ferrite nanoparticles prepared by honey-mediated sol-gel combustion

NASA Astrophysics Data System (ADS)

Yadav, Raghvendra Singh; Kuřitka, Ivo; Vilcakova, Jarmila; Havlica, Jaromir; Masilko, Jiri; Kalina, Lukas; Tkacz, Jakub; Enev, Vojtěch; Hajdúchová, Miroslava

2017-08-01

In this study, NiFe2O4 nanoparticles were synthesized using a honey-mediated sol-gel combustion method. The synthesized nanoparticles and samples annealed at 800 °C and 1100 °C were characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry (VSM). XRD and Raman spectroscopy confirmed the formation of a cubic spinel ferrite structure. FE-SEM demonstrated the octahedral morphology of the NiFe2O4 spinel ferrite nanoparticles with sizes ranging from 10 to 70 nm. Quantitative analysis based on XPS suggested a mixed spinel structure comprising NiFe2O4 nanoparticles. XPS analysis determined occupation formulae of (Ni0.212+ Fe0.443+)[Ni0.792+ Fe1.563+]O4 and (Ni0.232+ Fe0.503+)[Ni0.772+ Fe1.503+]O4, for the as-prepared NiFe2O4 nanoparticles and those annealed at 1100 °C, respectively. Magnetic measurements showed that the saturation magnetization increased with the crystallite size from 32.3 emu/g (20 nm) to 49.9 emu/g (163 nm), whereas the coercivity decreased with the crystallite size from 162 Oe (20 nm) to 47 Oe (163 nm). Furthermore, the dielectric constant, dielectric loss tangent, and AC conductivity of the NiFe2O4 nanoparticles were dependent on the frequency (1-107 Hz) and grain size. The influence of the grain size was also observed by modulus spectroscopy based on the Cole-Cole plot.

Ultralow Damping in Nanometer-Thick Epitaxial Spinel Ferrite Thin Films.

PubMed

Emori, Satoru; Yi, Di; Crossley, Sam; Wisser, Jacob J; Balakrishnan, Purnima P; Khodadadi, Behrouz; Shafer, Padraic; Klewe, Christoph; N'Diaye, Alpha T; Urwin, Brittany T; Mahalingam, Krishnamurthy; Howe, Brandon M; Hwang, Harold Y; Arenholz, Elke; Suzuki, Yuri

2018-06-08

Pure spin currents, unaccompanied by dissipative charge flow, are essential for realizing energy-efficient nanomagnetic information and communications devices. Thin-film magnetic insulators have been identified as promising materials for spin-current technology because they are thought to exhibit lower damping compared with their metallic counterparts. However, insulating behavior is not a sufficient requirement for low damping, as evidenced by the very limited options for low-damping insulators. Here, we demonstrate a new class of nanometer-thick ultralow-damping insulating thin films based on design criteria that minimize orbital angular momentum and structural disorder. Specifically, we show ultralow damping in <20 nm thick spinel-structure magnesium aluminum ferrite (MAFO), in which magnetization arises from Fe 3+ ions with zero orbital angular momentum. These epitaxial MAFO thin films exhibit a Gilbert damping parameter of ∼0.0015 and negligible inhomogeneous linewidth broadening, resulting in narrow half width at half-maximum linewidths of ∼0.6 mT around 10 GHz. Our findings offer an attractive thin-film platform for enabling integrated insulating spintronics.

Critical thickness investigation of magnetic properties in exchange-coupled bilayers

NASA Astrophysics Data System (ADS)

Rodríguez-Suárez, R. L.; Vilela-Leão, L. H.; Bueno, T.; Oliveira, A. B.; de Almeida, J. R. L.; Landeros, P.; Rezende, S. M.; Azevedo, A.

2011-06-01

We present a systematic investigation of the magnetic properties of two series of polycrystalline ferromagnetic-antiferromagnetic bilayers (FM-AF) of Ni81Fe19(10nm)/Ir20Mn80(tAF) grown by dc magnetron sputtering. One series was grown at an oblique angle of 50° and the other one was grown at 0°. Ferromagnetic resonance (FMR) was used to measure the exchange bias field HE, the rotatable anisotropy field HRA, and the FMR linewidth ΔH as a function of the antiferromagnetic layer thickness tAF. Three relaxation channels due to isotropic Gilbert damping, anisotropic two-magnon scattering, and mosaicity effects are simultaneously distinguished through the angular dependence of the FMR linewidth. In the regime of small IrMn layer thicknesses, not enough to establish the exchange bias anisotropy, the FMR linewidth shows a sharp peak due to the contribution of the two-magnon scattering mechanism. The results presented here are of general importance for understanding the dynamics of magnetization in the FM-AF structures.

Spin reorientations in Tb-Fe films grown on polyimide substrates

NASA Astrophysics Data System (ADS)

Maneesh, K. Sai; Arout Chelvane, J.; Talapatra, A.; Basumatary, Himalay; Mohanty, J.; Kamat, S. V.

2018-02-01

This paper reports the effect of film thickness and rapid thermal annealing on the spin reorientations in Tb-Fe films grown on flexible polyimide substrates. Magnetization studies indicated that the spins reorient from in-plane to out-of-plane direction with increase in film thicknesses. This was confirmed by magnetic force microscopy studies which showed weak featureless contrast for films deposited with lower thickness and a strong out-of-plane contrast for films grown with higher thicknesses. On subsequent rapid thermal annealing all the Tb-Fe films exhibited in-plane magnetic anisotropy. The results were explained based on competition between uniaxial and shape anisotropies, nature of residual stresses as well as nucleation of crystalline Fe phase in an amorphous Tb-Fe matrix on rapid thermal annealing.

Multiple antiferromagnet/ferromagnet interfaces as a probe of grain-size-dependent exchange bias in polycrystalline Co/Fe 50Mn 50

NASA Astrophysics Data System (ADS)

Bolon, Bruce T.; Haugen, M. A.; Abin-Fuentes, A.; Deneen, J.; Carter, C. B.; Leighton, C.

2007-02-01

We have used ferromagnet/antiferromagnet/ferromagnet trilayers and ferromagnet/antiferromagnet multilayers to probe the grain size dependence of exchange bias in polycrystalline Co/Fe 50Mn 50. X-ray diffraction and transmission electron microscopy show that the Fe 50Mn 50 (FeMn) grain size increases with increasing FeMn thickness in the Co (30 Å)/FeMn system. Hence, in Co(30 Å)/FeMn( tAF Å)/Co(30 Å) trilayers the two Co layers sample different FeMn grain sizes at the two antiferromagnet/ferromagnet interfaces. For FeMn thicknesses above 100 Å, where simple bilayers have a thickness-independent exchange bias, we are therefore able to deduce the influence of FeMn grain size on the exchange bias and coercivity (and their temperature dependence) simply by measuring trilayer and multilayer samples with varying FeMn thicknesses. This can be done while maintaining the (1 1 1) orientation, and with little variation in interface roughness. Increasing the average grain size from 90 to 135 Å results in a fourfold decrease in exchange bias, following an inverse grain size dependence. We interpret the results as being due to a decrease in uncompensated spin density with increasing antiferromagnet grain size, further evidence for the importance of defect-generated uncompensated spins.

Magnetic reversal dynamics of NiFe-based artificial spin ice: Effect of Nb layer in normal and superconducting state

NASA Astrophysics Data System (ADS)

Kaur, M.; Gupta, Anurag; Varandani, D.; Verma, Apoorva; Senguttuvan, T. D.; Mehta, B. R.; Budhani, R. C.

2017-11-01

Square arrays of artificial spin ice (ASI) constituting weakly interacting NiFe nano-islands, with length ˜312 nm, width ˜125 nm, thickness ˜20 nm, and lattice constant ˜570 nm, were fabricated on Nb thin film and on thermally grown 300 nm SiO2 on silicon. Detailed investigations of magnetic force microscopy (MFM) at room temperature, and magnetization M(H) loops and relaxation of remanent magnetization (Mr) at various temperatures were carried out in two in-plane field geometries, namely, parallel ("P"-parallel to the square lattice) and diagonal ("D"- 45° to the square lattice). The magnetic response of the ASI samples shows striking difference for insulating (SiO2), metallic (Nb, T > 6.6 K) and superconducting (Nb, T < 6.6 K) bases, and the field geometry. For instance, with the Nb base in the normal metallic state (T > 6.6 K), (1) in "P" geometry the M(H) loops are found to be more "S" shaped in comparison with that for SiO2 base; (2) the ratio of magnetic vertex population of Type II to Type III vertices extracted from MFM studies in "P"("D") geometry is ˜1:1.1(1.2:1) that changed for the SiO2 base to ˜2.1:1 (4: 1). However, the NiFe-ASI on both metallic Nb and SiO2 bases exhibit a highly athermal decay of magnetization, and the % change in Mr in about two hours at T = 10 K (300 K) lies in a range of ˜1.07-1.80 (0.25-0.62). With Nb base in superconducting state (T < 6.6 K), the M(H) loops not only look radically different from those with SiO2 and metallic Nb as bases but also show significant difference in "P" and "D" geometries. These results are discussed in terms of inter-island magnetostatic energy as influenced by field geometry, presence of metallic Nb base and competing vortex pinning energy of superconducting Nb base.

Realisation of magnetically and atomically abrupt half-metal/semiconductor interface: Co2FeSi0.5Al0.5/Ge(111)

PubMed Central

Nedelkoski, Zlatko; Kuerbanjiang, Balati; Glover, Stephanie E.; Sanchez, Ana M.; Kepaptsoglou, Demie; Ghasemi, Arsham; Burrows, Christopher W.; Yamada, Shinya; Hamaya, Kohei; Ramasse, Quentin M.; Hasnip, Philip J.; Hase, Thomas; Bell, Gavin R.; Hirohata, Atsufumi; Lazarov, Vlado K.

2016-01-01

Halfmetal-semiconductor interfaces are crucial for hybrid spintronic devices. Atomically sharp interfaces with high spin polarisation are required for efficient spin injection. In this work we show that thin film of half-metallic full Heusler alloy Co2FeSi0.5Al0.5 with uniform thickness and B2 ordering can form structurally abrupt interface with Ge(111). Atomic resolution energy dispersive X-ray spectroscopy reveals that there is a small outdiffusion of Ge into specific atomic planes of the Co2FeSi0.5Al0.5 film, limited to a very narrow 1 nm interface region. First-principles calculations show that this selective outdiffusion along the Fe-Si/Al atomic planes does not change the magnetic moment of the film up to the very interface. Polarized neutron reflectivity, x-ray reflectivity and aberration-corrected electron microscopy confirm that this interface is both magnetically and structurally abrupt. Finally, using first-principles calculations we show that this experimentally realised interface structure, terminated by Co-Ge bonds, preserves the high spin polarization at the Co2FeSi0.5Al0.5/Ge interface, hence can be used as a model to study spin injection from half-metals into semiconductors. PMID:27869132

Double-spiral magnetic structure of the Fe/Cr multilayer revealed by nuclear resonance reflectivity

NASA Astrophysics Data System (ADS)

Andreeva, M. A.; Baulin, R. A.; Chumakov, A. I.; Rüffer, R.; Smirnov, G. V.; Babanov, Y. A.; Devyaterikov, D. I.; Milyaev, M. A.; Ponomarev, D. A.; Romashev, L. N.; Ustinov, V. V.

2018-01-01

We have studied the magnetization depth profiles in a [57Fe (dFe) /Cr (dCr) ]30 multilayer with ultrathin Fe layers and nominal thickness of the chromium spacers dCr≈2.0 nm using nuclear resonance scattering of synchrotron radiation. The presence of a broad pure-magnetic half-order (1/2) Bragg reflection has been detected at zero external field. The joint fit of the reflectivity curves and Mössbauer spectra of reflectivity measured near the critical angle and at the "magnetic" peak reveals that the magnetic structure of the multilayer is formed by two spirals, one in the odd and another one in the even iron layers, with the opposite signs of rotation. The double-spiral structure starts from the surface with the almost-antiferromagnetic alignment of the adjacent Fe layers. The rotation of the two spirals leads to nearly ferromagnetic alignment of the two magnetic subsystems at some depth, where the sudden turn of the magnetic vectors by ˜180∘ (spin flop) appears, and both spirals start to rotate in opposite directions. The observation of this unusual double-spiral magnetic structure suggests that the unique properties of giant magnetoresistance devices can be further tailored using ultrathin magnetic layers.

Voltage Drop in a Ferroelectric Single Layer Capacitor by Retarded Domain Nucleation.

PubMed

Kim, Yu Jin; Park, Hyeon Woo; Hyun, Seung Dam; Kim, Han Joon; Kim, Keum Do; Lee, Young Hwan; Moon, Taehwan; Lee, Yong Bin; Park, Min Hyuk; Hwang, Cheol Seong

2017-12-13

Ferroelectric (FE) capacitor is a critical electric component in microelectronic devices. Among many of its intriguing properties, the recent finding of voltage drop (V-drop) across the FE capacitor while the positive charges flow in is especially eye-catching. This finding was claimed to be direct evidence that the FE capacitor is in negative capacitance (NC) state, which must be useful for (infinitely) high capacitance and ultralow voltage operation of field-effect transistors. Nonetheless, the NC state corresponds to the maximum energy state of the FE material, so it has been widely accepted in the community that the material alleviates that state by forming ferroelectric domains. This work reports a similar V-drop effect from the 150 nm thick epitaxial BaTiO 3 ferroelectric thin film, but the interpretation was completely disparate; the V-drop can be precisely simulated by the reverse domain nucleation and propagation of which charge effect cannot be fully compensated for by the supplied charge from the external charge source. The disappearance of the V-drop effect was also observed by repeated FE switching only up to 10 cycles, which can hardly be explained by the involvement of the NC effect. The retained reverse domain nuclei even after the subsequent poling can explain such behavior.

Synthesis and in vitro cellular interactions of superparamagnetic iron nanoparticles with a crystalline gold shell

NASA Astrophysics Data System (ADS)

Bandyopadhyay, Sulalit; Singh, Gurvinder; Sandvig, Ioanna; Sandvig, Axel; Mathieu, Roland; Anil Kumar, P.; Glomm, Wilhelm Robert

2014-10-01

Fe@Au core-shell nanoparticles (NPs) exhibit multiple functionalities enabling their effective use in applications such as medical imaging and drug delivery. In this work, a novel synthetic method was developed and optimized for the synthesis of highly stable, monodisperse Fe@Au NPs of average diameter ∼24 nm exhibiting magneto-plasmonic characteristics. Fe@Au NPs were characterized by a wide range of experimental techniques, including scanning (transmission) electron microscopy (S(T)EM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), dynamic light scattering (DLS) and UV-vis spectroscopy. The formed particles comprise an amorphous iron core with a crystalline Au shell of tunable thickness, and retain the superparamagnetic properties at room temperature after formation of a crystalline Au shell. After surface modification, PEGylated Fe@Au NPs were used for in vitro studies on olfactory ensheathing cells (OECs) and human neural stem cells (hNSCs). No adverse effects of the Fe@Au particles were observed post-labeling, both cell types retaining normal morphology, viability, proliferation, and motility. It can be concluded that no appreciable toxic effects on both cell types, coupled with multifunctionality and chemical stability make them ideal candidates for therapeutic as well as diagnostic applications.

Fe3O4 and metal-organic framework MIL-101(Fe) composites catalyze luminol chemiluminescence for sensitively sensing hydrogen peroxide and glucose.

PubMed

Qian Tang, Xue; Dan Zhang, Yi; Wei Jiang, Zhong; Mei Wang, Dong; Zhi Huang, Cheng; Fang Li, Yuan

2018-03-01

In this work, Fe 3 O 4 and metal-organic framework MIL-101(Fe) composites (Fe 3 O 4 /MIL-101(Fe)) was demonstrated to possess excellent catalytic property to directly catalyze luminol chemiluminescence without extra oxidants. We utilized Fe 3 O 4 /MIL-101(Fe) to develop a ultra-sensitive quantitative analytical method for H 2 O 2 and glucose. The possible mechanism of the chemiluminescence reaction had been investigated. Under optimal conditions, the relative chemiluminescence intensity was linearly proportional to the logarithm of H 2 O 2 concentration in the range of 5-150nM with a limit of detection of 3.7nM (signal-to-noise ratio = 3), and glucose could be linearly detected in the range from 5 to 100nM and the detection limit was 4.9nM (signal-to-noise ratio = 3). Furthermore, the present approach was successfully applied to quantitative determination of H 2 O 2 in medical disinfectant and glucose in human serum samples. Copyright © 2017 Elsevier B.V. All rights reserved.

Fabrication and metrology of lithium niobate narrowband optical filters for the solar orbiter

NASA Astrophysics Data System (ADS)

Gensemer, Stephen D.; Farrant, David

2014-06-01

We report on the fabrication of custom voltage tunable etalons for the SO/PHI spaceborne solar imaging instrument [A. Gandorfer, S. K. Solanki, J. Woch, V. M. Pillet, A. A. Herrero, and T. Appourchaux, J. Phys.: Conference Series 271, 012086 (2011)]. The etalons were manufactured to place a transmission maximum within 0.3 Å of the FeI emission line at 6175.0 Å. Meeting this specification requires an overall thickness specified to within ±15 nm, over a 60 mm aperture. We describe here the metrology, modelling and coating procedures we developed to achieve this.

Analytical electron microscopy in mineralogy; exsolved phases in pyroxenes

USGS Publications Warehouse

Nord, G.L.

1982-01-01

Analytical scanning transmission electron microscopy has been successfully used to characterize the structure and composition of lamellar exsolution products in pyroxenes. At operating voltages of 100 and 200 keV, microanalytical techniques of x-ray energy analysis, convergent-beam electron diffraction, and lattice imaging have been used to chemically and structurally characterize exsolution lamellae only a few unit cells wide. Quantitative X-ray energy analysis using ratios of peak intensities has been adopted for the U.S. Geological Survey AEM in order to study the compositions of exsolved phases and changes in compositional profiles as a function of time and temperature. The quantitative analysis procedure involves 1) removal of instrument-induced background, 2) reduction of contamination, and 3) measurement of correction factors obtained from a wide range of standard compositions. The peak-ratio technique requires that the specimen thickness at the point of analysis be thin enough to make absorption corrections unnecessary (i.e., to satisfy the "thin-foil criteria"). In pyroxenes, the calculated "maximum thicknesses" range from 130 to 1400 nm for the ratios Mg/Si, Fe/Si, and Ca/Si; these "maximum thicknesses" have been contoured in pyroxene composition space as a guide during analysis. Analytical spatial resolutions of 50-100 nm have been achieved in AEM at 200 keV from the composition-profile studies, and analytical reproducibility in AEM from homogeneous pyroxene standards is ?? 1.5 mol% endmember. ?? 1982.

Exceptional effect of glassy lithium fluorophosphate on Mn-rich olivine cathode material for high-performance Li ion batteries

NASA Astrophysics Data System (ADS)

Kim, Jongsoon; Kim, Hyungsub; Myung, Seung-Taek; Yoo, Jung-Keun; Lee, Seongsu

2018-01-01

Mn-rich olivine LiFe0.3Mn0.7PO4 is homogenously encapsulated by an ∼3-nm-thick conductive nanolayer composed of the glassy lithium fluorophosphate through simple non-stoichiometric synthesis using additives of small amounts of LiF and a phosphorus source. The coating of the glassy lithium fluorophosphate nanolayer is clearly verified using transmission electron microscopy and X-ray photoelectron spectroscopy. It enables significant decrease in charge transfer resistance of LiFe0.3Mn0.7PO4 and improvement of its sluggish Li diffusion. At a rate of 10C, the LiFe0.3Mn0.7PO4 encapsulated by conductive glassy lithium fluorophosphate (LiFe0.3Mn0.7PO4-GLFP) electrode delivers a capacity of ∼130 mAh g-1, which is ∼77% of its theoretical capacity (∼170 mAh g-1) and ∼1.5 times higher than that of the pristine counterpart at 10C. Furthermore, LiFe0.3Mn0.7PO4-GLFP achieves outstanding cycle stability (∼75% retention of its initial capacity over 500 cycles at 1C). The proposed olivine LiFe0.3Mn0.7PO4-GLFP battery is thus expected to be a promising candidate for large-scale energy storage applications.

Bottom-up Approach Design, Band Structure, and Lithium Storage Properties of Atomically Thin γ-FeOOH Nanosheets.

PubMed

Song, Yun; Cao, Yu; Wang, Jing; Zhou, Yong-Ning; Fang, Fang; Li, Yuesheng; Gao, Shang-Peng; Gu, Qin-Fen; Hu, Linfeng; Sun, Dalin

2016-08-24

As a novel class of soft matter, two-dimensional (2D) atomic nanosheet-like crystals have attracted much attention for energy storage devices due to the fact that nearly all of the atoms can be exposed to the electrolyte and involved in redox reactions. Herein, atomically thin γ-FeOOH nanosheets with a thickness of ∼1.5 nm are synthesized in a high yield, and the band and electronic structures of the γ-FeOOH nanosheet are revealed using density-functional theory calculations for the first time. The rationally designed γ-FeOOH@rGO composites with a heterostacking structure are used as an anode material for lithium-ion batteries (LIBs). A high reversible capacity over 850 mAh g(-1) after 100 cycles at 200 mA g(-1) is obtained with excellent rate capability. The remarkable performance is attributed to the ultrathin nature of γ-FeOOH nanosheets and 2D heterostacking structure, which provide the minimized Li(+) diffusion length and buffer zone for volume change. Further investigation on the Li storage electrochemical mechanism of γ-FeOOH@rGO indicates that the charge-discharge processes include both conversion reaction and capacitive behavior. This synergistic effect of conversion reaction and capacitive behavior originating from 2D heterostacking structure casts new light on the development of high-energy anode materials.

The AMBRE project: The thick thin disk and thin thick disk of the Milky Way

NASA Astrophysics Data System (ADS)

Hayden, M. R.; Recio-Blanco, A.; de Laverny, P.; Mikolaitis, S.; Worley, C. C.

2017-11-01

We analyze 494 main sequence turnoff and subgiant stars from the AMBRE:HARPS survey. These stars have accurate astrometric information from Gaia DR1, providing reliable age estimates with relative uncertainties of ±1 or 2 Gyr and allowing precise orbital determinations. The sample is split based on chemistry into a low-[Mg/Fe] sequence, which are often identified as thin disk stellar populations, and high-[Mg/Fe] sequence, which are often associated with thick disk stellar populations. We find that the high-[Mg/Fe] chemical sequence has extended star formation for several Gyr and is coeval with the oldest stars of the low-[Mg/Fe] chemical sequence: both the low- and high-[Mg/Fe] sequences were forming stars at the same time. We find that the high-[Mg/Fe] stellar populations are only vertically extended for the oldest, most-metal poor and highest [Mg/Fe] stars. When comparing vertical velocity dispersion for the low- and high-[Mg/Fe] sequences, the high-[Mg/Fe] sequence has lower vertical velocity dispersion than the low-[Mg/Fe] sequence for stars of similar age. This means that identifying either group as thin or thick disk based on chemistry is misleading. The stars belonging to the high-[Mg/Fe] sequence have perigalacticons that originate in the inner disk, while the perigalacticons of stars on the low-[Mg/Fe] sequence are generally around the solar neighborhood. From the orbital properties of the stars, the high-[Mg/Fe] and low-[Mg/Fe] sequences are most likely a reflection of the chemical enrichment history of the inner and outer disk populations, respectively; radial mixing causes both populations to be observed in situ at the solar position. Based on these results, we emphasize that it is important to be clear in defining what populations are being referenced when using the terms thin and thick disk, and that ideally the term thick disk should be reserved for purely geometric definitions to avoid confusion and be consistent with definitions in external galaxies.

Glass transition in thin supported polystyrene films probed by temperature-modulated ellipsometry in vacuum.

PubMed

Efremov, Mikhail Yu; Kiyanova, Anna V; Last, Julie; Soofi, Shauheen S; Thode, Christopher; Nealey, Paul F

2012-08-01

Glass transition in thin (1-200 nm thick) spin-cast polystyrene films on silicon surfaces is probed by ellipsometry in a controlled vacuum environment. A temperature-modulated modification of the method is used alongside a traditional linear temperature scan. A clear glass transition is detected in films with thicknesses as low as 1-2 nm. The glass transition temperature (T(g)) shows no substantial dependence on thickness for coatings greater than 20 nm. Thinner films demonstrate moderate T(g) depression achieving 18 K for thicknesses 4-7 nm. Less than 4 nm thick samples are excluded from the T(g) comparison due to significant thickness nonuniformity (surface roughness). The transition in 10-20 nm thick films demonstrates excessive broadening. For some samples, the broadened transition is clearly resolved into two separate transitions. The thickness dependence of the glass transition can be well described by a simple 2-layer model. It is also shown that T(g) depression in 5 nm thick films is not sensitive to a wide range of experimental factors including molecular weight characteristics of the polymer, specifications of solvent used for spin casting, substrate composition, and pretreatment of the substrate surface.

Effect of capping layer on interlayer coupling in synthetic spin valves

NASA Astrophysics Data System (ADS)

Li, Kebin; Qiu, Jinjun; Han, Guchang; Guo, Zaibing; Zheng, Yuankai; Wu, Yihong; Li, Jinshan

2005-01-01

The magnetic and transport properties of high quality synthetic spin-valves with the structure of Ta/NiFe/IrMn/CoFe/Ru/CoFe/NOL/CoFe/Cu/CoFe/CL were studied by using magnetoresistance measurements. Here Ti, Hf, and Al are used as the capping layer. It is found that both the thickness and materials properties of the capping layers can affect the interlayer coupling field. The interlayer coupling field oscillates weakly with respect to the thickness of the Ti and Hf capping layers. Extremely strong ferromagnetic coupling has been observed when the thickness of the Al capping layer is in a certain range where resonant exchange coupling takes place. The strength of the interlayer coupling is inversely proportional to the square of the thickness of the spacer. It is a typical characteristic of quantum size effect.

Core/shell face-centered tetragonal FePd/Pd nanoparticles as an efficient non-Pt catalyst for the oxygen reduction reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Huiyuan; Jiang, Guangming; Zhang, Xu

We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) via reductive annealing of core/shell Pd/Fe 3O 4 NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at similar to 8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO 4 with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Lastly,more » our study offers a general approach to enhance Pd catalysis in acid for ORB.« less

Core/shell face-centered tetragonal FePd/Pd nanoparticles as an efficient non-Pt catalyst for the oxygen reduction reaction

DOE PAGES

Zhu, Huiyuan; Jiang, Guangming; Zhang, Xu; ...

2015-10-04

We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) via reductive annealing of core/shell Pd/Fe 3O 4 NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at similar to 8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO 4 with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Lastly,more » our study offers a general approach to enhance Pd catalysis in acid for ORB.« less

Amorphous SiC as a structural layer in microbridge-based RF MEMS switches for use in software-defined radio

NASA Astrophysics Data System (ADS)

Parro, Rocco J.; Scardelletti, Maximilian C.; Varaljay, Nicholas C.; Zimmerman, Sloan; Zorman, Christian A.

2008-10-01

This paper reports an effort to develop amorphous silicon carbide (a-SiC) films for use in shunt capacitor RF MEMS microbridge-based switches. The films were deposited using methane and silane as the precursor gases. Switches were fabricated using 500 nm and 300 nm-thick a-SiC films to form the microbridges. Switches made from metallized 500 nm-thick SiC films exhibited favorable mechanical performance but poor RF performance. In contrast, switches made from metallized 300 nm-thick SiC films exhibited excellent RF performance but poor mechanical performance. Load-deflection testing of unmetallized and metallized bulk micromachined SiC membranes indicates that the metal layers have a small effect on the Young's modulus of the 500 nm and 300 nm-thick SiC MEMS. As for residual stress, the metal layers have a modest effect on the 500 nm-thick structures, but a significant affect on the residual stress in the 300 nm-thick structures.

Skyrmion states in thin confined polygonal nanostructures

NASA Astrophysics Data System (ADS)

Pepper, Ryan Alexander; Beg, Marijan; Cortés-Ortuño, David; Kluyver, Thomas; Bisotti, Marc-Antonio; Carey, Rebecca; Vousden, Mark; Albert, Maximilian; Wang, Weiwei; Hovorka, Ondrej; Fangohr, Hans

2018-03-01

Recent studies have demonstrated that skyrmionic states can be the ground state in thin-film FeGe disk nanostructures in the absence of a stabilising applied magnetic field. In this work, we advance this understanding by investigating to what extent this stabilisation of skyrmionic structures through confinement exists in geometries that do not match the cylindrical symmetry of the skyrmion—such as squares and triangles. Using simulation, we show that skyrmionic states can form the ground state for a range of system sizes in both triangular and square-shaped FeGe nanostructures of 10 nm thickness in the absence of an applied field. We further provide data to assist in the experimental verification of our prediction; to imitate an experiment where the system is saturated with a strong applied field before the field is removed, we compute the time evolution and show the final equilibrium configuration of magnetization fields, starting from a uniform alignment.

Spin Hall Effects in Metallic Antiferromagnets

DOE PAGES

Zhang, Wei; Jungfleisch, Matthias B.; Jiang, Wanjun; ...

2014-11-04

In this paper, we investigate four CuAu-I-type metallic antiferromagnets for their potential as spin current detectors using spin pumping and inverse spin Hall effect. Nontrivial spin Hall effects were observed for FeMn, PdMn, and IrMn while a much higher effect was obtained for PtMn. Using thickness-dependent measurements, we determined the spin diffusion lengths of these materials to be short, on the order of 1 nm. The estimated spin Hall angles of the four materials follow the relationship PtMn > IrMn > PdMn > FeMn, highlighting the correlation between the spin-orbit coupling of nonmagnetic species and the magnitude of the spinmore » Hall effect in their antiferromagnetic alloys. These experiments are compared with first-principles calculations. Finally, engineering the properties of the antiferromagnets as well as their interfaces can pave the way for manipulation of the spin dependent transport properties in antiferromagnet-based spintronics.« less

Thickness of Santa Fe Group sediments in the Espanola Basin south of Santa Fe, New Mexico, as estimated from aeromagnetic data

USGS Publications Warehouse

Phillips, Jeffrey D.; Grauch, V.J.S.

2004-01-01

In the southern Espa?ola basin south of Santa Fe, New Mexico, weakly magnetic Santa Fe Group sediments of Oligocene to Pleistocene age, which represent the primary aquifers for the region, are locally underlain by moderately to strongly magnetic igneous and volcaniclastic rocks of Oligocene age. Where this relationship exists, the thickness of Santa Fe Group sediments, and thus the maximum thickness of the aquifers, can be estimated from quantitative analysis of high-resolution aeromagnetic data. These thickness estimates provide guidance for characterizing the ground-water resources in between scattered water wells in this area of rapid urban development and declining water supplies. This report presents one such analysis based on the two-step extended Euler method for estimating depth to magnetic sources. The results show the general form of a north-trending synclinal basin located between the Cerrillos Hills and Eldorado with northward thickening of Santa Fe Group sediments. The increase in thickness is gradual from the erosional edge on the south to a U-shaped Santa Fe embayment hinge line, north of which sediments thicken much more dramatically. Along the north-south basin axis, Santa Fe Group sediments thicken from 300 feet (91 meters) at the hinge line near latitude 35o32'30'N to 2,000 feet (610 meters) at the Cerrillos Road interchange at Interstate 25, north of latitude 35o36'N. The depth analysis indicates that, superimposed on this general synclinal form, there are many local areas where the Santa Fe Group sediments may be thickened by a few hundred feet, presumably due to erosional relief on the underlying Oligocene volcanic and volcaniclastic rocks. Some larger areas of greater apparent thickening occur where the presence of magnetic rocks directly underlying the Santa Fe Group is uncertain. Where magnetic rocks are absent beneath the Santa Fe Group, the thickness cannot be estimated from the aeromagnetic data.

Phase transformation and magnetic properties of MnAl powders prepared by elemental-doping and salt-assisted ball milling

NASA Astrophysics Data System (ADS)

Qian, Hui-Dong; Si, Ping-Zhan; Choi, Chul-Jin; Park, Jihoon; Cho, Kyung Mox

2018-05-01

The effects of elemental doping of Si and Fe on the ɛ→τ phase transformation and the magnetic properties of MnAl were studied. The magnetic powders of Si- and Fe-doped MnAl were prepared by using induction melting followed by water-quenching, annealing, and salt-assisted ball-milling. The Fe-doped MnAl powders are mainly composed of the L10-structured τ-phase, while the Si-doped MnAl are composed of τ-phase and a small fraction of γ2- and β-phases. A unique thin leaves-like morphology with thickness of several tens of nanometers and diameter size up to 500 nm were observed in the Si-doped MnAl powders. The Fe-doped MnAl powders show irregular shape with much larger dimensions in the range from several to 10 μm. The morphology difference of the samples was ascribed to the variation of the mechanical properties affected by different doping elements. The phase transformation temperatures of the ɛ-phase of the samples were measured. The doping of Fe decreases the onset temperature of the massive phase transformation in MnAl, while the Si-doping increases the massive phase transformation temperature. Both Fe and Si increase the Curie temperature of MnAl. A substantially enhanced coercivity up to 0.45 T and 0.42 T were observed in the ball-milled MnAl powders doped with Si and Fe, respectively.

Self-assembly and electrical characteristics of 4-pentynoic acid functionalized Fe3O4-γ-Fe2O3 nanoparticles on SiO2/n-Si

NASA Astrophysics Data System (ADS)

Baharuddin, Aainaa Aqilah; Ang, Bee Chin; Wong, Yew Hoong

2017-11-01

A novel investigation on a relationship between temperature-influential self-assembly (70-300 °C) of 4-pentynoic acid functionalized Fe3O4-γ-Fe2O3 nanoparticles (NPs) on SiO2/n-Si with electrical properties was reported with the interests for metal-oxide-semiconductor applications. X-ray diffractometer (XRD) analysis conveyed that 8 ± 1 nm of the NPs were assembled. Increasing heating temperature induced growth of native oxide (SiO2). Raman analysis confirmed the coexistence of Fe3O4-γ-Fe2O3. Attenuated Total Reflectance Infrared (ATR-IR) spectra showed that self-assembly occurred via Sisbnd Osbnd C linkages. While Sisbnd Osbnd C linkages were broken down at elevated temperatures, formations of Si-OH defects were amplified; a consequence of physisorbed surfactants disintegration. Atomic force microscopy (AFM) showed that sample with more physisorbed surfactants exhibited the highest root-mean-square (RMS) roughness (18.12 ± 7.13 nm) whereas sample with lesser physisorbed surfactants displayed otherwise (12.99 ± 4.39 nm RMS roughness). Field Emission Scanning Electron Microscope (FE-SEM) analysis showed non-uniform aggregation of the NPs, deposited as film (12.6 μm thickness). The increased saturation magnetization (71.527 A m2/kg) and coercivity (929.942 A/m) acquired by vibrating sample magnetometer (VSM) of the sample heated at 300 °C verified the surfactants' disintegration. Leakage current density-electric field (J-E) characteristics showed that sample heated at 150 °C with the most aggregated NPs as well as the most developed Sisbnd Osbnd C linkages demonstrated the highest breakdown field and barrier height at 2.58 × 10-3 MV/cm and 0.38 eV respectively. Whereas sample heated at 300 °C with the least Sisbnd Osbnd C linkages as well as lesser aggregated NPs showed the lowest breakdown field and barrier height at 1.08 × 10-3 MV/cm and 0.19 eV respectively. This study opens up better understandings on how formation and breaking down of covalent linkages as well as accumulation of defects, particularly prior temperature influential self-assembly at the interfaces, affected electrical breakdown field and barrier height. Hence, possible future development of self-assembly silicon-based metal-oxide-semiconductor (MOS) structure particularly in the presence of SiO2 can be deliberated.

Distribution of dissolved labile and particulate iron and copper in Terra Nova Bay polynya (Ross Sea, Antarctica) surface waters in relation to nutrients and phytoplankton growth

NASA Astrophysics Data System (ADS)

Rivaro, Paola; Ianni, Carmela; Massolo, Serena; Abelmoschi, M. Luisa; De Vittor, Cinzia; Frache, Roberto

2011-05-01

The distribution of the dissolved labile and of the particulate Fe and Cu together with dissolved oxygen, nutrients, chlorophyll a and total particulate matter was investigated in the surface waters of Terra Nova Bay polynya in mid-January 2003. The measurements were conducted within the framework of the Italian Climatic Long-term Interactions of the Mass balance in Antarctica (CLIMA) Project activities. The labile dissolved fraction was operationally defined by employing the chelating resin Chelex-100, which retains free and loosely bound trace metal species. The dissolved labile Fe ranges from below the detection limit (0.15 nM) to 3.71 nM, while the dissolved labile Cu from below the detection limit (0.10 nM) to 0.90 nM. The lowest concentrations for both metals were observed at 20 m depth (the shallowest depth for which metals were measured). The concentration of the particulate Fe was about 5 times higher than the dissolved Fe concentration, ranging from 0.56 to 24.83 nM with an average of 6.45 nM. The concentration of the particulate Cu ranged from 0.01 to 0.71 nM with an average of 0.17 nM. The values are in agreement with the previous data collected in the same area. We evaluated the role of the Fe and Cu as biolimiting metals. The N:dissolved labile Fe ratios (18,900-130,666) would or would not allow a complete nitrate removal, on the basis of the N:Fe requirement ratios that we calculated considering the N:P and the C:P ratios estimated for diatoms. This finding partially agrees with the Si:N ratio that we found (2.29). Moreover we considered a possible influence of the dissolved labile Cu on the Fe uptake process.

Effect of capping and particle size on Raman laser-induced degradation of {gamma}-Fe{sub 2}O{sub 3} nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Varadwaj, K.S.K.; Panigrahi, M.K.; Ghose, J.

2004-11-01

Diol capped {gamma}-Fe{sub 2}O{sub 3} nanoparticles are prepared from ferric nitrate by refluxing in 1,4-butanediol (9.5nm) and 1,5-pentanediol (15nm) and uncapped particles are prepared by refluxing in 1,2-propanediol followed by sintering the alkoxide formed. X-ray diffraction (XRD) shows that all the samples have the spinel phase. Raman spectroscopy shows that the samples prepared in 1,4-butanediol and 1,5-pentanediol and 1,2-propanediol (sintered at 573 and 673K) are {gamma}-Fe{sub 2}O{sub 3} and the 773K-sintered sample is Fe{sub 3}O{sub 4}. Raman laser studies carried out at various laser powers show that all the samples undergo laser-induced degradation to {alpha}-Fe{sub 2}O{sub 3} at higher lasermore » power. The capped samples are however, found more stable to degradation than the uncapped samples. The stability of {gamma}-Fe{sub 2}O{sub 3} sample with large particle size (15.4nm) is more than the sample with small particle size (10.2nm). Fe{sub 3}O{sub 4} having a particle size of 48nm is however less stable than the smaller {gamma}-Fe{sub 2}O{sub 3} nanoparticles.« less

Synthesis of High Symmetry Phase of Hafnium Dioxide Thin Films and Nickel Ferrite's Effect on Microstructure in Composite Heterostructure

NASA Astrophysics Data System (ADS)

Straka, Weston J.

Hafnium dioxide has attracted a great deal of attention recently due to its potential use in two different electronic applications: CMOS and FeRAM. In CMOS, the usefulness of hafnia comes in due to its high dielectric constant and compatibility with current IC processing parameters. For FeRAM, hafnia's recent discovery to exhibit ferroelectricity in an orthorhombic phase makes this material attractive for replacement of the ferroelectric material in FeRAM. This study shows the feasibility of depositing thin films of hafnium oxide via chemical solution deposition for integration into these devices. The processing parameters necessary to produce this phase show how non-equilibrium processing plays a role in its synthesis. The temperature necessary to achieve the high symmetry phase was at 725 °C for 3 minutes on sapphire, silicon, and coated silicon substrates. The thermal conductivity of each was viewed as the property that allowed the hafnia formation. The dielectric constant of the hafnia films were between 30 and 32 with low dissipation factors and up to 47 with a poor dissipation factor all at 1 kHz. The formation of this phase was shown to be thickness independent with the high symmetry phase existing up to 300 nm film thickness. Interfacing the hafnia film with nickel ferrite was also studied to identify the possibility of using this composite for non-destructive reading of FeRAM. The magnetic properties showed an unchanged nickel ferrite film but the interface between the two was poor leading to the conclusion that more work must be done to successfully integrate these two films.

Structural Properties of Alternate Monatomic Layered [Fe/Co]n Epitaxial Films on MgO Substrate

NASA Astrophysics Data System (ADS)

Chu, In Chang; Saki, Yoshinobu; Kawasaki, Shohei; Doi, Masaaki; Sahashi, Masashi

2008-06-01

Body-centered-cubic (bcc) Fe50Co50 material is reported to show a high bulk spin scattering coefficient on current perpendicular to plane-giant magneto-resistance (CPP-GMR) system. But the origin of that phenomenon does not make sure yet. We prepared artificially alternate monatomic layered (AML) [Fe/Co] 41 MLs epitaxial films (Ts: 75, 250 °C) by monatomic deposition method and investigated the topology of AML [Fe/Co]n epitaxial films on MgO substrate with different orientation (001), (011) by the scanning tunnel microscopy (STM) and reflection high energy electron diffraction (RHEED), which we could confirm Frank-van der Merwe (FM) growth mode for AML [Fe/Co]n on MgO(001) and Volmer-Weber (VW) growth mode for that on Mg(011). The roughness of surface, Ra (0.20 nm) of AML [Fe/Co] 41 MLs epitaxial film grown at 75 °C on MgO(001) is smaller than that (0.46 nm) of AML [Fe/Co] grown at 250 °C on MgO(001), which has the large terraces of over 50 nm (Ra: 0.17 nm), even though there are some valleys between large terraces. Moreover we confirmed the structural properties of trilayered epitaxial films with AML [Fe/Co]n (Ra: 0.18 nm) and Fe50Co50 alloy epitaxial film on Au electrode by RHEED before confirming the characteristics of CPP-GMR devices.

Microstructure, Chemistry, and Origin of Grain Rims on ilmenite from the Lunar Soil Finest Fraction

NASA Technical Reports Server (NTRS)

Christoffersen, Roy; Keller, Lindsay P.; McKay, David S.

1996-01-01

Analytical transmission electron microscope (TEM) observations reveal that ilmenite grains sampled from the sub-10 micron size fraction of Apollo 11 (10084) and Apollo 16 (61221, 67701) soils have rims 10-300 nm thick that are chemically and microstructurally distinct from the host ilmenite. The rims have a thin outer sublayer 10-50 nm thick that contains the ilmenite-incompatible elements Si, Al, Ca and S. This overlies a relatively thicker (50-250 nm) inner sublayer of nanocrystalline Ti-oxide precipitates in a matrix of single-crystal ilmenite that is structurally continuous with the underlying host grain. Microstructural information, as well as data from x-ray spectrometry (EDS) and electron energy loss spectrometry (EELS) analysis of the inner sublayer, suggest that both the inner and outer sublayer assemblages are reduced and that the inner layer is depleted in Fe relative to the underlying ilmenite. The chemistry of the outer sublayer suggests that it is a surface deposit of sputtered or impact-vaporized components from the bulk lunar soil. The inner sublayer is part of the original host grain that has been physically and chemically processed, but not amorphized, by solar ion irradiation and possibly some subsolidus heating. The fact that the deposited outer sublayer is consistently much thinner than the radiation-altered inner sublayer indicates that only a minor fraction of the total rim volume is a product of vapor or sputter deposition. This finding is in contrast to recent descriptions of thick deposited layers on one-third of regolith silicate grains and indicates that ilmenite and silicate rims as a group are different in the fraction of deposited material that they contain.

Electrolyte induced rheological modulation of graphene oxide suspensions and its applications in adsorption

NASA Astrophysics Data System (ADS)

Ojha, Abhijeet; Thareja, Prachi

2018-03-01

In this study, we report the microstructure, rheology and adsorption characteristics of aqueous suspensions of Graphene Oxide (GO) at a volume fraction (ϕGO) = 0.018, which can be transformed into gels by cation induced charge shielding and cross-linking between GO nanosheets. GO nanosheets of average thickness ∼1.5 nm and a lateral dimension of ∼750 nm are synthesized by Hummer's process. At ϕGO= 0.018, cations of varying size and valence are systematically introduced with electrolytes NH4Cl, LiCl, NaCl, KCl, MgCl2 and FeCl3 at concentrations ranging from 10-5-10-1 M to investigate their effect on the rheology of GO suspensions. Our results suggest that depending on the electrolyte concentration, size and the valence of the cation: low viscosity suspensions, fragile gels and solid-like GO-electrolyte gels are formed. The storage modulus (G') of all GO-electrolyte gels increases with the increase in electrolyte concentration and G' follows the order GO-FeCl3 > GO-MgCl2> GO-KCl > GO-NaCl > GO-LiCl > GO-NH4Cl. FESEM analysis shows that lyophilized GO-electrolyte gels with 10-1 M electrolytes have a porous morphology resulting from the aggregation of GO nanosheets. The GO-electrolyte gels are shown to adsorb high quantities of oils, with GO-FeCl3 gels showing a higher adsorption capacity. The GO-NaCl and GO-FeCl3 lyophilized gels are also shown to adsorb methylene blue dye and follow the pseudo-second-order kinetics of adsorption. Along with higher oil and dye adsorption efficiency, GO-electrolyte gels are easy to recollect after the adsorption, thus avoiding the potential toxicity for bio-organisms in water caused by GO nanosheets.

Direct Observation of Interfacial Dzyaloshinskii-Moriya Interaction from Asymmetric Spin-wave Propagation in W/CoFeB/SiO2 Heterostructures Down to Sub-nanometer CoFeB Thickness

PubMed Central

Chaurasiya, Avinash Kumar; Banerjee, Chandrima; Pan, Santanu; Sahoo, Sourav; Choudhury, Samiran; Sinha, Jaivardhan; Barman, Anjan

2016-01-01

Interfacial Dzyaloshinskii-Moriya interaction (IDMI) is important for its roles in stabilizing the skyrmionic lattice as well as soliton-like domain wall motion leading towards new generation spintronic devices. However, achievement and detection of IDMI is often hindered by various spurious effects. Here, we demonstrate the occurrence of IDMI originating primarily from W/CoFeB interface in technologically important W/CoFeB/SiO2 heterostructures using Brillouin light scattering technique. Due to the presence of IDMI, we observe asymmetry in the peak frequency and linewidth of the spin-wave spectra in the Damon-Eshbach (DE) geometry at finite k wave-vectors. The DMI constant is found to scale as the inverse of CoFeB thickness, over the whole studied thickness range, confirming the presence of IDMI in our system without any extrinsic effects. Importantly, the W/CoFeB interface shows no degradation down to sub-nanometer CoFeB thickness, which would be useful for devices that aim to use pronounced interface effects. PMID:27586260

Compositional dependence of magnetic anisotropy in chemically synthesized Co3- x Fe x O4 (0 ≤ x ≤ 2)

NASA Astrophysics Data System (ADS)

Hayashi, Kensuke; Yamada, Keisuke; Shima, Mutsuhiro

2018-01-01

Magnetic anisotropy of Co3- x Fe x O4 (CFO, 0 ≤ x ≤ 2) thin-film and powder samples prepared by a sol-gel method has been investigated as a function of Fe composition x. Structural analyses by X-ray diffraction show that CFO powder samples exhibit diffraction peaks associated with the spinel structure when x < 2, while CFO thin-film samples with thickness of 130-510 nm yield the peaks when 0 ≤ x ≤ 2. CFO thin-film samples are highly (111)-oriented with the Lotgering factor greater than 0.9 when 0.6 ≤ x ≤ 1.3. The magnetic anisotropy constant K 1 of CFO powder samples estimated from their room-temperature hysteresis loops yields a minimum when x = 0.9. Relatively large in-plane magnetic anisotropy (K eff = 5.7 × 105 erg/cm3) is observed for the CFO thin-film sample when x = 1.3. With increasing x, the magnetic easy axis of the spinel CFO changes from 〈111〉 to 〈100〉 when x = 0.9.

Depth profiling of marker layers using x-ray waveguide structures

NASA Astrophysics Data System (ADS)

Gupta, Ajay; Rajput, Parasmani; Saraiya, Amit; Reddy, V. R.; Gupta, Mukul; Bernstorff, Sigrid; Amenitsch, H.

2005-08-01

It is demonstrated that x-ray waveguide structures can be used for depth profiling of a marker layer inside the guiding layer with an accuracy of better than 0.2 nm. A combination of x-ray fluorescence and x-ray reflectivity measurements can provide detailed information about the structure of the guiding layer. The position and thickness of the marker layer affect different aspects of the angle-dependent x-ray fluorescence pattern, thus making it possible to determine the structure of the marker layer in an unambiguous manner. As an example, effects of swift heavy ion irradiation on a Si/M/Si trilayer ( M=Fe , W), forming the cavity of the waveguide structure, have been studied. It is found that in accordance with the prediction of thermal spike model, Fe is much more sensitive to swift heavy ion induced modifications as compared to W, even in thin film form. However, a clear evidence of movement of the Fe marker layer towards the surface is observed after irradiation, which cannot be understood in terms of the thermal spike model alone.

Smart Pd Catalyst with Improved Thermal Stability Supported on High-Surface-Area LaFeO3 Prepared by Atomic Layer Deposition.

PubMed

Onn, Tzia Ming; Monai, Matteo; Dai, Sheng; Fonda, Emiliano; Montini, Tiziano; Pan, Xiaoqing; Graham, George W; Fornasiero, Paolo; Gorte, Raymond J

2018-04-11

The concept of self-regenerating or "smart" catalysts, developed to mitigate the problem of supported metal particle coarsening in high-temperature applications, involves redispersing large metal particles by incorporating them into a perovskite-structured support under oxidizing conditions and then exsolving them as small metal particles under reducing conditions. Unfortunately, the redispersion process does not appear to work in practice because the surface areas of the perovskite supports are too low and the diffusion lengths for the metal ions within the bulk perovskite too short. Here, we demonstrate reversible activation upon redox cycling for CH 4 oxidation and CO oxidation on Pd supported on high-surface-area LaFeO 3 , prepared as a thin conformal coating on a porous MgAl 2 O 4 support using atomic layer deposition. The LaFeO 3 film, less than 1.5 nm thick, was shown to be initially stable to at least 900 °C. The activated catalysts exhibit stable catalytic performance for methane oxidation after high-temperature treatment.

Influence of film thickness on topology and related magnetic interactions in Fe nanoparticle films

NASA Astrophysics Data System (ADS)

Ausanio, G.; Iannotti, V.; Amoruso, S.; Bruzzese, R.; Wang, X.; Aruta, C.; Arzeo, M.; Lanotte, L.

2013-08-01

Fe nanoparticle (NP)-assembled thin films with different thickness were prepared by femtosecond-pulsed laser deposition using different deposition times. The proper selection of the deposition time allows to control, to a certain degree, the morphology and topology of the deposited Fe nanoparticles (NPs) assembly, fostering non-uniform dense assemblies of NPs, with the consequent reduction of the influence of the exchange interactions on the macroscopic magnetic properties with decreasing thickness. The magnetic behavior of the Fe NP-assembled films with decreasing thickness is characterized by higher coercive field ( H c) values (a factor ≈4.5) and a good compromise between the hysteresis loops squareness and moderate exchange interactions, strongly correlated with the NPs topology.

High magnetization Fe-Co and Fe-Ni submicron and nanosize particles by thermal decomposition and hydrogen reduction

NASA Astrophysics Data System (ADS)

Cui, B. Z.; Marinescu, M.; Liu, J. F.

2014-05-01

This paper reports morphology, structure, and magnetic properties of air-stable soft magnetic FexCo100-x (x = 65, 50, and 34) and Fe50Ni50 (at. %) submicron and nanosize particles fabricated by template-free thermal decomposition of nitrates of Fe, Co, and Ni and subsequent hydrogen reduction. The particle compositions were tuned by modification of the precursor solution concentrations. The as-synthesized Fe-Co and Fe50Ni50 particles have body centered cubic and face centered cubic poly-nanocrystalline structures, respectively. The Fe-Co and Fe50Ni50 particles have particle sizes in the range of 28-200 nm and 70-480 nm, and average grain sizes of 16-29 nm and 20-24 nm, respectively. The particle and grain sizes were controlled by tuning particle composition, and the temperature and time of hydrogen reduction. Saturation magnetization Ms as high as 207-224 emu/g and intrinsic coercivity Hci of 59-228 Oe were obtained in the Fe-Co particles reduced at 550 °C for 90 min. Of special note, the Ms of 224 emu/g (˜2.3 T) obtained in the Fe65Co35 particles is among the highest values for Fe-Co particles reported so far. Ms of 135-137 emu/g and Hci of 59-111 Oe were obtained in the Fe50Ni50 particles reduced at 500 or 550 °C for 20 min.

Ultrasoft magnetic films investigated with Lorentz tranmission electron microscopy and electron holography.

PubMed

De Hosson, Jeff Th M; Chechenin, Nicolai G; Alsem, Daan-Hein; Vystavel, Tomas; Kooi, Bart J; Chezan, Antoni R; Boerma, Dik O

2002-08-01

As a tribute to the scientific work of Professor Gareth Thomas in the field of structure-property relationships this paper delineates a new possibility of Lorentz transmission electron microscopy (LTEM) to study the magnetic properties of soft magnetic films. We show that in contrast to the traditional point of view, not only does the direction of the magnetization vector in nano-crystalline films make a correlated small-angle wiggling, but also the magnitude of the magnetization modulus fluctuates. This fluctuation produces a rapid modulation in the LTEM image. A novel analysis of the ripple structure in nano-crystalline Fe-Zr-N film corresponds to an amplitude of the transversal component of the magnetization deltaMy of 23 mT and a longitudinal fluctuation of the magnetization of the order of deltaMx = 30 mT. The nano-crystalline (Fe99Zr1)1-xNx films have been prepared by DC magnetron reactive sputtering with a thickness between 50 and 1000 nm. The grain size decreased monotonically with N content from typically 100 nm in the case of N-free films to less than 10 nm for films containing 8 at%. The specimens were examined with a JEOL 2010F 200 kV transmission electron microscope equipped with a post column energy filter (GIF 2000 Gatan Imaging Filter). For holography, the microscope is mounted with a biprism (JEOL biprism with a 0.6 microm diameter platinum wire).

Reactive Iron Delivery to the Central Gulf of Alaska via Two Mesoscale Eddies (Invited)

NASA Astrophysics Data System (ADS)

Lippiatt, S. M.; Brown, M. T.; Lohan, M. C.; Bruland, K. W.

2010-12-01

Coastal waters in the northern Gulf of Alaska (GoA) are considered Fe-rich and nitrate-poor, in contrast to the Fe-poor, high-nitrate, low chlorophyll (HNLC) waters of the central GoA. Mixing between these two regimes can lead to enhanced primary productivity. Mesoscale anticyclonic eddies are an important mechanism for cross-shelf exchange of coastal and HNLC waters. This presentation will discuss findings from a cruise in the GoA during late summer 2007, namely dissolved Fe, leachable particulate Fe (defined as the portion of the particulate Fe that is solubilized with a two hour, 25% acetic acid leach with a short heating step and a reducing agent), and nitrate. Leachable particulate Fe concentrations in coastal surface waters between Yakutat, AK and the Kenai Peninsula ranged from over 1 uM in the Alsek River plume to less than 5 nM at the base of Cook Inlet, and were more variable and at least an order of magnitude higher than dissolved Fe concentrations. Relatively low and consistent dissolved Fe (~2 nM) suggests that the system’s ability to solubilize this large concentration of leachable particulate Fe is overwhelmed by the massive input of glacial-derived particulate Fe. Suspended leachable particulate Fe is available for exchange to the dissolved phase and is suggested to maintain a relatively constant 2 nM concentration of dissolved Fe in the coastal GoA. Glacial meltwaters were not a significant source of nitrate compared to central GoA HNLC or upwelled waters. The work completed in the coastal GoA set the stage for assessing the delivery of this glacial-derived coastal Fe to HNLC waters via mesoscale eddies. Two mesoscale eddies were sampled during this study: a Sitka eddy located off Yakutat, Alaska and a Kenai eddy sampled off the shelf break near Kodiak Island. The temperature and salinity structures of the eddies reflected their coastal origin; core waters were warmer and fresher than surrounding basin waters, coincident with elevated dissolved and leachable particulate Fe. In the core of the Yakutat eddy at 50 - 100 m depth there was on average 0.8 nM reactive Fe (dissolved + leachable particulate Fe), approximately five times more reactive Fe compared to adjacent GoA basin waters (0.16 nM). At the same depths in the core of the Kenai eddy there was on average 1.9 nM reactive Fe, ten times more reactive Fe than the basin waters (0.19 nM). In addition, for a given density, core waters had elevated nitrate and silicate compared to outside the eddy. Storms can mix Fe-enriched eddy core waters to the surface. Furthermore, anticyclonic GoA eddies can be a significant source of Fe to HNLC waters when they propagate into the central GoA and eventually relax with the Fe and nutrient rich subsurface waters rebounding or upwelling towards the surface. The transport of coastal waters into central GoA waters via mesoscale eddies is shown to be an important mechanism for Fe delivery into this HNLC region.

Patterned Growth of Carbon Nanotubes or Nanofibers

NASA Technical Reports Server (NTRS)

Delzeit, Lance D.

2004-01-01

A method and apparatus for the growth of carbon nanotubes or nanofibers in a desired pattern has been invented. The essence of the method is to grow the nanotubes or nanofibers by chemical vapor deposition (CVD) onto a patterned catalyst supported by a substrate. The figure schematically depicts salient aspects of the method and apparatus in a typical application. A substrate is placed in a chamber that contains both ion-beam sputtering and CVD equipment. The substrate can be made of any of a variety of materials that include several forms of silicon or carbon, and selected polymers, metals, ceramics, and even some natural minerals and similar materials. Optionally, the substrate is first coated with a noncatalytic metal layer (which could be a single layer or could comprise multiple different sublayers) by ion-beam sputtering. The choice of metal(s) and thickness(es) of the first layer (if any) and its sublayers (if any) depends on the chemical and electrical properties required for subsequent deposition of the catalyst and the subsequent CVD of the carbon nanotubes. A typical first-sublayer metal is Pt, Pd, Cr, Mo, Ti, W, or an alloy of two or more of these elements. A typical metal for the second sublayer or for an undivided first layer is Al at a thickness .1 nm or Ir at a thickness .5 nm. Proper choice of the metal for a second sublayer of a first layer makes it possible to use a catalyst that is chemically incompatible with the substrate. In the next step, a mask having holes in the desired pattern is placed over the coated substrate. The catalyst is then deposited on the coated substrate by ion-beam sputtering through the mask. Optionally, the catalyst could be deposited by a technique other than sputtering and/or patterned by use of photolithography, electron- beam lithography, or another suitable technique. The catalytic metal can be Fe, Co, Ni, or an alloy of two or more of these elements, deposited to a typical thickness in the range from 0.1 to 20 nm.

Structural and optical properties of ZnO thin films prepared by RF sputtering at different thicknesses

NASA Astrophysics Data System (ADS)

Hammad, Ahmed H.; Abdel-wahab, M. Sh.; Vattamkandathil, Sajith; Ansari, Akhalakur Rahman

2018-07-01

Hexagonal nanocrystallites of ZnO in the form of thin films were prepared by radio frequency sputtering technique. X-ray diffraction analysis reveals two prominent diffraction planes (002) and (103) at diffraction angles around 34.3 and 62.8°, respectively. The crystallite size increases through (103) plane from 56.1 to 64.8 Å as film thickness changed from 31 nm up to 280 nm while crystallites growth through (002) increased from 124 to 136 Å as film thickness varies from 31 to 107 nm and dropped to 115.8 Å at thickness 280 nm. The particle shape changes from spherical to longitudinal form. The particle size is 25 nm for films of thickness below 107 nm and increases at higher thicknesses (134 and 280 nm) from 30 to 40 nm, respectively. Optical band gap is deduced to be direct with values varied from 3.22 to 3.28 eV and the refractive index are evaluated based on the optical band values according to Moss, Ravindra-Srivastava, and Dimitrov-Sakka models. All refractive index models gave values around 2.3.

Fe-Al interface intermixing and the role of Ti, V, and Zr as a stabilizing interlayer at the interface

NASA Astrophysics Data System (ADS)

Priyantha, W.; Smith, R. J.; Chen, H.; Kopczyk, M.; Lerch, M.; Key, C.; Nachimuthu, P.; Jiang, W.

2009-03-01

Fe-Al bilayer interfaces with and without interface stabilizing layers (Ti, V, Zr) were fabricated using dc magnetron sputtering. Intermixing layer thickness and the effectiveness of the stabilizing layer (Ti, V, Zr) at the interface were studied using Rutherford backscattering spectrometry (RBS) and x-ray reflectometry (XRR). The result for the intermixing thickness of the AlFe layer is always higher when Fe is deposited on Al as compared to when Al is deposited on Fe. By comparing measurements with computer simulations, the thicknesses of the AlFe layers were determined to be 20.6 Å and 41.1 Å for Al/Fe and Fe/Al bilayer systems, respectively. The introduction of Ti and V stabilizing layers at the Fe-Al interface reduced the amount of intermixing between Al and Fe, consistent with the predictions of model calculations. The Zr interlayer, however, was ineffective in stabilizing the Fe-Al interface in spite of the chemical similarities between Ti and Zr. In addition, analysis suggests that the Ti interlayer is not effective in stabilizing the Fe-Al interface when the Ti interlayer is extremely thin (˜3 Å) for these sputtered metallic films.

Room temperature luminescence and ferromagnetism of AlN:Fe

NASA Astrophysics Data System (ADS)

Li, H.; Cai, G. M.; Wang, W. J.

2016-06-01

AlN:Fe polycrystalline powders were synthesized by a modified solid state reaction (MSSR) method. Powder X-ray diffraction and transmission electron microscopy results reveal the single phase nature of the doped samples. In the doped AlN samples, Fe is in Fe2+ state. Room temperature ferromagnetic behavior is observed in AlN:Fe samples. Two photoluminescence peaks located at about 592 nm (2.09 eV) and 598 nm (2.07 eV) are observed in AlN:Fe samples. Our results suggest that AlN:Fe is a potential material for applications in spintronics and high power laser devices.

Characterisation of iron-rich atmospheric submicrometre particles in the roadside environment

NASA Astrophysics Data System (ADS)

Sanderson, P.; Su, S. S.; Chang, I. T. H.; Delgado Saborit, J. M.; Kepaptsoglou, D. M.; Weber, R. J. M.; Harrison, Roy M.

2016-09-01

Human exposure to ambient metallic nanoparticles is an area of great interest owing to their potential health impacts. Ambient metallic nanoparticles found in the roadside environment are contributed by combustion engines and wear of brakes, tyres and road surfaces. Submicrometre atmospheric particles collected at two UK urban sites have been subject to detailed characterisation. It is found that many metallic nanoparticles collected from roadside sampling sites are rich in iron. The Fe-rich nanoparticles can be classified into (1) high Fe content (ca 90 wt%) with each alloying element less than 1 wt%; and (2) moderate Fe content (<75 wt%) with high manganese and silicon content. Both clusters contain a variable mix of minor constituents, Mn, S and Si being most important in the high-Fe group. The moderate Fe group also contains Zn, Cu, Ba, Al and Ca. The Fe-rich nanoparticles exhibit primary particle sizes ranging between 20 and 30 nm, although some much larger particles up to around 100 nm can also be observed, along with some very small particles of 10 nm or less. These tend to agglomerate forming clusters ranging from ∼200 nm to 1 μm in diameter. The iron-rich particles observed are oxides, taking the form of spheres or multifaceted regular polyhedra. Analysis by EELS shows that both high- and moderate-Fe groups include particles of FeO, Fe3O4, α-Fe2O3 and γ-Fe2O3 of which γ-Fe2O3 is the most prominent. Internal mixing of different Fe-oxides is not observed.

Magneto-optical properties of nanometer crystal giant magneto-optical BiAlDyIG thin film materials post-treated by rapid recurrent thermal annealing method

NASA Astrophysics Data System (ADS)

Qing-hui, Yang; Huai-wu, Zhang; Ying-li, Liu; Qiye, Wen

2014-05-01

In this paper, high quality BiAlDyIG thin films with different bismuth contents have been prepared by using a sol-gel method and post-treated by a rapid recurrent thermal annealing (RRTA) method. Results indicate that the RRTA method improves the Faraday Effect of the films notably, a maximum Faraday angle of -4.9° in the 450 nm thickness film (Bi1.96Dy1.04Fe4AlO12) was obtained at the wavelength of 520 nm, which is about two times larger than that of the common thermal annealed sample, and furthermore the reason of giant Faraday angle was also analyzed in detail. These results are potentially helpful to improve the recording density and signal-to-noise ratio of magneto-optical disk.

Electrochemical and in-situ Surface-Enhanced Raman Spectroscopic (SERS) study of passive films formed on low-carbon steel in highly alkaline environments

NASA Astrophysics Data System (ADS)

Mancio, Mauricio

In reinforced concrete, a passive layer forms because of the alkaline conditions in the pores of the cement paste, where large concentrations of hydroxides create a solution with pH typically between 12 and 14. The corrosion resistance of the material depends on the characteristics and integrity of the passive film; however, currently very limited information is available about the passive films formed on carbon steel under such conditions. This work presents an electrochemical and in-situ Surface-Enhanced Raman Spectroscopic (SERS) study of passive films formed on low-carbon steel in highly alkaline environments. More specifically, the study focuses on the characterization of the films formed on ASTM A36 steel reinforcing bar exposed to aqueous solutions that aim to reproduce the chemistry of the environment typically found within the cement paste. Electrochemical techniques such as cyclic potentiodynamic polarization curves, galvanostatic cathodic polarization and linear polarization resistance were employed, in addition to in-situ Surface Enhanced Raman Spectroscopy (SERS). The experimental setup was built in a way that SERS experiments could be performed simultaneously with potentiodynamic polarization curves, enabling a detailed analysis of the formation and reduction of the surface films as a function of applied potential. Three solutions with different pH levels were used for the polarization and SERS experiments, namely 0.55M KOH + 0.16M NaOH ([OH-]=0.71), 0.08M KOH + 0.02M NaOH ([OH-]=0.10) and 0.008M KOH + 0.002M NaOH ([OH-]=0.01). Additional NaOH solutions in which the pH was varied from 13 to 9 and the ionic strength from 10 -5 to 10-1 were prepared for a pilot study using linear polarization resistance. Results show that the features observed in the cyclic potentiodynamic polarization curves correlated well with the potential arrests observed in the GCP plots as well as with the changes observed in the SERS spectra, providing valuable information about the formation of passive films on carbon steel in each of the environments studied in this research. Although there are key differences among the films formed in the different solutions tested---particularly regarding their thickness and protectiveness---once the film-formation processes had been completed, generally the films were characterized by an inner layer of Fe(II) and an outer layer of Fe(III). A Fe(OH)2-like species appears consistently as dominating the inner Fe(II) layer, while the outer typically composed mostly by gamma-Fe2O3 and/or gamma-FeOOH. Film thickness varied from about 22 nm to 266 nm depending on the pH of the solution, and decreased as pH was reduced.

Self-current induced spin-orbit torque in FeMn/Pt multilayers

NASA Astrophysics Data System (ADS)

Xu, Yanjun; Yang, Yumeng; Yao, Kui; Xu, Baoxi; Wu, Yihong

2016-05-01

Extensive efforts have been devoted to the study of spin-orbit torque in ferromagnetic metal/heavy metal bilayers and exploitation of it for magnetization switching using an in-plane current. As the spin-orbit torque is inversely proportional to the thickness of the ferromagnetic layer, sizable effect has only been realized in bilayers with an ultrathin ferromagnetic layer. Here we demonstrate that, by stacking ultrathin Pt and FeMn alternately, both ferromagnetic properties and current induced spin-orbit torque can be achieved in FeMn/Pt multilayers without any constraint on its total thickness. The critical behavior of these multilayers follows closely three-dimensional Heisenberg model with a finite Curie temperature distribution. The spin torque effective field is about 4 times larger than that of NiFe/Pt bilayer with a same equivalent NiFe thickness. The self-current generated spin torque is able to switch the magnetization reversibly without the need for an external field or a thick heavy metal layer. The removal of both thickness constraint and necessity of using an adjacent heavy metal layer opens new possibilities for exploiting spin-orbit torque for practical applications.

Characteristics of blue organic light emitting diodes with different thick emitting layers

NASA Astrophysics Data System (ADS)

Li, Chong; Tsuboi, Taiju; Huang, Wei

2014-08-01

We fabricated blue organic light emitting diodes (called blue OLEDs) with emitting layer (EML) of diphenylanthracene derivative 9,10-di(2-naphthyl)anthracene (ADN) doped with blue-emitting DSA-ph (1-4-di-[4-(N,N-di-phenyl)amino]styryl-benzene) to investigate how the thickness of EML and hole injection layer (HIL) influences the electroluminescence characteristics. The driving voltage was observed to increase with increasing EML thickness from 15 nm to 70 nm. The maximum external quantum efficiency of 6.2% and the maximum current efficiency of 14 cd/A were obtained from the OLED with 35 nm thick EML and 75 nm thick HIL. High luminance of 120,000 cd/m2 was obtained at 7.5 V from OLED with 15 nm thick EML.

Iron-rich colloids as carriers of phosphorus in streams: A field-flow fractionation study.

PubMed

Baken, Stijn; Regelink, Inge C; Comans, Rob N J; Smolders, Erik; Koopmans, Gerwin F

2016-08-01

Colloidal phosphorus (P) may represent an important fraction of the P in natural waters, but these colloids remain poorly characterized. In this work, we demonstrate the applicability of asymmetric flow field-flow fractionation (AF4) coupled to high resolution ICP-MS for the characterization of low concentrations of P-bearing colloids. Colloids from five streams draining catchments with contrasting properties were characterized by AF4-ICP-MS and by membrane filtration. All streams contain free humic substances (2-3 nm) and Fe-bearing colloids (3-1200 nm). Two soft water streams contain primary Fe oxyhydroxide-humic nanoparticles (3-6 nm) and aggregates thereof (up to 150 nm). In contrast, three harder water streams contain larger aggregates (40-1200 nm) which consist of diverse associations between Fe oxyhydroxides, humic substances, clay minerals, and possibly ferric phosphate minerals. Despite the diversity of colloids encountered in these contrasting streams, P is in most of the samples predominantly associated with Fe-bearing colloids (mostly Fe oxyhydroxides) at molar P:Fe ratios between 0.02 and 1.5. The molar P:Fe ratio of the waters explains the partitioning of P between colloids and truly dissolved species. Waters with a high P:Fe ratio predominantly contain truly dissolved species because the Fe-rich colloids are saturated with P, whereas waters with a low P:Fe ratio mostly contain colloidal P species. Overall, AF4-ICP-MS is a suitable technique to characterize the diverse P-binding colloids in natural waters. Such colloids may increase the mobility or decrease the bioavailability of P, and they therefore need to be considered when addressing the transport and environmental effects of P in catchments. Copyright © 2016 Elsevier Ltd. All rights reserved.

Space-Weathering on Mercury: Inferences Based on Comparison of MESSENGER Spectral Data and Experimental Space Weathering Data

NASA Astrophysics Data System (ADS)

Gillis-Davis, J. J.; Blewett, D. T.; Lawrence, D. J.; Izenberg, N. R.; McClintock, W. E.; Holsclaw, G. M.; Domingue, D. L.

2009-12-01

Production and accumulation of submicroscopic metallic iron (SMFe) is a principal mechanism by which surfaces of airless silicate bodies in the Solar System, exposed to the space weathering environment, experience spectral modification. Micrometeorite impact vaporization and solar-wind sputtering produce coatings of vapor-deposited SMFe. Both processes can be more intense on Mercury and, as a result, more efficient at creating melt and vapor. In addition, Ostwald ripening may cause SMFe particles to grow larger due to the high surface temperatures on Mercury (as great as 450°C). Spectral effects on the ultraviolet-visible-near-infrared continuum change with the amount and size of SMFe present. Thus, the physical properties and abundance of iron in Mercury’s regolith can be understood by comparing spectral data from controlled space-weathering experiments with spectra from MESSENGER’s Mercury Atmospheric and Surface Composition Spectrometer (MASCS). Knowledge of SMFe size and abundance may provide information on the space weathering conditions under which it was produced or subsequently modified. Reflectance spectra of laboratory-produced samples with varying SMFe grain sizes (average grain sizes of 8, 15, 35, and 40 nm) and iron compositions (from 0.005 to 3.8 wt% Fe as SMFe) are compared with MASCS disk-integrated reflectance from the first flyby of Mercury and will be compared with observations of spectral end members targeted for the third flyby. We compare spectra from 300 nm to 1400 nm wavelength, scaled to 1 at 700 nm, from the laboratory and MASCS. This comparison between laboratory and remote-sensing spectra reveals an excellent match with observations of Mercury for samples with an average iron metal grain size of 8 nm and 1.65 wt% FeO and 15 nm and 0.13 wt% Fe. These average grain sizes of the SMFe component are larger than the average grain size determined for lunar soil samples using transmission electron microscopy (3 nm in rims and 10-15 nm in agglutinates) but are smaller than values obtained from lunar spectra with the methods used here (15-25 nm). We can also infer that silicates in Mercury's high reflectance plains are potentially iron poor, precluding thick vapor deposits coating - both spectral data sets lack a 1-μm absorption and the experimental iron particles are suspended in an iron-free silica gel. Thus, our conclusion on the basis of spectral comparison is that SMFe on Mercury is potentially smaller than on the Moon and that Ostwald ripening is not a major influence on the surface of Mercury. The absence of pronounced darkening of the equatorial regions of Mercury in images from Mariner 10 and MESSENGER's Mercury Dual Imaging System supports also suggest an apparent lack of Ostwald ripening.

Phase Competition Induced Bio-Electrochemical Resistance and Bio-Compatibility Effect in Nanocrystalline Zr x -Cu100-x Thin Films.

PubMed

Badhirappan, Geetha Priyadarshini; Nallasivam, Vignesh; Varadarajan, Madhuri; Leobeemrao, Vasantha Priya; Bose, Sivakumar; Venugopal, Elakkiya; Rajendran, Selvakumar; Angleo, Peter Chrysologue

2018-07-01

Nano-crystalline Zrx-Cu100-x (x = 20-100 at.%) thin films with thickness ranging from 50 to 185 nm were deposited by magnetron co-sputtering with individual Zr and Cu targets. The as-sputtered thin films were characterized by Field Emission Scanning Electron Microscope (FE-SEM), Atomic Force Microscopy (AFM) and Glancing Incidence X-ray Diffraction (GIXRD) for structural and morphological properties. The crystallite size was found to decrease from 57 nm to 37 nm upon increasing the Zr content from 20 to 30 at.% with slight increase in the lattice strain from 0.17 to 0.33%. Further, increase in Zr content to 40 at.% leads to increase in the crystallite size to 57 nm due to stabilization of C10Zr7 phase along with the presence of nanocrystalline Cu-Zr phase. A bimodal distribution of grain size was observed from FE-SEM micrograph was attributed to the highest surface roughness in Zr30Cu70 thin films comprised of Cu10Zr7, Cu9Zr2, Cu-Zr intermetallic phases. In-vitro electrochemical behaviors of nano-crystalline Zrx-Cu100-x thin films in simulated body fluid (SBF) were investigated using potentiodynamic polarization studies. Electrochemical impedance spectroscopy (EIS) data fitting by equivalent electrical circuit fit model suggests that inner bulk layer contributes to high bio-corrosion resistance in Zrx-Cu100-x thin films with increase in Zr content. The results of cyto-compatibility assay suggested that Zr-Cu thin film did not introduce cytotoxicity to osteoblast cells, indicating its suitability as a bio-coating for minimally invasive medical devices.

Modeling the effects of strain profiles and defects on precessional magnetic switching in multiferroic heterostructures

NASA Astrophysics Data System (ADS)

Chavez, Andres C.; Kundu, Auni A.; Lynch, Christopher S.; Carman, Gregory P.

2018-03-01

Strain-mediated multiferroic heterostructures relying on fast 180° precessional magnetic switching have been proposed as a pathway for energy efficient and high density memory/logic devices. However, proper device performance requires precisely timed high frequency ( GHz) voltage pulses dependent on the magnetization dynamics of the structure. In turn, the dynamic response of the device is greatly influenced by the device geometry, strain amplitude, and strain rate. Hence, we study the effects of increasing the voltage amplitude and application rate on the in-plane magnetization dynamics of a single-domain CoFeB ellipse (100 nm x 80 nm x 6 nm) on a 500 nm thick PZT substrate in addition to studying defects in the geometry. Both a coupled micromagnetics, electrostatics and elastodynamics finite element model and a conventional micromagnetics software was used to study the strain-induced magnetic response of the CoFeB ellipse. Both models predict increased 90° magnetic reorientation speed with increased strain amplitude and rate. However, the fully-coupled model predicts slower reorientation and incoherency in comparison to the uncoupled model. This occurs because the fully-coupled model can capture the expected strain gradients of a fabricated device while the micromagnetics model can only represent uniform strain states. Additional studies which introduce geometric defects result in faster precessional motion under the same strain amplitude and rate. This is attributed to localized changes in the magnetization that influence neighboring regions via exchange and demagnetization effects. The results of these studies can help design better devices that will be less sensitive to defects and voltage applications for future strain-mediated multiferroic devices.

Perpendicular magnetic anisotropy and spin reorientation transition in L1{sub 0} FePt films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahn, Jae Young; Lee, Nyun Jong; Kim, Tae Hee

2011-04-01

We investigated the thickness and composition dependence of perpendicular magnetic anisotropy (PMA) in L1{sub 0} Fe{sub 1-x}Pt{sub x} (x = 0.4, 0.5, and 0.55) films. The FePt films with different thicknesses of 35 and 70 A were grown at the substrate temperature T{sub s} = 300 deg. C by molecular beam epitaxy coevaporation technique. A (001)-oriented epitaxial L1{sub 0} FePt film was grown on the thin (001)-oriented fcc Pt layer, while a poorly crystallized FePt film was formed on the (111)-textured Pt layer. Our results showed that, at a fixed thickness of 70 A, the PMA of FePt alloy filmsmore » is enhanced as Pt content increases from 40% to 55%.« less

Dust variations in the diffuse interstellar medium: constraints on Milky Way dust from Planck-HFI observations

NASA Astrophysics Data System (ADS)

Ysard, N.; Köhler, M.; Jones, A.; Miville-Deschênes, M.-A.; Abergel, A.; Fanciullo, L.

2015-05-01

Context. The Planck-HFI all-sky survey from 353 to 857 GHz combined with the IRAS data at 100 μm (3000 GHz, IRIS version of the data) show that the dust properties vary from line of sight to line of sight in the diffuse interstellar medium (ISM) at high Galactic latitude (1019 ≤ NH ≤ 2.5 × 1020 H/cm2, for a sky coverage of ~12%). Aims: These observations contradict the usual thinking of uniform dust properties, even in the most diffuse areas of the sky. Thus, our aim is to explain these variations with changes in the ISM properties and with evolution of the grain properties. Methods: Our starting point is the latest core-mantle dust model. This model consists of small aromatic-rich carbon grains, larger amorphous carbonaceous grains with an aliphatic-rich core and an aromatic-rich mantle, and amorphous silicates (mixture of olivine and pyroxene types) with Fe/FeS nano-inclusions covered by aromatic-rich carbon mantles. We explore whether variations in the radiation field or in the gas density distribution in the diffuse ISM could explain the observed variations. The dust properties are also varied in terms of their mantle thickness, metallic nano-inclusions, carbon abundance locked in the grains, and size distributions. Results: We show that variations in the radiation field intensity and gas density distribution cannot explain variations observed with Planck-HFI but that radiation fields harder than the standard ISRF may participate in creating part of the observed variations. We further show that variations in the mantle thickness on the grains coupled with changes in their size distributions can reproduce most of the observations. We concurrently put a limit on the mantle thickness of the silicates, which should not exceed ~ 10 to 15 nm, and find that aromatic-rich mantles are definitely needed for the carbonaceous grain population with a thickness of at least 5 to 7.5 nm. We also find that changes in the carbon cosmic abundance included in the grains could explain part of the variations in dust observations. Finally, we show that varying the composition of metallic nano-inclusions in the silicates cannot account for the variations, at the same time showing that the amount of FeS they contain cannot be > 50% by volume. Conclusions: With small variations in the dust properties, we are able to explain most of the variations in the dust emission observed by Planck-HFI in the diffuse ISM. We also find that the small realistic changes in the dust properties that we consider almost perfectly match the anti-correlation and scatter in the observed β - T relation.

Reductive and oxidative degradation of iopamidol, iodinated X-ray contrast media, by Fe(III)-oxalate under UV and visible light treatment.

PubMed

Zhao, Cen; Arroyo-Mora, Luis E; DeCaprio, Anthony P; Sharma, Virender K; Dionysiou, Dionysios D; O'Shea, Kevin E

2014-12-15

Iopamidol, widely employed as iodinated X-ray contrast media (ICM), is readily degraded in a Fe(III)-oxalate photochemical system under UV (350 nm) and visible light (450 nm) irradiation. The degradation is nicely modeled by pseudo first order kinetics. The rates of hydroxyl radical (OH) production for Fe(III)-oxalate/H2O2/UV (350 nm) and Fe(III)-oxalate/H2O2/visible (450 nm) systems were 1.19 ± 0.12 and 0.30 ± 0.01 μM/min, respectively. The steady-state concentration of hydroxyl radical (OH) for the Fe(III)-oxalate/H2O2/UV (350 nm) conditions was 10.88 ± 1.13 × 10(-14) M and 2.7 ± 0.1 × 10(-14) M for the Fe(III)-oxalate/H2O2/visible (450 nm). The rate of superoxide anion radical (O2(-)) production under Fe(III)-oxalate/H2O2/UV (350 nm) was 0.19 ± 0.02 μM/min with a steady-state concentration of 5.43 ± 0.473 × 10(-10) M. Detailed product studies using liquid chromatography coupled to Q-TOF/MS demonstrate both reduction (multiple dehalogenations) and oxidation (aromatic ring and side chains) contribute to the degradation pathways. The reduction processes appear to be initiated by the carbon dioxide anion radical (CO2(-)) while oxidation processes are consistent with OH initiated reaction pathways. Unlike most advanced oxidation processes the Fe(III)-oxalate/H2O2/photochemical system can initiate to both reductive and oxidative degradation processes. The observed reductive dehalogenation is an attractive remediation strategy for halogenated organic compounds as the process can dramatically reduce the formation of the problematic disinfection by-products often associated with oxidative treatment processes. Copyright © 2014 Elsevier Ltd. All rights reserved.

Properties of Ferrite Garnet (Bi, Lu, Y)3(Fe, Ga)5O12 Thin Film Materials Prepared by RF Magnetron Sputtering

PubMed Central

Nur-E-Alam, Mohammad; Belotelov, Vladimir; Alameh, Kamal

2018-01-01

This work is devoted to physical vapor deposition synthesis, and characterisation of bismuth and lutetium-substituted ferrite-garnet thin-film materials for magneto-optic (MO) applications. The properties of garnet thin films sputtered using a target of nominal composition type Bi0.9Lu1.85Y0.25Fe4.0Ga1O12 are studied. By measuring the optical transmission spectra at room temperature, the optical constants and the accurate film thicknesses can be evaluated using Swanepoel’s envelope method. The refractive index data are found to be matching very closely to these derived from Cauchy’s dispersion formula for the entire spectral range between 300 and 2500 nm. The optical absorption coefficient and the extinction coefficient data are studied for both the as-deposited and annealed garnet thin-film samples. A new approach is applied to accurately derive the optical constants data simultaneously with the physical layer thickness, using a combination approach employing custom-built spectrum-fitting software in conjunction with Swanepoel’s envelope method. MO properties, such as specific Faraday rotation, MO figure of merit and MO swing factor are also investigated for several annealed garnet-phase films. PMID:29789463

Microstructure optimization for high-performance PrBa0.5Sr0.5Co1.5Fe0.5O5+δ-La2NiO4+δ core-shell cathode of solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Li, Jin; Qiu, Peng; Xia, Meng; Jia, Lichao; Chi, Bo; Pu, Jian; Li, Jian

2018-03-01

Four PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF)-La2NiO4+δ (LN) core-shell cathodes, designated as PL-0, PL-1, PL-3 and PL-5, are prepared by infiltrating LN solution into PBSCF scaffold, and they are investigated in terms of the effect of LN thickness on their electrochemical performance. PL-3 with a continuous LN coating of a moderate average thickness (∼9 nm) demonstrates the lowest initial polarization resistance (0.51 Ω cm2) and highest power density (0.71 W cm-2) among all the cathodes. Polarized at 400 mA cm-2 and 700 °C for up to 40 h, the polarization resistance of all the prepared cathodes increases to approach a stable level after early stage decrease due to current activation, and PL-3 exhibits a slower average rate of performance degradation (25%). The electrochemical performance improvement is mainly attributed to that LN has a relatively high oxygen surface exchange coefficient and continuous LN coating depresses Sr segregation at PBSCF/LN interface.

Ultrasound-assisted fabrication of nanoporous CdS films.

PubMed

Singh, R S; Sanagapalli, S; Jayaraman, V; Singh, V P

2004-01-01

A new method for fabricating nanoporous CdS films is reported. It involves exposing the CdS solution with ultrasound waves during the process of dip coating. Indium tin oxide (ITO)-coated glass and plastic (commercial transparency) were used as substrates. In each case three different precursors were used for dip coating. The precursors used were CdCl2 and thiourea in one case and CdS nanoparticles prepared by sonochemical and microwave-assisted methods in the other two cases. X-ray diffraction studies performed on these powders show a phase corresponding to cubic CdS. The Field Emission Scanning Electron Microscopy (FE-SEM) images of the films on plastic showed uniform pores with a diameter of 80 nm for all three methods. Optical absorption measurements indicated a blue shift and multiple peaks in the absorption curve. The FE-SEM observations of the films on an ITO/glass substrate indicated a crystalline film with voids. The UV-vis absorption results indicated a blue shift in the absorption with an absorption edge at 435, 380, and 365 nm for CdS films made by solution growth, sonochemical, and microwave routes, respectively. The magnitude of the absorption is dependent on film thickness, and the observed blue shift in the absorption can be explained on the basis of quantum confinement effects.

Electrodeposition and magnetic characterization of iron and iron-silicon alloys from the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate.

PubMed

Giridhar, Pulletikurthi; Weidenfeller, Bernd; El Abedin, Sherif Zein; Endres, Frank

2014-11-10

The electrodeposition of soft magnetic iron and iron-silicon alloys for magnetic measurements is presented. The preparation of these materials in 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate, [Py1,4]TfO, at 100 °C with FeCl2 and FeCl2 +SiCl4 was studied by using cyclic voltammetry. Constant-potential electrolysis was carried out to deposit either Fe or FeSi, and deposits of approximately 10 μm thicknesses were obtained. By using scanning electron microscopy and X-ray diffraction, the microstructure and crystallinity of the deposits were investigated. Grain sizes in the nanometer regime (50-80 nm) were found and the presence of iron-silicon alloys was verified. Frequency-dependent magnetic polarizations, coercive forces, and power losses of some deposits were determined by using a digital hysteresis recorder. Corresponding to the small grain sizes, the coercive forces are around 950-1150 A m(-1) and the power losses were at 6000 J m(-3), which is much higher than in commercial Fe(3.2 wt %)Si electrical steel. Below a polarization of 1.8 T, the power losses are mainly caused by domain wall movements and, above 1.8 T, by rotation of magnetic moments as well as domain wall annihilation and recreation. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photo-Hall-effect study of excitation and recombination in Fe-doped GaN

NASA Astrophysics Data System (ADS)

Look, David C.; Leach, Jacob H.; Metzger, Robert

2017-02-01

The photo-Hall-effect was applied to the study of electron dynamics in semi-insulating Fe-doped GaN. High-powered light-emitting diodes of wavelengths λ = 940, 536, 449, 402, and 365 nm were used to excite steady-state free-electron volume concentrations Δn = 105-108 cm-3, depending on λ and intensity I0. Electron lifetime τ was determined from the energy E dependence of the excited sheet electron concentration Δns through the relationship Δns = I0τA(E), where the absorbance A(E) is a known function of sample thickness d and absorption coefficient α, and the energy dependence of α is taken from a theory of deep-center photoionization. The major sample impurities were Fe, Si, and C, with [Fe] ≫ [Si] and [C]. Fitted lifetimes τ ranged from 15 to 170 ps, depending on [Fe]. It was found that Δns ∝ I0 for [Si] > [C] and ∝ I01/2 for [Si] < [C]; the latter dependence arises possibly from self-compensation of neutral C impurities by N-vacancy donors. For [Si] > [C], some of the neutral Fe3+ is converted to Fe2+ with ground state Fe2+(5E) and excited state Fe2+(5T2); a fit of n vs. temperature T over the range of 290-325 K in the dark establishes E5E with respect to the conduction band: ECB - E5E = 0.564 eV - β5ET, where β5E = 3.6 × 10-4 eV/K. At room temperature, 294 K, ECB - E5E = 0.46 eV and ECB - E5T2 = 0.07 eV.

Influence of Fe doping on the structural, optical and acetone sensing properties of sprayed ZnO thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prajapati, C.S.; Kushwaha, Ajay; Sahay, P.P., E-mail: dr_ppsahay@rediffmail.com

2013-07-15

Graphical abstract: All the films are found to be polycrystalline ZnO possessing hexagonal wurtzite structure. The intensities of all the peaks are diminished strongly in the Fe-doped films, indicating their lower crystallinity as compared to the undoped ZnO film. The average crystallite size decreases from 35.21 nm (undoped sample) to 15.43 nm (1 at% Fe-doped sample). - Highlights: • Fe-doped ZnO films show smaller crystallinity with crystallite size: 15–26 nm. • Optical band gap in ZnO films decreases on Fe doping. • Fe-doped films exhibit the normal dispersion for the wavelength range 450–600 nm. • PL spectra of the Fe-dopedmore » films show quenching of the broad green-orange emission. • Acetone response of the Fe-doped films increases considerably at 300 °C. - Abstract: The ZnO thin films (undoped and Fe-doped) deposited by chemical spray pyrolysis technique have been analyzed by X-ray powder diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Results show that all the films possess hexagonal wurtzite structure of zinc oxide having crystallite sizes in the range 15–36 nm. On 1 at% Fe doping, the surface roughness of the film increases which favors the adsorption of atmospheric oxygen on the film surface and thereby increase in the gas response. Optical studies reveal that the band gap decreases due to creation of some defect energy states below the conduction band edge, arising out of the lattice disorder in the doped films. The refractive index of the films decreases on Fe doping and follows the Cauchy relation of normal dispersion. Among all the films examined, the 1 at% Fe-doped film exhibits the maximum response (∼72%) at 300 °C for 100 ppm concentration of acetone in air.« less

Hexaferrite multiferroics: from bulk to thick films

NASA Astrophysics Data System (ADS)

Koutzarova, T.; Ghelev, Ch; Peneva, P.; Georgieva, B.; Kolev, S.; Vertruyen, B.; Closset, R.

2018-03-01

We report studies of the structural and microstructural properties of Sr3Co2Fe24O41 in bulk form and as thick films. The precursor powders for the bulk form were prepared following the sol-gel auto-combustion method. The prepared pellets were synthesized at 1200 °C to produce Sr3Co2Fe24O41. The XRD spectra of the bulks showed the characteristic peaks corresponding to the Z-type hexaferrite structure as a main phase and second phases of CoFe2O4 and Sr3Fe2O7-x. The microstructure analysis of the cross-section of the bulk pellets revealed a hexagonal sheet structure. Large areas were observed of packages of hexagonal sheets where the separate hexagonal particles were ordered along the c axis. Sr3Co2Fe24O41 thick films were deposited from a suspension containing the Sr3Co2Fe24O41 powder. The microstructural analysis of the thick films showed that the particles had the perfect hexagonal shape typical for hexaferrites.

Study on industrial wastewater treatment using superconducting magnetic separation

NASA Astrophysics Data System (ADS)

Zhang, Hao; Zhao, Zhengquan; Xu, Xiangdong; Li, Laifeng

2011-06-01

The mechanism of industrial wastewater treatment using superconducting magnetic separation is investigated. Fe 3O 4 nanoparticles were prepared by liquid precipitation and characterized by X-ray diffraction (XRD). Polyacrylic acid (PAA) film was coated on the magnetic particles using plasma coating technique. Transmission electron microscope (TEM) observation and infrared spectrum measurement indicate that the particle surface is well coated with PAA, and the film thickness is around 1 nm. Practical paper factory wastewater treatment using the modified magnetic seeds in a superconducting magnet (SCM) was carried out. The results show that the maximum removal rate of chemical oxygen demand (COD) by SCM method can reach 76%.

Multipurpose setup for low-temperature conversion electron Mössbauer spectroscopy

NASA Astrophysics Data System (ADS)

Augustyns, V.; Trekels, M.; Gunnlaugsson, H. P.; Masenda, H.; Temst, K.; Vantomme, A.; Pereira, L. M. C.

2017-05-01

We describe an experimental setup for conversion electron Mössbauer spectroscopy (CEMS) at low temperature. The setup is composed of a continuous flow cryostat (temperature range of 4.2-500 K), detector housing, three channel electron multipliers, and corresponding electronics. We demonstrate the capabilities of the setup with CEMS measurements performed on a sample consisting of a thin enriched 57Fe film, with a thickness of 20 nm, deposited on a silicon substrate. We also describe exchangeable adaptations (lid and sample holder) which extend the applicability of the setup to emission Mössbauer spectroscopy as well as measurements under an applied magnetic field.

Superconducting and Magnetic Properties of Vanadium/iron Superlattices.

NASA Astrophysics Data System (ADS)

Wong, Hong-Kuen

A novel ultrahigh vacuum evaporator was constructed for the preparation of superlattice samples. The thickness control was much better than an atomic plane. With this evaporator we prepared V/Fe superlattice samples on (0001) sapphire substrates with different thicknesses. All samples showed a good bcc(110) structure. Mossbauer experiments showed that the interface mixing extended a distance of about one atomic plane indicating an almost rectangular composition profile. Because of this we were able to prepare samples with layer thickness approaching one atomic plane. Even with ultrathin Fe layers, the samples are ferromagnetic, at least at lower temperatures. Superparamagnetism and spin glass states were not seen. In the absence of an external field, the magnetic moments lie close to the film plane. In addition to this shape anisotropy, there is some uniaxial anisotropy. No magnetic dead layers have been observed. The magnetic moments within the Fe layers vary little with the distance from the interfaces. At the interfaces the Fe moment is reduced and an antiparallel moment is induced on the vanadium atoms. It is observed that ultrathin Fe layers behave in a 2D fashion when isolated by sufficiently thick vanadium layers; however, on thinning the vanadium layers, a magnetic coupling between the Fe layers has been observed. We also studied the superconducting properties of V/Fe sandwiches and superlattices. In both cases, the Fe layer, a strong pair-breaker, suppresses the superconducting transition temperature consistent with the current knowledge of the magnetic proximity effect. For the sandwiches with thin (thick) vanadium layers, the temperature dependence of the upper critical fields is consistent with the simple theory for a 2D (3D) superconductor. For the superlattices, when the vanadium layer is on the order of the BCS coherence length and the Fe layer is only a few atomic planes thick, a 2D-3D crossover has been observed in the temperature dependence of the parallel upper critical field. This implies the coexistence of superconductivity and ferromagnetism. We observe three dimensional behavior for thinner Fe layers ((TURN)1 atomic plane) and two dimensional behavior for thicker Fe layers (greater than 10 atomic planes).

Spin scattering asymmetric coefficients and enhanced specific interfacial resistance of fully epitaxial current-perpendicular-to-plane giant magnetoresistance spin valves using alternate monatomic layered [Fe/Co]n and a Ag spacer layer

NASA Astrophysics Data System (ADS)

Jung, J. W.; Shiozaki, R.; Doi, M.; Sahashi, M.

2011-04-01

Using current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) measurement, we have evaluated the bulk and interface spin scattering asymmetric coefficients, βF and γF/N and the specific interfacial resistance, AR*F/N, for exchange-biased spin-valves consisting of artificially ordered B2 structure Fe50Co50 and Ag spacer layer. Artificially epitaxial ordered Fe50Co50 superlattices have been successfully fabricated on MgO (001) substrate by alternate monatomic layer (AML) deposition at a substrate temperature of 75 °C. The structural properties of the full epitaxial trilayer, AML[Fe/Co]n/Ag/AML[Fe/Co]n, on the Ag electrode have been confirmed by in situ reflection high-energy electron diffraction and transmission electron diffraction microscopy. A considerably large resistance-area product change and MR ratio (ΔRA > 3 mΩμm2 and MR ratio ˜5%) were confirmed even at thin AML[Fe/Co]n layer at room temperature (RT) in our spin-valve elements. The estimated values of βF and γF/N were 0.80 and 0.84 ± 0.02, respectively, from the Valet-Fert theory analysis of ΔRA as a function of thickness of the ferromagnetic layer (3, 4, and 5 nm) on the basis of the two-current model.

Polarized neutron reflectivity study of perpendicular magnetic anisotropy in MgO/CoFeB/W thin films

NASA Astrophysics Data System (ADS)

Ambaye, Haile; Zhan, Xiao; Li, Shufa; Lauter, Valeria; Zhu, Tao

In this work we study the origin of PMA in MgO/CoFeB/W trilayer systems using polarized neutron reflectivity. Recently, the spin Hall effect in the heavy metals, such as Pt and Ta, has been of significant interest for highly efficient magnetization switching of the ultrathin ferromagnets sandwiched by such a heavy metal and an oxide, which can be used for spintronic based memory and logic devices. Most work has focused on heavy-metal/ferromagnet/oxide trilayer (HM/FM/MO) structures with perpendicular magnetic anisotropy (PMA), where the oxide layer plays the role of breaking inversion symmetry .No PMA was found in W/CoFeB/MgO films. An insertion of Hf layer in between the W and CoFeB layers, however, has been found to create a strong PMA. Roughness and formation of interface alloys by interdiffusion influences the extent of PMA. We intend to identify these influences using the depth sensitive technique of PNR. In our previous study, we have successfully performed polarized neutron reflectometry (PNR) measurements on the Ta/CoFeB/MgO/CoFeB/Ta thin film with MgO thickness of 1 nm. The PNR measurements were carried out using the BL-4A Magnetic Reflectometer at SNS. This work has been supported by National Basic Research Program of China (2012CB933102). Research at SNS was supported by the Office of BES, DOE.

Comparative study of genotoxicity and tissue distribution of nano and micron sized iron oxide in rats after acute oral treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Shailendra Pratap; Rahman, M.F.; Murty, U.S.N.

2013-01-01

Though nanomaterials (NMs) are being utilized worldwide, increasing use of NMs have raised concerns over their safety to human health and environment. Iron oxide (Fe{sub 2}O{sub 3}) NMs have important applications. The aim of this study was to assess the genotoxicity of Fe{sub 2}O{sub 3}-30 nm and Fe{sub 2}O{sub 3}-bulk in female Wistar rats. Fe{sub 2}O{sub 3}-30 nm was characterized by using transmission electron microscopy, dynamic light scattering, laser Doppler velocimetry and surface area analysis. The rats were treated orally with the single doses of 500, 1000, 2000 mg/kg bw of Fe{sub 2}O{sub 3}-30 nm and Fe{sub 2}O{sub 3} –bulk.more » The genotoxicity was evaluated at 6, 24, 48 and 72 h by the comet assay in leucocytes, 48 and 72 h by micronucleus test (MNT) in peripheral blood cells, 18 and 24 h by chromosomal aberration (CA) assay and 24 and 48 h by MNT in bone marrow cells. The biodistribution of iron (Fe) was carried out at 6, 24, 48 and 72 h after treatment in liver, spleen, kidney, heart, brain, bone marrow, urine and feces by using atomic absorption spectrophotometry. The % tail DNA, frequencies of micronuclei and CAs were statistically insignificant (p > 0.05) at all doses. These results suggest that Fe{sub 2}O{sub 3}-30 nm and Fe{sub 2}O{sub 3}-bulk was not genotoxic at the doses tested. Bioavailability of Fe was size and dose dependent in all the tissues from the groups exposed to Fe{sub 2}O{sub 3}-30 nm. Fe{sub 2}O{sub 3} NMs were able to enter in the organs and the rats are biocompatible with much higher concentration of Fe. However, the accumulated Fe did not cause significant genotoxicity. This study provides additional knowledge about the toxicology of Fe{sub 2}O{sub 3} NMs. -- Highlights: ► Fe{sub 2}O{sub 3}-30 nm and Fe{sub 2}O{sub 3}-bulk were orally administered to rats with single doses. ► The nano and bulk Fe{sub 2}O{sub 3} showed insignificant results with MNT, comet and CA assays. ► The bulk was excreted via feces whereas the NMs were found both in urine and feces. ► The NMs mainly accumulated in the liver, spleen, kidney, heart and bone marrow. ► However the accumulated Fe did not cause significant genotoxicological effects.« less

Electrical Characteristics CuFe2O4 Thick Film Ceramics Made with Different Screen Size Utiizing Fe2O3 Nanopowder Derived from Yarosite for NTC Thermistor

NASA Astrophysics Data System (ADS)

Wiendartun, Syarif, Dani Gustaman

2010-10-01

Fabrication of CuFe2O4 thick film ceramics utilizing Fe2O3 derived from yarosite using screen printing technique for NTC thermistor has been carried out. Effect of thickness variation due to different size of screen (screen 225; 300 and 375 mesh) has been studied. X-ray diffraction analyses (XRD) was done to know crystal structure and phases formation. SEM analyses was carried out to know microstructure of the films. Electrical properties characterization was done through measurement of electrical resistance at various temperatures (room temperature to 100° C). The XRD data showed that the films crystalize in tetragonal spinel. The SEM images showed that the screen with the smaller of the hole size, made the grain size was bigger. Electrical data showed that the larger the screen different size thickness variation (mesh), the larger the resistance, thermistor constant and sensitivity. From the electrical characteristics data, it was known that the electrical characteristics of the CuFe2O4 thick film ceramics followed the NTC characteristic. The value of B and RRT of the produced CuFe2O4 ceramics namely B = 3241-3484 K and RRT = 25.6-87.0 M Ohm, fitted market requirement.

Phytosynthesis of Iron Nanoparticle from Averrhoa Bilimbi Linn.

NASA Astrophysics Data System (ADS)

Rosli, I. R.; Zulhaimi, H. I.; Ibrahim, S. K. M.; Gopinath, S. C. B.; Kasim, K. F.; Akmal, H. M.; Nuradibah, M. A.; Sam, T. S.

2018-03-01

This paper demonstrates iron nanoparticles (FeNP) was synthesized from natural sources of Averrhoa bilimbi Linn. The plant extracts act as natural reducing agent in producing FeNP. There is no addition of any surfactants during the nanoparticles formation. Gravimetric analysis is used to calculate the percentage yield of plant extracts. TPC and DPPH assay method were used to evaluate antioxidant activity in different A. bilimbi extracts and synthesized FeNP. Based on the analyses, it showed that fruit has the highest percentage yield and antioxidant activity followed by leaf, twig and bark. Analysis from TPC, fruit contains 27.26 mg GAE/g and 39.46 mg GAE/g for FeNP. DPPH assay showed fruit extract has the highest free radical antioxidant activity with 61.93% in A. bilimbi and 80.00% in FeNP. Phytosynthesis of FeNP were examine by using UV-Vis spectrophotometer. Based on the spectra, it showed that FeNP recorded peak absorbance at 465 nm, 450 nm, 460 nm and 440 nm for UAE-F, UAE-L, UAE-T and UAE-B, respectively. FTIR analysis shows the presence of strong alcoholic bond, aldehyde, stretch amine and alkene that was responsible in reduction process to form FeNP. The result of UV-Vis and FTIR showed that the existance of FeNP and involvement of functional group that were responsible on the formation of nanoparticles.

Characterization of microbially Fe(III)-reduced nontronite: Environmental cell-transmission electron microscopy study

USGS Publications Warehouse

Kim, Jin-wook; Furukawa, Yoko; Daulton, Tyrone L.; Lavoie, Dawn L.; Newell, Steven W.

2003-01-01

Microstructural changes induced by the microbial reduction of Fe(III) in nontronite by Shewanella oneidensis were studied using environmental cell (EC)-transmission electron microscopy (TEM), conventional TEM, and X-ray powder diffraction (XRD). Direct observations of clays by EC-TEM in their hydrated state allowed for the first time an accurate and unambiguous TEM measurement of basal layer spacings and the contraction of layer spacing caused by microbial effects, most likely those of Fe(III) reduction. Non-reduced and Fe(III)-reduced nontronite, observed by EC-TEM, exhibited fringes with mean d001 spacings of 1.50 nm (standard deviation, σ = 0.08 nm) and 1.26 nm (σ = 0.10 nm), respectively. In comparison, the same samples embedded with Nanoplast resin, sectioned by microtome, and observed using conventional TEM, displayed layer spacings of 1.0–1.1 nm (non-reduced) and 1.0 nm (reduced). The results from Nanoplast-embedded samples are typical of conventional TEM studies, which have measured nearly identical layer spacings regardless of Fe oxidation state. Following Fe(III) reduction, both EC- and conventional TEM showed an increase in the order of nontronite selected area electron diffraction patterns while the images exhibited fewer wavy fringes and fewer layer terminations. An increase in stacking order in reduced nontronite was also suggested by XRD measurements. In particular, the ratio of the valley to peak intensity (v/p) of the 1.7 nm basal 001 peak of ethylene glycolated nontronite was measured at 0.65 (non-reduced) and 0.85 (microbially reduced).

Comparison of magnetic properties and high-temperature phase stability of phosphate- and oleic acid-capped iron oxide nanoparticles

NASA Astrophysics Data System (ADS)

Muthukumaran, T.; Pati, S. S.; Singh, L. H.; de Oliveira, A. C.; Garg, V. K.; Philip, John

2018-03-01

We study the influence of dynamic capping of Fe3O4 nanoparticles with phosphate and oleic acid, on their structure, magnetic properties and thermal stability of magnetic nanoparticles. It is observed that the phosphate coating on iron oxide lowers the dipole-dipole interaction significantly, as compared to oleic acid capping. The Mössbauer results show that the spin canting order of oxidized shell and the mean hyperfine field values follow the order Fe0 (uncoated) > FeOA (oleic acid capped) > FP1 (phosphate capped). The uncoated Fe3O4 nanoparticle is non-stoichiometric in nature due to oxidation, whereas FP1 and FeOA are of the correct stoichiometry. Mössbauer and photoacoustic spectroscopic studies on air-annealed phosphate-coated magnetite nanoparticles confirm that the magnetic iron oxide phase is preserved up to 833 K and a complete conversion of Fe3O4 into the non-magnetic hematite phase occurs at 1173 K. The iron oxide air annealed at 833 K is found to have a shell of orthorhombic α-Fe2O3 over the magnetite core. However, in oleic acid-coated nanoparticles, the magnetic to non-magnetic phase transformation commences at 623 K and the conversion was complete at 823 K. The photoacoustic spectra of the air-annealed phosphate-coated Fe3O4 particles showed a flipping of the absorption intensity between 500-700 nm and 800-1000 nm, due to the conversion of Fe3O4 to γ-Fe2O3 at 923 and γ-Fe2O3 to α-Fe2O3 at 1173 K, respectively. The γ-Fe2O3 showed an intense absorption peak above 750 nm, whereas the α-Fe2O3 showed a peak broadening in the wavelength range of 600-700 nm, in addition to the strong peaks at a wavelength above 750 nm. This study suggests that the photoacoustic spectroscopy can distinguish clearly the three polymorphs of iron oxide i.e., Fe3O4, γ-Fe2O3 and α-Fe2O3. Our results confirm the ability of phosphate-capped iron oxide particles to retard the oxidation of Fe2+ contents during the crystal growth process.

Synergistic effect of Fe2O3/Ho2O3 Co-modified 2D-titanate heterojunctions on enhanced photocatalytic degradation

NASA Astrophysics Data System (ADS)

Zhao, Xiaona; Liu, Xinzhao; Lu, Dingze; Wu, Pei; Yan, Qiuyang; Liu, Min; Fang, Pengfei

2017-01-01

TiO2-based nanosheets (TNSs) co-modified by Fe2O3 and Ho2O3 were synthesized by one-pot hydrothermal method using Fe(NO3)3 and Ho(NO3)3 as precursors compositing with TiO2. The Fe2O3/Ho2O3-TNSs heterojunctions possessed a thickness of approximately 3-4 nm, large specific surface area of 210-310 cm2/g, with Fe2O3 and Ho2O3 nanoparticles highly dispersed over the surface of the nanosheets. The crystallization of the samples gradually increased with the amount of Fe2O3 nanoparticles, which was confirmed by the XRD, BET and Raman spectra, indicating that Ho2O3 and Fe2O3 influenced the crystallinity and structure evolution of the TNSs, besides, led to an improved the visible-light absorption. Surface photocurrent and fluorescence spectral studies revealed that the photo-generated charge carrier separation efficiency could be efficiently improved by an appropriate amount of modification. The Fe2O3/Ho2O3-TNSs exhibited synergistic effect on photocatalytic degradation of RhB as well as MO under visible light. The highest efficiency was obtained by 0.05%-Fe2O3/Ho2O3-TNSs (Fe:Ho:Ti = 0.05:1:100), which was 8.86 and 6.72 times than that of individual 1.0%-Ho2O3-TNSs (Ho:Ti = 1:100) and 0.05%-Fe2O3-TNSs (Fe:Ti = 0.05:100), respectively. The possible mechanism for enhanced visible-light-induced photocatalytic activity was proposed. Ho2O3 introduced in the photocatalysts may act as the hole capture while Fe2O3 may share the same Fermi levels with TNSs and serve as the electron capture center in the n-n-p system, which reduced the recombination rate of photo-induced electron-hole pairs.

Temperature Dependence of Magnetically Active Charge Excitations in Magnetite across the Verwey Transition

NASA Astrophysics Data System (ADS)

Taguchi, M.; Chainani, A.; Ueda, S.; Matsunami, M.; Ishida, Y.; Eguchi, R.; Tsuda, S.; Takata, Y.; Yabashi, M.; Tamasaku, K.; Nishino, Y.; Ishikawa, T.; Daimon, H.; Todo, S.; Tanaka, H.; Oura, M.; Senba, Y.; Ohashi, H.; Shin, S.

2015-12-01

We study the electronic structure of bulk single crystals and epitaxial films of Fe3 O4 . Fe 2 p core level spectra show clear differences between hard x-ray (HAX) and soft x-ray photoemission spectroscopy (PES). The bulk-sensitive spectra exhibit temperature (T ) dependence across the Verwey transition, which is missing in the surface-sensitive spectra. By using an extended impurity Anderson full-multiplet model—and in contrast to an earlier peak assignment—we show that the two distinct Fe species (A and B site) and the charge modulation at the B site are responsible for the newly found double peaks in the main peak above TV and its T -dependent evolution. The Fe 2 p HAXPES spectra show a clear magnetic circular dichroism (MCD) in the metallic phase of magnetized 100-nm-thick films. The model calculations also reproduce the MCD and identify the contributions from magnetically distinct A and B sites. Valence band HAXPES shows a finite density of states at EF for the polaronic half metal with a remnant order above TV and a clear gap formation below TV. The results indicate that the Verwey transition is driven by changes in the strongly correlated and magnetically active B -site electronic states, consistent with resistivity and optical spectra.

Solvothermal Synthesis of a Hollow Micro-Sphere LiFePO4/C Composite with a Porous Interior Structure as a Cathode Material for Lithium Ion Batteries

PubMed Central

Liu, Yang; Zhang, Jieyu; Li, Ying; Hu, Yemin; Li, Wenxian; Zhu, Mingyuan; Hu, Pengfei; Chou, Shulei; Wang, Guoxiu

2017-01-01

To overcome the low lithium ion diffusion and slow electron transfer, a hollow micro sphere LiFePO4/C cathode material with a porous interior structure was synthesized via a solvothermal method by using ethylene glycol (EG) as the solvent medium and cetyltrimethylammonium bromide (CTAB) as the surfactant. In this strategy, the EG solvent inhibits the growth of the crystals and the CTAB surfactant boots the self-assembly of the primary nanoparticles to form hollow spheres. The resultant carbon-coat LiFePO4/C hollow micro-spheres have a ~300 nm thick shell/wall consisting of aggregated nanoparticles and a porous interior. When used as materials for lithium-ion batteries, the hollow micro spherical LiFePO4/C composite exhibits superior discharge capacity (163 mAh g−1 at 0.1 C), good high-rate discharge capacity (118 mAh g−1 at 10 C), and fine cycling stability (99.2% after 200 cycles at 0.1 C). The good electrochemical performances are attributed to a high rate of ionic/electronic conduction and the high structural stability arising from the nanosized primary particles and the micro-sized hollow spherical structure. PMID:29099814

Room temperature luminescence and ferromagnetism of AlN:Fe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, H., E-mail: lihui@mail.iee.ac.cn, E-mail: wjwang@aphy.iphy.ac.cn; Cai, G. M.; Wang, W. J., E-mail: lihui@mail.iee.ac.cn, E-mail: wjwang@aphy.iphy.ac.cn

2016-06-15

AlN:Fe polycrystalline powders were synthesized by a modified solid state reaction (MSSR) method. Powder X-ray diffraction and transmission electron microscopy results reveal the single phase nature of the doped samples. In the doped AlN samples, Fe is in Fe{sup 2+} state. Room temperature ferromagnetic behavior is observed in AlN:Fe samples. Two photoluminescence peaks located at about 592 nm (2.09 eV) and 598 nm (2.07 eV) are observed in AlN:Fe samples. Our results suggest that AlN:Fe is a potential material for applications in spintronics and high power laser devices.

Nanohybrids of magnetic iron-oxide particles in hydrophobic organoclays for oil recovery.

PubMed

Hsu, Ru-Siou; Chang, Wen-Hsin; Lin, Jiang-Jen

2010-05-01

Nanohybrids with magnetic iron-oxide nanoparticles (FeNPs) embedded in the multilayered silicate clay were synthesized by in situ Fe(2+)/Fe(3+) coprecipitation. The natural clay, sodium montmorillonite (Na(+)-MMT), was first modified with hydrophobic poly(oxypropylene)amine salts (POP at 2000 and 4000 g/mol M(w)). The two POP-intercalated organoclays, with a silicate interlayer expansion from 1.2 to 5.2 and 9.2 nm, respectively, are suitable for embedding FeNPs. The presence of POP organics in layered structure created the space for intercalating with FeNPs of 2-4 nm in diameter, observed by transmission electronic microscope. The synthesized nanohybrids of POP4000/MMT-FeNP was composed of 17% iron oxide and 51 wt % POP within the silicate basal spacing of 5.0 nm. In contrast, the lower molecular weight of POP2000 intercalated MMT failed to encapsulate FeNPs in a significant amount, but resulting a "crowding-out effect" that caused the silicate interlayer space to shrink from 5.2 to 1.8 nm because of the replacement of the POP salt by Fe(2+)/Fe(3+) ions. The synthesis required the use of high molecular weight POP4000 and low temperatures (<4 degrees C) for a better dispersion in the reaction medium. The presence of POP in the layered silicate facilitated a homogeneous POP/MMT in water, associating with Fe(2+)/Fe(3+) ions and spatially accommodating for the subsequently generated FeNPs. The synthesized nanostructure consisting of POP and FeNP could be used as a pollutant remedy because of its ability to adsorbing crude oil and it is maneuverable under an applied magnetism.

Enhanced off-resonance magnetoelectric response in laser annealed PZT thick film grown on magnetostrictive amorphous metal substrate

NASA Astrophysics Data System (ADS)

Palneedi, Haribabu; Maurya, Deepam; Kim, Gi-Yeop; Priya, Shashank; Kang, Suk-Joong L.; Kim, Kwang-Ho; Choi, Si-Young; Ryu, Jungho

2015-07-01

A highly dense, 4 μm-thick Pb(Zr,Ti)O3 (PZT) film is deposited on amorphous magnetostrictive Metglas foil (FeBSi) by granule spray in vacuum process at room temperature, followed by its localized annealing with a continuous-wave 560 nm ytterbium fiber laser radiation. This longer-wavelength laser radiation is able to anneal the whole of thick PZT film layer without any deteriorative effects, such as chemical reaction and/or atomic diffusion, at the interface and crystallization of amorphous Metglas substrate. Greatly enhanced dielectric and ferroelectric properties of the annealed PZT are attributed to its better crystallinity and grain growth induced by laser irradiation. As a result, a colossal off-resonance magnetoelectric (ME) voltage coefficient that is two orders of magnitude larger than previously reported output from PZT/Metglas film-composites is achieved. The present work addresses the problems involved in the fabrication of PZT/Metglas film-composites and opens up emerging possibilities in employing piezoelectric materials with low thermal budget substrates (suitable for integrated electronics) and designing laminate composites for ME based devices.

Investigation of the annealing temperature dependence of the spin pumping in Co20Fe60B20/Pt systems

NASA Astrophysics Data System (ADS)

Belmeguenai, M.; Aitoukaci, K.; Zighem, F.; Gabor, M. S.; Petrisor, T.; Mos, R. B.; Tiusan, C.

2018-03-01

Co20Fe60B20/Pt systems with variable thicknesses of Co20Fe60B20 and of Pt have been sputtered and then annealed at various temperatures (Ta) up to 300 °C. Microstrip line ferromagnetic resonance (MS-FMR) has been used to investigate Co20Fe60B20 and Pt thickness dependencies of the magnetic damping enhancement due to the spin pumping. Using diffusion and ballistic models for spin pumping, the spin mixing conductance and the spin diffusion length have been deduced from the Co20Fe60B20 and the Pt thickness dependencies of the Gilbert damping parameter α of the Co20Fe60B20/Pt heterostructures, respectively. Within the ballistic simple model, both the spin mixing conductance at the CoFeB/Pt interface and the spin-diffusion length of Pt increase with the increasing annealing temperature and show a strong enhancement at 300 °C annealing temperature. In contrast, the spin mixing conductance, which increases with Ta, shows a different trend to the spin diffusion length when using the diffusion model. Moreover, MS-FMR measurements revealed that the effective magnetization varies linearly with the Co20Fe60B20 inverse thickness due to the perpendicular interface anisotropy, which is found to decrease as the annealing temperature increases. It also revealed that the angular dependence of the resonance field is governed by small uniaxial anisotropy which is found to vary linearly with the Co20Fe60B20 inverse thickness of the annealed films, in contrast to that of the as grown ones.

Synthesis of Fe3O4/Polyacrylonitrile Composite Electrospun Nanofiber Mat for Effective Adsorption of Tetracycline.

PubMed

Liu, Qing; Zhong, Lu-Bin; Zhao, Quan-Bao; Frear, Craig; Zheng, Yu-Ming

2015-07-15

Novel Fe3O4/polyacrylonitrile (PAN) composite nanofibers (NFs) were prepared by a simple two-step process, an electrospinning and solvothermal method. Characterization by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) demonstrated formation of a uniform nanoparticles coating (about 20 nm in thickness) on the PAN nanofiber backbone. The coating was constructed by well-crystallized cubic phase Fe3O4 nanoparticles as examined by X-ray diffraction spectroscopy (XRD). The coating doubled the specific surface area of NFs, from 8.4 to 17.8 m2 g(-1), as confirmed by nitrogen sorption isotherm analysis. To evaluate the feasibility of Fe3O4/PAN composite NFs as a potential adsorbent for antibiotic removal, batch adsorption experiments were conducted using tetracycline (TC) as the model antibiotic molecule. The results showed that Fe3O4/PAN composite NFs were effective in removing TC with no impactful loss of Fe in the pH regime of environmental interest (5-8). The adsorption of TC onto Fe3O4/PAN composite NFs better fitted the pseudo-second-order kinetics model, and the maximum adsorption capacity calculated from Langmuir isotherm model was 257.07 mg g(-1) at pH 6. The composite NFs also exhibited good regenerability over repeated adsorption/desorption cycles. Surface complexation between TC and the composite NFs contributed most to the adsorption as elucidated by X-ray photoelectron spectroscopy (XPS). This highly effective and novel adsorbent can be easily modularized and separated, promising its huge potential in drinking and wastewater treatment for antibiotic removal.

Properties and rapid low-temperature consolidation of nanocrystalline Fe-ZrO2 composite by pulsed current activated sintering

NASA Astrophysics Data System (ADS)

Kang, Hyun-Su; Ko, In-Yong; Yoon, Jin-Kook; Doh, Jung-Mann; Hong, Kyung-Tae; Shon, In-Jin

2011-02-01

Nanopowders of Fe and ZrO2 were synthesized from Fe2O3 and Zr by high-energy ball milling. The powder sizes of Fe and ZrO2 were 70 nm and 12 nm, respectively. Highly dense nanostructured 4/3Fe-ZrO2 composite was consolidated by a pulsed current activated sintering method within 1 minute from the mechanically synthesized powders (Fe-ZrO2) and horizontal milled Fe2O3+Zr powders under the 1 GPa pressure. The grain sizes of Fe and ZrO2 in the composite were calculated. The average hardness and fracture toughness values of nanostuctured 4/3Fe-ZrO2 composite were investigated.

Perpendicular exchange coupling effects in ferrimagnetic TbFeCo/GdFeCo hard/soft structures

NASA Astrophysics Data System (ADS)

Wang, Ke; Wang, Yahong; Ling, Fujin; Xu, Zhan

2018-04-01

Bilayers consisting of magnetically hard TbFeCo and soft GdFeCo alloy were fabricated. Exchange-spring and sharp switching in a step-by-step fashion were observed in the TbFeCo/GdFeCo hard/soft bilayers with increasing GdFeCo thickness. A perpendicular exchange bias field of several hundred Oersteds is observed from the shift of minor loops pinned by TbFeCo layer. The perpendicular exchange energy is derived to be in the range of 0.18-0.30 erg/cm2. The exchange energy is shown to increase with the thickness of GdFeCo layer in the bilayers, which can be attributed to the enhanced perpendicular anisotropy of GdFeCo layer in our experimental range.

Magneto-optical properties of α-Fe2O3@ZnO nanocomposites prepared by the high energy ball-milling technique

NASA Astrophysics Data System (ADS)

Chaudhury, Chandana Roy; Roychowdhury, Anirban; Das, Anusree; Das, Dipankar

2016-05-01

Magnetic-fluorescent nanocomposites (NCs) with 10 wt% of α-Fe2O3 in ZnO have been prepared by the high energy ball-milling. The crystallite sizes of α-Fe2O3 and ZnO in the NCs are found to vary from 65 nm to 20 nm and 47 nm to 15 nm respectively as milling time is increased from 2 to 30 h. XRD analysis confirms presence of α-Fe2O3 and ZnO in pure form in all the NCs. UV-vis study of the NCs shows a continuous blue-shift of the absorption peak and a steady increase of band gap of ZnO with increasing milling duration that are assigned to decreasing particle size of ZnO in the NCs. Photoluminescence (PL) spectra of the NCs reveal three weak emission bands in the visible region at 421, 445 and 485 nm along with the strong near band edge emission at 391 nm. These weak emission bands are attributed to different defect - related energy levels e.g. Zn-vacancy, Zn interstitial and oxygen vacancy. Dc and ac magnetization measurements show presence of weakly interacting superparamagnetic (SPM) α-Fe2O3 particles in the NCs. 57Fe-Mössbauer study confirms presence of SPM hematite in the sample milled for 30 h. Positron annihilation lifetime measurements indicate presence of cation vacancies in ZnO nanostructures confirming results of PL studies.

Scanning transmission electron microscopy (STEM) study on surface modified CVD diamond/Si(111) film post implanted Fe-B and NiFe-B related to GMR properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Purwanto, Setyo, E-mail: setyo-p@batan.go.id, E-mail: purwantosetyo@yahoo.com; Dimyati, A., E-mail: arbi-dimyati@hotmail.com; Iskandar, R.

Nanostructure investigation on the post implantation by Fe-B and NiFe-B on CVD diamond/Si(111) film have been studied by means of STEM related to their GMR phenomena. Two samples were investigated carefully, firstly sample is post NiFe-B at E=70keV and dose= 10{sup 15} ions/cm{sup 2} (denoted as A-E3D1). Secondly, is post FeB at E=20 keV and dose= 10{sup 15} ions/cm{sup 2} (denoted as B-E1D1). Based on FPP measurement at room temperature (RT) and H{sub applied} = 8 kOe, A-E3D1 sample has MR ratio almost 80% and MR ratio in B-E1D1 sample is 45%. Based on STEM-EDX investigation, there are two aspectsmore » of how MR ratio of A-E3D1 more higher than those of B-E1D1. Firstly, surface nanostructure on the top of A-E3D1 film is more grazing than on the top of B-E1D1. Analysis with Scanning Transmission Electron Microscope (STEM) equipped with Electron Energy Loss Spectroscopy (EELS) the growth of amorphous carbon layer on top of the implanted diamond film with thickness around 100 nm and only 20 nm on the no implanted sample have observed. Boron atoms were found inside the carbon amorphous layer distributed homogenously. Secondly, oxygen content at the interface between diamond film and silicon substrate in sample A-E3D1 was lower than those in B-E1D1 sample. This condition gives the resistance value in A-E3D1 lower than value in B-E1D1. This result is close to the Raman Spectroscopy data measurement which obviously suggests changes on the Raman spectrum due to implantation related to Oxygen excitation from B-E1D1 sample.« less

Monodisperse NixFe3-xO4 nanospheres: Metal-ion-steered size/composition control mechanism, static magnetic and enhanced microwave absorbing properties

NASA Astrophysics Data System (ADS)

Jiang, Kedan; Liu, Yun; Pan, Yefei; Wang, Ru; Hu, Panbing; He, Rujia; Zhang, Lingli; Tong, Guoxiu

2017-05-01

An easy metal-ion-steered solvothermal method was developed for the one-step synthesis of monodisperse, uniform NixFe3-xO4 polycrystalline nanospheres with tunable sphere diameter (40-400 nm) and composition (0 ≤ x ≤ 0.245) via changing just Ni2+/Fe3+ molar ratio (γ). With g increased from 0:1 to 2:1, sphere diameter gradually decreased and crystal size exhibited an inversed U-shaped change tendency, followed by increased Ni/Fe atom ratio from 0% to 0.0888%. An in situ-reduction, coordination-precipitation transformation mechanism was proposed to interpret the metal-ion-steered growth. Size- and composition-dependent static magnetic and microwave absorbing properties were systematically investigated. Saturation magnetization declines with g in a Boltzmann model due to the changes of crystal size, sphere diameter, and Ni content. The coercivity reaches a maximum at γ = 0.75:1 because of the critical size of Fe3O4 single domain (25 nm). Studies on microwave absorption reveal that 150-400 nm Fe3O4 nanospheres mainly obey the quarter-wavelength cancellation model with the single-band absorption; 40-135 nm NixFe3-xO4 nanospheres (0 ≤ x ≤ 0.245) obey the one and three quarter-wavelength cancellation model with the multi-band absorption. 150 nm Fe3O4 nanospheres exhibit the optimal EM wave-absorbing property with an absorbing band of 8.94 GHz and the maximum RL of -50.11 dB.

Thermodynamics of the Solar Corona and Evolution of the Solar Magnetic Field as Inferred from the Total Solar Eclipse Observations of 11 July 2010

NASA Technical Reports Server (NTRS)

Habbal, Shadia Rifai; Druckmueller, Miloslav; Morgan, Huw; Ding, Adalbert; Johnson, Judd; Druckmuellerova, Hana; Daw, Adrian; Arndt, Martina B.; Dietzel, Martin; Saken, Jon

2011-01-01

We report on multi-wavelength observations of the corona taken simultaneously in broadband white light, and in seven spectral lines, H-alpha 656.3 nm, Fe IX 435.9 nm, Fe X 637.4 nm, Fe XI 789.2 nm, Fe XIII 1074.7 nm, Fe XIV 530.3 nm and Ni XV 670.2 nm. The observations were made during the total solar eclipse of 11 July 2010 from the atoll of Tatakoto in French Polynesia. Simultaneous imaging with narrow bandpass filters in each of these spectral lines and in their corresponding underlying continua maximized the observing time during less than ideal observing conditions and yielded outstanding quality data. The application of two complementary image processing techniques revealed the finest details of coronal structures at 1" resolution in white light, and 6.5" in each of the spectral lines. This comprehensive wavelength coverage confirmed earlier eclipse findings that the solar corona has a clear two-temperature structure: The open field lines, expanding outwards from the solar surface, are characterized by electron temperatures near 1 X 10(exp 6) K, while the hottest plasma around 2X 10(exp 6) K resides in loop-like structures forming the bulges of streamers. The first images of the corona in the forbidden lines of Fe IX and Ni XV, showed that there was very little coronal plasma at temperatures below 5 X 10(exp 5) K and above 2.5X 10(exp 6) K. The data also enabled temperature differentiations as low as 0:2 X 10(exp 6) K in different density structures. These observations showed how the passage of CMEs through the corona, prior to totality, produced large scale ripples and very sharp streaks, which could be identified with distinct temperatures for the first time. The ripples were most prominent in emission from spectral lines associated with temperatures around 10(exp 6) K. The most prominent streak was associated with a conical-shaped void in the emission from the coolest line of Fe IX and from the hottest line of Ni XV. A prominence, which erupted prior to totality, appeared in the shape of a hook in the cooler lines of Fe X and Fe XI, spanning 0.5 R(solar) in extent starting at a heliocentric distance of 1.3 R(solar), with a complex trail of hot and cool twisted structures connecting it to the solar surface. Simultaneous Fe X 17.4 nm observations from space by Proba2/SWAP provided an ideal opportunity for comparing emission from a coronal forbidden line, namely Fe X 637.4 nm, with a space-based EUV allowed line. Comparison of the Fe X 17.4 nm and 637.4 nm emission provided the first textbook example of the role of radiative excitation in extending the detectability of coronal emission to much larger heliocentric distances than its collisionally excited component. These eclipse observations demonstrate the unique capabilities of coronal forbidden lines for exploring the evolution of the coronal magnetic field in the heliocentric distance range of 1 - 3 R(solar), which is currently inaccessible to any space-borne or ground-based observatory.

Particle size dependence of heating power in MgFe2O4 nanoparticles for hyperthermia therapy application

NASA Astrophysics Data System (ADS)

Reza Barati, Mohammad; Selomulya, Cordelia; Suzuki, Kiyonori

2014-05-01

Magnetic nanoparticles with narrow size distributions have successfully been synthesized by an ultrasonic assisted co-precipitation method. The effects of particle size on magnetic properties, heat generation by AC fields, and the cell cytotoxicity were investigated for MgFe2O4 nanoparticles with mean diameters varying from 7 ± 0.5 nm to 29 ± 1 nm. The critical size for superparamagnetic to ferrimagnetic transition (DS→F) of MgFe2O4 was determined to be about 13 ± 0.5 nm at 300 K. The specific absorption rate (SAR) of MgFe2O4 nanoparticles was strongly size dependent; it showed a maximum value of 19 W/g when the particle size was 10 ± 0.5 nm at which the Néel and Brownian relaxations are the major cause of heating. The SAR value was suppressed dramatically by 46% with increasing particle size from 10 ± 0.5 nm to 13 ± 0.5 nm, where Néel relaxation slows down and SAR results primarily from Brownian relaxation loss. A further reduction in SAR value was evident when the size was increased from 13 ± 0.5 nm to 16 ± 1 nm, where the superparamagnetic to ferromagnetic transition occurs. However, SAR showed a tendency to increase with particle size again above 16 ± 1 nm where hysteresis loss becomes the dominant mechanism of heat generation. The particle size dependence of SAR in the superparamagnetic region was well described by considering the effective relaxation time estimated based on a log-normal size distribution. The clear size dependence of SAR is attributable to the high degree of monodispersity of particles synthesized here. The high SAR value of water-based MgFe2O4 magnetic suspension combined with low cell cytotoxicity suggests a great potential of MgFe2O4 nanoparticles for magnetic hyperthermia therapy applications.

Thin Co/Ni-based bottom pinned spin-transfer torque magnetic random access memory stacks with high annealing tolerance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tomczak, Y., E-mail: Yoann.Tomczak@imec.be; Department of Chemistry, KU Leuven; Swerts, J.

2016-01-25

Spin-transfer torque magnetic random access memory (STT-MRAM) is considered as a replacement for next generation embedded and stand-alone memory applications. One of the main challenges in the STT-MRAM stack development is the compatibility of the stack with CMOS process flows in which thermal budgets up to 400 °C are applied. In this letter, we report on a perpendicularly magnetized MgO-based tunnel junction (p-MTJ) on a thin Co/Ni perpendicular synthetic antiferromagnetic layer with high annealing tolerance. Tunnel magneto resistance (TMR) loss after annealing occurs when the reference layer loses its perpendicular magnetic anisotropy due to reduction of the CoFeB/MgO interfacial anisotropy. Amore » stable Co/Ni based p-MTJ stack with TMR values of 130% at resistance-area products of 9 Ω μm{sup 2} after 400 °C anneal is achieved via moment control of the Co/Ta/CoFeB reference layer. Thinning of the CoFeB polarizing layer down to 0.8 nm is the key enabler to achieve 400 °C compatibility with limited TMR loss. Thinning the Co below 0.6 nm leads to a loss of the antiferromagnetic interlayer exchange coupling strength through Ru. Insight into the thickness and moment engineering of the reference layer is displayed to obtain the best magnetic properties and high thermal stability for thin Co/Ni SAF-based STT-MRAM stacks.« less

Microchemical and Structural Evidence for Space Weathering in Soils from Asteroid Itokawa

NASA Technical Reports Server (NTRS)

Thompson, M. S.; Christoffersen, R.; Zega, T. J.

2013-01-01

The chemistry, microstructure and optical properties of grains on the surfaces of airless bodies are continu-ously modified due to their interactions predominantly with solar energetic ions and micrometeorite impacts. Collectively known as space weathering, this phenomenon results in a discrepancy between remotely sensed spectra from asteroids and those ac-quired directly from meteorites. The return of pristine samples from the asteroid Itokawa provides insight into surface processes on airless bodies and will help in correlating remote sensing data with laboratory analysis of meteorites. Samples and Methods: We examined Itokawa samples RA-QD02-0042-01 and RA-QD-02-0042-02, ultramicrotomed sec-tions of a singular grain prepared by the Hayabusa sample cura-tion team. We analyzed these slices using a 200 keV JEOL 2010F transmission electron microscope (TEM) at Arizona State Uni-versity and a 200 keV JEOL 2500SE TEM at NASA JSC. Both field emission TEMs are equipped with energy-dispersive X-ray spectrometers (EDS) and scanning TEM (STEM) detectors. Results and Discussion: TEM observations reveal that the sectioned grain predominantly consists of a single crystal of low-Ca orthopyroxene, with subsidiary smaller regions of olivine, Fe-Ni sulfide, and Fe-Ni metal. EDS-spectrum imaging and high-resolution TEM (HRTEM) show local, nanocrystalline regions of the outermost 2 to 5 nm of the pyroxene are composed of an Fe-Mg-S-rich and Si- and O-depleted layer that is underlain by a 2- to 5-nm thick amorphous zone enriched in Si. These layers occur in multiple microtome slices and have uniform thicknesses. We also observe localized 'islands' of material on the surface of the pyroxene which HRTEM imaging indicates are amorphous and EDS measurements show are compositionally heterogeneous. A 10- to 60-nm thick partially amorphous zone occurs below the compositionally distinct rim. While this this zone is associated with the compositionally heterogeneous outer layer, it also occurs as a local stand-alone feature on the exterior rim of the grain. Ar-eas of the pyroxene grain rim also exhibit a vesicular texture. The TEM data indicate a complex history of space weather-ing for samples RA-QD02-0042-01 and -02. The outermost layer of nanocrystalline material with varied composition is consistent with previously suggested [3-4] chemical and structural pro-cessing by solar wind ions, with a possible additional role for im-pact vapor deposition [3-4]. The amorphous and compositionally distinct islands on the surface of this grain, similar to lunar glasses, suggest formation through vapor deposition via micrometeor-ite impact events. In comparison, the amorphization and vesicula-tion textures are likely a product of radiation damage from the solar wind. The depth and degree of amorphization, in conjunction with model calculations, will help provide an upper limit on exposure time for these particles.

Self-current induced spin-orbit torque in FeMn/Pt multilayers

PubMed Central

Xu, Yanjun; Yang, Yumeng; Yao, Kui; Xu, Baoxi; Wu, Yihong

2016-01-01

Extensive efforts have been devoted to the study of spin-orbit torque in ferromagnetic metal/heavy metal bilayers and exploitation of it for magnetization switching using an in-plane current. As the spin-orbit torque is inversely proportional to the thickness of the ferromagnetic layer, sizable effect has only been realized in bilayers with an ultrathin ferromagnetic layer. Here we demonstrate that, by stacking ultrathin Pt and FeMn alternately, both ferromagnetic properties and current induced spin-orbit torque can be achieved in FeMn/Pt multilayers without any constraint on its total thickness. The critical behavior of these multilayers follows closely three-dimensional Heisenberg model with a finite Curie temperature distribution. The spin torque effective field is about 4 times larger than that of NiFe/Pt bilayer with a same equivalent NiFe thickness. The self-current generated spin torque is able to switch the magnetization reversibly without the need for an external field or a thick heavy metal layer. The removal of both thickness constraint and necessity of using an adjacent heavy metal layer opens new possibilities for exploiting spin-orbit torque for practical applications. PMID:27185656

Self-Poling of BiFeO3 Thick Films.

PubMed

Khomyakova, Evgeniya; Sadl, Matej; Ursic, Hana; Daniels, John; Malic, Barbara; Bencan, Andreja; Damjanovic, Dragan; Rojac, Tadej

2016-08-03

Bismuth ferrite (BiFeO3) is difficult to pole because of the combination of its high coercive field and high electrical conductivity. This problem is particularly pronounced in thick films. The poling, however, must be performed to achieve a large macroscopic piezoelectric response. This study presents evidence of a prominent and reproducible self-poling effect in few-tens-of-micrometer-thick BiFeO3 films. Direct and converse piezoelectric measurements confirmed that the as-sintered BiFeO3 thick films yield d33 values of up to ∼20 pC/N. It was observed that a significant self-poling effect only appears in cases when the films are heated and cooled through the ferroelectric-paraelectric phase transition (Curie temperature TC ∼ 820 °C). These self-poled films exhibit a microstructure with randomly oriented columnar grains. The presence of a compressive strain gradient across the film thickness cooled from above the TC was experimentally confirmed and is suggested to be responsible for the self-poling effect. Finally, the macroscopic d33 response of the self-poled BiFeO3 film was characterized as a function of the driving-field frequency and amplitude.

Tailoring Curie temperature and magnetic anisotropy in ultrathin Pt/Co/Pt films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parakkat, Vineeth Mohanan; Ganesh, K. R.; Anil Kumar, P. S., E-mail: anil@physics.iisc.ernet.in

The dependence of perpendicular magnetization and Curie temperature (T{sub c}) of Pt/Co/Pt thin films on the thicknesses of Pt seed (Pt{sub s}) and presence of Ta buffer layer has been investigated in this work. Pt and Co thicknesses were varied between 2 to 8 nm and 0.35 to 1.31 nm (across the spin reorientation transition thickness) respectively and the T{sub c} was measured using SQUID magnetometer. We have observed a systematic dependence of T{sub c} on the thickness of Pt{sub s}. For 8 nm thickness of Pt{sub s} the Co layer of 0.35 nm showed ferromagnetism with perpendicular anisotropy atmore » room temperature. As the thickness of the Pt{sub s} was decreased to 2 nm, the T{sub c} went down below 250 K. XRD data indicated polycrystalline growth of Pt{sub s} on SiO{sub 2}. On the contrary Ta buffer layer promoted the growth of Pt(111). As a consequence Ta(5 nm)/Pt(3 nm)/Co(0.35 nm)/Pt(2 nm) had much higher T{sub c} (above 300 K) with perpendicular anisotropy when compared to the same stack without the Ta layer. Thus we could tune the ferromagnetic T{sub c} and anisotropy by varying the Pt{sub s} thickness and also by introducing Ta buffer layer. We attribute these observations to the micro-structural evolution of Pt{sub s} layer which hosts the Co layer.« less

Plasma assisted molecular beam epitaxy growth and effect of varying buffer thickness on the formation of ultra-thin In{sub 0.17}Al{sub 0.83}N/GaN heterostructure on Si(111)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chowdhury, Subhra, E-mail: subhra1109@gmail.com; Biswas, Dhrubes; Department of E and E C E, Indian Institute of Technology Kharagpur, Kharagpur 721302

2015-02-23

This work reports on the detailed plasma-assisted molecular beam epitaxy (PAMBE) growth of ultra-thin In{sub 0.17}Al{sub 0.83}N/GaN heterostructures on Si(111) substrate with three different buffer thickness (600 nm, 400 nm, and 200 nm). Growth through critical optimization of growth conditions is followed by the investigation of impact of varying buffer thickness on the formation of ultra-thin 1.5 nm, In{sub 0.17}Al{sub 0.83}N–1.25 nm, GaN–1.5 nm, In{sub 0.17}Al{sub 0.83}N heterostructure, in terms of threading dislocation (TD) density. Analysis reveals a drastic reduction of TD density from the order 10{sup 10 }cm{sup −2} to 10{sup 8 }cm{sup −2} with increasing buffer thickness resulting smooth ultra-thin active region for thick buffer structure.more » Increasing strain with decreasing buffer thickness is studied through reciprocal space mapping analysis. Surface morphology through atomic force microscopy analysis also supports our study by observing an increase of pits and root mean square value (0.89 nm, 1.2 nm, and 1.45 nm) with decreasing buffer thickness which are resulted due to the internal strain and TDs.« less

Thickness-dependent carrier mobility of ambipolar MoTe2: Interplay between interface trap and Coulomb scattering

NASA Astrophysics Data System (ADS)

Ji, Hyunjin; Lee, Gwanmu; Joo, Min-Kyu; Yun, Yoojoo; Yi, Hojoon; Park, Ji-Hoon; Suh, Dongseok; Lim, Seong Chu

2017-05-01

The correlation between the channel thickness and the carrier mobility is investigated by conducting static and low frequency (LF) noise characterization for ambipolar carriers in multilayer MoTe2 transistors. For channel thicknesses in the range of 5-15 nm, both the low-field carrier mobility and the Coulomb-scattering-limited carrier mobility (μC) are maximal at a thickness of ˜10 nm. For LF noise, the interplay of interface trap density (NST), which was minimal at ˜10 nm, and the interfacial Coulomb scattering parameter (αSC), which decreased up to 10 nm and saturated above 10 nm, explained the mobility (μC) peaked near 10 nm by the carrier fluctuation and charge distribution.