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Sample records for room temperature ferromagnetism

  1. Novel room temperature ferromagnetic semiconductors

    SciTech Connect

    Gupta, Amita

    2004-06-01

    Today's information world, bits of data are processed by semiconductor chips, and stored in the magnetic disk drives. But tomorrow's information technology may see magnetism (spin) and semiconductivity (charge) combined in one 'spintronic' device that exploits both charge and 'spin' to carry data (the best of two worlds). Spintronic devices such as spin valve transistors, spin light emitting diodes, non-volatile memory, logic devices, optical isolators and ultra-fast optical switches are some of the areas of interest for introducing the ferromagnetic properties at room temperature in a semiconductor to make it multifunctional. The potential advantages of such spintronic devices will be higher speed, greater efficiency, and better stability at a reduced power consumption. This Thesis contains two main topics: In-depth understanding of magnetism in Mn doped ZnO, and our search and identification of at least six new above room temperature ferromagnetic semiconductors. Both complex doped ZnO based new materials, as well as a number of nonoxides like phosphides, and sulfides suitably doped with Mn or Cu are shown to give rise to ferromagnetism above room temperature. Some of the highlights of this work are discovery of room temperature ferromagnetism in: (1) ZnO:Mn (paper in Nature Materials, Oct issue, 2003); (2) ZnO doped with Cu (containing no magnetic elements in it); (3) GaP doped with Cu (again containing no magnetic elements in it); (4) Enhancement of Magnetization by Cu co-doping in ZnO:Mn; (5) CdS doped with Mn, and a few others not reported in this thesis. We discuss in detail the first observation of ferromagnetism above room temperature in the form of powder, bulk pellets, in 2-3 mu-m thick transparent pulsed laser deposited films of the Mn (<4 at. percent) doped ZnO. High-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) spectra recorded from 2 to 200nm areas showed homogeneous distribution of Mn substituting

  2. Room Temperature Ferromagnetic Mn:Ge(001)

    PubMed Central

    Lungu, George Adrian; Stoflea, Laura Elena; Tanase, Liviu Cristian; Bucur, Ioana Cristina; Răduţoiu, Nicoleta; Vasiliu, Florin; Mercioniu, Ionel; Kuncser, Victor; Teodorescu, Cristian-Mihail

    2014-01-01

    We report the synthesis of a room temperature ferromagnetic Mn-Ge system obtained by simple deposition of manganese on Ge(001), heated at relatively high temperature (starting with 250 °C). The samples were characterized by low energy electron diffraction (LEED), scanning tunneling microscopy (STM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), superconducting quantum interference device (SQUID), and magneto-optical Kerr effect (MOKE). Samples deposited at relatively elevated temperature (350 °C) exhibited the formation of ~5–8 nm diameter Mn5Ge3 and Mn11Ge8 agglomerates by HRTEM, while XPS identified at least two Mn-containing phases: the agglomerates, together with a Ge-rich MnGe~2.5 phase, or manganese diluted into the Ge(001) crystal. LEED revealed the persistence of long range order after a relatively high amount of Mn (100 nm) deposited on the single crystal substrate. STM probed the existence of dimer rows on the surface, slightly elongated as compared with Ge–Ge dimers on Ge(001). The films exhibited a clear ferromagnetism at room temperature, opening the possibility of forming a magnetic phase behind a nearly ideally terminated Ge surface, which could find applications in integration of magnetic functionalities on semiconductor bases. SQUID probed the co-existence of a superparamagnetic phase, with one phase which may be attributed to a diluted magnetic semiconductor. The hypothesis that the room temperature ferromagnetic phase might be the one with manganese diluted into the Ge crystal is formulated and discussed. PMID:28788444

  3. Room temperature ferromagnetism in Teflon due to carbon dangling bonds.

    PubMed

    Ma, Y W; Lu, Y H; Yi, J B; Feng, Y P; Herng, T S; Liu, X; Gao, D Q; Xue, D S; Xue, J M; Ouyang, J Y; Ding, J

    2012-03-06

    The ferromagnetism in many carbon nanostructures is attributed to carbon dangling bonds or vacancies. This provides opportunities to develop new functional materials, such as molecular and polymeric ferromagnets and organic spintronic materials, without magnetic elements (for example, 3d and 4f metals). Here we report the observation of room temperature ferromagnetism in Teflon tape (polytetrafluoroethylene) subjected to simple mechanical stretching, cutting or heating. First-principles calculations indicate that the room temperature ferromagnetism originates from carbon dangling bonds and strong ferromagnetic coupling between them. Room temperature ferromagnetism has also been successfully realized in another polymer, polyethylene, through cutting and stretching. Our findings suggest that ferromagnetism due to networks of carbon dangling bonds can arise in polymers and carbon-based molecular materials.

  4. Room-temperature ferromagnetism in cerium dioxide powders

    SciTech Connect

    Rakhmatullin, R. M. Pavlov, V. V.; Semashko, V. V.; Korableva, S. L.

    2015-08-15

    Room-temperature ferromagnetism is detected in a CeO{sub 2} powder with a grain size of about 35 nm and a low (<0.1 at %) manganese and iron content. The ferromagnetism in a CeO{sub 2} sample with a submicron crystallite size and the same manganese and iron impurity content is lower than in the nanocrystalline sample by an order of magnitude. Apart from ferromagnetism, both samples exhibit EPR spectra of localized paramagnetic centers, the concentration of which is lower than 0.01 at %. A comparative analysis of these results shows that the F-center exchange (FCE) mechanism cannot cause ferromagnetism. This conclusion agrees with the charge-transfer ferromagnetism model proposed recently.

  5. Room-temperature ferromagnetism observed in alumina films

    NASA Astrophysics Data System (ADS)

    Zheng, Y. L.; Zhen, C. M.; Wang, X. Q.; Ma, L.; Li, X. L.; Hou, D. L.

    2011-08-01

    We have prepared alumina thin films on Si substrates using a radio frequency (RF) sputtering method, and have observed room-temperature ferromagnetism (RTFM) in the thin films. When the thin films were annealed in vacuum, the saturation magnetization (Ms) increased, while annealing the sample in the air contributed to a decrease in the value of Ms. The Ms of the thin film also decreased as the thickness increased. We confirm that the unpaired electron spins responsible for ferromagnetism (FM) in Al 2O 3-δ thin films have their origin in the oxygen vacancies, especially at the interface of the Al 2O 3-δ thin film and the Si substrate.

  6. Disorder-induced room temperature ferromagnetism in glassy chromites.

    PubMed

    Araujo, C Moyses; Nagar, Sandeep; Ramzan, Muhammad; Shukla, R; Jayakumar, O D; Tyagi, A K; Liu, Yi-Sheng; Chen, Jeng-Lung; Glans, Per-Anders; Chang, Chinglin; Blomqvist, Andreas; Lizárraga, Raquel; Holmström, Erik; Belova, Lyubov; Guo, Jinghua; Ahuja, Rajeev; Rao, K V

    2014-04-15

    We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spectroscopic techniques and first-principles calculations. We find that the observed order-disorder transformation is accompanied by an insulator-metal transition arising from a wide distribution of Cr-O-Cr bond angles and the consequent metallization through free carriers. Similar results also found in YbCrO3-films suggest that the observed phenomenon is more general and should, in principle, apply to a wider range of oxide systems. The ability to tailor ferromagnetic order above room temperature in oxide materials opens up many possibilities for novel technological applications of this counter intuitive effect.

  7. Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites

    NASA Astrophysics Data System (ADS)

    Araujo, C. Moyses; Nagar, Sandeep; Ramzan, Muhammad; Shukla, R.; Jayakumar, O. D.; Tyagi, A. K.; Liu, Yi-Sheng; Chen, Jeng-Lung; Glans, Per-Anders; Chang, Chinglin; Blomqvist, Andreas; Lizárraga, Raquel; Holmström, Erik; Belova, Lyubov; Guo, Jinghua; Ahuja, Rajeev; Rao, K. V.

    2014-04-01

    We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spectroscopic techniques and first-principles calculations. We find that the observed order-disorder transformation is accompanied by an insulator-metal transition arising from a wide distribution of Cr-O-Cr bond angles and the consequent metallization through free carriers. Similar results also found in YbCrO3-films suggest that the observed phenomenon is more general and should, in principle, apply to a wider range of oxide systems. The ability to tailor ferromagnetic order above room temperature in oxide materials opens up many possibilities for novel technological applications of this counter intuitive effect.

  8. Room Temperature Ferromagnetic Polymer and the Correlated Anomalous Magnetoresistance Phenomenon

    NASA Astrophysics Data System (ADS)

    Huang, Jinsong; Yang, Bin; Shield, Jeffrey

    2011-03-01

    Organic magnetoresistance (OMAR) has been observed in organic semiconductor devices where resistance can change in a relatively small external magnetic field at room temperature. Since a weak magnetic field is involved, the hyperfine interaction (HFI) is employed to explain OMAR in the reported literatures. None of these issues consider the magnetic properties of the organic semiconductors themselves. However, the we recently discovered that polymer semiconductors, such as poly(3-hexylthiophene) P3HT, can have room temperature (RT) ferromagnetic properties in their crystalline phase and when mixed with phenyl-C61-butyric acid methyl ester (PCBM). Here, we will report the possible correlation between the ferromagnetic property of the P3HT:PCBM and anomalous OMAR phenomenon including the anisotropic and hysteretic OMAR behavior. The magnetic property of the polymer including the anisotropic and photo induced change of magnetism will be also discussed to explore the possible mechanism of the room temperature ferromagnetism.~ This work is partially supported by the NSF MRSEC program at University.

  9. Room temperature ferromagnetism in a phthalocyanine based carbon material

    SciTech Connect

    Honda, Z. Sato, K.; Sakai, M.; Fukuda, T.; Kamata, N.; Hagiwara, M.; Kida, T.

    2014-02-07

    We report on a simple method to fabricate a magnetic carbon material that contains nitrogen-coordinated transition metals and has a large magnetic moment. Highly chlorinated iron phthalocyanine was used as building blocks and potassium as a coupling reagent to uniformly disperse nitrogen-coordinated iron atoms on the phthalocyanine based carbon material. The iron phthalocyanine based carbon material exhibits ferromagnetic properties at room temperature and the ferromagnetic phase transition occurs at T{sub c} = 490 ± 10 K. Transmission electron microscopy observation, X-ray diffraction analysis, and the temperature dependence of magnetization suggest that the phthalocyanine molecules form three-dimensional random networks in the iron phthalocyanine based carbon material.

  10. Investigation of Room temperature Ferromagnetism in Mn doped Ge

    NASA Astrophysics Data System (ADS)

    Colakerol Arslan, Leyla; Toydemir, Burcu; Onel, Aykut Can; Ertas, Merve; Doganay, Hatice; Gebze Inst of Tech Collaboration; Research Center Julich Collaboration

    2014-03-01

    We present a systematic investigation of structural, magnetic and electronic properties of MnxGe1 -x single crystals. MnxGe1-x films were grown by sequential deposition of Ge and Mn by molecular-beam epitaxy at low substrate temperatures in order to avoid precipitation of ferromagnetic Ge-Mn intermetallic compounds. Reflected high energy electron diffraction and x-ray diffraction observations revealed that films are epitaxially grown on Si (001) substrates from the initial stage without any other phase formation. Magnetic measurements carried out using a physical property measurement system showed that all samples exhibited ferromagnetism at room temperature. Electron spin resonance indicates the presence of magnetically ordered localized spins of divalent Mn ions. X-ray absorption measurements at the Mn L-edge confirm significant substitutional doping of Mn into Ge-sites. The ferromagnetism was mainly induced by Mn substitution for Ge site, and indirect exchange interaction of these magnetic ions with the intrinsic charge carriers is the origin of ferromagnetism. The magnetic interactions were better understood by codoping with nonmagnetic impurities. This work was supported by Marie-Curie Reintegration Grant (PIRG08-GA-2010-276973).

  11. Above room temperature ferromagnetism in Mn-ion implanted Si

    NASA Astrophysics Data System (ADS)

    Bolduc, M.; Awo-Affouda, C.; Stollenwerk, A.; Huang, M. B.; Ramos, F. G.; Agnello, G.; Labella, V. P.

    2005-01-01

    Above room temperature ferromagnetic behavior is achieved in Si through Mn ion implantation. Three-hundred-keV Mn+ ions were implanted to 0.1% and 0.8% peak atomic concentrations, yielding a saturation magnetization of 0.3emu/g at 300K for the highest concentration as measured using a SQUID magnetometer. The saturation magnetization increased by ˜2× after annealing at 800°C for 5min . The Curie temperature for all samples was found to be greater than 400K . A significant difference in the temperature-dependent remnant magnetization between the implanted p-type and n-type Si is observed, giving strong evidence that a Si-based diluted magnetic semiconductor can be achieved.

  12. Enhanced room temperature ferromagnetism in antiferromagnetic NiO nanoparticles

    SciTech Connect

    Ravikumar, Patta; Kisan, Bhagaban; Perumal, A.

    2015-08-15

    We report systematic investigations of structural, vibrational, resonance and magnetic properties of nanoscale NiO powders prepared by ball milling process under different milling speeds for 30 hours of milling. Structural properties revealed that both pure NiO and as-milled NiO powders exhibit face centered cubic structure, but average crystallite size decreases to around 11 nm along with significant increase in strain with increasing milling speed. Vibrational properties show the enhancement in the intensity of one-phonon longitudinal optical (LO) band and disappearance of two-magnon band due to size reduction. In addition, two-phonon LO band exhibits red shift due to size-induced phonon confinement effect and surface relaxation. Pure NiO powder exhibit antiferromagnetic nature, which transforms into induced ferromagnetic after size reduction. The average magnetization at room temperature increases with decreasing the crystallite size and a maximum moment of 0.016 μ{sub B}/f.u. at 12 kOe applied field and coercivity of 170 Oe were obtained for 30 hours milled NiO powders at 600 rotation per minute milling speed. The change in the magnetic properties is also supported by the vibrational properties. Thermomagnetization measurements at high temperature reveal a well-defined magnetic phase transition at high temperature (T{sub C}) around 780 K due to induced ferromagnetic phase. Electron paramagnetic resonance (EPR) studies reveal a good agreement between the EPR results and magnetic properties. The observed results are described on the basis of crystallite size variation, defect density, large strain, oxidation/reduction of Ni and interaction between uncompensated surfaces and particle core with lattice expansion. The obtained results suggest that nanoscale NiO powders with high T{sub C} and moderate magnetic moment at room temperature with cubic structure would be useful to expedite for spintronic devices.

  13. Room-temperature ferromagnetism in (Zn,Cr)Te

    NASA Astrophysics Data System (ADS)

    Saito, Hidekazu

    2006-03-01

    Ferromagnetic diluted magnetic semiconductors (DMSs) are the key material to developing semiconductor spintronic devices. One of the most characteristics physical phenomena in DMS is a strong interaction between sp-carriers and localized d-spins (sp-d exchange interaction) [1]. Confirmation of this interaction is essential to prove a synthesis of real DMS, and can be done directly by the magneto-optical studies such as a magnetic circular dichroism (MCD) measurement [2]. Here, we report room-temperature (RT) ferromagnetism with the sp-d exchange interaction in Zn1-xCrxTe (x=0.20) [3]. Zn1-xCrxTe films with x.3ex<=x 0.20 were grown on GaAs (001) substrates by a molecular beam epitaxy method. No sign of a secondary phase was detected in any films by the reflection high-energy electron and X-ray diffractions. MCD spectra were measured in a transmission mode. Magnetization (M) measurements were carried out using a SQUID. The M-H curves of Zn1-xCrxTe (x=0.20) showed a ferromagnetic behavior up to about RT. Curie temperature TC was estimated to be 300±10 K by the Arrott plot analysis. A strong enhancement of the MCD signal at the optical transition energies of critical points of host ZnTe was observed in Zn1-xCrxTe, indicating a strong sp-d exchange interaction. The MCD spectra of Zn1-xCrxTe at any magnetic field could be superposed upon a single spectrum, indicating that the observed MCD signals come from a single material, that is, Zn1-xCrxTe. The magnetic field dependence of MCD intensity showed the ferromagnetic feature, which coincides with the M-H curves measured using a SQUID. Furthermore, the MCD data showed the same TC as that obtained from magnetization data. These results indicate that Zn1-xCrxTe (x=0.20) is an intrinsic DMS with RT ferromagnetism. References [1] J. K. Furdyna, J. Appl. Phys. 64, R29 (1988). [2] K. Ando, in Magneto-Optics, Springer Series in Solid-State Science, edited by S. Sugano and N. Kojima (Springer, Berlin, 2000), Vol.128, p. 211. [3

  14. Theory of room temperature ferromagnetism in Cr modified DNA nanowire

    NASA Astrophysics Data System (ADS)

    Paruğ Duru, Izzet; Değer, Caner; Eldem, Vahap; Kalayci, Taner; Aktaş, Şahin

    2016-04-01

    We investigated the magnetic properties of Cr3+ (J  <  0) ion-modified DNA (M-DNA) nanowire (1000 base) at room temperature under a uniform magnetic field (˜100 Oe) for different doping concentrations. A Monte Carlo simulation method-based Metropolis algorithm is used to figure out the thermodynamic quantities of nanowire formed by Cr M-DNA followed by analysing the dependency of the ferromagnetic behaviour of the M-DNA to dopant concentration. It is understood that ion density/base and ion density/helical of Cr3+ ions can be a tuning parameter, herewith the dopant ratio has an actual importance on the magnetic characterization of M-DNA nanowire (3%-20%). We propose the source of magnetism as an exchange interaction between Cr and DNA helical atoms indicated in the Heisenberg Hamiltonian.

  15. Room-temperature ferromagnetism in pure ZnO nanoflowers

    NASA Astrophysics Data System (ADS)

    Bie, Xiaofei; Wang, Chunzhong; Ehrenberg, H.; Wei, Yingjin; Chen, Gang; Meng, Xing; Zou, Guangtian; Du, Fei

    2010-08-01

    ZnO nanoflowers are synthesized by hydrothermal method. The morphology of ZnO is captured by SEM, TEM and HRTEM, which is composed of closely packed nanorods of about 100 nm in diameter and 1 μm in length. The ZFC/FC curves show superparamagnetic features. The abnormal increase in magnetization curves below 14 K comes from the isolated vacancy clusters with no interaction. The magnetic hysteresis at 300 K displays saturation state and confirms room-temperature ferromagnetism. While the magnetic hysteresis at 5 K shows nonsaturation state due to the enhanced effects of vacancy clusters. The O 1s XPS results can be fitted to three Gaussian peaks. The existence of medium-binding energy located at 531.16 eV confirms the deficiency of O ions at the surface of ZnO nanoflowers.

  16. Electrically-induced ferromagnetism at room temperature in (Ti,Co)O2: carrier-mediated ferromagnetism

    NASA Astrophysics Data System (ADS)

    Fukumura, Tomoteru

    2013-03-01

    Oxide-diluted magnetic semiconductors (DMS) is expected to have high Curie temperature via carrier-mediated ferromagnetism through heavy electron mass and large electron carrier density. We have studied various oxide-DMS such as (Zn,Mn)O, and discovered room temperature ferromagnetism in (Ti,Co)O2. The origin of ferromagnetism has been discussed for a decade. Previously, the control of ferromagnetism was demonstrated through carrier control by chemical doping. But it was difficult to exclude the defect-mediated ferromagnetism, since the electron donor was the oxygen vacancy. In order to evidence the carrier-mediated ferromagnetism, the electric field control of ferromagnetism is useful. The control of ferromagnetism at room temperature is also important for implementation of spintronic devices. By gating with electric double layer transistor, the ferromagnetism was induced at room temperature, representing electron carrier-mediated ferromagnetism. Chemical doping study in (Ti,Co)O2 for wider range of carrier density exhibited clearer paramagnetic insulator to ferromagnetic metal transition with increasing carrier density. At a medium carrier density, a ferromagnetic insulator phase appeared possibly related with a phase separation between ferromagnetic and paramagnetic phases. Also, a superparamagnetic phase appeared for excessively reduced sample. Taking all these results into account, previously proposed extrinsic mechanisms such as oxygen vacancy-mediated mechanism, metal segregation, and superparamagnetism are not correct picture of the ferromagnetism. This study was in collaboration with Y. Yamada, K. Ueno, M. Kawasaki, H. T. Yuan, H. Shimotani, Y. Iwasa, L. Gu, S. Tsukimoto, Y. Ikuhara, A. Fujimori, and T. Mizokawa. This research was in part supported by JSPS through NEXT Program initiated by CSTP.

  17. Room-Temperature Spin Filtering in Metallic Ferromagnet-Multilayer Graphene-Ferromagnet Junctions.

    PubMed

    Cobas, Enrique D; van 't Erve, Olaf M J; Cheng, Shu-Fan; Culbertson, James C; Jernigan, Glenn G; Bussman, Konrad; Jonker, Berend T

    2016-11-22

    We report room-temperature negative magnetoresistance in ferromagnet-graphene-ferromagnet (FM|Gr|FM) junctions with minority spin polarization exceeding 80%, consistent with predictions of strong minority spin filtering. We fabricated arrays of such junctions via chemical vapor deposition of multilayer graphene on lattice-matched single-crystal NiFe(111) films and standard photolithographic patterning and etching techniques. The junctions exhibit metallic transport behavior, low resistance, and the negative magnetoresistance characteristic of a minority spin filter interface throughout the temperature range 10 to 300 K. We develop a device model to incorporate the predicted spin filtering by explicitly treating a metallic minority spin channel with spin current conversion and a tunnel barrier majority spin channel and extract spin polarization of at least 80% in the graphene layer in our structures. The junctions also show antiferromagnetic coupling, consistent with several recent predictions. The methods and findings are relevant to fast-readout low-power magnetic random access memory technology, spin logic devices, and low-power magnetic field sensors.

  18. Toward room temperature ferromagnetism of Ge:Mn systems

    NASA Astrophysics Data System (ADS)

    D'Orazio, F.; Lucari, F.; Pinto, N.; Morresi, L.; Murri, R.

    2004-05-01

    We investigate the magnetic properties of Mn xGe 1- x/Ge(1 0 0) films. We show that the choice of growth temperature and Mn content is crucial for achieving optimal magnetic performance. With a substrate temperature of 160°C during film deposition, and Mn concentration between 2.7% and 4.4%, hysteresis is observed up to about 250 K. However, the magnetic loop maintains a saturating behaviour at high fields up to room temperature. For larger Mn concentrations the magnetic response is strongly suppressed, suggesting a possible segregation of manganese.

  19. Thermopower and resistivity in ferromagnetic thin films near room temperature

    NASA Astrophysics Data System (ADS)

    Avery, A. D.; Sultan, Rubina; Bassett, D.; Wei, D.; Zink, B. L.

    2011-03-01

    We present measurements of thermopower (Seebeck coefficient) and electrical resistivity of a wide selection of polycrystalline ferromagnetic films with thicknesses ranging from 60-167 nm. For comparison, a copper film of similar thickness was measured with the same techniques. Both the thermal and electrical measurements, made as a function of temperature from 77-325 K, are made using a micromachined thermal isolation platform consisting of a suspended, patterned silicon-nitride membrane. We observe a strong correlation between the resistivity of the films and the thermopower. Films with higher resistivity and residual resistivity ratios, indicating a higher concentration of static defects such as impurities or grain boundaries, with rare exception show thermopower of the same sign, but with absolute magnitude reduced from the thermopower of the corresponding bulk material. In addition, iron films exhibit the pronounced low-temperature peak in thermopower associated with magnon drag, with a magnitude similar to that seen in bulk iron alloys. These results provide important groundwork for ongoing studies of related thermoelectric effects in nanomagnetic systems, such as the spin Seebeck effect.

  20. First principle prediction of half-metallic ferromagnetism above room temperature in half-heusler alloys

    SciTech Connect

    Van An Dinh; Sato, Kazunori; Katayama-Yoshida, Hiroshi

    2010-01-04

    A first principle study of half-metallicity and ferromagnetism in half-heusler alloys NiMnZ (Z = Si, P, Ge, As, and Sb) is given. The half-metallicity and ferromagnetism are predicted via the calculation of electronic structure, and Curie temperature. The stability of the orthorhombic and tetragonal structures and C1{sub b} at various values of lattice parameters is also studied by means of the pseudo-potential method. All alloys exhibit the half-metallicity and ferromagnetism above room temperature.

  1. Ferromagnetism at room temperature in Cr-doped anodic titanium dioxide nanotubes

    SciTech Connect

    Liao, Yulong E-mail: hwzhang@uestc.edu.cn; Zhang, Huaiwu E-mail: hwzhang@uestc.edu.cn; Li, Jie; Yu, Guoliang; Zhong, Zhiyong; Bai, Feiming; Jia, Lijun; Zhang, Shihong; Zhong, Peng

    2014-05-07

    This study reports the room-temperature ferromagnetism in Cr-doped TiO{sub 2} nanotubes (NTs) synthesized via the electrochemical method followed by a novel Cr-doping process. Scanning electron microscopy and transmission electron microscopy showed that the TiO{sub 2} NTs were highly ordered with length up to 26 μm, outer diameter about 110 nm, and inner diameter about 100 nm. X-ray diffraction results indicated there were no magnetic contaminations of metallic Cr clusters or any other phases except anatase TiO{sub 2}. The Cr-doped TiO{sub 2} NTs were further annealed in oxygen, air and argon, and room-temperature ferromagnetism was observed in all Cr-doped samples. Moreover, saturation magnetizations and coercivities of the Cr-doped under various annealing atmosphere were further analyzed, and results indicate that oxygen content played a critical role in the room-temperature ferromagnetism.

  2. The role of hydrogen in room-temperature ferromagnetism at graphite surfaces

    SciTech Connect

    Ohldag, Hendrik

    2011-08-12

    We present a x-ray dichroism study of graphite surfaces that addresses the origin and magnitude of ferromagnetism in metal-free carbon. We find that, in addition to carbon {pi} states, also hydrogen-mediated electronic states exhibit a net spin polarization with significant magnetic remanence at room temperature. The observed magnetism is restricted to the top {approx}10 nm of the irradiated sample where the actual magnetization reaches {approx_equal} 15 emu/g at room temperature. We prove that the ferromagnetism found in metal-free untreated graphite is intrinsic and has a similar origin as the one found in proton bombarded graphite.

  3. Joint effect of ferromagnetic and non-ferromagnetic cations for adjusting room temperature ferromagnetism of highly luminescent CuNiInS quaternary nanocrystals

    NASA Astrophysics Data System (ADS)

    Shen, Jin; Wang, Chunlei; Xu, Shuhong; Lv, Changgui; Zhang, Ruohu; Cui, Yiping

    2017-01-01

    In this work, highly luminescent quaternary CuNiInS nanocrystals (NCs) are put forward as a good prototype for investigating defect-induced room temperature ferromagnetism. A ferromagnetic Ni cation can preserve the strong luminescence of NCs without introducing intermediate energy levels in the center of the forbidden band. The strong luminescence of NCs is used as an indicator for monitoring the concentration of vacancy defects inside them, facilitating the investigation of the origin of room temperature ferromagnetism in CuNiInS NCs. Our results reveal that the patching of Cu vacancies ({{{{V}}}{{Cu}}}-) with Ni will result in bound magnetic polarons composed of both {{{{V}}}{{Cu}}}- and a substitution of Cu by Ni ({{{{Ni}}}{{Cu}}}+), giving rise to the room temperature ferromagnetism of CuNiInS NCs. Either the ferromagnetic Ni or the non-ferromagnetic Cu cation can tune the magnetism of CuNiInS NCs because of the change of bound magnetic polaron concentration at the altered concentration ratio of {{{{V}}}{{Cu}}}- and {{{{Ni}}}{{Cu}}}+.

  4. Room temperature d{sup 0} ferromagnetism in ZnS nanocrystals

    SciTech Connect

    Proshchenko, Vitaly; Horoz, Sabit; Tang, Jinke; Dahnovsky, Yuri

    2016-06-14

    Room temperature ferromagnetic semiconductors have a great deal of advantage because of their easy integration into semiconductor devices. ZnS nanocrystals (NCs), bulk, and surfaces exhibit d{sup 0} ferromagnetism at room temperature. The experiments reveal that NC ferromagnetism takes place at low and room temperatures only due to Zn vacancies (S vacancies do not contribute). To understand the mechanism of d{sup 0} ferromagnetism, we introduce the surface-bulk model of a nanocrystal, which includes both surface and bulk magnetizations. The calculations demonstrate that the surface has the higher than bulk magnetization. We find the mechanism of the ferromagnetism is due to sulfur s- and p-electrons in a tetrahedral crystal field. The bulk magnetic moment increases with Zn vacancy concentration at small concentrations and then goes down at larger concentrations. A surface magnetic moment behaves differently with the concentration. It is always a monotonically rising function. We find that the total NC magnetic moment increases with the size and concentration of Zn vacancies (only low concentrations). We also study the magnetization per unit cell where we find that it decreases for the surface and increases for bulk magnetism with the NC size.

  5. Robust room temperature ferromagnetism and band gap tuning in nonmagnetic Mg doped ZnO films

    NASA Astrophysics Data System (ADS)

    Quan, Zhiyong; Liu, Xia; Qi, Yan; Song, Zhilin; Qi, Shifei; Zhou, Guowei; Xu, Xiaohong

    2017-03-01

    Mg doped ZnO films with hexagonal wurtzite structure were deposited on c-cut sapphire Al2O3 substrates by pulsed laser deposition. Both room temperature ferromagnetism and band gap of the films simultaneously tuned by the concentration of oxygen vacancies were performed. Our results further reveal that the singly occupied oxygen vacancies should be responsible for the room temperature ferromagnetism and band gap narrowing. Singly occupied oxygen vacancies having the localized magnetic moments form bound magnetic polarons, which results in a long-range ferromagnetic ordering due to Mg doping. Moreover, band gap narrowing of the films is probably due to the formation of impurity band in the vicinity of valence band, originating from singly occupied oxygen vacancies. These results may build a bridge to understand the relationship between the magnetic and optical properties in oxide semiconductor, and are promising to integrate multiple functions in one system.

  6. Room-temperature spin-polarized organic light-emitting diodes with a single ferromagnetic electrode

    SciTech Connect

    Ding, Baofu Alameh, Kamal; Song, Qunliang

    2014-05-19

    In this paper, we demonstrate the concept of a room-temperature spin-polarized organic light-emitting diode (Spin-OLED) structure based on (i) the deposition of an ultra-thin p-type organic buffer layer on the surface of the ferromagnetic electrode of the Spin-OLED and (ii) the use of oxygen plasma treatment to modify the surface of that electrode. Experimental results demonstrate that the brightness of the developed Spin-OLED can be increased by 110% and that a magneto-electroluminescence of 12% can be attained for a 150 mT in-plane magnetic field, at room temperature. This is attributed to enhanced hole and room-temperature spin-polarized injection from the ferromagnetic electrode, respectively.

  7. Reversible switching of room temperature ferromagnetism in CeO2-Co nanoparticles

    NASA Astrophysics Data System (ADS)

    Sacanell, J.; Paulin, M. A.; Ferrari, V.; Garbarino, G.; Leyva, A. G.

    2012-04-01

    We investigated the reversible ferromagnetic (FM) behavior of pure and Co doped CeO2 nanopowders. The as-sintered samples displayed an increasing paramagnetic contribution upon Co doping. Room temperature FM is obtained simply by performing thermal treatments in vacuum at temperatures as low as 500 °C and it can be switched off by performing thermal treatments in oxidizing conditions. The FM contribution is enhanced as we increase the time of the thermal treatment in vacuum. Those systematic experiments establish a direct relation between ferromagnetism and oxygen vacancies and open a path for developing materials with tailored properties.

  8. Room temperature ferromagnetism in liquid-phase pulsed laser ablation synthesized nanoparticles of nonmagnetic oxides

    SciTech Connect

    Singh, S. C. Gopal, R.; Kotnala, R. K.

    2015-08-14

    Intrinsic Room Temperature Ferromagnetism (RTF) has been observed in undoped/uncapped zinc oxide and titanium dioxide spherical nanoparticles (NPs) obtained by a purely green approach of liquid phase pulsed laser ablation of corresponding metal targets in pure water. Saturation magnetization values observed for zinc oxide (average size, 9 ± 1.2 nm) and titanium dioxide (average size, 4.4 ± 0.3 nm) NPs are 62.37 and 42.17 memu/g, respectively, which are several orders of magnitude larger than those of previous reports. In contrast to the previous works, no postprocessing treatments or surface modification is required to induce ferromagnetism in the case of present communication. The most important result, related to the field of intrinsic ferromagnetism in nonmagnetic materials, is the observation of size dependent ferromagnetism. Degree of ferromagnetism in titanium dioxide increases with the increase in particle size, while it is reverse for zinc oxide. Surface and volume defects play significant roles for the origin of RTF in zinc oxide and titanium dioxide NPs, respectively. Single ionized oxygen and neutral zinc vacancies in zinc oxide and oxygen and neutral/ionized titanium vacancies in titanium dioxide are considered as predominant defect centres responsible for observed ferromagnetism. It is expected that origin of ferromagnetism is a consequence of exchange interactions between localized electron spin moments resulting from point defects.

  9. Room temperature ferromagnetism in liquid-phase pulsed laser ablation synthesized nanoparticles of nonmagnetic oxides

    NASA Astrophysics Data System (ADS)

    Singh, S. C.; Kotnala, R. K.; Gopal, R.

    2015-08-01

    Intrinsic Room Temperature Ferromagnetism (RTF) has been observed in undoped/uncapped zinc oxide and titanium dioxide spherical nanoparticles (NPs) obtained by a purely green approach of liquid phase pulsed laser ablation of corresponding metal targets in pure water. Saturation magnetization values observed for zinc oxide (average size, 9 ± 1.2 nm) and titanium dioxide (average size, 4.4 ± 0.3 nm) NPs are 62.37 and 42.17 memu/g, respectively, which are several orders of magnitude larger than those of previous reports. In contrast to the previous works, no postprocessing treatments or surface modification is required to induce ferromagnetism in the case of present communication. The most important result, related to the field of intrinsic ferromagnetism in nonmagnetic materials, is the observation of size dependent ferromagnetism. Degree of ferromagnetism in titanium dioxide increases with the increase in particle size, while it is reverse for zinc oxide. Surface and volume defects play significant roles for the origin of RTF in zinc oxide and titanium dioxide NPs, respectively. Single ionized oxygen and neutral zinc vacancies in zinc oxide and oxygen and neutral/ionized titanium vacancies in titanium dioxide are considered as predominant defect centres responsible for observed ferromagnetism. It is expected that origin of ferromagnetism is a consequence of exchange interactions between localized electron spin moments resulting from point defects.

  10. Room temperature ferromagnetism and ferroelectricity in cobalt-doped LiNbO{sub 3} film

    SciTech Connect

    Song, C.; Wang, C. Z.; Yang, Y. C.; Liu, X. J.; Zeng, F.; Pan, F.

    2008-06-30

    (5 at. %) cobalt-doped LiNbO{sub 3} (Co:LN) films were prepared by combinatorial laser molecular-beam epitaxy on Si (100). The Co:LN films with Co{sup 2+} replacing Nb exhibit room temperature ferromagnetism of 1.2{mu}{sub B}/Co and Curie temperature of {approx}540 K. Through a Ag/Co:LN/Si metal-ferroelectric-semiconductor field effect transistor configuration, ferroelectric measurements show that the films display hysteresis loops at 300 K and ferroelectric transition temperature of {approx}610 K. The hysteresis and the asymmetry in capacitance-voltage and leakage-voltage curves are ascribed to trapping/detrapping process of charges at the Co:LN/Si interface. The coexistence of room temperature ferromagnetism and ferroelectricity makes Co:LN a promising single-phase multiferroic.

  11. Signature of room temperature ferromagnetism in Mn doped CeO{sub 2} nanoparticles

    SciTech Connect

    Kumar, Shalendra; Ahmed, Faheem; Anwar, M.S.; Choi, H.K.; Chung, Hanshik; Koo, B.H.

    2012-10-15

    We report structural and magnetic properties of Mn doped CeO{sub 2} nanoparticles using X-ray diffraction (XRD), field emission transmission electron microscopy (FE-TEM) and dc magnetization measurements. XRD results infer that all the samples have single phase nature and lattice parameters decrease with Mn doping. The particle size calculated using XRD and TEM analysis was found to decrease with Mn doping. Field cooled magnetization measurement shows that the transition temperature is above room temperature. Magnetic hysteresis loop studies indicate that undoped and Mn doped CeO{sub 2} nanoparticles show weak ferromagnetic behavior at room temperature.

  12. Synthesis and properties of Ag-doped ZnO films with room temperature ferromagnetism

    NASA Astrophysics Data System (ADS)

    Xu, Qin; Wang, Zhi-Jun; Chang, Ze-Jiang; Liu, Jing-Jin; Ren, Ya-Xuan; Sun, Hui-Yuan

    2016-12-01

    A series of Ag-doped ZnO films were prepared by DC magnetron sputtering. XRD and SEM results showed that the doping amount of Ag had a great influence on the films' morphology and ferromagnetism, and their magnetism can be improved by doping an appropriate amount of Ag. The theoretical analysis suggested that the magnetism resulted mainly from the film grain boundary surfaces. Further research revealed that these films had strong timeliness. Such a result indicated that the room temperature ferromagnetism of Ag-doped ZnO films did not stem from the cation vacancies but from the oxygen vacancies on the boundary surfaces.

  13. Room temperature ferromagnetism and structural properties of nano BaTiO3

    NASA Astrophysics Data System (ADS)

    Rajamanickam, N.; Rajashabala, S.; Ramachandran, K.

    2015-06-01

    Perovskite barium titanate (BTO) is a ferroelectric material and here an attempt is made to observe ferromagnetism, for multiferroics. BTO nanostructures (NS) were prepared by coprecipitation method. Perovskite structured tetragonal phase was observed by XRD and Rietveld method. The absorption spectrum of UV-Vis exhibited a band gap of 3.23 eV, blue shifted from bulk. The flower like structure for morphology was observed in SEM. Ferromagnetic behavior is observed by VSM measurement at room temperature (RT) and the possible reasons are discussed.

  14. Stable room-temperature ferromagnetic phase at the FeRh(100) surface

    SciTech Connect

    Pressacco, Federico; Uhlir, Vojtech; Gatti, Matteo; Bendounan, Azzedine; Fullerton, Eric E.; Sirotti, Fausto

    2016-03-03

    Interfaces and low dimensionality are sources of strong modifications of electronic, structural, and magnetic properties of materials. FeRh alloys are an excellent example because of the first-order phase transition taking place at ~400 K from an antiferromagnetic phase at room temperature to a high temperature ferromagnetic one. It is accompanied by a resistance change and volume expansion of about 1%. We have investigated the electronic and magnetic properties of FeRh(100) epitaxially grown on MgO by combining spectroscopies characterized by different probing depths, namely X-ray magnetic circular dichroism and photoelectron spectroscopy. Furthermore, we find that the symmetry breaking induced at the Rh-terminated surface stabilizes a surface ferromagnetic layer involving five planes of Fe and Rh atoms in the nominally antiferromagnetic phase at room temperature. First-principles calculations provide a microscopic description of the structural relaxation and the electron spin-density distribution that support the experimental findings.

  15. Stable room-temperature ferromagnetic phase at the FeRh(100) surface

    PubMed Central

    Pressacco, Federico; Uhlίř, Vojtěch; Gatti, Matteo; Bendounan, Azzedine; Fullerton, Eric E.; Sirotti, Fausto

    2016-01-01

    Interfaces and low dimensionality are sources of strong modifications of electronic, structural, and magnetic properties of materials. FeRh alloys are an excellent example because of the first-order phase transition taking place at ~400 K from an antiferromagnetic phase at room temperature to a high temperature ferromagnetic one. It is accompanied by a resistance change and volume expansion of about 1%. We have investigated the electronic and magnetic properties of FeRh(100) epitaxially grown on MgO by combining spectroscopies characterized by different probing depths, namely X-ray magnetic circular dichroism and photoelectron spectroscopy. We find that the symmetry breaking induced at the Rh-terminated surface stabilizes a surface ferromagnetic layer involving five planes of Fe and Rh atoms in the nominally antiferromagnetic phase at room temperature. First-principles calculations provide a microscopic description of the structural relaxation and the electron spin-density distribution that support the experimental findings. PMID:26935274

  16. Room temperature ferromagnetism in low dose ion implanted counter-doped Ge:Mn, As

    NASA Astrophysics Data System (ADS)

    Donarelli, M.; Kazakova, O.; Ortolani, L.; Morandi, V.; Impellizzeri, G.; Priolo, F.; Passacantando, M.; Ottaviano, L.

    2017-10-01

    We demonstrate room-temperature ferromagnetism in germanium counter-doped with manganese and arsenic at concentrations up to approximately 2.1 × 1020 at/cm3: these values are one order of magnitude lower than those at which ferromagnetic behavior has previously been observed. Synthesis proceeded by ion implantation at 513 K followed by annealing in argon at 673 K. High resolution TEM, STEM, and EDX show single-phase diamond cubic material lacking Mn or As precipitates. These findings are consistent with the prediction of Chen et al. that counter-doping with approximately equal concentrations of a single-electron donor permits Mn, a two-electron acceptor, to be incorporated at high enough concentrations to yield a diluted magnetic semiconductor with a Curie temperature above room temperature.

  17. Room Temperature Ferromagnetic, Anisotropic, Germanium Rich FeGe(001) Alloys.

    PubMed

    Lungu, George A; Apostol, Nicoleta G; Stoflea, Laura E; Costescu, Ruxandra M; Popescu, Dana G; Teodorescu, Cristian M

    2013-02-21

    Ferromagnetic FexGe1-x with x = 2%-9% are obtained by Fe deposition onto Ge(001) at high temperatures (500 °C). Low energy electron diffraction (LEED) investigation evidenced the preservation of the (1 × 1) surface structure of Ge(001) with Fe deposition. X-ray photoelectron spectroscopy (XPS) at Ge 3d and Fe 2p core levels evidenced strong Fe diffusion into the Ge substrate and formation of Ge-rich compounds, from FeGe₃ to approximately FeGe₂, depending on the amount of Fe deposited. Room temperature magneto-optical Kerr effect (MOKE) evidenced ferromagnetic ordering at room temperature, with about 0.1 Bohr magnetons per Fe atom, and also a clear uniaxial magnetic anisotropy with the in-plane easy magnetization axis. This compound is a good candidate for promising applications in the field of semiconductor spintronics.

  18. Room temperature ferromagnetism in undoped and Fe doped ZnO nanorods: Microwave-assisted synthesis

    SciTech Connect

    Limaye, Mukta V.; Singh, Shashi B.; Das, Raja; Poddar, Pankaj; Kulkarni, Sulabha K.

    2011-02-15

    One-dimensional (1D) undoped and Fe doped ZnO nanorods of average length {approx}1 {mu}m and diameter {approx}50 nm have been obtained using a microwave-assisted synthesis. The magnetization (M) and coercivity (H{sub c}) value obtained for undoped ZnO nanorods at room temperature is {approx}5x10{sup -3} emu/g and {approx}150 Oe, respectively. The Fe doped ZnO samples show significant changes in M -H loop with increasing doping concentration. Both undoped and Fe doped ZnO nanorods exhibit a Curie transition temperature (T{sub c}) above 390 K. Electron spin resonance and Moessbauer spectra indicate the presence of ferric ions. The origin of ferromagnetism in undoped ZnO nanorods is attributed to localized electron spin moments resulting from surface defects/vacancies, where as in Fe doped samples is explained by F center exchange mechanism. -- Graphical abstract: Room temperature ferromagnetism has been reported in undoped and Fe doped ZnO nanorods of average length {approx}1 {mu}m and diameter {approx}50 nm. Display Omitted Research Highlights: {yields} Microwave-assisted synthesis of undoped and Fe doped ZnO nanorods. {yields} Observation of room temperature ferromagnetism in undoped and Fe doped ZnO nanorods. {yields} Transition temperature (T{sub c}) obtained in undoped and doped samples is above 390 K. {yields} In undoped ZnO origin of ferromagnetism is explained in terms of defects/vacancies. {yields} Ferromagnetism in Fe doped ZnO is explained by F-center exchange mechanism.

  19. The role of hydrogen in room-temperature ferromagnetism at graphite surfaces

    SciTech Connect

    Ohldag, H.; Esquinazi, P.; Arenholz, E.; Spemann, D.; Rothermel, M.; Setzer, A.; Butz, T.

    2010-05-01

    We present a x-ray dichroism study of graphite surfaces that addresses the origin and magnitude of ferromagnetism in metal-free carbon. We find that, in addition to carbon {pi} states, also hydrogen-mediated electronic states exhibit a net spin polarization with significant magnetic remanence at room temperature. The observed magnetism is restricted to the top {approx}10 nm of the irradiated sample where the average magnetization reaches {approx_equal} 15 emu/g at room temperature. We prove that the ferromagnetism found in metal-free untreated graphite is intrinsic and has a similar origin as the one found in proton bombarded graphite. Also, our findings show that the magnetic properties of graphite surfaces, thin films or two dimensional graphene samples can be reliably studied using soft x-ray dichroism. Fundamental new insight into the magnetic properties of carbon based systems can thus be obtained.

  20. Room temperature ferromagnetism in Mn-doped NiO nanoparticles

    NASA Astrophysics Data System (ADS)

    Layek, Samar; Verma, H. C.

    2016-01-01

    Mn-doped NiO nanoparticles of the series Ni1-xMnxO (x=0.00, 0.02, 0.04 and 0.06) are successfully synthesized using a low temperature hydrothermal method. Samples up to 6% Mn-doping are single phase in nature as observed from powder x-ray diffraction (XRD) studies. Rietveld refinement of the XRD data shows that all the single phase samples crystallize in the NaCl like fcc structure with space group Fm-3m. Unit cell volume decreases with increasing Mn-doping. Pure NiO nanoparticles show weak ferromagnetism, may be due to nanosize nature. Introduction of Mn within NiO lattice improves the magnetic properties significantly. Room temperature ferromagnetism is found in all the doped samples whereas the magnetization is highest for 2% Mn-doping and then decreases with further doping. The ZFC and FC branches in the temperature dependent magnetization separate well above 350 K indicating transition temperature well above room temperature for 2% Mn-doped NiO Nanoparticle. The ferromagnetic Curie temperature is found to be 653 K for the same sample as measured by temperature dependent magnetization study using vibrating sample magnetometer (VSM) in high vacuum.

  1. Tunable room-temperature ferromagnet using an iron-oxide and graphene oxide nanocomposite

    NASA Astrophysics Data System (ADS)

    Lin, Aigu L.; Rodrigues, J. N. B.; Su, Chenliang; Milletari, M.; Loh, Kian Ping; Wu, Tom; Chen, Wei; Neto, A. H. Castro; Adam, Shaffique; Wee, Andrew T. S.

    2015-06-01

    Magnetic materials have found wide application ranging from electronics and memories to medicine. Essential to these advances is the control of the magnetic order. To date, most room-temperature applications have a fixed magnetic moment whose orientation is manipulated for functionality. Here we demonstrate an iron-oxide and graphene oxide nanocomposite based device that acts as a tunable ferromagnet at room temperature. Not only can we tune its transition temperature in a wide range of temperatures around room temperature, but the magnetization can also be tuned from zero to 0.011 A m2/kg through an initialization process with two readily accessible knobs (magnetic field and electric current), after which the system retains its magnetic properties semi-permanently until the next initialization process. We construct a theoretical model to illustrate that this tunability originates from an indirect exchange interaction mediated by spin-imbalanced electrons inside the nanocomposite.

  2. Light Control of Ferromagnetism in ZnO Films on Pt Substrate at Room Temperature

    PubMed Central

    Xie, Jihao; Qin, Hongwei; Hao, Yanming; Cheng, Bin; Liu, Weikang; Liu, Liang; Ren, Shaoqing; Zhou, Guangjun; Ji, Ziwu; Hu, Jifan

    2017-01-01

    The control of ferromagnetism by light at room temperature is essential for the development of some optical-magnetic coupling devices, data storage and quantum computation techniques. In the present work, we demonstrate that the ferromagnetism of a semiconducting ZnO film on Pt substrate can be controlled by nonpolarized ultraviolet or violet light. The illumination of light with sufficiently high frequency photons could excite photogenerated electron-hole pairs in the semiconducting ZnO film. The amount of oxygen vacancies in the ZnO film and the appearance of built-in electric field due to the heterostructured ZnO/Pt may play important roles in the light-induced changes in the ferromagnetism of the ZnO film. PMID:28393834

  3. Room-temperature ferromagnetism in Fe-doped In2O3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Wongsaprom, Kwanruthai; Sonsupap, Somchai; Maensiri, Santi; Kidkhunthod, Pinit

    2015-10-01

    Nanoparticles of Fe-doped In2O3 [(In1- x Fe x )2O3, 0 ≤ x ≤ 0.10] are prepared by a simple polymerized complex method using indium (III) nitrate hydrate, iron (III) nitrate nonahydrate and polyvinyl pyrrolidone as the starting materials. The XRD, Raman and electron diffraction analysis results indicated that the calcined samples have the cubic structure of In2O3. An X-ray absorption spectroscopy including X-ray absorption near-edge spectroscopy is used in order to address both qualitative and quantitative of doped Fe valence states. The undoped sample exhibits a diamagnetic behavior, whereas all the Fe-doped samples are ferromagnetic having the magnetizations of ~0.0019-0.2959 emu/g at 10 kOe. Our results indicate that room-temperature ferromagnetism of Fe-doped In2O3 system is intrinsic and is not a result of any ferromagnetic impurity phases.

  4. Proximity induced room temperature ferromagnetism in graphene probed with spin currents

    NASA Astrophysics Data System (ADS)

    Leutenantsmeyer, Johannes Christian; Kaverzin, Alexey A.; Wojtaszek, Magdalena; van Wees, Bart J.

    2017-03-01

    We present a direct measurement of the exchange interaction in room temperature ferromagnetic graphene. We study the spin transport in exfoliated graphene on an yttrium-iron-garnet substrate where the observed spin precession clearly indicates the presence and strength of an exchange field that is an unambiguous evidence of induced ferromagnetism. We describe the results with a modified Bloch diffusion equation and extract an average exchange field of the order of 0.2 T. Further, we demonstrate that a proximity induced 2D ferromagnet can efficiently modulate a spin current by controlling the direction of the exchange field. These findings can create a building block for magnetic-gate tuneable spin transport in one-atom-thick spintronic devices.

  5. Room-temperature ferromagnetism in lightly Cr-doped ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Duan, L. B.; Zhao, X. R.; Liu, J. M.; Wang, T.; Rao, G. H.

    2010-06-01

    Zn1- x Cr x O (0≤ x≤0.15) nanoparticles were synthesized by an auto-combustion method and characterized by x-ray diffraction and Raman scattering techniques. The solubility limit for Cr in ZnO was determined as x≈0.03. Room-temperature ferromagnetism (RT-FM) was observed in lightly Cr-doped ZnO nanoparticles with x=0.01 and 0.02. Raman scattering spectra of the lightly Cr-doped and Co-doped ZnO were studied and compared. The enhancement of both the magnetization and the intensity of Raman scattering peak associated with donor defects (Zni and/or VO) and carriers indicates that light Cr doping in ZnO could be an effective way to achieve pronounced RT-FM and the ferromagnetism is closely related to the dopant-donor hybridization besides the ferromagnetic Cr-O-Cr superexchange interactions.

  6. A room-temperature magnetic semiconductor from a ferromagnetic metallic glass

    PubMed Central

    Liu, Wenjian; Zhang, Hongxia; Shi, Jin-an; Wang, Zhongchang; Song, Cheng; Wang, Xiangrong; Lu, Siyuan; Zhou, Xiangjun; Gu, Lin; Louzguine-Luzgin, Dmitri V.; Chen, Mingwei; Yao, Kefu; Chen, Na

    2016-01-01

    Emerging for future spintronic/electronic applications, magnetic semiconductors have stimulated intense interest due to their promises for new functionalities and device concepts. So far, the so-called diluted magnetic semiconductors attract many attentions, yet it remains challenging to increase their Curie temperatures above room temperature, particularly those based on III–V semiconductors. In contrast to the concept of doping magnetic elements into conventional semiconductors to make diluted magnetic semiconductors, here we propose to oxidize originally ferromagnetic metals/alloys to form new species of magnetic semiconductors. We introduce oxygen into a ferromagnetic metallic glass to form a Co28.6Fe12.4Ta4.3B8.7O46 magnetic semiconductor with a Curie temperature above 600 K. The demonstration of p–n heterojunctions and electric field control of the room-temperature ferromagnetism in this material reflects its p-type semiconducting character, with a mobility of 0.1 cm2 V−1 s−1. Our findings may pave a new way to realize high Curie temperature magnetic semiconductors with unusual multifunctionalities. PMID:27929059

  7. A room-temperature magnetic semiconductor from a ferromagnetic metallic glass

    NASA Astrophysics Data System (ADS)

    Liu, Wenjian; Zhang, Hongxia; Shi, Jin-An; Wang, Zhongchang; Song, Cheng; Wang, Xiangrong; Lu, Siyuan; Zhou, Xiangjun; Gu, Lin; Louzguine-Luzgin, Dmitri V.; Chen, Mingwei; Yao, Kefu; Chen, Na

    2016-12-01

    Emerging for future spintronic/electronic applications, magnetic semiconductors have stimulated intense interest due to their promises for new functionalities and device concepts. So far, the so-called diluted magnetic semiconductors attract many attentions, yet it remains challenging to increase their Curie temperatures above room temperature, particularly those based on III-V semiconductors. In contrast to the concept of doping magnetic elements into conventional semiconductors to make diluted magnetic semiconductors, here we propose to oxidize originally ferromagnetic metals/alloys to form new species of magnetic semiconductors. We introduce oxygen into a ferromagnetic metallic glass to form a Co28.6Fe12.4Ta4.3B8.7O46 magnetic semiconductor with a Curie temperature above 600 K. The demonstration of p-n heterojunctions and electric field control of the room-temperature ferromagnetism in this material reflects its p-type semiconducting character, with a mobility of 0.1 cm2 V-1 s-1. Our findings may pave a new way to realize high Curie temperature magnetic semiconductors with unusual multifunctionalities.

  8. Room-temperature ferromagnetism in doped face-centered cubic fe nanoparticles.

    PubMed

    Wei, Bingqing; Shima, Mutsuhiro; Pati, Ranjit; Nayak, Saroj K; Singh, David J; Ma, Renzhi; Li, Yubao; Bando, Yoshio; Nasu, Saburo; Ajayan, Pulickel M

    2006-06-01

    The magnetism of Fe and its alloys has been at the center of scientific and technological interest for decades. Along with the ferromagnetic nature of body-centered cubic Fe, the magnetic properties of face-centered cubic (fcc) Fe have attracted much attention. It is well known that fcc Fe is thermodynamically unstable at ambient conditions and not ferromagnetic. Contrary to what is known, we report that elongated nanoparticles of fcc Fe, grown within graphitic nanotubes, remain structurally stable and appear ferromagnetic at room temperature. The magnetic moment (2+/-0.5 microB) in these nanoparticles and the hyperfine fields for two different components of 57Fe (33 and 21 T), measured by Mössbauer spectroscopy, are explained by carbon interstitials in the expanded fcc Fe lattice, that is, FeC(x) where x approximately 0.10, which result in the formation of a dominant Fe4C stoichiometry. First-principles calculations suggest that the ferromagnetism observed in the fcc Fe is related to both lattice expansion and charge transfer between iron and carbon. The understanding of strain- and dopant-induced ferromagnetism in the fcc Fe could lead to the development of new fcc Fe-based alloys for magnetic applications.

  9. Room temperature ferromagnetism of tin oxide nanocrystal based on synthesis methods

    NASA Astrophysics Data System (ADS)

    Sakthiraj, K.; Hema, M.; Balachandrakumar, K.

    2016-04-01

    The experimental conditions used in the preparation of nanocrystalline oxide materials play an important role in the room temperature ferromagnetism of the product. In the present work, a comparison was made between sol-gel, microwave assisted sol-gel and hydrothermal methods for preparing tin oxide nanocrystal. X-ray diffraction analysis indicates the formation of tetragonal rutile phase structure for all the samples. The crystallite size was estimated from the HRTEM images and it is around 6-12 nm. Using optical absorbance measurement, the band gap energy value of the samples has been calculated. It reveals the existence of quantum confinement effect in all the prepared samples. Photoluminescence (PL) spectra confirms that the luminescence process originates from the structural defects such as oxygen vacancies present in the samples. Room temperature hysteresis loop was clearly observed in M-H curve of all the samples. But the sol-gel derived sample shows the higher values of saturation magnetization (Ms) and remanence (Mr) than other two samples. This study reveals that the sol-gel method is superior to the other two methods for producing room temperature ferromagnetism in tin oxide nanocrystal.

  10. Reconsidering the possibility of room temperature ferromagnetism in Mn-doped zirconium oxide

    NASA Astrophysics Data System (ADS)

    Chakraborty, Akash; Bouzerar, Georges

    2013-12-01

    The possibility to induce long-range ferromagnetic order by doping oxides with transition metal ions has become a very exciting challenge in the last decade. Theoretically, it has been claimed that Mn-doped ZrO2 could be a very promising spintronic candidate and that high critical temperatures could be already achieved even for a low Mn concentration. Some experiments have reported room temperature ferromagnetism (RT-FM) whilst some others only paramagnetism. When observed, the nature of RT-FM appears to be controversial and not clearly understood. In this study, we propose to clarify and shed light on some of theses existing issues. A detailed study of the critical temperatures and low-energy magnetic excitations in Mn-doped ZrO2 is performed. We show that the Curie temperatures were largely overestimated previously, due to the inadequate treatment of both thermal and transverse fluctuations, and disorder. It appears that the Mn-Mn couplings cannot explain the observed RT-FM. We argue, that this can be attributed to the interaction between large moments induced in the vicinity of the manganese. This is similar to the non-magnetic defect-induced ferromagnetism reported in oxides, semiconductors and graphene/graphite.

  11. Manganese mono-boride, an inexpensive room temperature ferromagnetic hard material

    PubMed Central

    Ma, Shuailing; Bao, Kuo; Tao, Qiang; Zhu, Pinwen; Ma, Teng; Liu, Bo; Liu, Yazhou; Cui, Tian

    2017-01-01

    We synthesized orthorhombic FeB-type MnB (space group: Pnma) with high pressure and high temperature method. MnB is a promising soft magnetic material, which is ferromagnetic with Curie temperature as high as 546.3 K, and high magnetization value up to 155.5 emu/g, and comparatively low coercive field. The strong room temperature ferromagnetic properties stem from the positive exchange-correlation between manganese atoms and the large number of unpaired Mn 3d electrons. The asymptotic Vickers hardness (AVH) is 15.7 GPa which is far higher than that of traditional ferromagnetic materials. The high hardness is ascribed to the zigzag boron chains running through manganese lattice, as unraveled by X-ray photoelectron spectroscopy result and first principle calculations. This exploration opens a new class of materials with the integration of superior mechanical properties, lower cost, electrical conductivity, and fantastic soft magnetic properties which will be significant for scientific research and industrial application as advanced structural and functional materials. PMID:28262805

  12. Manganese mono-boride, an inexpensive room temperature ferromagnetic hard material.

    PubMed

    Ma, Shuailing; Bao, Kuo; Tao, Qiang; Zhu, Pinwen; Ma, Teng; Liu, Bo; Liu, Yazhou; Cui, Tian

    2017-03-06

    We synthesized orthorhombic FeB-type MnB (space group: Pnma) with high pressure and high temperature method. MnB is a promising soft magnetic material, which is ferromagnetic with Curie temperature as high as 546.3 K, and high magnetization value up to 155.5 emu/g, and comparatively low coercive field. The strong room temperature ferromagnetic properties stem from the positive exchange-correlation between manganese atoms and the large number of unpaired Mn 3d electrons. The asymptotic Vickers hardness (AVH) is 15.7 GPa which is far higher than that of traditional ferromagnetic materials. The high hardness is ascribed to the zigzag boron chains running through manganese lattice, as unraveled by X-ray photoelectron spectroscopy result and first principle calculations. This exploration opens a new class of materials with the integration of superior mechanical properties, lower cost, electrical conductivity, and fantastic soft magnetic properties which will be significant for scientific research and industrial application as advanced structural and functional materials.

  13. Manganese mono-boride, an inexpensive room temperature ferromagnetic hard material

    NASA Astrophysics Data System (ADS)

    Ma, Shuailing; Bao, Kuo; Tao, Qiang; Zhu, Pinwen; Ma, Teng; Liu, Bo; Liu, Yazhou; Cui, Tian

    2017-03-01

    We synthesized orthorhombic FeB-type MnB (space group: Pnma) with high pressure and high temperature method. MnB is a promising soft magnetic material, which is ferromagnetic with Curie temperature as high as 546.3 K, and high magnetization value up to 155.5 emu/g, and comparatively low coercive field. The strong room temperature ferromagnetic properties stem from the positive exchange-correlation between manganese atoms and the large number of unpaired Mn 3d electrons. The asymptotic Vickers hardness (AVH) is 15.7 GPa which is far higher than that of traditional ferromagnetic materials. The high hardness is ascribed to the zigzag boron chains running through manganese lattice, as unraveled by X-ray photoelectron spectroscopy result and first principle calculations. This exploration opens a new class of materials with the integration of superior mechanical properties, lower cost, electrical conductivity, and fantastic soft magnetic properties which will be significant for scientific research and industrial application as advanced structural and functional materials.

  14. Enhancement of room temperature ferromagnetism in Mn-implanted Si by He implantation

    NASA Astrophysics Data System (ADS)

    Chen, Jihong; Guo, Liping; Liu, Congxiao; Luo, Fengfeng; Li, Tiecheng; Zheng, Zhongcheng; Jin, Shuoxue; Yang, Zheng

    2012-09-01

    Room temperature ferromagnetism in Mn-implanted p-Si was enhanced dramatically by implantation of He. A 75 nm end-of-range region was found in the sample, with large scale and inhomogeneous damaging but preserved Si lattice periodicity. The end-of-range region shows an intrinsic magnetization of ˜100 emu/cm3. High resolution transmission electron microscopy and x-ray photoelectron spectroscopy measurements indicate that the spin polarization of Si dangling bonds rather than Mn impurity was the major source for the enhanced magnetism.

  15. Stable room-temperature ferromagnetic phase at the FeRh(100) surface

    DOE PAGES

    Pressacco, Federico; Uhlir, Vojtech; Gatti, Matteo; ...

    2016-03-03

    Interfaces and low dimensionality are sources of strong modifications of electronic, structural, and magnetic properties of materials. FeRh alloys are an excellent example because of the first-order phase transition taking place at ~400 K from an antiferromagnetic phase at room temperature to a high temperature ferromagnetic one. It is accompanied by a resistance change and volume expansion of about 1%. We have investigated the electronic and magnetic properties of FeRh(100) epitaxially grown on MgO by combining spectroscopies characterized by different probing depths, namely X-ray magnetic circular dichroism and photoelectron spectroscopy. Furthermore, we find that the symmetry breaking induced at themore » Rh-terminated surface stabilizes a surface ferromagnetic layer involving five planes of Fe and Rh atoms in the nominally antiferromagnetic phase at room temperature. First-principles calculations provide a microscopic description of the structural relaxation and the electron spin-density distribution that support the experimental findings.« less

  16. Possible Room-Temperature Ferromagnetism in Self-Assembled Ensembles of Paramagnetic and Diamagnetic Molecular Semiconductors.

    PubMed

    Dhara, Barun; Tarafder, Kartick; Jha, Plawan K; Panja, Soumendra N; Nair, Sunil; Oppeneer, Peter M; Ballav, Nirmalya

    2016-12-15

    Owing to long spin-relaxation time and chemically customizable physical properties, molecule-based semiconductor materials like metal-phthalocyanines offer promising alternatives to conventional dilute magnetic semiconductors/oxides (DMSs/DMOs) to achieve room-temperature (RT) ferromagnetism. However, air-stable molecule-based materials exhibiting both semiconductivity and magnetic-order at RT have so far remained elusive. We present here the concept of supramolecular arrangement to accomplish possibly RT ferromagnetism. Specifically, we observe a clear hysteresis-loop (Hc ≈ 120 Oe) at 300 K in the magnetization versus field (M-H) plot of the self-assembled ensembles of diamagnetic Zn-phthalocyanine having peripheral F atoms (ZnFPc; S = 0) and paramagnetic Fe-phthalocyanine having peripehral H atoms (FePc; S = 1). Tauc plot of the self-assembled FePc···ZnFPc ensembles showed an optical band gap of ∼1.05 eV and temperature-dependent current-voltage (I-V) studies suggest semiconducting characteristics in the material. Using DFT+U quantum-chemical calculations, we reveal the origin of such unusual ferromagnetic exchange-interaction in the supramolecular FePc···ZnFPc system.

  17. Room temperature ferromagnetism in Co-incorporated TiO2 thin films.

    PubMed

    Sharma, Sudesh; Chaudhary, Sujeet; Panwar, N; Kashyap, Subhash C; Pandya, D K

    2011-03-01

    Observation of room temperature ferromagnetism (RTFM) in nano-crystalline Co-incorporated titanium dioxide [Ti(1-x)Co(x)O2(x = 0.05)] thin films prepared by spray pyrolysis technique is reported. While only the anatase phase was detected in as-deposited 5 at.% Co-incorporated TiO2 film, a small amount of rutile phase developed following its vacuum annealing. Besides, no X-ray diffraction peak corresponding to cobalt metal could be detected in any of the two films. SQUID magnetometry of both pristine and Co-doped thin films at room temperature elucidated distinct ferromagnetic behavior in 5 at.% Co-incorporated as-deposited film with saturation moment M(s) approximately 5.6 emu/cm3 which got enhanced up to 11.8 emu/cm3 on subsequent vacuum annealing. From the zero field cooled magnetization measurement we confirmed the absence of Co-metal clusters. The electrical resistivity was found to be greater than 108 omega-cm for the films. Based on the magnetic and electrical measurements the origin of RTFM has been attributed to the bound magnetic polaron (BMP) model.

  18. Room temperature ferromagnetic ordering in indium substituted nano-nickel-zinc ferrite

    NASA Astrophysics Data System (ADS)

    Thakur, Sangeeta; Katyal, S. C.; Gupta, A.; Reddy, V. R.; Singh, M.

    2009-04-01

    Nano-nickel-zinc-indium ferrite (NZIFO)(Ni0.58Zn0.42InxFe2-xO4) with varied quantities of indium (x =0,0.1,0.2) have been synthesized via reverse micelle technique. X-ray diffraction and transmission electron microscopy confirmed the size, structure, and morphology of the nanoferrites. The addition of indium in nickel-zinc ferrite (NZFO) has been shown to play a crucial role in enhancing the magnetic properties. Room temperature Mössbauer spectra revealed that the nano-NZFO ferrite exhibit collective magnetic excitations, while indium doped NZFO samples have the ferromagnetic phase. The dependence of Mössbauer parameters, viz. isomer shift, quadrupole splitting, linewidth, and hyperfine magnetic field, on In3+ concentration has been studied. Mössbauer study on these nanosystems shows that the cation distribution not only depends on the particle size but also on the preparation route. Mössbauer results are also supported by magnetization data. Well defined sextets and appearance of hysteresis at room temperature indicate the existence of ferromagnetic couplings which makes nano-NZIFO ferrite suitable for magnetic storage data.

  19. Strain induced room temperature ferromagnetism in epitaxial magnesium oxide thin films

    SciTech Connect

    Jin, Zhenghe; Kim, Ki Wook; Nori, Sudhakar; Lee, Yi-Fang; Narayan, Jagdish; Kumar, D.; Wu, Fan; Prater, J. T.

    2015-10-28

    We report on the epitaxial growth and room-temperature ferromagnetic properties of MgO thin films deposited on hexagonal c-sapphire substrates by pulsed laser deposition. The epitaxial nature of the films has been confirmed by both θ-2θ and φ-scans of X-ray diffraction pattern. Even though bulk MgO is a nonmagnetic insulator, we have found that the MgO films exhibit ferromagnetism and hysteresis loops yielding a maximum saturation magnetization up to 17 emu/cc and large coercivity, H{sub c} = 1200 Oe. We have also found that the saturation magnetization gets enhanced and that the crystallization degraded with decreased growth temperature, suggesting that the origin of our magnetic coupling could be point defects manifested by the strain in the films. X-ray (θ-2θ) diffraction peak shift and strain analysis clearly support the presence of strain in films resulting from the presence of point defects. Based on careful investigations using secondary ion mass spectrometer and X-ray photoelectron spectroscopy studies, we have ruled out the possibility of the presence of any external magnetic impurities. We discuss the critical role of microstructural characteristics and associated strain on the physical properties of the MgO films and establish a correlation between defects and magnetic properties.

  20. Electronic structure and room temperature ferromagnetism of C doped TiO2

    NASA Astrophysics Data System (ADS)

    Ablat, Abduleziz; Wu, Rong; Mamat, Mamatrishat; Ghupur, Yasin; Aimidula, Aimierding; Bake, Muhammad Ali; Gholam, Turghunjan; Wang, Jiaou; Qian, Haijie; Wu, Rui; Ibrahim, Kurash

    2016-10-01

    C-doped TiO2 nanoparticles were successfully synthesized using a simple hydrothermal synthesis method. After this preparation, a portion of the samples were annealed separately in air on the one hand, and in argon on the other, and another portion remained untreated. The results of X-ray diffraction show that the untreated samples primarily display anatase and rutile structures. However, after annealing, the samples displayed the rutile structure only. The Ti K-edge and L-edge Near Edge X-ray Absorption Fine Structure analyses clearly show that C atoms were successfully incorporated into the TiO2 host lattice. All doped samples exhibit ferromagnetism at room temperature. The saturation magnetization (Ms) and coercive fields (Hc) tend to decrease after the samples are annealed in argon and in air. The maximum Ms of the untreated samples was approximately 0.038 emu/g.

  1. Room temperature ferromagnetism in Mg-doped ZnO nanoparticles

    SciTech Connect

    Singh, Jaspal Vashihth, A.; Gill, Pritampal Singh; Verma, N. K.

    2015-06-24

    Zn{sub 1-x}Mg{sub x}O (x = 0, 0,10) nanoparticles were successfully synthesized using sol-gel method. X-ray diffraction (XRD) confirms that the synthesized nanoparticles possess wurtzite phase having hexagonal structure. Morphological analysis was carried out using transmission electron microscopy (TEM) which depicts the spherical morphology of ZnO nanoparticles. Energy dispersive spectroscopy (EDS) showed the presence of Mg in ZnO nanoparticles. Electron spin resonance (ESR) signal was found to be decreasing with increasing of Mg-doping concentration. The room temperature ferromagnetism was observed in undoped and Mg-doped ZnO nanoparticles. The increase of Mg-doping concentration resulted in decrease of saturation magnetization value which could be attributed to decrease of oxygen vacancies present in host nanoparticles.

  2. Enhancement of room temperature ferromagnetism in tin oxide nanocrystal using organic solvents

    NASA Astrophysics Data System (ADS)

    Sakthiraj, K.; Hema, M.; Balachandra Kumar, K.

    2017-10-01

    The effect of organic solvents (ethanol & ethylene glycol) on the room temperature ferromagnetism in nanocrystalline tin oxide has been studied. The samples were synthesized using sol-gel method with the mixture of water & organic liquid as solvent. It is found that pristine SnO2 nanocrystal contain two different types of paramagnetic centres over their surface:(i) surface chemisorbed oxygen species and (ii) Sn interstitial & oxygen vacancy defect pair. The magnetic moment induced in the as-prepared samples is mainly contributed by the alignment of local spin moments resulting from these defects. These surface defect states are highly activated by the usage of ethylene glycol solvent rather than ethylene in tin oxide nanostructure synthesis. Powder X-ray diffraction, transmission electron microscope imaging, energy dispersive spectrometry, Fourier transformed infrared spectroscopy, UV-vis absorption spectroscopy, photoluminescence spectroscopy, vibrating sample magnetometer measurement and electron spin resonance spectroscopy were employed to characterize the nanostructured tin oxide materials.

  3. Room temperature ferromagnetism in Co defused CdTe nanocrystalline thin films

    SciTech Connect

    Rao, N. Madhusudhana; Kaleemulla, S.; Begam, M. Rigana

    2014-04-24

    Nanocrystalline Co defused CdTe thin films were prepared using electron beam evaporation technique by depositing CdTe/Co/CdTe stacked layers with different Co thickness onto glass substrate at 373 K followed by annealing at 573K for 2 hrs. Structural, morphological and magnetic properties of of all the Co defused CdTe thin films has been investigated. XRD pattern of all the films exhibited zinc blende structure with <111> preferential orientation without changing the crystal structure of the films. The grain size of the films increased from 31.5 nm to 48.1 nm with the increase of Co layer thickness from 25nm to 100nm. The morphological studies showed that uniform texture of the films and the presence of Co was confirmed by EDAX. Room temperature magnetization curves indicated an improved ferromagnetic behavior in the films with increase of the Co thickness.

  4. Above room-temperature ferromagnetism of Mn delta-doped GaN nanorods

    SciTech Connect

    Lin, Y. T.; Wadekar, P. V.; Kao, H. S.; Chen, T. H.; Chen, Q. Y.; Tu, L. W.; Huang, H. C.; Ho, N. J.

    2014-02-10

    One-dimensional nitride based diluted magnetic semiconductors were grown by plasma-assisted molecular beam epitaxy. Delta-doping technique was adopted to dope GaN nanorods with Mn. The structural and magnetic properties were investigated. The GaMnN nanorods with a single crystalline structure and with Ga sites substituted by Mn atoms were verified by high-resolution x-ray diffraction and Raman scattering, respectively. Secondary phases were not observed by high-resolution x-ray diffraction and high-resolution transmission electron microscopy. In addition, the magnetic hysteresis curves show that the Mn delta-doped GaN nanorods are ferromagnetic above room temperature. The magnetization with magnetic field perpendicular to GaN c-axis saturates easier than the one with field parallel to GaN c-axis.

  5. d carrier induced intrinsic room temperature ferromagnetism in Nb:TiO2 film

    NASA Astrophysics Data System (ADS)

    Yang, J. Y.; Han, Y. L.; He, L.; Dou, R. F.; Xiong, C. M.; Nie, J. C.

    2012-05-01

    High crystalline anatase TiO2 and Nb:TiO2 thin films were fabricated on LaAlO3 (100) substrates by pulsed laser deposition. Room temperature ferromagnetism was obtained in Nb:TiO2 but absent in pure TiO2. The Kondo effect and anomalous Hall effect observed in metallic Nb:TiO2 strongly confirmed the existence of exchange interaction between intrinsic local magnetic moments and carriers. High energy resolution x-ray photoelectron spectroscopy studies of the Nb:TiO2 thin film revealed clear signals of Ti3+ and Nb4+ ions, which had one unpaired d electron responsible for the local magnetic moments. This result consisted quite well with the spin polarized first principle calculation.

  6. Room-temperature decay and light reactivation of high-Tc ferromagnetism in an oxide-diluted magnetic semiconductor.

    PubMed

    Pan, Dengyu; Wan, Jianguo; Xu, Guoliang; Lv, Liya; Wu, Yujie; Min, Han; Liu, Junming; Wang, Guanghou

    2006-10-04

    We present a novel route for manipulation of the ferromagnetic order in Co-doped TiO2 using UV laser irradiation. The ferromagnetic order of the nanocrystal films decays with aging in air at room temperature, which can be reactivated and enhanced by UV irradiation, whereas the coercive force reduces with irradiation time. Photoinduced trapped electrons were suggested to induce the ferromagnetic order. We believe that light manipulation is a general method for tuning the magnetic properties of oxide-based diluted magnetic semiconductors, which can find practical applications in future integrated magneto-optical nanoelectronics.

  7. Room-temperature dilute ferromagnetic dislocations in S r1 -xM nxTi O3 -δ

    NASA Astrophysics Data System (ADS)

    Ishikawa, Ryo; Shimbo, Yoichi; Sugiyama, Issei; Lugg, Nathan R.; Shibata, Naoya; Ikuhara, Yuichi

    2017-07-01

    Room-temperature dilute ferromagnetism has been reported for many semiconducting or insulating materials, which are usually in the forms of bulk or thin film. Here, we successfully fabricated dilute ferromagnetic nanowires by using dislocations—one-dimensional lattice defects—embedded between optically transparent, nonmagnetic SrTi O3 single crystals. At the dislocation cores, we have both locally codoped magnetic M n2 + ions and electron donors. The structure, chemistry, and ferromagnetism of dislocations were studied by atomic-resolution scanning transmission electron microscopy combined with magnetic force microscopy. We discuss the origin of dilute ferromagnetism at the dislocations in terms of the percolation of bound magnetic polarons along the dislocation cores, where antiferromagnetic coupling between the high spin state of M n2 + ions and electron donors leads to the long-range Mn-Mn ferromagnetic exchange interaction.

  8. Room temperature ferromagnetism in Co-doped amorphous carbon composites from the spin polarized semiconductor band

    SciTech Connect

    Hsu, H. S. Chien, P. C.; Chang, Y. Y.; Sun, S. J.; Lee, C. H.

    2014-08-04

    This study provides conclusive evidence of room temperature ferromagnetism in Co-doped amorphous carbon (a-C) composites from the spin polarized semiconductor band. These composites are constructed from discontinuous [Co(3 nm)/a-C(d{sub c} nm)]{sub 5} multilayers with d{sub c} = 3 nm and d{sub c} = 6 nm. Only remnant circular dichroism (CD) was observed from the d{sub c} = 3 nm sample but not when d{sub c} = 6 nm. In addition, the remnant CD peaks at 5.5 eV, which is comparable with the absorption peak associated with the C σ-σ* gap transition. We suggest that the possible mechanism for this coupling can be considered as a magnetic proximity effect in which a ferromagnetic moment in the C medium is induced by Co/C interfaces.

  9. Intrinsic and extrinsic origins of room temperature ferromagnetism in Ni-doped ZnO films

    NASA Astrophysics Data System (ADS)

    Liu, X. J.; Zhu, X. Y.; Song, C.; Zeng, F.; Pan, F.

    2009-02-01

    The structural, electrical and magnetic properties of Ni-doped ZnO films with different Ni concentrations (x = 0-0.11, x: Ni concentration) and thicknesses (d = 15-330 nm, d: film thickness) prepared by radio-frequency magnetron sputtering have been systematically investigated. The structural characterizations indicate that Ni ions in the 2+ valence state, uniformly distributed in the film, almost substitute for the Zn ions when x <= 0.07, whereas when x increases up to 0.11, a second phase Ni is formed. Room temperature (RT) ferromagnetism (FM) has been observed for all the Ni-doped ZnO wurtzite films. The saturated magnetization varies drastically with the Ni concentration and the film thickness. A large magnetic moment of 2.80 μB/Ni is obtained in the 15 nm thick Zn0.96Ni0.04O film at RT. The results show that the FM observed is intrinsic for Ni-doped ZnO films and can be explained in terms of the bound magnetic polaron mechanism based on the presence of defects. In addition, the Ni precipitates owing to the excessive doping of Ni in ZnO, as an extrinsic origin, also contribute to the ferromagnetic properties in highly doped samples.

  10. Abnormal room temperature ferromagnetism in CuO/ZnO nanocomposites via hydrothermal method

    NASA Astrophysics Data System (ADS)

    Lu, Ping; Zhou, Wei; Li, Ying; Wang, Jianchun; Wu, Ping

    2017-03-01

    CuO/ZnO nanocomposites have been successfully synthesized by a one-step hydrothermal method with different phase ratios. Field emission scanning electron microscopy and transmission electron microscopy results show that the obtained products of nanosheets are composed of small primary particles with an average size of about 20 nm. With the increasing proportion of CuO phase, nanosheets have significant collapse and the amount of small sheets increases obviously. The abnormal room temperature ferromagnetism was discovered at the interface between diamagnetic ZnO and antiferromagnetic CuO, which can be tuned by changing the phase ratios. Optical spectra indicate that the interaction between ZnO and CuO modifies the electronic structure of nanocomposites. XPS results verify the valence change of Cu ions and the presence of oxygen vacancies, which are ultimately responsible for the observed ferromagnetism. The indirect double-exchange model was employed to explain the origin of magnetism. Our study suggests that magnetically functional interfaces exhibit very appealing properties for novel devices.

  11. Enhancement of room temperature ferromagnetic behavior of rf sputtered Ni-CeO2 thin films

    NASA Astrophysics Data System (ADS)

    Murugan, R.; Vijayaprasath, G.; Mahalingam, T.; Ravi, G.

    2016-12-01

    Ni-doped CeO2 thin films were prepared under Ar+ atmosphere on glass substrates using rf magnetron sputtering. To assess the properties of the prepared thin films, the influence of various amounts of Ni dopant on structural, morphological, optical, vibrational, compositional and magnetic properties of the CeO2 films were studied by using X-Ray diffraction (XRD), atomic force microscope (AFM), photoluminescence (PL), micro-Raman, X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM). XRD patterns for all the samples revealed the expected CeO2 cubic fluorite-type structure and Ni ions were uniformly distributed in the samples. AFM images of the prepared samples indicate high dense, columnar structure with uniform distribution of CeO2. Room-temperature photoluminescence (PL) and micro-Raman spectroscopic studies revealed an increase of oxygen vacancies with higher concentration of Ni in CeO2. XPS results confirm the presence of Ni2p, O1s and Ce and depict that cerium is present as both Ce4+ and Ce3+ oxidation states in Ce1-xNixO2 (x = 15%) thin film. Field dependent magnetization measurements revealed a paramagnetic behavior for pure CeO2, while a ferromagnetic behavior appeared when Ni is doped in CeO2 films. Doping dependent magnetization measurements suggest that the observed ferromagnetism is due to the presence of metallic Ni clusters with nanometric size and broad size distribution.

  12. Origin of room temperature ferromagnetism in SnO2 films

    NASA Astrophysics Data System (ADS)

    Li, Jing; Bai, Guohua; Jiang, Yinzhu; Du, Youwei; Wu, Chen; Yan, Mi

    2017-03-01

    SnO2 films exhibiting room temperature ferromagnetism (RTFM) have been prepared on Si (001) by pulsed laser deposition. The saturation magnetization (Ms) of the films experiences a decreasing trend followed by increasing with the growth temperature increased from RT to 400 ℃. The growth temperature affects both the concentration and the location of the oxygen vacancies as the origin of the RTFM. With lower growth temperatures (<300 ℃), more oxygen vacancies exist in the inner film for the samples with less crystallinity, resulting in enhanced magnetism. Higher deposition temperature leads to less oxygen vacancies in the inner film but more oxygen defects at the film surface, which is also beneficial to achieve greater magnetism. Various oxygen pressures during growth and post-annealing have also been used to confirm the role of oxygen vacancies. The study demonstrates that the surface oxygen defects and the positively charged monovalent O vacancies (VO+) in the inner film are the origin of the magnetism in SnO2 films.

  13. Room-temperature ferromagnetism in zincblende CrSb grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Zhao, J. H.; Matsukura, F.; Takamura, K.; Abe, E.; Chiba, D.; Ohno, H.

    2001-10-01

    Thin films of CrSb grown by solid-source molecular-beam epitaxy on GaAs, (Al, Ga)Sb, and GaSb are found to exhibit ferromagnetism. Reflection high-energy electron diffraction and high-resolution cross sectional transmission electron microscopy both indicate that the structure is zincblende. Temperature dependence of remanent magnetization shows that the ferromagnetic transition temperature is beyond 400 K.

  14. Search for Origin of Room Temperature Ferromagnetism Properties in Ni-Doped ZnO Nanostructure.

    PubMed

    Rana, Amit Kumar; Kumar, Yogendra; Rajput, Parasmani; Jha, Shambhu Nath; Bhattacharyya, Dibyendu; Shirage, Parasharam M

    2017-03-01

    The origin of room temperature (RT) ferromagnetism (FM) in Zn1-xNixO (0< x < 0.125) samples are systematically investigated through physical, optical, and magnetic properties of nanostructure, prepared by simple low-temperature wet chemical method. Reitveld refinement of X-ray diffraction pattern displays an increase in lattice parameters with strain relaxation and contraction in Zn/O occupancy ratio by means of Ni-doping. Similarly, scanning electron microscope demonstrates modification in the morphology from nanorods to nanoflakes with Ni doping, suggests incorporation of Ni ions in ZnO. More interestingly, XANES (X-ray absorption near edge spectroscopy) measurements confirm that Ni is being incorporated in ZnO as Ni(2+). EXAFS (extended X-ray absorption fine structure) analysis reveals that structural disorders near the Zn sites in the ZnO samples upsurges with increasing Ni concentration. Raman spectroscopy exhibits additional defect driven vibrational mode (at 275 cm(-1)), appeared only in Ni-doped samples and the shift with broadening in 580 cm(-1) peak, which manifests the presence of the oxygen vacancy (VO) related defects. Moreover, in photoluminescence (PL) spectra, we have observed a peak at 524 nm, indicating the presence of singly ionized VO(+), which may be activating bound magnetic polarons (BMPs) in dilute magnetic semiconductors (DMSs). Magnetization measurements indicate weak ferromagnetism at RT, which rises with increasing Ni concentration. It is therefore proposed that the effect of the Ni ions as well as the inherent exchange interactions arising from VO(+) assist to produce BMPs, which are accountable for the RT-FM in Zn1-xNixO (0< x < 0.125) system.

  15. Room temperature magnetocaloric effect in Ni-Mn-In-Cr ferromagnetic shape memory alloy thin films

    NASA Astrophysics Data System (ADS)

    Akkera, Harish Sharma; Singh, Inderdeep; Kaur, Davinder

    2017-02-01

    The influence of Cr substitution for In on the martensitic phase transformation and magnetocaloric effect (MCE) has been investigated in Ni-Mn-Cr-In ferromagnetic shape memory alloy (FSMA) thin films fabricated by magnetron sputtering. Temperature dependent magnetization (M-T) measurements demonstrated that the martensitic transformation temperatures (TM) monotonously increase with the increase of Cr content due to change in valence electron concentration (e/a) and cell volume. From the study of isothermal magnetization curves (M-H), magnetocaloric effect around the martensitic transformation has been investigated in these FSMA thin films. The magnetic entropy change ∆SM of 7.0 mJ/cm3-K was observed in Ni51.1Mn34.9In9.5Cr4.5 film at 302 K in an applied field of 2 T. Further, the refrigerant capacity (RC) was also calculated for all the films in an applied field of 2 T. These findings indicate that the Cr doped Ni-Mn-In FSMA thin films are potential candidates for room temperature micro-length-scale magnetic refrigeration applications.

  16. Tunability of room-temperature ferromagnetism in spintronic semiconductors through nonmagnetic atoms

    NASA Astrophysics Data System (ADS)

    Leedahl, Brett; Abooalizadeh, Zahra; LeBlanc, Kyle; Moewes, Alexander

    2017-07-01

    The implementation and control of room-temperature ferromagnetism (RTFM) by adding magnetic atoms to a semiconductor's lattice has been one of the most important problems in solid-state physics in the last decade. Herein we report on the mechanism that allows RTFM to be tuned by the inclusion of nonmagnetic aluminum in nickel ferrite. This material, NiFe2 -xAlxO4 (x =0 ,0.5 ,1.5 ), has already shown much promise for magnetic semiconductor technologies, and we are able to add to its versatility technological viability with our results. The site occupancies and valencies of Fe atoms (Fe3 +Td , Fe2 +Oh , and Fe3 +Oh ) can be methodically controlled by including aluminum. Using the fact that aluminum strongly prefers a 3+ octahedral environment, we can selectively fill iron sites with aluminum atoms, and hence specifically tune the magnetic contributions for each of the iron sites, and therefore the bulk material as well. Interestingly, the influence of the aluminum is weak on the electronic structure, allowing one to retain the desirable electronic properties while achieving desirable magnetic properties.

  17. Room temperature ferromagnetism in nanocrystalline Ni-doped ZnO synthesized by co-precipitation

    NASA Astrophysics Data System (ADS)

    El-Hilo, M.; Dakhel, A. A.; Ali-Mohamed, A. Y.

    2009-07-01

    Ni-doped ZnO powder was synthesized by thermal co-decomposition of a mixture of bis(acetylacetonato) zinc(II)hydrate and bis(dimethylglyoximato)nickel(II) complexes. The samples were characterised by X-ray diffraction (XRD), Energy dispersion X-ray fluorescence (EDXRF), and FT-IR spectroscopy. The atomic ratio Ni/Zn of the samples was determined by the EDXRF method to be 1%, 4.3%, 7.4% and 22.5 wt%. The XRD studies show the formation of nanocrystalline (14-18 nm) of Ni-doped ZnO along with nanoparticles of NiO. By magnetic measurements, it was observed that powder contains 1%Ni, 4.3%Ni, 7.4%Ni exhibits superparamagnetic behaviour while the sample of 22.5%Ni prepared in closed atmospheric environment shows clear ferromagnetic (FM) loop at room temperature due to the formation of solid solution Zn 1-xNi xO.

  18. Room temperature ferromagnetism in Mn doped ZnO: Co nanoparticles by co-precipitation method

    NASA Astrophysics Data System (ADS)

    Pazhanivelu, V.; Selvadurai, A. Paul Blessington; Zhao, Yongsheng; Thiyagarajan, R.; Murugaraj, R.

    2016-01-01

    In this present work, the Mn2+ and Co2+ ions doping and co-doping effect on the structural, vibrational, morphological, optical and magnetic behaviors of ZnO based dilute magnetic semiconductors are reported. The Zn0.95Co0.05O (ZC), Zn0.95Mn0.05O (ZM) and Zn0.90Co0.05Mn0.05O (ZCM) samples were prepared by co-precipitation method. From the XRD analysis, it was observed that on the doping of Mn2+ ion in ZnO matrix, decreases their crystalline nature as well as the crystallite size significantly. The Raman spectra, Photoluminescence and electron paramagnetic resonance spectroscopy measurements reveal that the presence of defects in prepared samples. The UV-DRS spectroscopic exhibits the incorporation of dopant ions and their effect on the band gap subsequently. The magnetization measurements suggest the room temperature ferromagnetism (RTFM) in the prepared samples. The observed RTFM phenomenon was discussed based on the defects and grain confinement.

  19. Structural, optical and room-temperature ferromagnetic properties of Fe-doped CuO nanostructures

    NASA Astrophysics Data System (ADS)

    Mohamed Basith, N.; Judith Vijaya, J.; John Kennedy, L.; Bououdina, M.

    2013-09-01

    Pure CuO and Fe-doped CuO nanostructures with different weight ratios (0.5, 1.0, 1.5, and 2.0 at wt% of Fe) were synthesized via the microwave combustion method. The synthesized samples were characterized by X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy and vibrating sample magnetometry (VSM). XRD patterns refined by the Rietveld method indicated the formation of single-phase monoclinic structure and also confirmed that Fe ions successfully incorporated into CuO crystal lattice by occupying Cu ionic sites. Interestingly, the morphology was found to change considerably from nanoflowers to nano-rod and disk-shaped then to nanoparticles with the variation of Fe content. The optical band gap calculated using DRS was found to be 2.8 eV for pure CuO and increases up to 3.4 eV with increasing ‘Fe’ content. Photoluminescence measurements also confirm these results. The magnetic measurements indicated that the obtained nanostructures are found to be room temperature ferromagnetism (RTF) with an optimum value of saturation magnetization at 2.0 wt% of Fe-doped CuO, i.e. 1.2960×10-3 emu/g.

  20. Ferromagnetism at room temperature with a large magnetic moment in anatase V-doped TiO2 thin films

    NASA Astrophysics Data System (ADS)

    Hong, Nguyen Hoa; Sakai, Joe; Hassini, Awatef

    2004-04-01

    V-doped TiO2 thin films were grown by laser ablation on LaAlO3 substrates. In the chosen range of the growth conditions, all V:TiO2 films have an anatase structure and exhibit semiconducting and ferromagnetic behaviors at room temperature. V:TiO2 films have a giant magnetic moment and they seem to be far better ferromagnetic than Co/Fe/Ni-doped TiO2 films. This study has proved that a few percent of V substituting for Ti in TiO2 can result in a potential diluted magnetic semiconductor.

  1. Room temperature ferromagnetism in Sn1-xVxO2 films prepared by sol-gel method

    NASA Astrophysics Data System (ADS)

    Zhang, Li; Ge, Shihui; Zuo, Yalu; Zhou, Xueyun; Xiao, Yuhua; Yan, Shiming; Han, Xiufeng; Wen, Zhenchao

    2008-12-01

    The structure and magnetic properties of Sn1-xVxO2 (x =0.02-0.22) thin films fabricated on Si (111) substrate using a sol-gel method and spin coating technique have been investigated. All the samples have pure rutile polycrystalline structure and exhibit room temperature ferromagnetism. The magnetic moment per V reaches 2.92μB for the Sn0.98V0.02O2 film and drops rapidly as V content is increased. X-ray photoelectron spectroscopy study reveals that vanadium is in V4+ chemical state. Various annealing treatments were performed to explore the origin of the ferromagnetism. It is found that the ferromagnetism of Sn0.98V0.02O2 film disappears after annealing in a rich-oxygen atmosphere and occurs again after annealing in a low vacuum condition. Furthermore, an annealing in Sn vapor leads to the decrease in ferromagnetism. These results confirm that the oxygen vacancies play a critical role in introducing ferromagnetism of Sn1-xVxO2 films; therefore, the origin of the ferromagnetism in our samples can be understood in the framework of the bound magnetic polaron model.

  2. Extrinsic origin of room-temperature ferromagnetism in Co-doped ZnO annealed in Zn vapor

    NASA Astrophysics Data System (ADS)

    Yan, Guoqing; Xuan, Haicheng

    2011-08-01

    Co-doped ZnO and CoO were prepared at 950 °C by the solid-state reaction method, then were annealed in N2 flow at 950 °C, and finally annealed in Zn vapor at 600 °C or 800 °C. The samples before annealing in Zn vapor have no ferromagnetism, but after annealing in Zn vapor, Co-doped ZnO and CoO both exhibit room-temperature ferromagnetism. Through x-ray diffraction and element composition measurements, it was found that the ferromagnetism of Co-doped ZnO annealed in Zn vapor is extrinsic and comes from cubic Co5Zn21 and/or cubic CoZn.

  3. Electric field control of ferromagnetism at room temperature in GaCrN (p-i-n) device structures

    NASA Astrophysics Data System (ADS)

    El-Masry, N. A.; Zavada, J. M.; Reynolds, J. G.; Reynolds, C. L.; Liu, Z.; Bedair, S. M.

    2017-08-01

    We have demonstrated a room temperature dilute magnetic semiconductor based on GaCrN epitaxial layers grown by metalorganic chemical vapor deposition. Saturation magnetization Ms increased when the GaCrN film is incorporated into a (p-GaN/i-GaCrN/n-GaN) device structure, due to the proximity of mediated holes present in the p-GaN layer. Zero field cooling and field cooling were measured to ascertain the absence of superparamagnetic behavior in the films. A (p-GaN/i-GaCrN/n-GaN) device structure with room temperature ferromagnetic (FM) properties that can be controlled by an external applied voltage has been fabricated. In this work, we show that the applied voltage controls the ferromagnetic properties, by biasing the (p-i-n) structure. With forward bias, ferromagnetism in the GaCrN layer was increased nearly 4 fold of the original value. Such an enhancement is due to carrier injection of holes into the Cr deep level present in the i-GaCrN layer. A "memory effect" for the FM behavior of the (p-i-n) GaCrN device structure persisted for 42 h after the voltage bias was turned off. These measurements also support that the observed ferromagnetism in the GaCrN film is not due to superparamagnetic clusters but instead is a hole-mediated phenomenon.

  4. Enhanced room temperature ferromagnetism in Ni doped SnO2 nanoparticles: A comprehensive study

    NASA Astrophysics Data System (ADS)

    Ahmed, Ateeq; Ali, T.; Naseem Siddique, M.; Ahmad, Abid; Tripathi, P.

    2017-08-01

    We emphasized on a detailed investigation of the structural, optical, and magnetic properties of pure and Ni-doped SnO2 nanoparticles (NPs) synthesized by a sol-gel process. An extensive structural study has been carried out using various characterization techniques. The X-ray Diffraction (XRD) spectra show the formation of the single phase tetragonal structure of pure and Ni-doped SnO2 NPs without any noticeable impurity phase such as NiO. XRD results indicate that the crystallite size of SnO2 is found to be decreased with Ni doping, which has also been confirmed by the Field Emission Scanning Electron Microscopy study. X-ray Photoelectron Spectroscopy (XPS) measurements displayed a clear sign for Ni2+ ions occupying the lattice sites of Sn4+ in the SnO2 host which also gives clear evidence for the formation of single phase Sn1-xNixO2 NPs. The optical analysis shows a significant decrease in the energy gap of SnO2, i.e., (from 3.71 eV to 3.28 eV) as Ni concentration increases which may be correlated with the core level valence band XPS analysis. Photoluminescence studies show that Ni doping creates oxygen vacancies due to dissimilar ionic radii of Ni2+ and Sn4+. Superconducting quantum interference device measurements revealed that the Ni doped SnO2 NPs exhibit strong ferromagnetic behavior at room temperature and this analysis has been well fitted with a simple relationship to find out magnetic parameters proposed by Stearns and Cheng et al. Hence, our results demonstrate that Ni-doping has strong impact on the structural, optical, and magnetic properties.

  5. Sol-gel derived Zn1-xFexS diluted magnetic semiconductor thin films: Compositional dependent room or above room temperature ferromagnetism

    NASA Astrophysics Data System (ADS)

    Goktas, A.

    2015-06-01

    Zn1-xFexS (where x = 0.00, 0.01, 0.03, 0.05, 0.1 and 0.2) thin films were synthesized by sol-gel method. To investigate the origin of room or above room temperature ferromagnetism in these films several tools such as XRD, SEM, XPS, UV-Vis spectrophotometer and SQUİD magnetometer were used. The XRD studies showed that the phase singularity of ZnS zinc blende (hexagonal) structure. The SEM images indicated the homogeneous film surface with no cracking and increased particle size with increasing Fe-doping ratio except for 1 at.% Fe dopant. The presence of Zn, Fe, S, Si and O atoms in the films was observed in EDS spectrum. The XPS studies confirmed that the existence of Fe3+ ions in host ZnS thin films. In the UV-Vis measurements the band gap energy corresponding to the absorption edge was estimated to be approximately in the range of 3.59-2.08 eV, depending on the Fe doping level. The magnetization measurements revealed that the films had paramagnetic or ferromagnetic order depending on Fe doping ratio at 5, 100, 200, 300 and 350 K. The observed room or above room temperature ferromagnetism can be attributed to the strong p-d exchange interaction between Fe3+ d and anion (S2-) p orbitals as well as impurities.

  6. Synthesis and room-temperature ferromagnetism of CeO2 nanocrystals with nonmagnetic Ca2+ doping

    NASA Astrophysics Data System (ADS)

    Chen, Xiaobo; Li, Guangshe; Su, Yiguo; Qiu, Xiaoqing; Li, Liping; Zou, Zhigang

    2009-03-01

    This work initiates an investigation on the creation of room-temperature ferromagnetism in diamagnetic solid via a nonmagnetic doping. CeO2 is taken as a prototype compound. A series of Ce1-xCaxO2-δ solid solutions with x = 0-0.25 were prepared by a solution combustion method using L-glutamic acid as the fuel. Sample characterization indicates that all as-prepared samples crystallized in a pure face-centered cubic fluorite structure with crystallite sizes smaller than 10 nm. On increasing the dopant content, the crystallite size decreased from about 8 to 4 nm, while the lattice parameter increased systematically. At room temperature, all samples are ferromagnetic admixed with an apparent diamagnetic component, as composed to a mixture of paramagnetic and antiferromagnetic behaviors or the absence of the ferromagnetism reported in the literature (Bouaine et al 2007 J. Phys. Chem. C 111 2924-8 Ney et al 2008 Phys. Rev. Lett. 100 157201) for magnetically doped semiconductors such as Sn1-xCoxO2 and Zn1-xCoxO. The coercivity and saturation magnetization for x = 0 are 110 Oe and 2.01 × 10-4 emu g-1, respectively, which slightly increased to 148 Oe and 2.26 × 10-4 emu g-1 on increasing the dopant content to x = 0.10. Upon annealing the as-prepared samples at 800 °C for 2 h, these magnetic parameters were weakened. This observation was interpreted in terms of the mixed valence state of Ce3+/Ce4+ and the doping effects. Finally, the nature of the room-temperature ferromagnetism is discussed by taking into account the oxygen vacancies and defects at the surface/interfaces that act as the electron and hole traps.

  7. Room Temperature Ferromagnetism of FeCo-Codoped ZnO Nanorods Prepared by Chemical Vapor Deposition

    SciTech Connect

    Chen, J.; Liu, J.; West, A.; Yan, Y.; Yu, M.; Zhou, W.

    2008-11-01

    FeCo-codoped ZnO nanorods with room temperature ferromagnetic ordering have been synthesized by chemical vapor deposition. Detailed nanostructures were investigated by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and nanoprobe X-ray energy dispersive spectroscopy (EDS). The ZnO nanorods were grown along c-axis of a single crystalline wurtzite structure and no second phase was observed by high resolution TEM. EDS analysis along the nanowires indicated that Co and Fe were successfully doped into the ZnO lattice with concentrations about 0.6-1.0 at.%. Magnetic measurement demonstrates a ferromagnetic ordering with Curie temperature higher than 300 K presents in the ZnO nanorods.

  8. Electrodeposition and room temperature ferromagnetic anisotropy of Co and Ni-doped ZnO nanowire arrays

    SciTech Connect

    Cui, J.B.; Gibson, U.J.

    2005-09-26

    Cobalt and nickel doped ZnO nanowire arrays were synthesized by an electrochemical process at a temperature of 90 deg. C. Energy dispersive x-ray spectroscopy and x-ray diffraction show that the dopants are incorporated into the wurtzite-structure ZnO. Anisotropic ferromagnetism with an easy direction of magnetization either perpendicular or parallel to the wire axis, depending on the wire geometry and density, was observed in 1.7% Co and 2.2% Ni-doped ZnO nanowires at room temperature. The anisotropic magnetism was explained in terms of a competition between self-demagnetization and magnetostatic coupling among the nanowires.

  9. Observation of room-temperature magnetic skyrmions and their current-driven dynamics in ultrathin metallic ferromagnets

    NASA Astrophysics Data System (ADS)

    Woo, Seonghoon; Litzius, Kai; Krüger, Benjamin; Im, Mi-Young; Caretta, Lucas; Richter, Kornel; Mann, Maxwell; Krone, Andrea; Reeve, Robert M.; Weigand, Markus; Agrawal, Parnika; Lemesh, Ivan; Mawass, Mohamad-Assaad; Fischer, Peter; Kläui, Mathias; Beach, Geoffrey S. D.

    2016-05-01

    Magnetic skyrmions are topologically protected spin textures that exhibit fascinating physical behaviours and large potential in highly energy-efficient spintronic device applications. The main obstacles so far are that skyrmions have been observed in only a few exotic materials and at low temperatures, and fast current-driven motion of individual skyrmions has not yet been achieved. Here, we report the observation of stable magnetic skyrmions at room temperature in ultrathin transition metal ferromagnets with magnetic transmission soft X-ray microscopy. We demonstrate the ability to generate stable skyrmion lattices and drive trains of individual skyrmions by short current pulses along a magnetic racetrack at speeds exceeding 100 m s-1 as required for applications. Our findings provide experimental evidence of recent predictions and open the door to room-temperature skyrmion spintronics in robust thin-film heterostructures.

  10. Structural and room temperature ferromagnetic properties of Ni doped ZnO nanoparticles via low-temperature hydrothermal method

    NASA Astrophysics Data System (ADS)

    Xu, Kun; Liu, Changzhen; Chen, Rui; Fang, Xiaoxiang; Wu, Xiuling; Liu, Jie

    2016-12-01

    A series of Zn1-xNixO (x=0, 1%, 3%, 5%) nanoparticles have been synthesized via a low-temperature hydrothermal method. Influence of Ni doping concentration on the structure, morphology, optical properties and magnetism of the samples was investigated by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, UV-vis spectrophotometer and vibrating sample magnetometer instruments. The results show that the undoped and doped ZnO nanoparticles are both hexagonal wurtzite structures. The surface analysis was performed using X-ray photoelectron spectroscopic studies. The images of SEM reveal that the structure of pure ZnO and Ni doped samples are nanoparticles which intended to form flakes with thickness of few nanometers, being overlain with each one to develop the network with some pores and voids. Based on the ultraviolet-visible (UV-vis) spectroscopy analysis, it indicates that the band gap energy decreases with the increasing concentration of Ni. Furthermore, The Ni doped ZnO samples didn't exhibit higher ultraviolet-light-driven photocatalytic activity compared to the undoped ZnO sample. Vibrating sample magnetometer was used for the magnetic property investigations, and the result indicates that room temperature ferromagnetism property of 3% Ni doped sample is attributed to oxygen vacancy and interaction between doped ions.

  11. Room-temperature ferromagnetism in Co and Nb co-doped TiO{sub 2} nanoparticles

    SciTech Connect

    Hachisu, M.; Mori, K.; Hyodo, K.; Morimoto, S.; Yamazaki, T.; Ichiyanagi, Y.

    2015-02-27

    Co- and Nb-doped TiO{sub 2} nanoparticles encapsulated with amorphous SiO{sub 2} were synthesized by our novel preparation method. An anatase TiO{sub 2} single-phase structure was confirmed using X-ray diffraction. The particle size could be controlled to be about 5 nm. The composition of these nanoparticles was investigated by X-ray fluorescence analysis. X-ray absorption near-edge structure spectra showed that the Ti{sup 4+} and Co{sup 2+} states were dominant in our prepared samples. A reduction in the coordination number was also confirmed. The dependence of the electrical conductivity on the frequency was measured by an LCR meter, and the carrier concentration was determined. The magnetization curves for the nanoparticles indicated ferromagnetic behavior at room temperature. We concluded that the ferromagnetism originated in oxygen vacancies around the transition metal ions.

  12. Phase-transfer induced room temperature ferromagnetic behavior in 1T@2H-MoSe2 nanosheets

    PubMed Central

    Xia, Baorui; Wang, Tongtong; Xiao, Wen; Zhang, Rongfang; Liu, Peitao; Ding, Jun; Gao, Daqiang; Xue, Desheng

    2017-01-01

    Manipulating electronic and magnetic properties of two-dimensional transitional-metal dichalcogenides has raised a lot of attention recently. Herein we report the synthesis and ferromagnetic properties of phase-transfer induced room temperature ferromagnetic behavior in 1 T@2H-MoSe2 nanosheets. Experimental results indicate the saturated magnetization of the 1 T@2H-MoSe2 compound increases first and then decreases as the increasing of 1 T-MoSe2 phase, where 65.58% 1 T-MoSe2 phase incorporation in 2H-MoSe2 could enhance the saturated magnetization from 0.32 memu/g to 8.36 memu/g. Besides, obvious magnetoresistance behaviors are observed in these samples, revealing their potential applications in future spintronics. PMID:28349939

  13. Room temperature p-type conductivity and coexistence of ferroelectric order in ferromagnetic Li doped ZnO nanoparticles

    SciTech Connect

    Awan, Saif Ullah E-mail: ullahphy@gmail.com; Hasanain, S. K.; Anjum, D. H.; Awan, M. S.; Shah, Saqlain A.

    2014-10-28

    Memory and switching devices acquired new materials which exhibit ferroelectric and ferromagnetic order simultaneously. We reported multiferroic behavior in Zn{sub 1−y}Li{sub y}O(0.00≤y≤0.10) nanoparticles. The analysis of transmission electron micrographs confirmed the hexagonal morphology and wurtzite crystalline structure. We investigated p-type conductivity in doped samples and measured hole carriers in range 2.4 × 10{sup 17}/cc to 7.3 × 10{sup 17}/cc for different Li contents. We found that hole carriers are responsible for long range order ferromagnetic coupling in Li doped samples. Room temperature ferroelectric hysteresis loops were observed in 8% and 10% Li doped samples. We demonstrated ferroelectric coercivity (remnant polarization) 2.5 kV/cm (0.11 μC/cm{sup 2}) and 2.8 kV/cm (0.15 μC/cm{sup 2}) for y = 0.08 and y = 0.10 samples. We propose that the mechanism of Li induced ferroelectricity in ZnO is due to indirect dipole interaction via hole carriers. We investigated that if the sample has hole carriers ≥5.3 × 10{sup 17}/cc, they can mediate the ferroelectricity. Ferroelectric and ferromagnetic measurements showed that higher electric polarization and larger magnetic moment is attained when the hole concentration is larger and vice versa. Our results confirmed the hole dependent coexistence of ferromagnetic and ferroelectric behavior at room temperature, which provide potential applications for switchable and memory devices.

  14. Room temperature ferromagnetism in Eu-doped ZnO nanoparticulate powders prepared by combustion reaction method

    NASA Astrophysics Data System (ADS)

    Franco, A.; Pessoni, H. V. S.; Soares, M. P.

    2014-04-01

    Nanoparticulate powders of Eu-doped ZnO with 1.0, 1.5, 2.0 and 3.0 at% Eu were synthesized by combustion reaction method using zinc nitrate, europium nitrate and urea as fuel without subsequent heat treatments. X-ray diffraction patterns (XRD) of all samples showed broad peaks consistent with the ZnO wurtzite structure. The absence of extra reflections in the diffraction patterns ensures the phase purity, except for x=0.03 that exhibits small reflection corresponding to Eu2O3 phase. The average crystallite size determined from the most prominent (1 0 1) peak of the diffraction using Scherrer's equation was in good agreement with those determined by transmission electron microscopy (TEM); being ~26 nm. The magnetic properties measurements were performed using a vibrating sample magnetometer (VSM) in magnetic fields up to 2.0 kOe at room temperature. The hysteresis loops, typical of magnetic behaviors, indicating that the presence of an ordered magnetic structure can exist in the Eu-doped ZnO wurtzite structure at room temperature. The room temperature ferromagnetism behavior increases with the Eu3+ doping concentration. All samples exhibited the same Curie temperature (TC) around ~726 K, except for x=0.01; TC~643 K. High resolution transmission electron microscopy (HRTEM) images revealed defects/strain in the lattice and grain boundaries of Eu-doped ZnO nanoparticulate powders. The origin of room temperature ferromagnetism in Eu-doped ZnO nanoparticulate powders was discussed in terms of these defects, which increase with the Eu3+ doping concentration.

  15. Ferromagnetism at room temperature in La{endash}Ba{endash}Ca{endash}Mn{endash}O thin films

    SciTech Connect

    Hong, Nguyen Hoa; Sakai, Joe; Imai, Syozo

    2001-06-01

    The effects of substitution of Ca by Ba in La{sub 1{minus}x}Ca{sub x}MnO{sub 3} (LCMO) with x{lt}0.5 were investigated systematically in order to clarify the role of the size of the A cations. As for the La{sub 1{minus}x}(Ba{endash}Ca){sub x}MnO{sub 3} (LBCMO) films of ferromagnetic metallic (FMM) region (x=0.2; 0.3; and 0.4), by doping Ba, the ferromagnetic transition temperature (T{sub C}) and the insulator-to-metal (IM) transition temperature (T{sub IM}) were improved about 30{endash}60 K, compared with those of LCMO thin films with the same ratio of Mn{sup 3+}:Mn{sup 4+}. Especially, La{sub 0.7}Ba{sub 0.1}Ca{sub 0.2}MnO{sub 3} thin films have an anomalously high T{sub C} (about room temperature) and a T{sub IM} of 275 K under zero field. In the ferromagnetic insulating (FMI) region (x=0.15; 0.1), the Ba doping enables the IM transition and remarkably heightens the T{sub C} as well. The phase diagram shows that in the slightly doped region (x{lt}0.5), Ba doping has made the FMM phase significantly expanded. {copyright} 2001 American Institute of Physics.

  16. Defect-mediated room temperature ferromagnetism in vanadium dioxide thin films

    NASA Astrophysics Data System (ADS)

    Yang, Tsung-Han; Nori, Sudhakar; Zhou, Honghui; Narayan, Jagdish

    2009-09-01

    High quality epitaxial undoped vanadium oxide (VO2) thin films on c-plane sapphire (0001) substrate have been grown using pulsed laser deposition technique. The as-grown films exhibited excellent structural and transport properties without requiring further annealing treatments for these oxygen-deficient oxide films. The epitaxial growth has been achieved via domain matching epitaxy, where matching of integral multiples of planes occurs across the film-substrate interface. The magnetic properties of vanadium oxide (VO2) films investigated at different temperatures in the range of 10-360 K showed significant magnetic hysteresis as well as saturation of the magnetic moment. The origin of ferromagnetic properties with an estimated Curie temperature above 500 K is discussed in the absence of magnetic impurities in VO2 thin films as determined by x-ray photoelectron spectroscopy, x-ray diffraction, and transmission electron microscopy.

  17. Origin of ferromagnetism and oxygen-vacancy ordering induced cross-controlled magnetoelectric effects at room temperature

    NASA Astrophysics Data System (ADS)

    Wei, X. K.; Zou, T.; Wang, F.; Zhang, Q. H.; Sun, Y.; Gu, L.; Hirata, A.; Chen, M. W.; Yao, Y.; Jin, C. Q.; Yu, R. C.

    2012-04-01

    In dilute magnetic oxide hexagonal Ba(Ti0.9Fe0.1)O2.81 bulk ceramic, we report on combined ferromagnetism and improper ferroelectricity as well as cross-controlled magnetoelectric effects at room temperature. The annular-bright-field (ABF) imaging technique in scanning transmission electron microscopy (STEM) demonstrates an oxygen vacancy ordering in the hexagonal closest-packed Ba1-O1 layers and severe distortion of the octahedra and pyramids. Strong dependencies of the susceptibility on temperature and magnetic field as well as the frequency dependence of magnetization under an ac electric field reveal that the intrinsic ferromagnetism of the highly insulating system dynamically evolves from a paramagnetic ground state, and dynamic exchanges of trapped electrons in the ordered polarons are attributed to the ferromagnetic interaction. Accordingly, aided by the motion of oxygen vacancies, responses of the trapped electrons to the ac magnetic field result in the reversal of magnetically induced voltages between high and low states. Our results not only expand our understanding on the magnetoelectric coupling mechanism, but also provide a grand opportunity toward designing novel multiferroic materials through introducing ordered point defects into a centrosymmetric matrix.

  18. Room temperature ferromagnetism and luminescent behavior of Ni doped ZnO nanoparticles prepared by coprecipitation method

    SciTech Connect

    Arora, Deepawali; Mahajan, Aman; Kaur, Parvinder; Singh, Gurinder Pal; Kumar, Sunil; Singh, D. P.; Ashokan, K.

    2016-05-23

    The samples of Zn{sub 1-x}Ni{sub x}O (x= 0.00 and 0.05) were prepared using coprecipitation method and annealed at different temperatures. The effect of Ni ion substitution on the structural and optical properties has been studied using X-ray Diffraction, UV-Visible, Photoluminescence and Magnetic measurements. XRD measurements demonstrate that all the prepared samples are wurtzite polycrystalline single phase in nature, ruling out the presence of any secondary phase formation. Ultraviolet visible measurements showed a decrease in band gap with the increase in annealing temperature and doping concentration. The PL data shows the red shift in all the samples and luminescence quenching with Ni doping. Compared to undoped ZnO, Ni doped ZnO showed room temperature ferromagnetism.

  19. Room temperature insulating ferromagnetism induced by charge transfer in ultrathin (110) La0.7Sr0.3MnO3 films

    NASA Astrophysics Data System (ADS)

    Quan, Zhiyong; Wu, Biao; Zhang, Fei; Zhou, Guowei; Zang, Julu; Xu, Xiaohong

    2017-02-01

    The achievement of high temperature ferromagnetism in perovskite manganites has proved both fundamentally and technologically important for spintronics devices. However, high operating temperatures have not been achieved due to the depression of the Curie temperature and the rapid spin filtering efficiency loss, which are the main obstacles for practical applications. Here, we report unexpected room temperature insulating ferromagnetism in ultrathin (110) oriented La0.7Sr0.3MnO3 (LSMO) films. The relationships between room temperature ferromagnetism, charge transfer, and orbital occupancy are investigated, with X-ray absorption spectroscopy (XAS) and X-ray linear dichroism (XLD) measurements. Our results suggest that the room temperature insulating ferromagnetism is originated from super-exchange interaction between Mn2+ and Mn3+. The formation of Mn2+ ions is related to the charge transfer induced by oxygen vacancies. Moreover, a preferential orbital occupancy of eg(3z2-r2) in Mn3+ ions is crucial to the in-plane super-exchange coupling in ultrathin (110) LSMO films, resulting in insulating ferromagnetic behavior. This work may lead to the development of barrier materials in spin filter tunnel junctions and understanding of ferromagnetic coupling in insulating perovskite films.

  20. Imaging of room-temperature ferromagnetic nano-domains at the surface of a non-magnetic oxide

    NASA Astrophysics Data System (ADS)

    Taniuchi, T.; Motoyui, Y.; Morozumi, K.; Rödel, T. C.; Fortuna, F.; Santander-Syro, A. F.; Shin, S.

    2016-06-01

    Two-dimensional electron gases at oxide surfaces or interfaces show exotic ordered states of matter, like superconductivity, magnetism or spin-polarized states, and are a promising platform for alternative oxide-based electronics. Here we directly image a dense population of randomly distributed ferromagnetic domains of ~40 nm typical sizes at room temperature at the oxygen-deficient surface of SrTiO3, a non-magnetic transparent insulator in the bulk. We use laser-based photoemission electron microscopy, an experimental technique that gives selective spin detection of the surface carriers, even in bulk insulators, with a high spatial resolution of 2.6 nm. We furthermore find that the Curie temperature in this system is as high as 900 K. These findings open perspectives for applications in nano-domain magnetism and spintronics using oxide-based devices, for instance through the nano-engineering of oxygen vacancies at surfaces or interfaces of transition-metal oxides.

  1. Investigation of room temperature ferromagnetic nanoparticles of Gd5Si4

    DOE PAGES

    Hadimani, R. L.; Gupta, S.; Harstad, S. M.; ...

    2015-07-06

    Gd5(SixGe1-x)4 compounds undergo first-order phase transitions close to room temperature when x ~ = 0.5, which are accompanied by extreme changes of properties. We report the fabrication of the nanoparticles of one of the parent compounds-Gd5Si4-using high-energy ball milling. Crystal structure, microstructure, and magnetic properties have been investigated. Particles agglomerate at long milling times, and the particles that are milled >20 min lose crystallinity and no longer undergo magnetic phase transition close to 340 K, which is present in a bulk material. The samples milled for >20 min exhibit a slightly increased coercivity. As a result, magnetization at a highmore » temperature of 275K decreases with the increase in the milling time.« less

  2. Room temperature ferromagnetism in undoped and Ni doped In{sub 2}O{sub 3} thin films

    SciTech Connect

    Krishna, N. Sai; Kaleemulla, S. Rao, N. Madhusudhana; Krishnamoorthi, C.; Begam, M. Rigana; Amarendra, G.

    2015-06-24

    Undoped and Ni (5 at.%) doped In{sub 2}O{sub 3} thin films were deposited on glass substrate using electron beam evaporation technique and Ni doped In{sub 2}O{sub 3} thin films were annealed at 450 oC. A systematic study was carried out on the structural, chemical and magnetic properties of the as deposited and annealed thin films. X-ray diffraction analysis revealed that all the films were cubic in structure and exhibied ferromagnetism at room temperature. The undoped In{sub 2}O{sub 3} thin films exhibited a saturation magnetization of 24.01 emu/cm3. Ni doped In{sub 2}O{sub 3} thin films annealed at 450 oC showed a saturation magnetization of 53.81 emu/cm3.

  3. Room-temperature electronically-controlled ferromagnetism at the LaAlO3/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Bi, Feng; Huang, Mengchen; Ryu, Sangwoo; Lee, Hyungwoo; Bark, Chung-Wung; Eom, Chang-Beom; Irvin, Patrick; Levy, Jeremy

    2014-09-01

    Reports of emergent conductivity, superconductivity and magnetism have helped to fuel intense interest in the rich physics and technological potential of complex-oxide interfaces. Here we employ magnetic force microscopy to search for room-temperature magnetism in the well-studied LaAlO3/SrTiO3 system. Using electrical top gating to control the electron density at the oxide interface, we directly observe the emergence of an in-plane ferromagnetic phase as electrons are depleted from the interface. Itinerant electrons that are reintroduced into the interface align antiferromagnetically with the magnetization at first screening and then destabilizing it as the conductive regime is approached. Repeated cycling of the gate voltage results in new, uncorrelated magnetic patterns. This newfound control over emergent magnetism at the interface between two non-magnetic oxides portends a number of important technological applications.

  4. Room-temperature electronically-controlled ferromagnetism at the LaAlO₃/SrTiO₃ interface.

    PubMed

    Bi, Feng; Huang, Mengchen; Ryu, Sangwoo; Lee, Hyungwoo; Bark, Chung-Wung; Eom, Chang-Beom; Irvin, Patrick; Levy, Jeremy

    2014-09-25

    Reports of emergent conductivity, superconductivity and magnetism have helped to fuel intense interest in the rich physics and technological potential of complex-oxide interfaces. Here we employ magnetic force microscopy to search for room-temperature magnetism in the well-studied LaAlO3/SrTiO3 system. Using electrical top gating to control the electron density at the oxide interface, we directly observe the emergence of an in-plane ferromagnetic phase as electrons are depleted from the interface. Itinerant electrons that are reintroduced into the interface align antiferromagnetically with the magnetization at first screening and then destabilizing it as the conductive regime is approached. Repeated cycling of the gate voltage results in new, uncorrelated magnetic patterns. This newfound control over emergent magnetism at the interface between two non-magnetic oxides portends a number of important technological applications.

  5. Room-temperature ferromagnetism observed in Nd-doped In2O3 dilute magnetic semiconducting nanowires

    NASA Astrophysics Data System (ADS)

    Lv, Zhanpeng; Zhang, Junran; Niu, Wei; Zhang, Minhao; Song, Li; Zhu, Hairong; Wang, Xuefeng

    2016-09-01

    Nd-doped In2O3 nanowires were fabricated by an Au-catalyzed chemical vapor deposition method. Nd atoms were successfully doped into the In2O3 host lattice structure, as revealed by energy dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, and x-ray diffraction. Robust room temperature ferromagnetism was observed in Nd-doped In2O3 nanowires, which was attributed to the long-range-mediated magnetization among Nd3+-vacancy complexes through percolation-bound magnetic polarons. Project supported by the National Natural Science Foundation of China (Grant No. 11274003), the Priority Academic Program Development of Jiangsu Higher Education Institutions, China, and the Fundamental Research Funds for the Central Universities, China.

  6. Room-temperature ferromagnetism in CrSi2(core)/SiO2(shell) semiconducting nanocables

    NASA Astrophysics Data System (ADS)

    Hou, Te-Chien; Han, You-Hong; Lo, Shen-Chuan; Lee, Cheng-Tse; Ouyang, Hao; Chen, Lih-Juann

    2011-05-01

    Room-temperature ferromagnetism has been observed in high density free-standing CrSi2(core)/SiO2(shell) semiconducting nanocables, which is contrast to diamagnetic properties of both CrSi2 and SiO2 in bulk. The hexagonal CrSi2 C40-type nanowires, sheathed with a thin amorphous SiO2 layer, grow along [0001] direction. The results of first-principles simulations indicate that Cr atoms around the interface are with anomalously high magnetization (about 2 μB/atom), due to distorted/dangling bonds and surrounded oxygen atoms. Evaluations can be very consistent with measurements by further considering the effects of interfacial roughness and more distribution of oxygen around the interface. These results point toward a different way to tune nanomagnetism in core/shell nanowires.

  7. Room-temperature ferromagnetism in Cr-doped Si achieved by controlling atomic structure, Cr concentration, and carrier densities: A first-principles study

    SciTech Connect

    Wei, Xin-Yuan; Yang, Zhong-Qin; Zhu, Yan; Li, Yun

    2015-04-28

    By using first-principles calculations, we investigated how to achieve a strong ferromagnetism in Cr-doped Si by controlling the atomic structure and Cr concentration as well as carrier densities. We found that the configuration in which the Cr atom occupies the tetrahedral interstitial site can exist stably and the Cr atom has a large magnetic moment. Using this doping configuration, room-temperature ferromagnetism can be achieved in both n-type and p-type Si by tuning Cr concentration and carrier densities. The results indicate that the carrier density plays a crucial role in realizing strong ferromagnetism in diluted magnetic semiconductors.

  8. Room-temperature five-tesla coercivity of a rare-earth-free shell-ferromagnet

    NASA Astrophysics Data System (ADS)

    Scheibel, F.; Spoddig, D.; Meckenstock, R.; Gottschall, T.; ćakır, A.; Krenke, T.; Farle, M.; Gutfleisch, O.; Acet, M.

    2017-05-01

    Ni2MnX-based Heusler (X: main group element), when enriched with Mn, will decompose into ferromagnetic Ni2MnX and antiferromagnetic NiMn when temper-annealed around 650 K. When the starting material is chosen such that the X-composition is about 5 at. % and the annealing takes place in the presence of a magnetic field of about 1 T, the resulting material is a composite of nanoprecipitate strongly pinned shell-ferromagnets with a soft ferromagnetic core embedded in the antiferromagnetic matrix. We show that the shells of the precipitates are so strongly pinned that the estimated field required to fully reorient the spins is in the order of 20 T. We examine in a Ni50.0Mn45.1In4.9 sample the pinning and the magnetic interactions of the precipitate and the matrix with magnetization and ferromagnetic resonance studies carried out in fields ranging up to 14 and 12 T, respectively.

  9. Giant electric field modulation of double exchange ferromagnetism at room temperature in the perovskite manganite/titanate p-n junction.

    PubMed

    Tanaka, Hidekazu; Zhang, Jun; Kawai, Tomoji

    2002-01-14

    We report on the electrical modulation of double exchange ferromagnetism at room temperature in hole-doped manganites of a metal oxide p-n junction. In this (La0.9Ba0.1)MnO(3)/Nb doped SrTiO3 p-n junction, the temperature dependence of the junction resistance shows a metal-insulator transition whose temperature, corresponding to that of ferromagnetic transition, is hugely modulated from 290 to 340 K by a bias voltage increasing from +1.0 to +1.8 V. The magnetoresistance can also be modulated electrically.

  10. Sample-size resonance, ferromagnetic resonance and magneto-permittivity resonance in multiferroic nano-BiFeO3/paraffin composites at room temperature

    NASA Astrophysics Data System (ADS)

    Wang, Lei; Li, Zhenyu; Jiang, Jia; An, Taiyu; Qin, Hongwei; Hu, Jifan

    2017-01-01

    In the present work, we demonstrate that ferromagnetic resonance and magneto-permittivity resonance can be observed in appropriate microwave frequencies at room temperature for multiferroic nano-BiFeO3/paraffin composite sample with an appropriate sample-thickness (such as 2 mm). Ferromagnetic resonance originates from the room-temperature weak ferromagnetism of nano-BiFeO3. The observed magneto-permittivity resonance in multiferroic nano-BiFeO3 is connected with the dynamic magnetoelectric coupling through Dzyaloshinskii-Moriya (DM) magnetoelectric interaction or the combination of magnetostriction and piezoelectric effects. In addition, we experimentally observed the resonance of negative imaginary permeability for nano BiFeO3/paraffin toroidal samples with longer sample thicknesses D=3.7 and 4.9 mm. Such resonance of negative imaginary permeability belongs to sample-size resonance.

  11. Room-temperature Magnetism in Carbon Dots and Enhanced Ferromagnetism in Carbon Dots-Polyaniline Nanocomposite.

    PubMed

    Liu, Jian; Bi, Hong; Cesar Morais, Paulo; Zhang, Xiang; Zhang, Fapei; Hu, Lin

    2017-05-19

    Room temperature magnetic ordering is reported for very small carbon dots (CDs), mat-like polyaniline nanofibers (Mat-PANI) and a composite of CDs@Mat-PANI containing 0.315 wt% CDs. We have found saturation magnetization (M S ) of CDs, Mat-PANI and CDs@Mat-PANI at 5 (20/300) K equals to 0.0079 (0.0048/0.0019), 0.0116 (0.0065/0.0055) and 0.0349 (0.0085/0.0077) emu/g, respectively. The M S enhancement in CDs@Mat-PANI (200% and 40% at 5 K and 300 K, respectively) is attributed to electron transfer from Mat-PANI imine N-atoms to the encapsulated CDs. Changes in M S values reveal that 0.81 (0.08) electron/CD is transferred at 5 (300) K, which is supported by observation of CDs photoluminescence (PL) redshift while in CDs@Mat-PANI. Band-bending and bandgap-renormalization calculations are used to predict a redshift of 117 meV at 300 K as a result of the electron transfer, in excellent agreement with the PL data (110 meV). Raman, X-ray diffraction and X-ray photoelectron spectroscopy data are used to confirm the electron transfer process as well as the strong interaction of CDs with PANI within CDs@Mat-PANI, which increases the crystalline domain size of Mat-PANI from about 4.8 nm to 9.2 nm while reducing the tensile strain from about 6.2% to 1.8%.

  12. Thermal plasma processed ferro-magnetically ordered face-centered cubic iron at room temperature

    SciTech Connect

    Raut, Suyog A.; Kanhe, Nilesh S.; Bhoraskar, S. V.; Mathe, V. L.; Das, A. K.

    2014-10-28

    Here, we report tailor made phase of iron nanoparticles using homogeneous gas phase condensation process via thermal plasma route. It was observed that crystal lattice of nano-crystalline iron changes as a function of operating parameters of the plasma reactor. In the present investigation iron nanoparticles have been synthesized in presence of argon at operating pressures of 125–1000 Torr and fixed plasma input DC power of 6 kW. It was possible to obtain pure fcc, pure bcc as well as the mixed phases for iron nanoparticles in powder form as a function of operating pressure. The as synthesized product was characterized for understanding the structural and magnetic properties by using X-ray diffraction, vibrating sample magnetometer, and Mössbauer spectroscopy. The data reveal that fcc phase is ferromagnetically ordered with high spin state, which is unusual whereas bcc phase is found to be ferromagnetic as usual. Finally, the structural and magnetic properties are co-related.

  13. Imaging of room-temperature ferromagnetic nano-domains at the surface of a non-magnetic oxide.

    PubMed

    Taniuchi, T; Motoyui, Y; Morozumi, K; Rödel, T C; Fortuna, F; Santander-Syro, A F; Shin, S

    2016-06-10

    Two-dimensional electron gases at oxide surfaces or interfaces show exotic ordered states of matter, like superconductivity, magnetism or spin-polarized states, and are a promising platform for alternative oxide-based electronics. Here we directly image a dense population of randomly distributed ferromagnetic domains of ∼40 nm typical sizes at room temperature at the oxygen-deficient surface of SrTiO3, a non-magnetic transparent insulator in the bulk. We use laser-based photoemission electron microscopy, an experimental technique that gives selective spin detection of the surface carriers, even in bulk insulators, with a high spatial resolution of 2.6 nm. We furthermore find that the Curie temperature in this system is as high as 900 K. These findings open perspectives for applications in nano-domain magnetism and spintronics using oxide-based devices, for instance through the nano-engineering of oxygen vacancies at surfaces or interfaces of transition-metal oxides.

  14. Imaging of room-temperature ferromagnetic nano-domains at the surface of a non-magnetic oxide

    PubMed Central

    Taniuchi, T.; Motoyui, Y.; Morozumi, K.; Rödel, T. C.; Fortuna, F.; Santander-Syro, A. F.; Shin, S.

    2016-01-01

    Two-dimensional electron gases at oxide surfaces or interfaces show exotic ordered states of matter, like superconductivity, magnetism or spin-polarized states, and are a promising platform for alternative oxide-based electronics. Here we directly image a dense population of randomly distributed ferromagnetic domains of ∼40 nm typical sizes at room temperature at the oxygen-deficient surface of SrTiO3, a non-magnetic transparent insulator in the bulk. We use laser-based photoemission electron microscopy, an experimental technique that gives selective spin detection of the surface carriers, even in bulk insulators, with a high spatial resolution of 2.6 nm. We furthermore find that the Curie temperature in this system is as high as 900 K. These findings open perspectives for applications in nano-domain magnetism and spintronics using oxide-based devices, for instance through the nano-engineering of oxygen vacancies at surfaces or interfaces of transition-metal oxides. PMID:27283225

  15. Defect mediated room temperature ferromagnetism and resistance minima study in epitaxial ZnGa0.002Al0.02O transparent conducting oxide films

    NASA Astrophysics Data System (ADS)

    Temizer, Namik K.; Nori, Sudhakar; Kumar, D.; Narayan, Jagdish

    2016-09-01

    We report on the micro-structural, transport, optical and magnetic properties in ZnGa0.002Al0.02O (AGZO) films grown by pulsed laser deposition under different growth conditions. AGZO films grown at substrate temperatures of 600 °C show metal-like behavior with a resistivity minima at lower temperatures, whereas films grown at 300 °C and ambient oxygen partial pressure of 1 mTorr show metallic nature with resistivity values on the order of 100 µΩ · cm at room temperature. The most interesting features are the concomitant occurrence of high temperature resistivity minima and room temperature ferromagnetism with a saturation magnetic moment of 1000 A m-1 and with coercivity in the range 100-240 Oe. The temperature dependent resistivity data has been interpreted in the light of quantum corrections to conductivity in disordered systems, suggesting that the e-e interactions is the dominant mechanism in the weak-localization (WL) limit in the case of films showing resisitivity minima. The simultaneous ferromagnetic ordering coupled with the enhancements in electrical conductivity in AGZO system should have their origin in native point defects in the form of oxygen and zinc vacancies and interstitials and their complexes. We propose that formation of oxygen vacancy-zinc interstitial defect complex (V O-I Zn) is responsible for the enhancement in n-type conductivity, and zinc vacancies (V Zn) for the observed room temperature ferromagnetism.

  16. Room-Temperature Electronically-Controlled Ferromagnetism at the LaAlO3/SrTiO3 Interface

    NASA Astrophysics Data System (ADS)

    Bi, Feng; Huang, Mengchen; Bark, Chung-Wung; Ryu, Sangwoo; Eom, Chang-Beom; Irvin, Patrick; Levy, Jeremy

    2014-03-01

    Reports of emergent conductivity, superconductivity, and magnetism at oxide interfaces have helped to fuel intense interest in their rich physics and technological potential. We employ magnetic force microscopy to search for room-temperature magnetism in the well-studied LaAlO3/SrTiO3 system.[2] Using electrical top gating to deplete electrons from the oxide interface, we directly observe an in-plane ferromagnetic phase with sharply defined domain walls. Itinerant electrons, introduced by a top gate, align antiferromagnetically with the magnetization, at first screening and then destabilizing it as the conductive state is reached. Subsequent depletion of electrons results in a new, uncorrelated magnetic pattern. This newfound control over emergent magnetism at the interface between two non-magnetic oxides portends a number of important technological applications. We gratefully acknowledge support for this work from ARO MURI W911NF-08-1-0317 (JL), AFOSR MURI FA9550-10-1-0524 (CBE, JL) FA9550-12-1-0342 (CBE), and grants from the National Science Foundation DMR-1104191 (JL), DMR-1124131 (CBE, JL), DMR-1234096(CBE).

  17. Post-annealing effect on the room-temperature ferromagnetism in Cu-doped ZnO thin films

    SciTech Connect

    Hu, Yu-Min Kuang, Chein-Hsiun; Han, Tai-Chun; Yu, Chin-Chung; Li, Sih-Sian

    2015-05-07

    In this work, we investigated the structural and magnetic properties of both as-deposited and post-annealed Cu-doped ZnO thin films for better understanding the possible mechanisms of room-temperature ferromagnetism (RT-FM) in ZnO-based diluted magnetic oxides. All of the films have a c-axis-oriented wurtzite structure and display RT-FM. X-ray photoelectron spectroscopy results showed that the incorporated Cu ions in as-deposited films are in 1+ valence state merely, while an additional 2+ valence state occurs in post-annealed films. The presence of Cu{sup 2+} state in post-annealed film accompanies a higher magnetization value than that of as-deposited film and, in particular, the magnetization curves at 10 K and 300 K of the post-annealed film separate distinctly. Since Cu{sup 1+} ion has a filled 3d band, the RT-FM in as-deposited Cu-doped ZnO thin films may stem solely from intrinsic defects, while that in post-annealed films is enhanced due to the presence of CuO crystallites.

  18. Preparation of Fe-doped TiO2 nanotube arrays and their room-temperature ferromagnetic properties.

    PubMed

    Wang, Jianli; Liu, Chao; Shen, Weidong; Cao, Chunlan; Song, Sihong

    2014-08-01

    Fe-doped titania nanotube arrays (NTs) were fabricated by electrochemical anodization on a Ti foil using Fe(NO3)3 · 2H2O as iron source. Their morphology, structure and optical properties were investigated by field emission scanning electron microscopy, X-ray diffraction, UV-visible absorption spectroscopy and photoluminescence spectroscopy. The UV-visible reflection spectrum of the Fe-doped TiO2 NTs showed a red shift in wavelength of absorption and greater reflectivity compared with the undoped sample due to the Fe ion incorportion in TiO2 lattices. The photoluminescence spectrum of the Fe-doped TiO2 NTs shows two strong new peaks centered at 388 nm and 694 nm, besides the UV emission peak owing to the electronic transition mediated by the defect levels such as oxygen vacancies in the band gap. The magnetic property of the Fe-doped TiO2 NTs exhibits a room temperature ferromagnetic characteristic with a saturation magnetization (Ms) of 0.146 x 10(-2) emu/cm3 and a coercive field of 60 Oe. And the cause of the magnetic properties has been discussed in detail.

  19. Enhanced Room Temperature Ferromagnetism by Fe Doping in Zn0.96Cu0.04O Diluted Magnetic Semiconductors

    NASA Astrophysics Data System (ADS)

    Muthukumaran, S.; Ashokkumar, M.

    2016-02-01

    Zn0.96- x Cu0.04Fe x O (0 ≤ x ≤ 0.04) nanoparticles synthesized via the sol-gel technique had a hexagonal wurtzite ZnO structure without any Fe/Cu-related secondary phases. The crystallite size was reduced from Fe = 0% (23 nm) to Fe = 4% (16 nm) due to the suppression of grain surface growth by foreign impurities. Doping of higher Fe concentrations into Zn-Cu-O suppressed the ultra-violet (UV) emission band and balanced the defect-related visible emissions. The decrease of the UV and green emission intensity ratio ( I UV/ I green) and the UV and blue emission intensity ratio ( I UV/ I blue) in photoluminescence spectra implied an increase of defect states with the increase of Fe concentrations. All the samples showed clear room temperature ferromagnetism. The saturation magnetization was increased by Fe co-doping which was attributed to the interaction between Fe-Fe ions. X-ray photoelectron spectra confirmed the absence of secondary phases like Fe3O4.

  20. Role of donor defects in stabilizing room temperature ferromagnetism in (Mn, Co) co-doped ZnO nanoparticles.

    PubMed

    Naeem, M; Hasanain, S K

    2012-06-20

    We report the effects of co-doping ZnO with Co and Mn in an n-type environment on ferromagnetism (FM). Two sets of samples, Zn(0.95-x)Co(0.04)Mn(x)O (0.000 ≤ x ≤ 0.02) and Zn(0.95-y)Co(y)Mn(0.04)O (0.000 ≤ y ≤ 0.02), were synthesized by the chemical route with oxygen vacancies introduced via annealing in a forming gas (reducing the atmosphere). In addition to the magnetization, the particles were characterized by x-ray diffraction, diffuse reflectance spectroscopy and x-ray absorption near-edge emission spectroscopy. The Co and Mn ions were determined to be in the + 2 state in a tetrahedral symmetry, with no evidence of metallic Co or Mn. We find that while a purely Mn-doped sample exhibits weak FM at room temperature, the general effect of Mn as a co-dopant with Co, in an n-type environment, is to decrease the moment strongly. All of our results can be systematically explained within the context of defect mediated FM in these wide bandgap semiconductors, where the coincidence of the spin-split-impurity (defect) band states and the 3d states leads to the development of a net moment alongside the formation of spin polarons.

  1. Enhanced room temperature ferromagnetism and photoluminescence behavior of Cu-doped ZnO co-doped with Mn

    NASA Astrophysics Data System (ADS)

    Ashokkumar, M.; Muthukumaran, S.

    2015-05-01

    Cu, Mn co-doped ZnO nanoparticles were successfully synthesized by the sol-gel technique. XRD pattern described that Mn-doping did not affect the hexagonal wurtzite structure of the samples and no secondary phases were found. The reduced crystallite size at Mn=2% is due to the suppression of grain surface growth by foreign impurity. The enhancement of crystal size after Mn=2% is due to the expansion of lattice volume produced by the distortion around the dopant ion. The better dielectric constant and conductivity noticed at Mn=2% are explained by charge carrier density and crystallite size. The suppression of broad UV band by Mn-doping is discussed based on the generation of non-radiative recombination centers. Hysteresis loop showed the clear room temperature ferromagnetism in all the samples and the magnetization increased with Mn-doping. Better electrical and magnetic behavior of Zn0.94Cu0.04Mn0.02O sample is suggested for effective opto-magnetic devices.

  2. Thermal ionization induced metal-semiconductor transition and room temperature ferromagnetism in trivalent doped ZnO codoped with lithium

    SciTech Connect

    Sivagamasundari, A.; Chandrasekar, S.; Pugaze, R.; Kannan, R.; Rajagopan, S.

    2014-03-07

    Thermal ionization induced metallic to semiconductor (MST) transition occurring at 460 K for Zn{sub 0.97}Al{sub 0.03}O, 463 K for Zn{sub 0.94}Al{sub 0.03}Li{sub 0.03}O, and 503 K for Zn{sub 0.91}Al{sub 0.03}Li{sub 0.03}Mn{sub 0.03}O has been found in the sol-gel synthesized (using hexamethylenetetramine), trivalent doped (Al, Mn) ZnO codoped with lithium. Increase in the thermally ionized carrier concentration due to Al doping is responsible for near band edge (NBE) peak shift causing Fermi level to move into conduction band making it metallic consistent with resistivity results. Free carrier (thermally activated) neutralization with ionized donor is responsible for semiconducting nature, which is supported from the free carrier screening produced energy shift in the NBE of photoluminescence peak. Furthermore, independently band gap shrinkage is also obtained from UV-Visible studies confirming localization induced MST. An anti-correlation is found between defect density (DLE) and room temperature ferromagnetism (RTFM) indicating intrinsic defects are not directly responsible for RTFM.

  3. Effect of Cu doping on room temperature ferromagnetic behavior of Mn doped LiNbO3 films

    NASA Astrophysics Data System (ADS)

    Bu, Dechong; Fu, Yuting; Sun, Ning; Li, Chunjing; Li, Yanghua; An, Yukai; Liu, Jiwen

    2016-11-01

    Cu and Mn co-doped LiNbO3 films were deposited on Si (111) substrates by rf-magnetron sputtering. XRD shows a randomly oriented polycrystalline R3C structure of LiNbO3 was formed in the films annealed at 1000 °C for 1 h in air. XPS and XAFS determine that Mn2+ substitutes on the Li site with a Li vacancy and Cu2+ substitutes on the Nb site with an oxygen vacancy in the LiNbO3 lattice. SQUID measurements indicate that all the films exhibit room temperature ferromagnetism, attributed to a strong d-d electron interaction between Mn and Nb and the bound magnetic polarons resulting from the oxygen vacancies. The saturated magnetization increases but the atom magnetic moment decreases with increasing Cu content in the films. The drop of the atom magnetic moment may arise from the antiferromagnetic coupling among adjacent Cu ions and an antiparallel configuration between Cu2+ ions and their trapped electrons.

  4. Room temperature ferromagnetism in Ist group elements codoped ZnO:Fe nanoparticles by co-precipitation method

    NASA Astrophysics Data System (ADS)

    Pazhanivelu, V.; Paul Blessington Selvadurai, A.; Kannan, R.; Murugaraj, R.

    2016-04-01

    In this paper, we report on the structural, vibrational and magnetic behavior of Ist group elements (Li+, Na+ and K+) codoping effect in ZnO:Fe nanoparticles (NPs) prepared by co-precipitation method. The single crystalline phase of the prepared NPs was identified as Wurtizite structure and the Raman spectra expressed the local structural change and the presence of complex lattice defects such as Zinc interstitial (Zni) and Oxygen vacanvy (V+o) defects in the NPs. The presence of functional groups was confirmed by FT-IR spectral analysis. The optical absorption properties of the prepared NPs were characterised by UV-Drs spectroscopy. The valance state of Zinc ions and the role of Oxygen related defects were analysed from x-ray photoelectron spectroscopy (XPS) spectra. The electron paramagnetic resonance (EPR) spectral line illustrated the presence of complex defects such as Zinc interstitial (Zni) and oxygen vacancy (V+o) defects in the sample. The observed room temperature ferromagnetism (RTFM) in the prepared sample was induced by lattice defects. The observed results are discussed and reported.

  5. Thermal ionization induced metal-semiconductor transition and room temperature ferromagnetism in trivalent doped ZnO codoped with lithium

    NASA Astrophysics Data System (ADS)

    Sivagamasundari, A.; Chandrasekar, S.; Pugaze, R.; Rajagopan, S.; Kannan, R.

    2014-03-01

    Thermal ionization induced metallic to semiconductor (MST) transition occurring at 460 K for Zn0.97Al0.03O, 463 K for Zn0.94Al0.03Li0.03O, and 503 K for Zn0.91Al0.03Li0.03Mn0.03O has been found in the sol-gel synthesized (using hexamethylenetetramine), trivalent doped (Al, Mn) ZnO codoped with lithium. Increase in the thermally ionized carrier concentration due to Al doping is responsible for near band edge (NBE) peak shift causing Fermi level to move into conduction band making it metallic consistent with resistivity results. Free carrier (thermally activated) neutralization with ionized donor is responsible for semiconducting nature, which is supported from the free carrier screening produced energy shift in the NBE of photoluminescence peak. Furthermore, independently band gap shrinkage is also obtained from UV-Visible studies confirming localization induced MST. An anti-correlation is found between defect density (DLE) and room temperature ferromagnetism (RTFM) indicating intrinsic defects are not directly responsible for RTFM.

  6. Synthesis aspects, structural, spectroscopic, antimicrobial and room temperature ferromagnetism of zinc iodide complex with Schiff based ligand

    NASA Astrophysics Data System (ADS)

    Shakila, K.; Kalainathan, S.

    2015-01-01

    In this paper, we report the successful growth of complex compound of zinc iodide with thiocarbamide by slow evaporation method. The single crystal XRD study reveals that the crystal belongs to monoclinic system with centrosymmetric space group and powder XRD analysis shows that the perfect crystalline nature of the crystal. The presence of functional group and element were confirmed from FT-IR and EDAX analysis. Optical absorbance of the grown crystal was studied by UV-Vis spectrophotometer. The optical constants were calculated from the optical absorbance data such as refractive index (n), extinction coefficient (K) and reflectance (R). The optical band gap (Eg) of thiocarbamide zinc iodide crystal is 4.22 eV. The magnetic properties of grown crystal have been determined by Vibrating Sample Magnetometry (VSM). Room temperature magnetization revealed a ferromagnetic behaviour for the grown crystal. The antibacterial and antifungal activities of the title compound were performed by well diffusion method and MIC method against the standard bacteria like Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia and against fungus like Aspergillus niger, Rhizopus sps and Penicillium sps. Thermal behaviour of the crystal has been investigated using thermogravimetric analysis (TGA) and differential thermal analysis (DTA).

  7. Room temperature ferromagnetism in Cr-doped In2O3 on high vacuum annealing of thin films and bulk samples

    NASA Astrophysics Data System (ADS)

    Kharel, P.; Sudakar, C.; Sahana, M. B.; Lawes, G.; Suryanarayanan, R.; Naik, R.; Naik, V. M.

    2007-05-01

    We report on the observation of room temperature ferromagnetism in Cr-doped In2O3 bulk samples and spin-coated thin films. The samples showed a clear ferromagnetism above 300K with magnetic moments of 0.008 and 0.22μB/Cr at 300K for the bulk and thin film, respectively, only after high vacuum (HV) annealing at 600°C. The vacuum annealed Cr-doped In2O3 thin films showed a typical semiconducting behavior with a room temperature resistivity of 0.73Ωcm, while bulk samples were more conducting (23mΩcm). We present systematic investigations on the influence of HV annealing on the carrier concentrations, resistivity, and magnetic properties of the samples.

  8. Origin of Room Temperature Ferromagnetism in Cr-Doped Lead-Free Ferroelectric Bi0.5Na0.5TiO3 Materials

    NASA Astrophysics Data System (ADS)

    Thanh, L. T. H.; Doan, N. B.; Dung, N. Q.; Cuong, L. V.; Bac, L. H.; Duc, N. A.; Bao, P. Q.; Dung, D. D.

    2017-01-01

    The development of multiferroic materials based on lead-free ferroelectric material provides an opportunity to fabricate next-generation electronic devices. In this work, Cr-doped lead-free ferroelectric Bi0.5Na0.5TiO3 materials were synthesized by using the sol-gel method. The optical band gap was reduced from 3.12 eV to 2.12 eV for undoped and 9 mol.% Cr-doped Bi0.5Na0.5TiO3 with the substitution of Cr at the Ti-site. Cr-doped Bi0.5Na0.5TiO3 materials exhibited weak ferromagnetism at room temperature. Saturation magnetization was approximately 0.08 μ B/Cr at 5 K. Our work will facilitate the further understanding of the role of transition metal ferromagnetism in lead-free ferroelectric materials at room temperature.

  9. Room temperature ferromagnetism in single-phase Zn1- x Mn x S diluted magnetic semiconductors fabricated by co-precipitation technique

    NASA Astrophysics Data System (ADS)

    Hassan, M.; Younas, S.; Sher, F.; Husain, S. S.; Riaz, S.; Naseem, S.

    2017-05-01

    In this study, we have prepared Mn-doped zinc sulfide diluted magnetic semiconductors with varying manganese concentrations ( x Mn = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10 mol%) using co-precipitation method. The single-phase nano-crystalline Zn1 - x Mn x S powders have been confirmed with X-ray diffraction. The residual strains also have been calculated, and have been observed to affect the lattice constants. The surface morphology is investigated with scanning electron microscopy, which illustrates the presence of smaller grains, which coalescence to form larger grains. The presence of the ferromagnetism at room temperature has been observed; however, significant paramagnetic contribution is also present. The observed weak ferromagnetism might be due to the structural and surface imperfections. The single-phase Zn1 - x Mn x S exhibiting magnetism at room temperature evidences the potential spintronic applications.

  10. A study on the origin of room temperature ferromagnetism in Ni1-xGdxO nanoparticles

    NASA Astrophysics Data System (ADS)

    Gokul, B.; Saravanan, P.; Vinod, V. T. P.; Černík, Miroslav; Sathyamoorthy, R.

    2015-11-01

    We herein report the existence of room temperature (RT) ferromagnetism (FM) in Gd-doped NiO nanoparticles prepared by hydrothermal process. The Gd-content in Ni1-xGdxO was varied from 0.01 to 0.1 and the resultant structural and magnetic properties due to Gd-doping were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), micro- Raman spectroscopy and vibrating sample magnetometer (VSM). The composition analysis and charge state were obtained from energy dispersive x-ray spectroscopy (EDS) and x-ray photoelectron spectroscopy (XPS), respectively. Both pure and Gd-doped NiO nanoparticles retained face centered cubic crystal structure. Formation of any secondary phases or metallic clusters related to pure Gd or Ni is not evident in the as-synthesized samples. TEM analysis revealed that the particles are spherical with sizes in the range of 8-18 nm. Micro-Raman spectra showed increase in Ni-vacancies with increase of Gd-concentration. XPS spectra of Gd-doped NiO revealed a shift in binding energy compared to the pure NiO, implies the replacement of Gd atoms in Ni-vacancies. Interesting RT-FM behavior is observed for the Gd concentrations of 7 and 10%; while the pure NiO and the other lower concentrations of Gd-doping demonstrated paramagnetic nature. The observed RT-FM can be attributed to the Ni vacancies induced by the doping of Gd3+ ions and this fact is explained on the basis of bound magnetic polaron model.

  11. Room temperature ferromagnetism in conducting α-(In{sub 1−x}Fe{sub x}){sub 2}O{sub 3} alloy films

    SciTech Connect

    Akaiwa, K.; Kaneko, K.; Fujita, S.; Chikoidze, E.; Dumont, Y.

    2015-02-09

    We have studied electronic transport and magnetic properties of α-(In{sub 1−x}Fe{sub x}){sub 2}O{sub 3} alloy films. Temperature dependence of resistivity of the films showed semiconducting behavior of conductivity. Room temperature ferromagnetism was observed. Relatively high coercive fields indicated that observed ferromagnetism in α-(In{sub 1−x}Fe{sub x}){sub 2}O{sub 3} films were not arisen from magnetic metallic iron nano-precipitates. Remanence measurement revealed the Curie temperature of 520 K and 620 K for α-(In{sub 0.52}Fe{sub 0.48}){sub 2}O{sub 3} and α-(In{sub 0.23}Fe{sub 0.77}){sub 2}O{sub 3} films, corresponding to a weakening of superexchange interactions in these alloys (with less magnetic iron cations) with respect to canted antiferromagnet α-Fe{sub 2}O{sub 3}. Nevertheless, Curie temperatures remain much higher than 300 K, and semiconducting behavior with low activation energy in resistivity for middle composition alloy, exhibiting combined multi-functionality of room ferromagnetism and semiconducting properties, in corundum alloys such as α-(Ga{sub 1−x}Fe{sub x}){sub 2}O{sub 3} or α-Fe{sub 2−x}Ti{sub x}O{sub 3}.

  12. Electronic coupling between sulfur adsorption and oxygen vacancy in TiO2 microstructures for room-temperature ferromagnetism

    NASA Astrophysics Data System (ADS)

    Wu, S. Y.; Ren, X. M.; Zhang, J. L.; Wu, X. L.; Liu, L. Z.

    2017-09-01

    The spin electronic states coupling associated with enhanced photocatalytic activity of TiO2 microstructures annealed in Ar and O2 are designed to explore its ferromagnetism. The samples annealed in Ar show 0.023 emu g-1 magnetic moments related to adsorbed S atom concentration, which is seven times larger than that of samples annealed in O2. Finally, their saturated magnetization decreases sharply as increasing annealing temperature. Spectral analysis and density function theory calculation disclose that the ferromagnetism originates from spin electronic state coupling between adsorbed S atoms and oxygen vacancies as well as magnetic moments disappearing arises from the changes of adsorbed S atom and O vacancy distribution as annealing temperature.

  13. Observation of room temperature ferromagnetic behavior in cluster-free, Co doped HfO2 films

    NASA Astrophysics Data System (ADS)

    Chang, Y. H.; Soo, Y. L.; Lee, W. C.; Huang, M. L.; Lee, Y. J.; Weng, S. C.; Sun, W. H.; Hong, M.; Kwo, J.; Lee, S. F.; Ablett, J. M.; Kao, C.-C.

    2007-08-01

    Extensive structural and magnetic analyses of Hf1-xCoxO2 thin films grown by molecular beam epitaxy are reported. Nearly cobalt cluster-free film with x =0.04-0.1 was obtained via 100°C growth, and Co ions are inferred to be located at interstitial site. Ferromagnetic behavior was observed up to 300K in both magnetization curves and temperature dependence of the moment. Via post-oxygen-annealing studies, a qualitative correlation between saturation magnetization and oxygen vacancy concentration is established, consistent with the impurity-band exchange model, and that the occurrence of ferromagnetic insulator behavior in the Co doped HfO2 is more probable than Co doped ZnO, TiO2, and SnO2 systems for doping concentrations under cation percolation threshold.

  14. Room-temperature extraction of spin lifetimes in metallic thin films via determination of the spin-pumping contribution to damping in ferromagnetic resonance experiments

    NASA Astrophysics Data System (ADS)

    Boone, Carl; Schoen, Martin; Shaw, Justin; Nembach, Hans; Silva, Thomas

    2014-03-01

    Recent room-temperature measurements yield spin diffusion lengths for Pt and Pd that are smaller than the bulk electron mean free path at room temperature. One proposed explanation is the thickness-dependence of conductivity that results in shorter momentum lifetimes at small Pt/Pd thicknesses. We measured spin transport properties in Pd and Pt thin films at room temperature via fitting of ferromagnetic resonance (FMR) damping vs. NM thickness with the spin pumping model for ferromagnet (FM)/normal metal (NM) multilayers. We use a broadband, perpendicular FMR system to obtain high-precision values for the damping. The fits are based upon spin diffusion equations that include both momentum and spin scattering processes. By measuring thickness-dependent conductivity of the same films, we correlate the charge and spin transport parameters, permitting us to test multiple models for spin scattering. We explicitly show that the spin scattering time τsf must be shorter than the momentum scattering time tau over some range of NM thicknesses to adequately fit the data. Invocation of a simple monotonic proportionality between τsf and τ fails to fit the data. However, an inverse proportionality τ ~ 1 /τsf can fit the data, and τ <τsf for sufficiently thin NM layer.

  15. Room-temperature ferromagnetism and optical properties in Mg-doped TiO{sub 2}: A density functional theory investigation

    SciTech Connect

    Liu, Yanyu; Zhou, Wei; Wu, Ping

    2014-03-28

    The magnetic and optical properties of Mg-doped anatase TiO{sub 2} have been theoretically investigated using the LDA+U method. The total induced moments are about 2 μ{sub B}, which mainly localize on the nearest apical oxygen atoms. Moreover, the hole-induced interactions indicate that the magnetic moments prefer to the ferromagnetic coupling with the antiferromagnetic state lying 1160 meV higher in energy. This implies that the ferromagnetic state can be stable against thermal fluctuations up to room temperature. Additionally, the Mg doping is able to enhance the absorption efficiency of solar spectrum, especially in the near-infrared light region, which origins from the isolated O 2p states above the valence-band maximum rather than the effect of band-gap narrowing.

  16. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Room-Temperature Anisotropic Ferromagnetism in Fe-Doped In2O3 Heteroepitaxial Films

    NASA Astrophysics Data System (ADS)

    Xing, Peng-Fei; Chen, Yan-Xue; Tang, Min-Jian; Yan, Shi-Shen; Liu, Guo-Lei; Mei, Liang-Mo; Jiao, Jun

    2009-11-01

    Fe-doped In2O3 films are grown epitaxially on YSZ (100) substrates by pulsed laser deposition. The in-situ reflection high-energy electron diffraction, the atomic force microscopy, and the x-ray diffraction patterns show that the films have a well defined cubic structure epitaxially oriented in the (100) direction. Room temperature ferromagnetism is observed by an alternating gradient magnetometer. Strong perpendicular magnetic anisotropy with a remnant magnetization ratio of 0.83 and a coercivity of 2.5kOe is revealed. Both the structural and the magnetic measurements suggest that this ferromagnetism is an intrinsic property deriving from the spin-orbit coupling between the diluted Fe atoms.

  17. Room-Temperature Ferromagnetism of Cu-Doped ZnO Films Probed by Soft X-Ray Magnetic Circular Dichroism

    SciTech Connect

    Herng, T.S.; Ku, W.; Qi, D.-C.; Berlijn, T.; Yi, J.B.; Yang, K.S.; Dai, Y.; Feng, Y.P.; Santoso, I.; Sanchez-Hanke, C.; Gao, X.Y.; Wee, A.T.S.; Ding, J.; Rusydi, A.

    2010-11-08

    We report direct evidence of room-temperature ferromagnetic ordering in O-deficient ZnO:Cu films by using soft x-ray magnetic circular dichroism and x-ray absorption. Our measurements have revealed unambiguously two distinct features of Cu atoms associated with (i) magnetically ordered Cu ions present only in the oxygen-deficient samples and (ii) magnetically disordered regular Cu{sup 2+} ions present in all the samples. We find that a sufficient amount of both oxygen vacancies (V{sub O}) and Cu impurities is essential to the observed ferromagnetism, and a non-negligible portion of Cu impurities is uninvolved in the magnetic order. Based on first-principles calculations, we propose a microscopic 'indirect double-exchange' model, in which alignments of localized large moments of Cu in the vicinity of the V{sub O} are mediated by the large-sized vacancy orbitals.

  18. Driving Curie temperature towards room temperature in the half-metallic ferromagnet K2Cr8O16 by soft redox chemistry.

    PubMed

    Pirrotta, I; Fernández-Sanjulián, J; Moran, E; Alario-Franco, M A; Gonzalo, E; Kuhn, A; García-Alvarado, F

    2012-02-14

    The half-metallic ferromagnet K(2)Cr(8)O(16) with the hollandite structure has been chemically modified using soft chemistry methods to increase the average oxidation state of chromium. The synthesis of the parent material has been performed under high pressure/high temperature conditions. Following this, different redox reactions have been carried out on K(2)Cr(8)O(16). Oxidation to obtain potassium-de-inserted derivatives, K(2-x)Cr(8)O(16) (0 ≤x≤ 1), has been investigated with electrochemical methods, while the synthesis of sizeable amounts was achieved chemically by using nitrosonium tetrafluoroborate as a highly oxidizing agent. The maximum amount of extracted K ions corresponds to x = 0.8. Upon oxidation the hollandite structure is maintained and the products keep high crystallinity. The de-insertion of potassium changes the Cr(3+)/Cr(4+) ratio, and therefore the magnetic properties. Interestingly, the Curie temperature increases from ca. 175 K to 250 K, getting therefore closer to room temperature.

  19. Free-standing and single-crystalline Fe(1-x)Mn(x)Si nanowires with room-temperature ferromagnetism and excellent magnetic response.

    PubMed

    Hung, Min-Hsiu; Wang, Chiu-Yen; Tang, Jianshi; Lin, Ching-Chun; Hou, Te-Chien; Jiang, Xiaowei; Wang, Kang L; Chen, Lih-Juann

    2012-06-26

    High-aspect-ratio Fe(1-x)Mn(x)Si nanowires with room-temperature ferromagnetism were synthesized by a chemical vapor deposition (CVD) method in one step. This is the first report of ternary silicide nanowires using magnetic Mn ions to partially replace metal sites in the host matrix. Here we report the excellent magnetic characteristics of Fe(1-x)Mn(x)Si nanowires, which exhibit strong ferromagnetism at room temperature and high magnetoresistance (MR) variation. As-synthesized Fe(1-x)Mn(x)Si nanowires show a hyperbranched morphology and a spin-disorder behavior. The strong spin interaction in Fe(1-x)Mn(x)Si nanowires, induced by the substitution of Fe sublattices for magnetic Mn ions, was revealed in the hysteresis loops. The magnetization versus magnetic field (M-H) curves of Fe(1-x)Mn(x)Si nanowires are much less sensitive to the temperature variation from 10 to 300 K than those of FeSi nanowires. Remarkably, the excellent MR performance, -41.6% at 25 K with a magnetic field of 9 T, was demonstrated in an individual Fe(0.88)Mn(0.12)Si nanowire.

  20. Observation of strong magnetoelectric coupling and ferromagnetism at room temperature in Fe substituted ferroelectric BaZr0.05Ti0.95O3 thin films

    NASA Astrophysics Data System (ADS)

    Kumari, Mukesh; Barrionuevo Diestra, Danilo G.; Katiyar, Ram; Shah, Jyoti; Kotnala, R. K.; Chatterjee, Ratnamala

    2017-01-01

    Single phase polycrystalline thin films (˜100 nm) of BaZr0.05(FexTi1-3x/4)0.95O3, with x = 0 (BZT) and 0.015 (BZFT15), were grown on Pt/TiO2/SiO2/Si substrate using pulsed laser deposition technique. Room temperature ferromagnetism with a remanent magnetization (Mr) ˜ 1.1 × 10-1 emu/cm3 and a coercive field (Hc) ˜ 0.1 kOe was observed in BZFT15 film. The ferroelectric domain switching in both BZT and BZFT15 films is confirmed by piezoresponse force microscopy (PFM). The magnetoelectric coupling coefficient (α) measured at room temperature in the BZFT15 film in in-plane magnetized-out of plane polarized configuration (L-T mode) was found to be ˜165 mV/cm Oe. It is argued that the observed ferromagnetism in BZFT15 films arises from the oxygen vacancy (Ov) mediated (Fe3+-Ov-Fe3+) exchange.

  1. Room-temperature ferromagnetism of 2H-SiC-α-Al2O3 solid solution nanowires and the physical origin.

    PubMed

    Sun, Yong; Lu, Cheng; Cui, Hao; Wang, Jing; Ma, Yanming; Wang, Chengxin

    2015-03-21

    In this work we report the first synthesis of 2H-SiC-α-Al2O3 solid solution (SS) nanowires with 2H-SiC as the host phase. The one dimensional (1D) fake binary-system exhibits interesting room-temperature ferromagnetism and spin-glass-like (SGL) behavior. This novel diluted magnetic semiconductor (DMS) was designed on the basis of SiC which is the most promising fundamental semiconductor used in next-generation electronics as the substitute for Si. A systematic investigation of the magnetic properties reveals the origin of the material's room-temperature ferromagnetism and spin-glass behavior. Spin-polarized density functional theory (DFT) calculations reveal that the net moment originates from a strong coupling between atoms around local Si vacancies produced by the SS defect reaction. Unlike random defects derived magnetic behavior, the SS resulted magnetism is significant to be utilized in functional devices since it belongs to a stable crystal structure that is possible to be prepared rationally in a controlled manner.

  2. Room-temperature ferromagnetism in Zn{sub 1-x}Co{sub x}O magnetic semiconductors prepared by sputtering

    SciTech Connect

    Dinia, A.; Schmerber, G.; Meny, C.; Pierron-Bohnes, V.; Beaurepaire, E.

    2005-06-15

    We have used magnetron cosputtering to grow Zn{sub 1-x}Co{sub x}O magnetic dilute semiconductors. The growth has been performed on SiO{sub 2}/Si and Al{sub 2}O{sub 3}(0001) substrates. The Co concentration has been varied between 0.1 and 0.25 and the substrate temperature between room temperature and 600 deg. C. X-ray diffraction analysis has shown that for the films grown on Si substrates the structural quality of the film is improved by increasing the growth temperature and/or postgrowth annealing. The films are textured with c axis of the wurtzite structure along the growth direction. However, for the films grown on Al{sub 2}O{sub 3} substrate quasi-epitaxial films have been obtained for 600 deg. C substrate temperature. Magnetization measurements have shown that the ferromagnetism is directly correlated to the structural quality and appears by increasing the growth temperature and/or postgrowth annealing. Moreover, for the highly textured film a clear magnetic perpendicular anisotropy has been evidenced with the easy magnetization axis along the growth direction. To evidence the intrinsic nature of the ferromagnetism in the films, transmission optical measurements have been used. They show three absorption bands that are characteristics of d-d transitions of tetrahedrally coordinated Co{sup 2+}. This has been supported by nuclear magnetic resonance and magnetic thermal variation.

  3. Ferromagnetism at room temperature of c- and m-plane GaN : Gd films grown on different substrates by reactive molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Ranchal, R.; Yadav, B. S.; Trampert, A.

    2013-02-01

    We report the magnetic properties of c- and m-plane GaN : Gd films grown on different substrate materials. Additionally, we have investigated the magnetic behaviour of the bare substrates in order to analyse their possible contribution on the properties of this material system. For the growth of c-phase GaN : Gd we have used 6H-SiC(0 0 0 1) and GaN/Al2O3 templates. Whereas templates only exhibit a diamagnetic behaviour, the SiC substrates show clear signatures of ferromagnetism at room temperature. Rutherford backscattering spectroscopy and secondary ions mass spectrometry have revealed traces of Fe in the SiC substrates. This Fe contamination seems to be related to the ferromagnetic ordering observed in these substrates. LiAlO2(0 0 1) is a good choice for growth of m-plane diluted nitrides due to its diamagnetic behaviour. The hysteresis loops of c- and m-phase GaN : Gd deposited on template and LiAlO2, respectively, show coercivity and magnetic saturation. These characteristics together with the magnetization curves are indications of an intrinsic ferromagnetic behaviour in the GaN : Gd.

  4. Magnetic properties of nitrogen-doped ZrO2: Theoretical evidence of absence of room temperature ferromagnetism

    NASA Astrophysics Data System (ADS)

    Albanese, Elisa; Leccese, Mirko; di Valentin, Cristiana; Pacchioni, Gianfranco

    2016-08-01

    N-dopants in bulk monoclinic ZrO2 and their magnetic interactions have been investigated by DFT calculations, using the B3LYP hybrid functional. The electronic and magnetic properties of the paramagnetic N species, substitutionals and interstitials, are discussed. Their thermodynamic stability has been estimated as a function of the oxygen partial pressure. At 300 K, N prefers interstitial sites at any range of oxygen pressure, while at higher temperatures (700–1000 K), oxygen poor-conditions facilitate substitutional dopants. We have considered the interaction of two N defects in various positions in order to investigate the possible occurrence of ferromagnetic ordering. A very small magnetic coupling constant has been calculated for several 2N-ZrO2 configurations, thus demonstrating that magnetic ordering can be achieved only at very low temperatures, well below liquid nitrogen. Furthermore, when N atoms replace O at different sites, resulting in slightly different positions of the corresponding N 2p levels, a direct charge transfer can occur between the two dopants with consequent quenching of the magnetic moment. Another mechanism that contributes to the quenching of the N magnetic moments is the interplay with oxygen vacancies. These effects contribute to reduce the concentration of magnetic impurities, thus limiting the possibility to establish magnetic ordering.

  5. Magnetic properties of nitrogen-doped ZrO2: Theoretical evidence of absence of room temperature ferromagnetism

    PubMed Central

    Albanese, Elisa; Leccese, Mirko; Di Valentin, Cristiana; Pacchioni, Gianfranco

    2016-01-01

    N-dopants in bulk monoclinic ZrO2 and their magnetic interactions have been investigated by DFT calculations, using the B3LYP hybrid functional. The electronic and magnetic properties of the paramagnetic N species, substitutionals and interstitials, are discussed. Their thermodynamic stability has been estimated as a function of the oxygen partial pressure. At 300 K, N prefers interstitial sites at any range of oxygen pressure, while at higher temperatures (700–1000 K), oxygen poor-conditions facilitate substitutional dopants. We have considered the interaction of two N defects in various positions in order to investigate the possible occurrence of ferromagnetic ordering. A very small magnetic coupling constant has been calculated for several 2N-ZrO2 configurations, thus demonstrating that magnetic ordering can be achieved only at very low temperatures, well below liquid nitrogen. Furthermore, when N atoms replace O at different sites, resulting in slightly different positions of the corresponding N 2p levels, a direct charge transfer can occur between the two dopants with consequent quenching of the magnetic moment. Another mechanism that contributes to the quenching of the N magnetic moments is the interplay with oxygen vacancies. These effects contribute to reduce the concentration of magnetic impurities, thus limiting the possibility to establish magnetic ordering. PMID:27527493

  6. Band-edge exciton transitions in (Ga 1- xMn x)N diluted magnetic semiconductor films with above room temperature ferromagnetic transition

    NASA Astrophysics Data System (ADS)

    Jeon, H. C.; Kang, T. W.; Kim, T. W.; Cho, Y. H.

    2006-06-01

    (Ga 1- xMn x)N thin films grown on GaN buffer layers by using molecular beam epitaxy were investigated with the goal of producing diluted magnetic semiconductors (DMSs) with band-edge exciton transitions for applications in optomagnetic devices. The magnetization curve as a function of the magnetic field at 5 K indicated that ferromagnetism existed in the (Ga 1- xMn x)N thin films, and the magnetization curve as a function of the temperature showed that the ferromagnetic transition temperature of the (Ga 1- xMn x)N thin film was above room temperature. Photoluminescence and photoluminescence excitation spectra showed that band-edge exciton transitions in (Ga 1- xMn x)N thin films appeared. These results indicate that the (Ga 1- xMn x)N DMSs with a magnetic single phase hold promise for potential applications in spin optoelectronic devices in the blue region of the spectrum.

  7. Enhanced room temperature ferromagnetism in electrodeposited Co-doped ZnO nanostructured thin films by controlling the oxygen vacancy defects

    SciTech Connect

    Simimol, A.; Anappara, Aji A.; Greulich-Weber, S.; Chowdhury, Prasanta; Barshilia, Harish C.

    2015-06-07

    We report the growth of un-doped and cobalt doped ZnO nanostructures fabricated on FTO coated glass substrates using electrodeposition method. A detailed study on the effects of dopant concentration on morphology, structural, optical, and magnetic properties of the ZnO nanostructures has been carried out systematically by varying the Co concentration (c.{sub Co}) from 0.01 to 1 mM. For c.{sub Co }≤ 0.2 mM, h-wurtzite phase with no secondary phases of Co were present in the ZnO nanostructures. For c.{sub Co} ≤ 0.2 mM, the photoluminescence spectra exhibited a decrease in the intensity of ultraviolet emission as well as band-gap narrowing with an increase in dopant concentration. All the doped samples displayed a broad emission in the visible range and its intensity increased with an increase in Co concentration. It was found that the defect centers such as oxygen vacancies and zinc interstitials were the source of the visible emission. The X-ray photoelectron spectroscopy studies revealed, Co was primarily in the divalent state, replacing the Zn ion inside the tetrahedral crystal site of ZnO without forming any cluster or secondary phases of Co. The un-doped ZnO nanorods exhibited diamagnetic behavior and it remained up to a c.{sub Co} of 0.05 mM, while for c.{sub Co }> 0.05 mM, the ZnO nanostructures exhibited ferromagnetic behavior at room temperature. The coercivity increased to 695 G for 0.2 mM Co-doped sample and then it decreased for c.{sub Co }> 0.2 mM. Our results illustrate that up to a threshold concentration of 0.2 mM, the strong ferromagnetism is due to the oxygen vacancy defects centers, which exist in the Co-doped ZnO nanostructures. The origin of strong ferromagnetism at room temperature in Co-doped ZnO nanostructures is attributed to the s-d exchange interaction between the localized spin moments resulting from the oxygen vacancies and d electrons of Co{sup 2+} ions. Our findings provide a new insight for tuning the

  8. Oxygen vacancy enhanced the room temperature ferromagnetism in Ni-doped TiO2 thin films

    NASA Astrophysics Data System (ADS)

    Hou, D. L.; Meng, H. J.; Jia, L. Y.; Ye, X. J.; Zhou, H. J.; Li, X. L.

    2007-04-01

    Ni-doped TiO2 anatase thin films were fabricated by reactive magnetron sputtering on SiO2 substrates. The doping and annealing effects on structure and magnetism for the films have been systematically investigated. The results show that ferromagnetism originated from the doped matrix and enhancement (suppression) of ferromagnetism is strongly correlated with the increase (decrease) of oxygen vacancies in TiO2.

  9. Investigation of room temperature ferromagnetic nanoparticles of Gd5Si4

    SciTech Connect

    Hadimani, R. L.; Gupta, S.; Harstad, S. M.; Pecharsky, V. K.; Jiles, D. C.

    2015-07-06

    Gd5(SixGe1-x)4 compounds undergo first-order phase transitions close to room temperature when x ~ = 0.5, which are accompanied by extreme changes of properties. We report the fabrication of the nanoparticles of one of the parent compounds-Gd5Si4-using high-energy ball milling. Crystal structure, microstructure, and magnetic properties have been investigated. Particles agglomerate at long milling times, and the particles that are milled >20 min lose crystallinity and no longer undergo magnetic phase transition close to 340 K, which is present in a bulk material. The samples milled for >20 min exhibit a slightly increased coercivity. As a result, magnetization at a high temperature of 275K decreases with the increase in the milling time.

  10. Microstructures and room temperature ferromagnetism of ordered porous ZrO2 thin films sputter deposited onto porous anodic alumina substrates

    NASA Astrophysics Data System (ADS)

    Han, Ru-shuai; Qi, Li-qian; Liu, Li-hu; Xu, Qin; Guo, Ge-Xin; Sun, Hui-yuan

    2017-04-01

    Ordered porous ZrO2 films with pore diameters in the 5-45 nm range have been prepared on porous anodic alumina substrates using DC-reactive magnetron sputtering of pure Zr targets. A saturation magnetization (MS) value as high as 119 emu/cm3 was obtained for the ZrO2 film with pores of 45 nm in diameter when the external field was perpendicular to the film surface. The significant out-of-plane saturation magnetization is associated with the porous structure of the film. Experimental and theoretical results showed that the origin of the room temperature ferromagnetism (RTFM) is closely related to the ordered porous structure and the single charged oxygen vacancies of the films. These findings suggest that porous ZrO2 films are promising to be applied to the spin electronic devices.

  11. Room-temperature ferromagnetism in thin films of LaMnO3 deposited by a chemical method over large areas.

    PubMed

    Vila-Fungueiriño, José Manuel; Rivas-Murias, Beatriz; Rodríguez-González, Benito; Txoperena, O; Ciudad, D; Hueso, Luis E; Lazzari, Massimo; Rivadulla, Francisco

    2015-03-11

    Hole-doping into the Mott insulator LaMnO3 results in a very rich magneto-electric phase diagram, including colossal magnetoresistance and different types of charge and orbital ordering. On the other hand, LaMnO3 presents an important catalytic activity for oxygen reduction, which is fundamental for increasing the efficiency of solid-oxide fuel cells and other energy-conversion devices. In this work, we report the chemical solution (water-based) synthesis of high-quality epitaxial thin films of LaMnO3, free of defects at square-centimeter scales, and compatible with standard microfabrication techniques. The films show a robust ferromagnetic moment and large magnetoresistance at room temperature. Through a comparison with films grown by pulsed laser deposition, we show that the quasi-equilibrium growth conditions characteristic of this chemical process can be exploited to tune new functionalities of the material.

  12. X-ray spectroscopic study of the charge state and local orderingof room-temperature ferromagnetic Mn oped ZnO

    SciTech Connect

    Guo, J.-H.; Gupta, Amita; Sharma, Parmanand; Rao, K.V.; Marcus,M.A.; Dong, C.L.; Guillen, J.M.O.; Butorin, S.M.; Mattesini, M.; Glans,P.A.; Smith, K.E.; Chang, C.L.; Ahuja, R.

    2007-08-07

    The charge state and local ordering of Mn doped into a pulsed laser deposited single-phase thin film of ZnO are investigated by using X-ray absorption spectroscopy at the O K-, Mn K- and L-edges, and X-ray emission spectroscopy at the O K- and Mn L-edge. This film is found to be ferromagnetic at room temperature. EXAFS measurement shows that Mn{sup 2+} replaces Zn site in tetrahedral symmetry, and there is no evidence for either metallic Mn or MnO in the film. Upon Mn doping, the top of O 2p valence band extends into the bandgap indicating additional charge carries being created.

  13. Visible photoluminescence and room temperature ferromagnetism in high In-content InGaN:Yb nanorods grown by molecular beam epitaxy

    SciTech Connect

    Dasari, K.; Palai, R.; Wang, J.; Jadwisienczak, W. M.; Guinel, M. J.-F.; Huhtinen, H.; Mundle, R.; Pradhan, A. K.

    2015-09-28

    We report the growth of high indium content InGaN:Yb nanorods grown on c-plane sapphire (0001) substrates using plasma assisted molecular beam epitaxy. The in situ reflection high energy electron diffraction patterns recorded during and after the growth revealed crystalline nature of the nanorods. The nanorods were examined using electron microscopy and atomic force microscopy. The photoluminescence studies of the nanorods showed the visible emissions. The In composition was calculated from x-ray diffraction, x-ray photoelectron spectroscopy, and the photoluminescence spectroscopy. The In-concentration was obtained from photoluminescence using modified Vegard's law and found to be around 37% for InGaN and 38% for Yb (5 ± 1%)-doped InGaN with a bowing parameter b = 1.01 eV. The Yb-doped InGaN showed significant enhancement in photoluminescence properties compared to the undoped InGaN. The Yb-doped InGaN nanorods demonstrated the shifting of the photoluminescence band at room temperature, reducing luminescence amplitude temperature dependent fluctuation, and significant narrowing of excitonic emission band as compared to the undoped InGaN. The magnetic properties measured by superconducting quantum interference devices reveals room temperature ferromagnetism, which can be explained by the double exchange mechanism and magnetostriction.

  14. Effect of Ar ion irradiation on the room temperature ferromagnetism of undoped and Cu-doped rutile TiO2 single crystals

    NASA Astrophysics Data System (ADS)

    Xu, Nan-Nan; Li, Gong-Ping; Lin, Qiao-Lu; Liu, Huan; Bao, Liang-Man

    2016-11-01

    Remarkable room-temperature ferromagnetism was observed both in undoped and Cu-doped rutile TiO2 single crystals (SCs). To tune their magnetism, Ar ion irradiation was quantitatively performed on the two crystals in which the saturation magnetizations for the samples were enhanced distinctively. The post-irradiation led to a spongelike layer in the near surface of the Cu-doped TiO2. Meanwhile, a new CuO-like species present in the sample was found to be dissolved after the post-irradiation. Analyzing the magnetization data unambiguously reveals that the experimentally observed ferromagnetism is related to the intrinsic defects rather than the exotic Cu ions, while these ions are directly involved in boosting the absorption in the visible region. Project supported by the National Natural Science Foundation of China (Grant No. 11575074), the Open Project of State Key laboratory of Crystal Material, Shandong University, China (Grant No. KF1311), the Open Project of Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, China (Grant No. LZUMMM2012003), the Open Project of Key Laboratory of Beam Technology and Material Modification of Ministry of Education, Beijing Normal University, China (Grant No. 201204), and the Fundamental Research Funds for the Central Universities, China (Grant No. lzujbky-2015-240).

  15. Comments on "Synthesis aspects, structural, spectroscopic, antimicrobial and room temperature ferromagnetism of zinc iodide complex with Schiff based ligand" by K. Shakila and S. Kalainathan, Spectrochim. Acta 135 A (2015) 1059-1065

    NASA Astrophysics Data System (ADS)

    Srinivasan, Bikshandarkoil R.; Nadkarni, V. S.

    2016-06-01

    Shakila and Kalainathan report on the synthetic and structural aspects of a zinc iodide complex with Schiff based ligand, which exhibits room temperature ferromagnetism. In this comment, many points of criticism, concerning the characterization of this so called zinc iodide complex of Schiff based ligand are highlighted to prove that the title paper is completely erroneous.

  16. ScRe 2O 6: A new ternary oxide with metallic Re-Re-bonds and a ferromagnetic component above room temperature

    NASA Astrophysics Data System (ADS)

    Mikhailova, D.; Ehrenberg, H.; Miehe, G.; Trots, D.; Hess, C.; Schneider, R.; Fuess, H.

    2008-01-01

    AbstactA new phase in the system Sc-Re-O, ScRe 2O 6, was synthesized for the first time in sealed silica tubes and its crystal structure was solved by single crystal X-ray diffraction. ScRe 2O 6 (space group P2 1/ a, a=5.6176(9) Å, b=4.7970(9) Å, c=7.5143(16) Å, β=97.49(2)°, Z=2) crystallizes in a new rutile-type structure, derived from three formula units by splitting the cation site in ratio 1:2. Re 2O 10 clusters can be considered as structural units, in which the rhenium ions form pairs by metallic bonds with a Re-Re distance of 2.523(3) Å. No phase transition was observed in the temperature range of 295-930 K. The compound has a metallic character of conductivity in the temperature range of at least 4-950 K and displays a ferromagnetic ordering above room temperature ("unconventional Re-magnetism").

  17. Influence of interstitial Mn on magnetism in the room-temperature ferromagnet Mn1+δSb

    DOE PAGES

    Taylor, Alice E.; Berlijn, Tom; Hahn, Steven E.; ...

    2015-06-15

    We repormore » t elastic and inelastic neutron scattering measurements of the high-TC ferromagnet Mn1+δSb. Measurements were performed on a large, TC = 434 K, single crystal with interstitial Mn content of δ ≈ 0.13. The neutron diffraction results reveal that the interstitial Mn has a magnetic moment, and that it is aligned antiparallel to the main Mn moment. We perform density functional theory calculations including the interstitial Mn, and find the interstitial to be magnetic in agreement with the diffraction data. The inelastic neutron scattering measurements reveal two features in the magnetic dynamics: i) a spin-wave-like dispersion emanating from ferromagnetic Bragg positions (H K 2n), and ii) a broad, non-dispersive signal centered at forbidden Bragg positions (H K 2n+1). The inelastic spectrum cannot be modeled by simple linear spin-wave theory calculations, and appears to be significantly altered by the presence of the interstitial Mn ions. Finally, the results show that the influence of the interstitial Mn on the magnetic state in this system is more important than previously understood.« less

  18. Oxygen vacancy induced phase formation and room temperature ferromagnetism in undoped and Co-doped TiO2 thin films

    NASA Astrophysics Data System (ADS)

    Mohanty, P.; Mishra, N. C.; Choudhary, R. J.; Banerjee, A.; Shripathi, T.; Lalla, N. P.; Annapoorni, S.; Rath, Chandana

    2012-08-01

    TiO2 and Co-doped TiO2 (CTO) thin films deposited at various oxygen partial pressures by pulsed laser deposition exhibit room temperature ferromagnetism (RTFM) independent of their phase. Films deposited at 0.1 mTorr oxygen partial pressure show a complete rutile phase confirmed from glancing angle x-ray diffraction and Raman spectroscopy. At the highest oxygen partial pressure, i.e. 300 mTorr, although the TiO2 film shows a complete anatase phase, a small peak corresponding to the rutile phase along with the anatase phase is identified in the case of CTO film. An increase in O to Ti/(Ti+Co) ratio with increase in oxygen partial pressure is observed from Rutherford backscattering spectroscopy. It is revealed from x-ray photoelectron spectroscopy (XPS) that oxygen vacancies are found to be higher in the CTO film than TiO2, while the valency of cobalt remains in the +2 state. Therefore, the CTO film deposited at 300 mTorr does not show a complete anatase phase unlike the TiO2 film deposited at the same partial pressure. We conclude that RTFM in both films is not due to impurities/contaminants, as confirmed from XPS depth profiling and cross-sectional transmission electron microscopy (TEM), but due to oxygen vacancies. The magnitude of moment, however, depends not only on the phase of TiO2 but also on the crystallinity of the films.

  19. Achieving High-Temperature Ferromagnetic Topological Insulator

    NASA Astrophysics Data System (ADS)

    Katmis, Ferhat

    Topological insulators (TIs) are insulating materials that display conducting surface states protected by time-reversal symmetry, wherein electron spins are locked to their momentum. This unique property opens new opportunities for creating next-generation electronic and spintronic devices, including TI-based quantum computation. Introducing ferromagnetic order into a TI system without compromising its distinctive quantum coherent features could lead to a realization of several predicted novel physical phenomena. In particular, achieving robust long-range magnetic order at the TI surface at specific locations without introducing spin scattering centers could open up new possibilities for devices. Here, we demonstrate topologically enhanced interface magnetism by coupling a ferromagnetic insulator (FMI) to a TI (Bi2Se3); this interfacial ferromagnetism persists up to room temperature, even though the FMI (EuS) is known to order ferromagnetically only at low temperatures (<17 K). The induced magnetism at the interface resulting from the large spin-orbit interaction and spin-momentum locking feature of the TI surface is found to greatly enhance the magnetic ordering (Curie) temperature of the TI/FMI bilayer system. Due to the short range nature of the ferromagnetic exchange interaction, the time-reversal symmetry is broken only near the surface of a TI, while leaving its bulk states unaffected. The topological magneto-electric response originating in such an engineered TI could allow for an efficient manipulation of the magnetization dynamics by an electric field, providing an energy efficient topological control mechanism for future spin-based technologies. Work supported by MIT MRSEC through the MRSEC Program of NSF under award number DMR-0819762, NSF Grant DMR-1207469, the ONR Grant N00014-13-1-0301, and the STC Center for Integrated Quantum Materials under NSF grant DMR-1231319.

  20. Room temperature ferromagnetic properties of epitaxial (111) Y0.225Sr0.775CoO3-δ thin film grown on single crystalline (111) MgO substrate

    NASA Astrophysics Data System (ADS)

    Seo, Jeongdae; Ahn, Yoonho; Yeog Son, Jong

    2015-08-01

    Epitaxial (111) Y0.225Sr0.775CoO3-δ (YSCO) thin films were deposited on single crystalline (111) MgO substrates by a pulsed laser deposition method. The YSCO thin film exhibited room temperature ferromagnetism with a remanent magnetization of 1.5×10-5 emu. The magnetic force microscopy (MFM) study revealed that the YSCO thin film had a mosaic MFM domain structure. The comparison of domain wall energy for the YSCO and PZT indicates that the large domain wall energy induce the large domain size, though the large magnetization value reduce the magnetic domain size in the case of Co. According to the optical conductivity analysis by spectroscopic ellipsometry, it is inferred that the transition from the intermediate spin state to the high spin state of the YSCO thin film is attributed to the ferromagnetism of the Co4+ ion.

  1. Systematic study of room-temperature ferromagnetism and the optical response of Zn1-x TM x S/Se (TM  =  Mn, Fe, Co, Ni) ferromagnets: first-principle approach

    NASA Astrophysics Data System (ADS)

    Mahmood, Q.; Hassan, M.; Noor, N. A.

    2016-12-01

    The structural, magnetic and optical characteristics of Zn1-x TM x S/Se (TM  =  Mn, Fe, Co, Ni and x  =  6.25%) have been investigated through the full-potential linearized augmented plane wave method within the framework of density functional theory. The optimized structures have been used to calculate the ferromagnetic and the antiferromagnetic ground-state energies. The stability of the ferromagnetic phase has been confirmed from the formation and the cohesive energies. The Heisenberg model is used to elucidate the Curie temperature (T c) of these alloys. From the band structures and density of states plots, it has been observed that TM-doped ZnS/Se alloys appear to be semiconductors and exhibit ferromagnetism. In addition, the observed ferromagnetism has also been explained in terms of direct exchange energy Δ x (d), exchange splitting energy Δ x (pd), crystal-field energy (E crys), exchange constants (N 0 α and N 0 β) and magnetic moments that shows potential spintronic applications. The optical behaviors of these alloys have been explained in terms of real and imaginary parts of the dielectric constant ɛ(ω), refractive index n(ω), extinction coefficient K(ω), reflectivity R(ω) and absorption coefficient σ(ω), in the energy range 0-25 eV. The calculated static limits of the band gaps and real part of the dielectric constants satisfy the Penn model. The critical limits of the imaginary part of the dielectric constants and absorption coefficients indicate that these alloys can be operated in the visible and the ultraviolet region of the electromagnetic spectrum; therefore, make them important for optoelectronic applications.

  2. Room temperature ferroelectric and ferromagnetic properties of multiferroics xLa0.7Sr0.3MnO3-(1-x )ErMnO3 (weight percent x =0.1, 0.2) composites

    NASA Astrophysics Data System (ADS)

    Dey, P.; Nath, T. K.; Nanda Goswami, M. L.; Kundu, T. K.

    2007-04-01

    A different kind of multiferroics with composite character, xLa0.7Sr0.3MnO3 (LSMO )-(1-x)ErMnO3 (EMO) (x =0.1, 0.2), where EMO is the ferroelectric (FE) and LSMO is the ferromagnetic (FM) component, has been studied. Magnetization versus magnetic field measurements at 300K show prominent hysteresis loops, attesting room temperature FM behavior of these multiferroic composites. Dielectric constant (ɛ) as a function of temperature reveals that paraelectric-FE transition temperature TC* (525K) and maximum value of ɛ (318) remain almost unaffected for x =0.1 composite compared to pure EMO. Polarization versus electric field study at 300K give conclusive evidence of the presence of spontaneous polarization in this x =0.1 composite. For x =0.2 composite, decreasing TC* (430K) with increase in ɛ value (774) indicates diffusive FE character.

  3. Degradation of the remanent ferromagnetic state under the action of ferroelectric relaxation processes in Co/(1-x)PMN-xPT/Co hybrids: Possible implications on cryogenic and room-temperature applications

    NASA Astrophysics Data System (ADS)

    Stamopoulos, D.; Zeibekis, M.; Vertsioti, G.; Zhang, S. J.

    2014-08-01

    Low-dimensional hybrid structures of heterogeneous constituents usually exhibit abnormal properties, a fact that makes such hybrids attractive for various cryogenic and room-temperature applications. Here, we studied Co/(1 - x)Pb(Mg1/3Nb2/3)O3-xPbTiO3/Co (Co/PMN-xPT/Co) with x = 0.29 and 0.30, specifically focusing on the evolution of the remanent ferromagnetic state, mrem of the Co outer layers in the whole temperature range from 300 K down to 10 K, upon application of an external electric field, Eex. We observed that mrem was vulnerable to degradation through the occurrence of electric field-induced magnetic instabilities (EMIs) that appeared only when Eex ≠ 0 kV/cm and were facilitated as Eex increases. However, EMIs completely ceased below a characteristic temperature Tces = 170 K even for the maximum |Eex| = 5 kV/cm applied in this work. A direct comparison of the magnetization data of the Co/PMN-xPT/Co hybrids reported here with the electromechanical properties of the parent PMN-xPT crystals plausibly indicates that EMIs are motivated by the coupling of the ferromagnetic domains of the Co outer layers with the ferroelectric domains of the PMN-xPT crystal. These results highlight the drawback of EMIs in relevant hybrids and delimit the temperature regime for the reliable operation of the Co/PMN-xPT/Co ones studied here.

  4. Taking Ferromagnetic Resonance to Millikelvin Temperatures

    NASA Astrophysics Data System (ADS)

    Huebl, Hans; Zollitsch, Christoph; Hocke, Fredrik; Weiler, Mathias; Radlmeier, Martin; Neumaier, Karl; Goennenwein, Sebastian T. B.; Gross, Rudolf

    2011-03-01

    Ferromagnetic Resonance (FMR) is a sensitive tool for the investigation of magnetic anisotropy and magnetization damping in thin magnetic films. Broadband FMR based on coplanar waveguide technology hereby is particularly attractive as it allows for the investigation of plain films as well as of single magnetic nanostructures. We here present broadband FMR data of 50~nm thick nickel and cobalt thin films, recorded at temperatures range from 4.2~K down to 50~mK. The excellent sensitivity of our setup allows for the detection of FMR with an incident microwave power of 100~fW at the base temperature of the dilution refrigerator. Our FMR measurements in Co and Ni reveal no distinct temperature dependence of the anisotropy and damping parameters in the temperature regime below 4.2~K, which appears consistent with the trend observed in measurements from room temperature down to 4.2~K. Our proof-of-principle experiments open the path for broadband FMR studies of magnetic anisotropy and magnetization damping at millikelvin temperatures a regime so far very scarcely explored. This project is financially supported by the Deutsche Forschungsgemeinschaft via SFB 631 and the Cluster of Excellence Nanosystems Initiative Munich (NIM).

  5. Isotope shift of the ferromagnetic transition temperature in itinerant ferromagnets

    NASA Astrophysics Data System (ADS)

    Yanagisawa, Takashi; Hase, Izumi; Odagiri, Kosuke

    2017-02-01

    We present a theory of the isotope effect of the Curie temperature Tc in itinerant ferromagnets. The isotope effect in ferromagnets occurs via the electron-phonon vertex correction and the effective attractive interaction mediated by the electron-phonon interaction. The decrease of the Debye frequency increases the relative strength of the Coulomb interaction, which results in a positive isotope shift of Tc when the mass M of an atom increases. Following this picture, we evaluate the isotope effect of Tc by using the Stoner theory and a spin-fluctuation theory. When Tc is large enough as large as or more than 100 K, the isotope effect on Tc can be measurable. Recently, precise measurements on the oxygen isotope effect on Tc have been performed for itinerant ferromagnet SrRuO3 with Tc ∼ 160 K. A clear isotope effect has been observed with the positive shift of Tc ∼ 1 K by isotope substitution (16O →18O). This experimental result is consistent with our theory.

  6. Finding the Curie Temperature for Ferromagnetic Materials

    ERIC Educational Resources Information Center

    Kizowski, Czeslaw; Budzik, Sylwia; Cebulski, Jozef

    2007-01-01

    The laboratory exercise described in this paper is based on a well-known qualitative demonstration of Curie temperature. A long ferromagnetic wire, in the form of a spiral, is attracted to a strong permanent magnet placed near its midpoint (see Fig. 1). The temperature of the wire is increased by passing a current through it. When the temperature…

  7. Finding the Curie Temperature for Ferromagnetic Materials

    ERIC Educational Resources Information Center

    Kizowski, Czeslaw; Budzik, Sylwia; Cebulski, Jozef

    2007-01-01

    The laboratory exercise described in this paper is based on a well-known qualitative demonstration of Curie temperature. A long ferromagnetic wire, in the form of a spiral, is attracted to a strong permanent magnet placed near its midpoint (see Fig. 1). The temperature of the wire is increased by passing a current through it. When the temperature…

  8. Study of room temperature ferromagnetic and ferroelectric properties in α-Fe1.6Ga0.4O3 alloy

    NASA Astrophysics Data System (ADS)

    Lone, Abdul Gaffar; Bhowmik, R. N.

    2015-04-01

    The compound α-Fe1.6Ga0.4O3 has been prepared by mechanical alloying and subsequent vacuum annealing at 800 °C. X-ray diffraction and Raman spectroscopy confirmed rhombohedral phase. The samples have shown enhanced ferromagnetic properties in comparison with α-Fe2O3 sample. The samples also exhibited good signature of ferroelectric polarization. Increase of alloying time has affected the variation of ferromagnetic and ferroelectric parameters. The samples with 50 h alloying time showed relatively large leakage of polarization, where as the samples at lower and higher alloying time showed better ferroelectric properties. Details of the ferroelectric loop have been studied at different applied voltages and frequencies. It has been found that leakage of polarization can be optimized by adjusting the frequency of the applied voltage. The ferroelectric properties have been understood by correlating the observations of the dielectric properties (dielectric loss, dielectric constant, and electrical conductivity) of the samples. The results are interesting for understanding the mechanism of ferroelectric properties in non-traditional ferroelectrics. This work opens a wide scope for reviewing the ferroelectric and multiferroic properties in metal doped hematite system, which is structurally different from orthorhombic phase of GaFeO3 that showed ferroelectric properties.

  9. Role of vanadium ions, oxygen vacancies, and interstitial zinc in room temperature ferromagnetism on ZnO-V2O5 nanoparticles

    PubMed Central

    2014-01-01

    In this work, we present the role of vanadium ions (V+5 and V+3), oxygen vacancies (VO), and interstitial zinc (Zni) to the contribution of specific magnetization for a mixture of ZnO-V2O5 nanoparticles (NPs). Samples were obtained by mechanical milling of dry powders and ethanol-assisted milling for 1 h with a fixed atomic ratio V/Zn?=?5% at. For comparison, pure ZnO samples were also prepared. All samples exhibit a room temperature magnetization ranging from 1.18?×?10−3 to 3.5?×?10−3 emu/gr. Pure ZnO powders (1.34?×?10−3 emu/gr) milled with ethanol exhibit slight increase in magnetization attributed to formation of Zni, while dry milled ZnO powders exhibit a decrease of magnetization due to a reduction of VO concentration. For the ZnO-V2O5 system, dry milled and thermally treated samples under reducing atmosphere exhibit a large paramagnetic component associated to the formation of V2O3 and secondary phases containing V+3 ions; at the same time, an increase of VO is observed with an abrupt fall of magnetization to σ?~?0.7?×?10−3 emu/gr due to segregation of V oxides and formation of secondary phases. As mechanical milling is an aggressive synthesis method, high disorder is induced at the surface of the ZnO NPs, including VO and Zni depending on the chemical environment. Thermal treatment restores partially structural order at the surface of the NPs, thus reducing the amount of Zni at the same time that V2O5 NPs segregate reducing the direct contact with the surface of ZnO NPs. Additional samples were milled for longer time up to 24 h to study the effect of milling on the magnetization; 1-h milled samples have the highest magnetizations. Structural characterization was carried out using X-ray diffraction and transmission electron microscopy. Identification of VO and Zni was carried out with Raman spectra, and energy-dispersive X-ray spectroscopy was used to verify that V did not diffuse into ZnO NPs as well to quantify O/Zn ratios. PMID:24708614

  10. Role of vanadium ions, oxygen vacancies, and interstitial zinc in room temperature ferromagnetism on ZnO-V2O5 nanoparticles.

    PubMed

    Olive-Méndez, Sion F; Santillán-Rodríguez, Carlos R; González-Valenzuela, Ricardo A; Espinosa-Magaña, Francisco; Matutes-Aquino, José A

    2014-04-07

    In this work, we present the role of vanadium ions (V+5 and V+3), oxygen vacancies (VO), and interstitial zinc (Zni) to the contribution of specific magnetization for a mixture of ZnO-V2O5 nanoparticles (NPs). Samples were obtained by mechanical milling of dry powders and ethanol-assisted milling for 1 h with a fixed atomic ratio V/Zn?=?5% at. For comparison, pure ZnO samples were also prepared. All samples exhibit a room temperature magnetization ranging from 1.18?×?10-3 to 3.5?×?10-3 emu/gr. Pure ZnO powders (1.34?×?10-3 emu/gr) milled with ethanol exhibit slight increase in magnetization attributed to formation of Zni, while dry milled ZnO powders exhibit a decrease of magnetization due to a reduction of VO concentration. For the ZnO-V2O5 system, dry milled and thermally treated samples under reducing atmosphere exhibit a large paramagnetic component associated to the formation of V2O3 and secondary phases containing V+3 ions; at the same time, an increase of VO is observed with an abrupt fall of magnetization to σ?~?0.7?×?10-3 emu/gr due to segregation of V oxides and formation of secondary phases. As mechanical milling is an aggressive synthesis method, high disorder is induced at the surface of the ZnO NPs, including VO and Zni depending on the chemical environment. Thermal treatment restores partially structural order at the surface of the NPs, thus reducing the amount of Zni at the same time that V2O5 NPs segregate reducing the direct contact with the surface of ZnO NPs. Additional samples were milled for longer time up to 24 h to study the effect of milling on the magnetization; 1-h milled samples have the highest magnetizations. Structural characterization was carried out using X-ray diffraction and transmission electron microscopy. Identification of VO and Zni was carried out with Raman spectra, and energy-dispersive X-ray spectroscopy was used to verify that V did not diffuse into ZnO NPs as well to quantify O/Zn ratios.

  11. Room temperature polyesterification

    SciTech Connect

    Moore, J.S.; Stupp, S.I. . Dept. of Materials Science and Engineering)

    1990-01-01

    A new room temperature polymerization method has been developed for the synthesis of high molecular weight polyesters directly from carboxylic acids and phenols. The solution polymerization reaction proceeds under mild conditions, near neutral pH, and also avoids the use of preactivated acid derivatives for esterification. The reaction is useful in the preparation of isoregic ordered chains with translational polar symmetry and also in the polymerization of functionalized or chiral monomers. The conditions required for polymerization in the carbodiimide-based reaction included catalysis by the 1:1 molecular complex formed by 4-(dimethylamino)pyridine and p-toluenesulfonic acid. These conditions were established through studies on a model system involving esterification of p-toluic acid and p-cresol. Self-condensation of several hydroxy acid monomers by this reaction has produced routinely good yields of polyesters with molecular weights greater than 15,000. It is believed that the high extents of reaction required for significant degrees of polymerization result from suppression of the side reaction leading to N-acylurea. The utility of this reaction in the formation of polar chains from sensitive monomers is demonstrated hereby the polycondensation of a chiral hydroxy acid.

  12. system at room temperature

    NASA Astrophysics Data System (ADS)

    Li, Shaoyuan; Ma, Wenhui; Zhou, Yang; Chen, Xiuhua; Xiao, Yongyin; Ma, Mingyu; Zhu, Wenjie; Wei, Feng

    2014-04-01

    In this paper, the moderately and lightly doped porous silicon nanowires (PSiNWs) were fabricated by the `one-pot procedure' metal-assisted chemical etching (MACE) method in the HF/H2O2/AgNO3 system at room temperature. The effects of H2O2 concentration on the nanostructure of silicon nanowires (SiNWs) were investigated. The experimental results indicate that porous structure can be introduced by the addition of H2O2 and the pore structure could be controlled by adjusting the concentration of H2O2. The H2O2 species replaces Ag+ as the oxidant and the Ag nanoparticles work as catalyst during the etching. And the concentration of H2O2 influences the nucleation and motility of Ag particles, which leads to formation of different porous structure within the nanowires. A mechanism based on the lateral etching which is catalyzed by Ag particles under the motivation by H2O2 reduction is proposed to explain the PSiNWs formation.

  13. Understanding the magnetic interaction between intrinsic defects and impurity ions in room-temperature ferromagnetic Mg1-x Fe x O thin films

    NASA Astrophysics Data System (ADS)

    Kapilashrami, Mukes; Wang, Yung Jui; Li, Xin; Glans, Per-Anders; Fang, Mei; Riazanova, Anastasia V.; Belova, Lyubov M.; Rao, K. V.; Luo, Yi; Barbiellini, Bernardo; Lin, Hsin; Markiewicz, Robert; Bansil, Arun; Hussain, Zahid; Guo, Jinghua

    2016-04-01

    Understanding the nature and characteristics of the intrinsic defects and impurities in the dielectric barrier separating the ferromagnetic electrodes in a magnetic tunneling junction is of great importance for understanding the often observed ‘barrier-breakdown’ therein. In this connection, we present herein systematic experimental (SQUID and synchrotron-radiation-based x-ray absorption spectroscopy) and computational studies on the electronic and magnetic properties of Mg1-x Fe x O thin films. Our studies reveal: (i) defect aggregates comprised of basic and trimer units (Fe impurity coupled to 1 or 2 Mg vacancies) and (ii) existence of two competing magnetic orders, defect- and dopant-induced, with spin densities aligning anti-parallel if the trimer is present in the oxide matrix. These findings open up new avenues for designing tunneling barriers with high endurance and tunneling effect upon tuning the concentration/distribution of the two magnetic orders.

  14. Structural and morphological properties of Zn1- x Zr x O with room-temperature ferromagnetism and fabricated by using the co-precipitation technique

    NASA Astrophysics Data System (ADS)

    Hassan, M.; Irfan, R.; Riaz, S.; Naseem, S.; Hussain, S. S.; Murtaza, G.

    2017-03-01

    In this study, ZnO was doped with various concentrations of zirconium ( x Zr = 0 - 5 mole%), by using the co-precipitation method so as to achieve successful formation of a single-phase diluted magnetic semiconductor. X-Ray diffraction results showed that the crystal structure of Zn1- x Zr x O was that of hexagonal wurtzite. The structural properties showed no additional phases at low impurity contents ( x Zr < 3%); however, impurity peaks belonging to ZrO2 appeared at high impurity contents ( x Zr ≥ 3%). The calculated ZnO lattice constants ` a' and ` c' were found to be 3.256 Å and 5.203 Å, respectively, which are in close match to the values found in the literature. For undoped ZnO, the average calculated particle size was 75.35 nm, and calculated bond length was 1.98 Å. The residual strains and the secondary phases of ZrO2 were found to affect the lattice parameters and the bond lengths. The scanning electron microscopy images showed a porous structure with non-uniform surface morphology. However, a few nano-scale dendrite-type structures were also present, indicating the potential applications of Zr-doped ZnO in nano-devices. Vibrating sample magnetometry (VSM) was employed to measure the magnetic properties, and the measurements showed undoped ZnO to be diamagnetic; however, doping with Zr induced a small ferromagnetic character at small magnetic fields. On the otherhand, a paramagnetic behavior was evident at higher magnetic fields. The magnetization at 1T was observed to degrade with increasing Zr content in the ZnO host lattice, which was due to the residual strains and the secondary phases.

  15. Magnetic heat pumping near room temperature

    NASA Technical Reports Server (NTRS)

    Brown, G. V.

    1976-01-01

    It is shown that magnetic heat pumping can be made practical at room temperature by using a ferromagnetic material with a Curie point at or near operating temperature and an appropriate regenerative thermodynamic cycle. Measurements are performed which show that gadolinium is a resonable working material and it is found that the application of a 7-T magnetic field to gadolinium at the Curie point (293 K) causes a heat release of 4 kJ/kg under isothermal conditions or a temperature rise of 14 K under adiabatic conditions. A regeneration technique can be used to lift the load of the lattice and electronic heat capacities off the magnetic system in order to span a reasonable temperature difference and to pump as much entropy per cycle as possible

  16. Magnetic heat pumping near room temperature

    NASA Technical Reports Server (NTRS)

    Brown, G. V.

    1976-01-01

    It is shown that magnetic heat pumping can be made practical at room temperature by using a ferromagnetic material with a Curie point at or near operating temperature and an appropriate regenerative thermodynamic cycle. Measurements are performed which show that gadolinium is a resonable working material and it is found that the application of a 7-T magnetic field to gadolinium at the Curie point (293 K) causes a heat release of 4 kJ/kg under isothermal conditions or a temperature rise of 14 K under adiabatic conditions. A regeneration technique can be used to lift the load of the lattice and electronic heat capacities off the magnetic system in order to span a reasonable temperature difference and to pump as much entropy per cycle as possible

  17. Switchable hardening of a ferromagnet at fixed temperature

    PubMed Central

    Silevitch, D. M.; Aeppli, G.; Rosenbaum, T. F.

    2010-01-01

    The intended use of a magnetic material, from information storage to power conversion, depends crucially on its domain structure, traditionally crafted during materials synthesis. By contrast, we show that an external magnetic field, applied transverse to the preferred magnetization of a model disordered uniaxial ferromagnet, is an isothermal regulator of domain pinning. At elevated temperatures, near the transition into the paramagnet, modest transverse fields increase the pinning, stabilize the domain structure, and harden the magnet, until a point where the field induces quantum tunneling of the domain walls and softens the magnet. At low temperatures, tunneling completely dominates the domain dynamics and provides an interpretation of the quantum phase transition in highly disordered magnets as a localization/delocalization transition for domain walls. While the energy scales of the rare earth ferromagnet studied here restrict the effects to cryogenic temperatures, the principles discovered are general and should be applicable to existing classes of highly anisotropic ferromagnets with ordering at room temperature or above. PMID:20133728

  18. Temperature limited heater utilizing non-ferromagnetic conductor

    DOEpatents

    Vinegar,; Harold J. , Harris; Kelvin, Christopher [Houston, TX

    2012-07-17

    A heater is described. The heater includes a ferromagnetic conductor and an electrical conductor electrically coupled to the ferromagnetic conductor. The ferromagnetic conductor is positioned relative to the electrical conductor such that an electromagnetic field produced by time-varying current flow in the ferromagnetic conductor confines a majority of the flow of the electrical current to the electrical conductor at temperatures below or near a selected temperature.

  19. Toward room temperature superconductivity?

    PubMed Central

    Patel, C. K. N.; Dynes, R. C.

    1988-01-01

    The last 12 months have witnessed frenzied activity in condensed matter physics, unmatched by any other since the invention of the laser. In this article, we summarize the status, promise, and problems in the field of high-temperature superconductivity. We also comment on the mechanisms and policies needed for the United States to economically benefit from the recent discoveries in the face of what can be best described as an international race to win the battle. Images

  20. High-temperature ferromagnetism in heavily Fe-doped ferromagnetic semiconductor (Ga,Fe)Sb

    SciTech Connect

    Tu, Nguyen Thanh; Hai, Pham Nam; Anh, Le Duc; Tanaka, Masaaki

    2016-05-09

    We show high-temperature ferromagnetism in heavily Fe-doped ferromagnetic semiconductor (Ga{sub 1−x},Fe{sub x})Sb (x = 23% and 25%) thin films grown by low-temperature molecular beam epitaxy. Magnetic circular dichroism spectroscopy and anomalous Hall effect measurements indicate intrinsic ferromagnetism of these samples. The Curie temperature reaches 300 K and 340 K for x = 23% and 25%, respectively, which are the highest values reported so far in intrinsic III-V ferromagnetic semiconductors.

  1. Ferromagnetism in metals at finite temperatures

    SciTech Connect

    Gyorffy, B.L.; Staunton, J.B.; Stocks, G.M.

    1984-01-01

    The conventional spin-polarized band theory is well known to give a reasonable description of the magnetic ground states of metals. Here it is generalized to finite temperatures. The resulting theory is the first first-principles theory of the ferromagnetic phase transition in metals. It is a mean-field theory. For iron we find T/sub c/ = 1250 K and chi/sup -1/(q = 0) follows a Curie-Weiss law. We also report on our results for the wave-vector dependent susceptibility chi(q) which is a measure of magnetic short-range order above T/sub c/.

  2. Room temperature terahertz polariton emitter

    SciTech Connect

    Geiser, Markus; Scalari, Giacomo; Castellano, Fabrizio; Beck, Mattias; Faist, Jerome

    2012-10-01

    Terahertz (THz) range electroluminescence from intersubband polariton states is observed in the ultra strong coupling regime, where the interaction energy between the collective excitation of a dense electron gas and a photonic mode is a significant portion of the uncoupled excitation energy. The polariton's increased emission efficiency along with a parabolic electron confinement potential allows operation up to room temperature in a nonresonant pumping scheme. This observation of room temperature electroluminescence of an intersubband device in the THz range is a promising proof of concept for more powerful THz sources.

  3. Inherent room temperature ferromagnetism and dopant dependent Raman studies of PbSe, Pb{sub 1−x}Cu{sub x}Se, and Pb{sub 1−x}Ni{sub x}Se

    SciTech Connect

    Gayner, Chhatrasal; Kar, Kamal K.

    2015-03-14

    Polycrystalline lead selenide (PbSe) doped with copper (Cu) and nickel (Ni) was prepared to understand its magnetic behaviour and Raman activity. The processing conditions, influence of dopants (magnetically active and non-active) and their respective compositions on the magnetic properties and Raman active mode were studied. A surprising/anomalous room temperature ferromagnetism (hysteresis loop) is noticed in bulk diamagnetic PbSe, which is found to be natural or inherent characteristic of material, and depends on the crystallite size, dopant, and developed strain due to dopant/defects. The magnetic susceptibility (−1.71 × 10{sup −4} emu/mol Oe) and saturated magnetic susceptibility (−2.74 × 10{sup −4} emu/mol Oe) are found to be higher than the earlier reported value (diamagnetic: −1.0 × 10{sup −4} emu/mol Oe) in bulk PbSe. With increase of Cu concentration (2% to 10%) in PbSe, the saturated magnetic susceptibility decreases from −1.22 × 10{sup −4} to −0.85 × 10{sup −4} emu/mol Oe. Whereas for Ni dopant, the saturated magnetic susceptibility increases to −2.96 × 10{sup −4} emu/mol Oe at 2% Ni doped PbSe. But it further decreases with dopant concentration. In these doped PbSe, the shifting of longitudinal (LO) phonon mode was also studied by the Raman spectroscopy. The shifting of LO mode is found to be dopant dependent, and the frequency shift of LO mode is associated with the induced strain that created by the dopants and vacancies. This asymmetry in LO phonon mode (peak shift and shape) may be due to the intraband electronic transition of dopants. The variation in magnetic susceptibility and Raman shifts are sensitive to crystallite size, nature of dopant, concentration of dopants, and induced strain due to dopants.

  4. Ferromagnetic ZnO bicrystal nanobelts fabricated in low temperature

    SciTech Connect

    Xu Congkang; Chun, Junghwan; Rho, Keehan; Lee, Hyo Jin; Jeong, Yoon Hee; Kim, Dong-Eon; Chon, Bonghwan; Hong, Sangsu; Joo, Taiha

    2006-08-28

    Zinc oxide bicrystal nanobelts were fabricated via a vapor phase transport of a powder mixture of Zn, BiI{sub 3}, and MnCl{sub 2}{center_dot}H{sub 2}O at temperatures as low as 300 deg. C. The bicrystal nanobelts, growing along the [011{sup -}3] direction, have the widths of 40-150 nm and lengths of tens of microns. The energy dispersive x-ray spectroscopy result verifies that the bicrystal nanobelts contain higher concentration of both Bi and Mn along the grain boundary. The investigation of the growth mechanism proposes that MnBi may induce the formation of bicrystal nanobelts. Photoluminescence spectra show that the ultraviolet emission of the bicrystal nanobelts has a blueshift of 18 meV as compared to Bi-ZnO nanowires at 10 K. The bicrystal nanobelts also exhibit ferromagnetism at room temperature.

  5. Polariton condensates at room temperature

    NASA Astrophysics Data System (ADS)

    Guillet, Thierry; Brimont, Christelle

    2016-10-01

    We review the recent developments of the polariton physics in microcavities featuring the exciton-photon strong coupling at room temperature, and leading to the achievement of room-temperature polariton condensates. Such cavities embed active layers with robust excitons that present a large binding energy and a large oscillator strength, i.e. wide bandgap inorganic or organic semiconductors, or organic molecules. These various systems are compared, in terms of figures of merit and of common features related to their strong oscillator strength. The various demonstrations of polariton laser are compared, as well as their condensation phase diagrams. The room-temperature operation indeed allows a detailed investigation of the thermodynamic and out-of-equilibrium regimes of the condensation process. The crucial role of the spatial dynamics of the condensate formation is discussed, as well as the debated issue of the mechanism of stimulated relaxation from the reservoir to the condensate under non-resonant excitation. Finally the prospects of polariton devices are presented.

  6. On the origin of high-temperature ferromagnetism in the low-temperature-processed Mn-Zn-O system.

    PubMed

    Kundaliya, Darshan C; Ogale, S B; Lofland, S E; Dhar, S; Metting, C J; Shinde, S R; Ma, Z; Varughese, B; Ramanujachary, K V; Salamanca-Riba, L; Venkatesan, T

    2004-10-01

    The recent discovery of ferromagnetism above room temperature in low-temperature-processed MnO(2)-ZnO has generated significant interest. Using suitably designed bulk and thin-film studies, we demonstrate that the ferromagnetism in this system originates in a metastable phase rather than by carrier-induced interaction between separated Mn atoms in ZnO. The ferromagnetism persists up to approximately 980 K, and further heating transforms the metastable phase and kills the ferromagnetism. By studying the interface diffusion and reaction between thin-film bilayers of Mn and Zn oxides, we show that a uniform solution of Mn in ZnO does not form under low-temperature processing. Instead, a metastable ferromagnetic phase develops by Zn diffusion into the Mn oxide. Direct low-temperature film growth of Zn-incorporated Mn oxide by pulsed laser deposition shows ferromagnetism at low Zn concentration for an optimum oxygen growth pressure. Our results strongly suggest that the observed ferromagnetic phase is oxygen-vacancy-stabilized Mn(2-x)Zn(x)O(3-delta.).

  7. High temperature magnetism and microstructure of ferromagnetic alloy Si1-x Mn x

    NASA Astrophysics Data System (ADS)

    Aronzon, B. A.; Davydov, A. B.; Vasiliev, A. L.; Perov, N. S.; Novodvorsky, O. A.; Parshina, L. S.; Presniakov, M. Yu; Lahderanta, E.

    2017-02-01

    The results of a detailed study of magnetic properties and of the microstructure of SiMn films with a small deviation from stoichiometry are presented. The aim was to reveal the origin of the high temperature ferromagnetic ordering in such compounds. Unlike SiMn single crystals with the Curie temperature ~30 K, considered Si1-x Mn x compounds with x  =  0.5  +Δx and Δx in the range of 0.01-0.02 demonstrate a ferromagnetic state above room temperature. Such a ferromagnetic state can be explained by the existence of highly defective B20 SiMn nanocrystallites. These defects are Si vacancies, which are suggested to possess magnetic moments. The nanocrystallites interact with each other through paramagnons (magnetic fluctuations) inside a weakly magnetic manganese silicide matrix giving rise to a long range ferromagnetic percolation cluster. The studied structures with a higher value of Δx  ≈  0.05 contained three different magnetic phases: (a)—the low temperature ferromagnetic phase related to SiMn; (b)—the above mentioned high temperature phase with Curie temperature in the range of 200-300 K depending on the growth history and (c)—superparamagnetic phase formed by separated noninteracting SiMn nanocrystallites.

  8. Annealing temperature dependent non-monotonic d0 ferromagnetism in pristine In2O3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Cao, Haiming; Xing, Pengfei; Yao, Dongsheng; Wu, Ping

    2017-05-01

    Cubic bixbyite In2O3 nanoparticles with room temperature d0 ferromagnetism were prepared by sol-gel method with the air annealing temperature ranging from 500 to 900 °C. X-ray diffraction, X-ray photoelectron spectroscopy, Raman-scattering and photoluminescence were carried out to demonstrate the presence of oxygen vacancies. The lattice constant, the atomic ratio of crystal O and In, the Raman peak at 369 cm-1, the PL emission peak at 396 nm and the saturation magnetization of d0 ferromagnetism all had a consistent non-monotonic change with the increasing annealing temperature. With further considering the relation between the grain size and the distribution of oxygen vacancies, we think that d0 ferromagnetism in our samples is directly related with the singly charged oxygen vacancies at the surface of In2O3 nanoparticles.

  9. Proximity effect and its enhancement by ferromagnetism in high-temperature superconductor-ferromagnet structures.

    PubMed

    Volkov, A F; Efetov, K B

    2009-02-20

    We consider a bilayer consisting of a d-wave layered superconductor and diffusive ferromagnet with a domain wall (DW). The c axis in the superconductor and DW in the ferromagnet are assumed to be perpendicular to the interface. We demonstrate that in such a heterostructure the inhomogeneous exchange field enhances the proximity effect. It is shown that, whereas in the absence of the exchange field the d-wave condensate decays in the normal metal on the mean free path l, the superconductivity penetrates the ferromagnet along the DW over much larger distances. This happens because the presence of the DW results in a generation of an odd-frequency triplet s-wave component of the condensate. The phenomenon discovered here may help to explain a recent experiment on high-temperature superconductor-ferromagnet bilayers.

  10. Extended magnetic exchange interactions in the high-temperature ferromagnet MnBi

    DOE PAGES

    Christianson, Andrew D.; Hahn, Steven E.; Fishman, Randy Scott; ...

    2016-05-09

    Here, the high-temperature ferromagnet MnBi continues to receive attention as a candidate to replace rare-earth-containing permanent magnets in applications above room temperature. This is due to a high Curie temperature, large magnetic moments, and a coercivity that increases with temperature. The synthesis of MnBi also allows for crystals that are free of interstitial Mn, enabling more direct access to the key interactions underlying the physical properties of binary Mn-based ferromagnets. In this work, we use inelastic neutron scattering to measure the spin waves of MnBi in order to characterize the magnetic exchange at low temperature. Consistent with the spin reorientationmore » that occurs below 140~K, we do not observe a spin gap in this system above our experimental resolution. A Heisenberg model was fit to the spin wave data in order to characterize the long-range nature of the exchange. It was found that interactions up to sixth nearest neighbor are required to fully parameterize the spin waves. Surprisingly, the nearest-neighbor term is antiferromagnetic, and the realization of a ferromagnetic ground state relies on the more numerous ferromagnetic terms beyond nearest neighbor, suggesting that the ferromagnetic ground state arises as a consequence of the long-ranged interactions in the system.« less

  11. Extended magnetic exchange interactions in the high-temperature ferromagnet MnBi

    SciTech Connect

    Christianson, Andrew D.; Hahn, Steven E.; Fishman, Randy Scott; Parker, David S.; McGuire, Michael A.; Sales, Brian C.; Lumsden, Mark D.; Williams, T. J.; Taylor, A. E.

    2016-05-09

    Here, the high-temperature ferromagnet MnBi continues to receive attention as a candidate to replace rare-earth-containing permanent magnets in applications above room temperature. This is due to a high Curie temperature, large magnetic moments, and a coercivity that increases with temperature. The synthesis of MnBi also allows for crystals that are free of interstitial Mn, enabling more direct access to the key interactions underlying the physical properties of binary Mn-based ferromagnets. In this work, we use inelastic neutron scattering to measure the spin waves of MnBi in order to characterize the magnetic exchange at low temperature. Consistent with the spin reorientation that occurs below 140~K, we do not observe a spin gap in this system above our experimental resolution. A Heisenberg model was fit to the spin wave data in order to characterize the long-range nature of the exchange. It was found that interactions up to sixth nearest neighbor are required to fully parameterize the spin waves. Surprisingly, the nearest-neighbor term is antiferromagnetic, and the realization of a ferromagnetic ground state relies on the more numerous ferromagnetic terms beyond nearest neighbor, suggesting that the ferromagnetic ground state arises as a consequence of the long-ranged interactions in the system.

  12. Extended magnetic exchange interactions in the high-temperature ferromagnet MnBi

    SciTech Connect

    Williams, T. J. Taylor, A. E.; Lumsden, M. D.; Christianson, A. D.; Hahn, S. E.; Fishman, R. S.; Parker, D. S.; McGuire, M. A.; Sales, B. C.

    2016-05-09

    The high-temperature ferromagnet MnBi continues to receive attention as a candidate to replace rare-earth-containing permanent magnets in applications above room temperature. This is due to a high Curie temperature, large magnetic moments, and a coercivity that increases with temperature. The synthesis of MnBi also allows for crystals that are free of interstitial Mn, enabling more direct access to the key interactions underlying the physical properties of binary Mn-based ferromagnets. In this work, we use inelastic neutron scattering to measure the spin waves of MnBi in order to characterize the magnetic exchange at low temperature. Consistent with the spin reorientation that occurs below 140 K, we do not observe a spin gap in this system above our experimental resolution. A Heisenberg model was fit to the spin wave data in order to characterize the long-range nature of the exchange. It was found that interactions up to sixth nearest neighbor are required to fully parametrize the spin waves. Surprisingly, the nearest-neighbor term is antiferromagnetic, and the realization of a ferromagnetic ground state relies on the more numerous ferromagnetic terms beyond nearest neighbor, suggesting that the ferromagnetic ground state arises as a consequence of the long-ranged interactions in the system.

  13. Extended magnetic exchange interactions in the high-temperature ferromagnet MnBi

    SciTech Connect

    Christianson, Andrew D.; Hahn, Steven E.; Fishman, Randy Scott; Parker, David S.; McGuire, Michael A.; Sales, Brian C.; Lumsden, Mark D.; Williams, T. J.; Taylor, A. E.

    2016-05-09

    Here, the high-temperature ferromagnet MnBi continues to receive attention as a candidate to replace rare-earth-containing permanent magnets in applications above room temperature. This is due to a high Curie temperature, large magnetic moments, and a coercivity that increases with temperature. The synthesis of MnBi also allows for crystals that are free of interstitial Mn, enabling more direct access to the key interactions underlying the physical properties of binary Mn-based ferromagnets. In this work, we use inelastic neutron scattering to measure the spin waves of MnBi in order to characterize the magnetic exchange at low temperature. Consistent with the spin reorientation that occurs below 140~K, we do not observe a spin gap in this system above our experimental resolution. A Heisenberg model was fit to the spin wave data in order to characterize the long-range nature of the exchange. It was found that interactions up to sixth nearest neighbor are required to fully parameterize the spin waves. Surprisingly, the nearest-neighbor term is antiferromagnetic, and the realization of a ferromagnetic ground state relies on the more numerous ferromagnetic terms beyond nearest neighbor, suggesting that the ferromagnetic ground state arises as a consequence of the long-ranged interactions in the system.

  14. Room temperature organic magnets derived from sp3 functionalized graphene

    NASA Astrophysics Data System (ADS)

    Tuček, Jiří; Holá, Kateřina; Bourlinos, Athanasios B.; Błoński, Piotr; Bakandritsos, Aristides; Ugolotti, Juri; Dubecký, Matúš; Karlický, František; Ranc, Václav; Čépe, Klára; Otyepka, Michal; Zbořil, Radek

    2017-02-01

    Materials based on metallic elements that have d orbitals and exhibit room temperature magnetism have been known for centuries and applied in a huge range of technologies. Development of room temperature carbon magnets containing exclusively sp orbitals is viewed as great challenge in chemistry, physics, spintronics and materials science. Here we describe a series of room temperature organic magnets prepared by a simple and controllable route based on the substitution of fluorine atoms in fluorographene with hydroxyl groups. Depending on the chemical composition (an F/OH ratio) and sp3 coverage, these new graphene derivatives show room temperature antiferromagnetic ordering, which has never been observed for any sp-based materials. Such 2D magnets undergo a transition to a ferromagnetic state at low temperatures, showing an extraordinarily high magnetic moment. The developed theoretical model addresses the origin of the room temperature magnetism in terms of sp2-conjugated diradical motifs embedded in an sp3 matrix and superexchange interactions via -OH functionalization.

  15. Room temperature organic magnets derived from sp(3) functionalized graphene.

    PubMed

    Tuček, Jiří; Holá, Kateřina; Bourlinos, Athanasios B; Błoński, Piotr; Bakandritsos, Aristides; Ugolotti, Juri; Dubecký, Matúš; Karlický, František; Ranc, Václav; Čépe, Klára; Otyepka, Michal; Zbořil, Radek

    2017-02-20

    Materials based on metallic elements that have d orbitals and exhibit room temperature magnetism have been known for centuries and applied in a huge range of technologies. Development of room temperature carbon magnets containing exclusively sp orbitals is viewed as great challenge in chemistry, physics, spintronics and materials science. Here we describe a series of room temperature organic magnets prepared by a simple and controllable route based on the substitution of fluorine atoms in fluorographene with hydroxyl groups. Depending on the chemical composition (an F/OH ratio) and sp(3) coverage, these new graphene derivatives show room temperature antiferromagnetic ordering, which has never been observed for any sp-based materials. Such 2D magnets undergo a transition to a ferromagnetic state at low temperatures, showing an extraordinarily high magnetic moment. The developed theoretical model addresses the origin of the room temperature magnetism in terms of sp(2)-conjugated diradical motifs embedded in an sp(3) matrix and superexchange interactions via -OH functionalization.

  16. Room temperature organic magnets derived from sp3 functionalized graphene

    PubMed Central

    Tuček, Jiří; Holá, Kateřina; Bourlinos, Athanasios B.; Błoński, Piotr; Bakandritsos, Aristides; Ugolotti, Juri; Dubecký, Matúš; Karlický, František; Ranc, Václav; Čépe, Klára; Otyepka, Michal; Zbořil, Radek

    2017-01-01

    Materials based on metallic elements that have d orbitals and exhibit room temperature magnetism have been known for centuries and applied in a huge range of technologies. Development of room temperature carbon magnets containing exclusively sp orbitals is viewed as great challenge in chemistry, physics, spintronics and materials science. Here we describe a series of room temperature organic magnets prepared by a simple and controllable route based on the substitution of fluorine atoms in fluorographene with hydroxyl groups. Depending on the chemical composition (an F/OH ratio) and sp3 coverage, these new graphene derivatives show room temperature antiferromagnetic ordering, which has never been observed for any sp-based materials. Such 2D magnets undergo a transition to a ferromagnetic state at low temperatures, showing an extraordinarily high magnetic moment. The developed theoretical model addresses the origin of the room temperature magnetism in terms of sp2-conjugated diradical motifs embedded in an sp3 matrix and superexchange interactions via –OH functionalization. PMID:28216636

  17. Low temperature magnetic force microscopy on ferromagnetic and superconducting oxides

    NASA Astrophysics Data System (ADS)

    Sirohi, Anshu; Sheet, Goutam

    2016-05-01

    We report the observation of complex ferromagnetic domain structures on thin films of SrRuO3 and superconducting vortices in high temperature superconductors through low temperature magnetic force microscopy. Here we summarize the experimental details and results of magnetic imaging at low temperatures and high magnetic fields. We discuss these data in the light of existing theoretical concepts.

  18. Topological Insulators at Room Temperature

    SciTech Connect

    Zhang, Haijun; Liu, Chao-Xing; Qi, Xiao-Liang; Dai, Xi; Fang, Zhong; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-03-25

    Topological insulators are new states of quantum matter with surface states protected by the time-reversal symmetry. In this work, we perform first-principle electronic structure calculations for Sb{sub 2}Te{sub 3}, Sb{sub 2}Se{sub 3}, Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} crystals. Our calculations predict that Sb{sub 2}Te{sub 3}, Bi{sub 2}T e{sub 3} and Bi{sub 2}Se{sub 3} are topological insulators, while Sb{sub 2}Se{sub 3} is not. In particular, Bi{sub 2}Se{sub 3} has a topologically non-trivial energy gap of 0.3eV , suitable for room temperature applications. We present a simple and unified continuum model which captures the salient topological features of this class of materials. These topological insulators have robust surface states consisting of a single Dirac cone at the {Lambda} point.

  19. Nanoengineering of an Si/MnGe quantum dot superlattice for high Curie-temperature ferromagnetism.

    PubMed

    Nie, Tianxiao; Kou, Xufeng; Tang, Jianshi; Fan, Yabin; Lee, Shengwei; He, Qinglin; Chang, Li-Te; Murata, Koichi; Gen, Yin; Wang, Kang L

    2017-03-02

    The realization and application of spintronic devices would be dramatically advanced if room-temperature ferromagnetism could be integrated into semiconductor nanostructures, especially when compatible with mature silicon technology. Herein, we report the observation of such a system - an Si/MnGe superlattice with quantum dots well aligned in the vertical direction successfully grown by molecular beam epitaxy. Such a unique system could take full advantage of the type-II energy band structure of the Si/Ge heterostructure, which could trap the holes inside MnGe QDs, significantly enhancing the hole-mediated ferromagnetism. Magnetic measurements indeed found that the superlattice structure exhibited a Curie temperature of above 400 K. Furthermore, zero-field cooling and field cooling curves could confirm the absence of ferromagnetic compounds, such as Ge8Mn11 (Tc ∼ 270 K) and Ge3Mn5 (Tc ∼ 296 K) in our system. Magnetotransport measurement revealed a clear magnetoresistance transition from negative to positive and a pronounced anomalous Hall effect. Such a unique Si/MnGe superlattice sets a new stage for strengthening ferromagnetism due to the enhanced hole-mediation by quantum confinement, which can be exploited for realizing the room-temperature Ge-based spin field-effect transistors in the future.

  20. A high-temperature ferromagnetic topological insulating phase by proximity coupling.

    PubMed

    Katmis, Ferhat; Lauter, Valeria; Nogueira, Flavio S; Assaf, Badih A; Jamer, Michelle E; Wei, Peng; Satpati, Biswarup; Freeland, John W; Eremin, Ilya; Heiman, Don; Jarillo-Herrero, Pablo; Moodera, Jagadeesh S

    2016-05-26

    Topological insulators are insulating materials that display conducting surface states protected by time-reversal symmetry, wherein electron spins are locked to their momentum. This unique property opens up new opportunities for creating next-generation electronic, spintronic and quantum computation devices. Introducing ferromagnetic order into a topological insulator system without compromising its distinctive quantum coherent features could lead to the realization of several predicted physical phenomena. In particular, achieving robust long-range magnetic order at the surface of the topological insulator at specific locations without introducing spin-scattering centres could open up new possibilities for devices. Here we use spin-polarized neutron reflectivity experiments to demonstrate topologically enhanced interface magnetism by coupling a ferromagnetic insulator (EuS) to a topological insulator (Bi2Se3) in a bilayer system. This interfacial ferromagnetism persists up to room temperature, even though the ferromagnetic insulator is known to order ferromagnetically only at low temperatures (<17 K). The magnetism induced at the interface resulting from the large spin-orbit interaction and the spin-momentum locking of the topological insulator surface greatly enhances the magnetic ordering (Curie) temperature of this bilayer system. The ferromagnetism extends ~2 nm into the Bi2Se3 from the interface. Owing to the short-range nature of the ferromagnetic exchange interaction, the time-reversal symmetry is broken only near the surface of a topological insulator, while leaving its bulk states unaffected. The topological magneto-electric response originating in such an engineered topological insulator could allow efficient manipulation of the magnetization dynamics by an electric field, providing an energy-efficient topological control mechanism for future spin-based technologies.

  1. A high-temperature ferromagnetic topological insulating phase by proximity coupling

    SciTech Connect

    Katmis, Ferhat; Lauter, Valeria; Nogueira, Flavio S.; Assaf, Badih A.; Jamer, Michelle E.; Wei, Peng; Satpati, Biswarup; Freeland, John W.; Eremin, Ilya; Heiman, Don; Jarillo-Herrero, Pablo; Moodera, Jagadeesh S.

    2016-05-09

    Topological insulators are insulating materials that display conducting surface states protected by time-reversal symmetry(1,)2, wherein electron spins are locked to their momentum. This unique property opens up new opportunities for creating next-generation electronic, spintronic and quantum computation devices(3-5). Introducing ferromagnetic order into a topological insulator system without compromising its distinctive quantum coherent features could lead to the realization of several predicted physical phenomena(6,7). In particular, achieving robust long-range magnetic order at the surface of the topological insulator at specific locations without introducing spin-scattering centres could open up new possibilities for devices. Here we use spin-polarized neutron reflectivity experiments to demonstrate topologically enhanced interface magnetism by coupling a ferromagnetic insulator (EuS) to a topological insulator (Bi2Se3) in a bilayer system. This interfacial ferromagnetism persists up to room temperature, even though the ferromagnetic insulator is known to order ferromagnetically only at low temperatures (<17 K). The magnetism induced at the interface resulting from the large spin-orbit interaction and the spin-momentum locking of the topological insulator surface greatly enhances the magnetic ordering (Curie) temperature of this bilayer system. The ferromagnetism extends similar to 2 nm into the Bi2Se3 from the interface. Owing to the short-range nature of the ferromagnetic exchange interaction, the time-reversal symmetry is broken only near the surface of a topological insulator, while leaving its bulk states unaffected. The topological magneto-electric response originating in such an engineered topological insulator(2,8) could allow efficient manipulation of the magnetization dynamics by an electric field, providing an energy-efficient topological control mechanism for future spin-based technologies.

  2. A high-temperature ferromagnetic topological insulating phase by proximity coupling

    NASA Astrophysics Data System (ADS)

    Katmis, Ferhat; Lauter, Valeria; Nogueira, Flavio S.; Assaf, Badih A.; Jamer, Michelle E.; Wei, Peng; Satpati, Biswarup; Freeland, John W.; Eremin, Ilya; Heiman, Don; Jarillo-Herrero, Pablo; Moodera, Jagadeesh S.

    2016-05-01

    Topological insulators are insulating materials that display conducting surface states protected by time-reversal symmetry, wherein electron spins are locked to their momentum. This unique property opens up new opportunities for creating next-generation electronic, spintronic and quantum computation devices. Introducing ferromagnetic order into a topological insulator system without compromising its distinctive quantum coherent features could lead to the realization of several predicted physical phenomena. In particular, achieving robust long-range magnetic order at the surface of the topological insulator at specific locations without introducing spin-scattering centres could open up new possibilities for devices. Here we use spin-polarized neutron reflectivity experiments to demonstrate topologically enhanced interface magnetism by coupling a ferromagnetic insulator (EuS) to a topological insulator (Bi2Se3) in a bilayer system. This interfacial ferromagnetism persists up to room temperature, even though the ferromagnetic insulator is known to order ferromagnetically only at low temperatures (<17 K). The magnetism induced at the interface resulting from the large spin-orbit interaction and the spin-momentum locking of the topological insulator surface greatly enhances the magnetic ordering (Curie) temperature of this bilayer system. The ferromagnetism extends ~2 nm into the Bi2Se3 from the interface. Owing to the short-range nature of the ferromagnetic exchange interaction, the time-reversal symmetry is broken only near the surface of a topological insulator, while leaving its bulk states unaffected. The topological magneto-electric response originating in such an engineered topological insulator could allow efficient manipulation of the magnetization dynamics by an electric field, providing an energy-efficient topological control mechanism for future spin-based technologies.

  3. Room temperature long range ferromagnetic ordering in Ni{sub 0.58}Zn{sub 0.42}Co{sub 0.10}Cu{sub 0.10}Fe{sub 1.8}O{sub 4} nano magnetic system

    SciTech Connect

    Sarveena, Chand, Jagdish; Verma, S.; Singh, M.; Kotnala, R. K.; Batoo, K. M.

    2015-06-24

    The structural and magnetic behavior of sol-gel autocombustion synthesized nanocrystalline Ni{sub 0.58}Zn{sub 0.42}Co{sub 0.10}Cu{sub 0.10}Fe{sub 1.8}O{sub 4} have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), Mössbauer spectroscopy and vibrating sample magnetometer(VSM). Sample of high purity and high homogeneity was obtained by calcination at low temperature (500°C) resulting in nanoparticles of average diameter ∼15nm as determined by XRD and further confirmed by TEM. X-ray diffraction (XRD) and selective area diffraction (SAED) confirmed the single phase of the sample. Mössbauer results are supported by magnetization data. Well defined sextets and appearance of hysteresis at room temperature indicate the existence of ferromagnetic coupling at room temperature finding material utility in magnetic storage data. The existence of iron in ferric state confirmed by isomer shift is a clear evidence of improved magnetic properties of the present system.

  4. Spin-valley caloritronics in silicene near room temperature

    NASA Astrophysics Data System (ADS)

    Zhai, Xuechao; Gao, Wenwen; Cai, Xinlong; Fan, Ding; Yang, Zhihong; Meng, Lan

    2016-12-01

    Two-dimensional silicene, with an observable intrinsic spin-orbit coupling, has a great potential to perform fascinating physics and new types of applications in spintronics and valleytronics. By introducing an electromotive force from a temperature difference in ferromagnetic silicene, we discover that a longitudinal spin Seebeck effect can be driven even near room temperature, with spin-up and spin-down currents flowing in opposite directions, originating from the asymmetric electron-hole spin band structures. We further propose a silicene field-effect transistor constructed of two ferromagnetic electrodes and a central dual-gated region, and find that a valley Seebeck effect appears, with currents from two different valleys flowing in opposite directions. The forbidden transport channels are determined by either spin-valley dependent band gaps or spin mismatch. By tuning the electric field in the central region, the transport gaps depending on spin and valley vary correspondingly, and a transition from valley Seebeck effect to spin Seebeck effect is observed. These spin-valley caloritronic results near room temperature are robust against many real perturbations, and thus suggest silicene to be an excellent candidate for future energy-saving technologies and bidirectional information processing in solid-state circuits.

  5. Thin film’s magnetostriction investigated by strain modulated ferromagnetic resonance at low temperature

    NASA Astrophysics Data System (ADS)

    Nesteruk, K.; Żuberek, R.; Piechota, S.; Gutowski, M. W.; Szymczak, H.

    2014-07-01

    The novel experimental setup for measurements of magnetostriction of thin films in the temperature range starting from 4.2 K up to the room temperature, using the strain modulated ferromagnetic resonance phenomenon, is presented. The sample under investigation is fixed at the anti-node of vibrations of the longitudinal mode sapphire resonator. The resonator is excited by means of a piezoelectric transducer via the mechanical waveguide. The sapphire rod is put into a helium flow cryostat, thus allowing the measurements in the wide temperature range. The temperature gradient along the resonator length is negligible due to the very high thermal conductivity of sapphire. The setup is controlled by specially designed electronic circuit interfaced to a computer. As an illustrative example, the measurements of epitaxial Fe/GaAs(001) films were performed with in-plane magnetic field, in the temperature range between 10 K and the room temperature.

  6. Strain-induced extrinsic high-temperature ferromagnetism in the Fe-doped hexagonal barium titanate.

    PubMed

    Zorko, A; Pregelj, M; Gomilšek, M; Jagličić, Z; Pajić, D; Telling, M; Arčon, I; Mikulska, I; Valant, M

    2015-01-09

    Diluted magnetic semiconductors possessing intrinsic static magnetism at high temperatures represent a promising class of multifunctional materials with high application potential in spintronics and magneto-optics. In the hexagonal Fe-doped diluted magnetic oxide, 6H-BaTiO3-δ, room-temperature ferromagnetism has been previously reported. Ferromagnetism is broadly accepted as an intrinsic property of this material, despite its unusual dependence on doping concentration and processing conditions. However, the here reported combination of bulk magnetization and complementary in-depth local-probe electron spin resonance and muon spin relaxation measurements, challenges this conjecture. While a ferromagnetic transition occurs around 700 K, it does so only in additionally annealed samples and is accompanied by an extremely small average value of the ordered magnetic moment. Furthermore, several additional magnetic instabilities are detected at lower temperatures. These coincide with electronic instabilities of the Fe-doped 3C-BaTiO3-δ pseudocubic polymorph. Moreover, the distribution of iron dopants with frozen magnetic moments is found to be non-uniform. Our results demonstrate that the intricate static magnetism of the hexagonal phase is not intrinsic, but rather stems from sparse strain-induced pseudocubic regions. We point out the vital role of internal strain in establishing defect ferromagnetism in systems with competing structural phases.

  7. Strain-Induced Extrinsic High-Temperature Ferromagnetism in the Fe-Doped Hexagonal Barium Titanate

    PubMed Central

    Zorko, A.; Pregelj, M.; Gomilšek, M.; Jagličić, Z.; Pajić, D.; Telling, M.; Arčon, I.; Mikulska, I.; Valant, M.

    2015-01-01

    Diluted magnetic semiconductors possessing intrinsic static magnetism at high temperatures represent a promising class of multifunctional materials with high application potential in spintronics and magneto-optics. In the hexagonal Fe-doped diluted magnetic oxide, 6H-BaTiO3-δ, room-temperature ferromagnetism has been previously reported. Ferromagnetism is broadly accepted as an intrinsic property of this material, despite its unusual dependence on doping concentration and processing conditions. However, the here reported combination of bulk magnetization and complementary in-depth local-probe electron spin resonance and muon spin relaxation measurements, challenges this conjecture. While a ferromagnetic transition occurs around 700 K, it does so only in additionally annealed samples and is accompanied by an extremely small average value of the ordered magnetic moment. Furthermore, several additional magnetic instabilities are detected at lower temperatures. These coincide with electronic instabilities of the Fe-doped 3C-BaTiO3-δ pseudocubic polymorph. Moreover, the distribution of iron dopants with frozen magnetic moments is found to be non-uniform. Our results demonstrate that the intricate static magnetism of the hexagonal phase is not intrinsic, but rather stems from sparse strain-induced pseudocubic regions. We point out the vital role of internal strain in establishing defect ferromagnetism in systems with competing structural phases. PMID:25572803

  8. Room-temperature helimagnetism in FeGe thin films.

    PubMed

    Zhang, S L; Stasinopoulos, I; Lancaster, T; Xiao, F; Bauer, A; Rucker, F; Baker, A A; Figueroa, A I; Salman, Z; Pratt, F L; Blundell, S J; Prokscha, T; Suter, A; Waizner, J; Garst, M; Grundler, D; van der Laan, G; Pfleiderer, C; Hesjedal, T

    2017-03-09

    Chiral magnets are promising materials for the realisation of high-density and low-power spintronic memory devices. For these future applications, a key requirement is the synthesis of appropriate materials in the form of thin films ordering well above room temperature. Driven by the Dzyaloshinskii-Moriya interaction, the cubic compound FeGe exhibits helimagnetism with a relatively high transition temperature of 278 K in bulk crystals. We demonstrate that this temperature can be enhanced significantly in thin films. Using x-ray scattering and ferromagnetic resonance techniques, we provide unambiguous experimental evidence for long-wavelength helimagnetic order at room temperature and magnetic properties similar to the bulk material. We obtain α intr = 0.0036 ± 0.0003 at 310 K for the intrinsic damping parameter. We probe the dynamics of the system by means of muon-spin rotation, indicating that the ground state is reached via a freezing out of slow dynamics. Our work paves the way towards the fabrication of thin films of chiral magnets that host certain spin whirls, so-called skyrmions, at room temperature and potentially offer integrability into modern electronics.

  9. Room temperature creep in metals and alloys

    SciTech Connect

    Deibler, Lisa Anne

    2014-09-01

    Time dependent deformation in the form of creep and stress relaxation is not often considered a factor when designing structural alloy parts for use at room temperature. However, creep and stress relaxation do occur at room temperature (0.09-0.21 Tm for alloys in this report) in structural alloys. This report will summarize the available literature on room temperature creep, present creep data collected on various structural alloys, and finally compare the acquired data to equations used in the literature to model creep behavior. Based on evidence from the literature and fitting of various equations, the mechanism which causes room temperature creep is found to include dislocation generation as well as exhaustion.

  10. IMPROVED SYNTHESIS OF ROOM TEMPERATURE IONIC LIQUIDS

    EPA Science Inventory

    Room temperature ionic liquids (RTILs), molten salts comprised of N-alkylimidazolium cations and various anions, have received significant attention due to their commercial potential in a variety of chemical applications especially as substitutes for conventional volatile organic...

  11. IMPROVED SYNTHESIS OF ROOM TEMPERATURE IONIC LIQUIDS

    EPA Science Inventory

    Room temperature ionic liquids (RTILs), molten salts comprised of N-alkylimidazolium cations and various anions, have received significant attention due to their commercial potential in a variety of chemical applications especially as substitutes for conventional volatile organic...

  12. Determining Camera Gain in Room Temperature Cameras

    SciTech Connect

    Joshua Cogliati

    2010-12-01

    James R. Janesick provides a method for determining the amplification of a CCD or CMOS camera when only access to the raw images is provided. However, the equation that is provided ignores the contribution of dark current. For CCD or CMOS cameras that are cooled well below room temperature, this is not a problem, however, the technique needs adjustment for use with room temperature cameras. This article describes the adjustment made to the equation, and a test of this method.

  13. Room temperature water Leidenfrost droplets.

    PubMed

    Celestini, Franck; Frisch, Thomas; Pomeau, Yves

    2013-10-28

    We experimentally investigate the Leidenfrost effect at pressures ranging from 1 to 0.05 atmospheric pressure. As a direct consequence of the Clausius–Clapeyron phase diagram of water, the droplet temperature can be at ambient temperature in a non-sophisticated lab environment. Furthermore, the lifetime of the Leidenfrost droplet is significantly increased in this low pressure environment. The temperature and pressure dependence of the evaporation rate is successfully tested against a recently proposed model. These results may pave the way for reaching efficient Leidenfrost micro-fluidic and milli-fluidic applications.

  14. Towards Room Temperature Spin Filtering in Oxide Tunnel Junctions

    NASA Astrophysics Data System (ADS)

    Iwata-Harms, Jodi; Wong, Franklin; Arenholz, Elke; Suzuki, Yuri

    2012-02-01

    Spin filtering, in which the magnetic tunnel barrier preferentially filters spin-up and spin-down electrons from a nonmagnetic electrode, has been demonstrated in junction heterostructures. By incorporating two spin filtering barriers, double spin filter magnetic tunnel junctions (DSF-MTJs) were predicted to yield magnetoresistance (MR) values orders of magnitude larger than that of conventional magnetic tunnel junctions. Recently, DSF-MTJs have exhibited spin filtering with magnetic electrodes at room temperature and at low temperature with nonmagnetic electrodes in EuS-based devices [1,2]. We have fabricated DSF-MTJs with nonmagnetic SrRuO3 electrodes and room temperature ferrimagnets, NiFe2O4 and CoFe2O4, for spin filters in pursuit of room temperature functionality. Atomic force microscopy shows smooth films quantified by roughness values between 0.1--0.5nm. X-ray magnetic circular dichroism reveals ferromagnetic Ni^2+ and Co^2+, and element-specific hysteresis loops indicate the independent switching of the two spin filters. Transport data reveals junction MR and non-linear I-V characteristics consistent with tunneling. [4pt] [1] M.G. Chapline et al., PRB, 74, 014418 (2006).[0pt] [2] G.- X. Miao et al., PRL, 102, 076601 (2009).

  15. Experimental Demonstration of Room-Temperature Spin Transport in n -Type Germanium Epilayers

    NASA Astrophysics Data System (ADS)

    Dushenko, S.; Koike, M.; Ando, Y.; Shinjo, T.; Myronov, M.; Shiraishi, M.

    2015-05-01

    We report an experimental demonstration of room-temperature spin transport in n -type Ge epilayers grown on a Si(001) substrate. By utilizing spin pumping under ferromagnetic resonance, which inherently endows a spin battery function for semiconductors connected with a ferromagnet, a pure spin current is generated in the n -Ge at room temperature. The pure spin current is detected by using the inverse spin-Hall effect of either a Pt or Pd electrode on n -Ge . From a theoretical model that includes a geometrical contribution, the spin diffusion length in n -Ge at room temperature is estimated to be 660 nm. Moreover, the spin relaxation time decreases with increasing temperature, in agreement with a recently proposed theory of donor-driven spin relaxation in multivalley semiconductors.

  16. Experimental Demonstration of Room-Temperature Spin Transport in n-Type Germanium Epilayers.

    PubMed

    Dushenko, S; Koike, M; Ando, Y; Shinjo, T; Myronov, M; Shiraishi, M

    2015-05-15

    We report an experimental demonstration of room-temperature spin transport in n-type Ge epilayers grown on a Si(001) substrate. By utilizing spin pumping under ferromagnetic resonance, which inherently endows a spin battery function for semiconductors connected with a ferromagnet, a pure spin current is generated in the n-Ge at room temperature. The pure spin current is detected by using the inverse spin-Hall effect of either a Pt or Pd electrode on n-Ge. From a theoretical model that includes a geometrical contribution, the spin diffusion length in n-Ge at room temperature is estimated to be 660 nm. Moreover, the spin relaxation time decreases with increasing temperature, in agreement with a recently proposed theory of donor-driven spin relaxation in multivalley semiconductors.

  17. Multiferroic Nanopatterned Hybrid Material with Room-Temperature Magnetic Switching of the Electric Polarization.

    PubMed

    Cai, Ronggang; Antohe, Vlad-Andrei; Hu, Zhijun; Nysten, Bernard; Piraux, Luc; Jonas, Alain M

    2017-02-01

    A nanopatterned hybrid layer is designed, wherein the electric polarization can be flipped at room temperature by a magnetic field aided by an electrical field. This is achieved by embedding ferromagnetic nanopillars in a continuous organic ferroelectric layer, and amplifying the magnetostriction-generated stress gradients by scaling down the supracrystalline cell of the material.

  18. Influence of interstitial Mn on magnetism in the room-temperature ferromagnet Mn1+δSb

    SciTech Connect

    Taylor, Alice E.; Berlijn, Tom; Hahn, Steven E.; May, Andrew F.; Williams, Travis J.; Poudel, Lekhanath N; Calder, Stuart A.; Fishman, Randy Scott; Stone, Matthew B.; Aczel, Adam A.; Cao, Huibo; Lumsden, Mark D.; Christianson, Andrew D.

    2015-06-15

    We report elastic and inelastic neutron scattering measurements of the high-TC ferromagnet Mn1+δSb. Measurements were performed on a large, TC = 434 K, single crystal with interstitial Mn content of δ ≈ 0.13. The neutron diffraction results reveal that the interstitial Mn has a magnetic moment, and that it is aligned antiparallel to the main Mn moment. We perform density functional theory calculations including the interstitial Mn, and find the interstitial to be magnetic in agreement with the diffraction data. The inelastic neutron scattering measurements reveal two features in the magnetic dynamics: i) a spin-wave-like dispersion emanating from ferromagnetic Bragg positions (H K 2n), and ii) a broad, non-dispersive signal centered at forbidden Bragg positions (H K 2n+1). The inelastic spectrum cannot be modeled by simple linear spin-wave theory calculations, and appears to be significantly altered by the presence of the interstitial Mn ions. Finally, the results show that the influence of the interstitial Mn on the magnetic state in this system is more important than previously understood.

  19. Cobalt-doped anatase TiO2: A room temperature dilute magnetic dielectric material

    NASA Astrophysics Data System (ADS)

    Griffin, K. A.; Pakhomov, A. B.; Wang, C. M.; Heald, S. M.; Krishnan, Kannan M.

    2005-05-01

    We experimentally investigate the room temperature ferromagnetism observed in insulating Co doped anatase TiO2 thin films grown by sputter deposition. The Co was uniformly incorporated in the lattice as Co(II) with no evidence of Co metal. A series of annealing treatments were carried out to optimize the ferromagnetic ordering and a saturation moment of 1.1μB/Co atom at 300 K was obtained with UHV annealing at 450 °C. Both as-deposited and annealed films were highly insulating at room temperature. Results show that the ferromagnetism is strongly dependent on the number and distribution of oxygen vacancies in the Co:TiO2 lattice.

  20. Towards a new class of heavy ion doped magnetic semiconductors for room temperature applications

    NASA Astrophysics Data System (ADS)

    Lee, Juwon; Subramaniam, Nagarajan Ganapathi; Agnieszka Kowalik, Iwona; Nisar, Jawad; Lee, Jaechul; Kwon, Younghae; Lee, Jaechoon; Kang, Taewon; Peng, Xiangyang; Arvanitis, Dimitri; Ahuja, Rajeev

    2015-11-01

    The article presents, using Bi doped ZnO, an example of a heavy ion doped oxide semiconductor, highlighting a novel p-symmetry interaction of the electronic states to stabilize ferromagnetism. The study includes both ab initio theory and experiments, which yield clear evidence for above room temperature ferromagnetism. ZnBixO1-x thin films are grown using the pulsed laser deposition technique. The room temperature ferromagnetism finds its origin in the holes introduced by the Bi doping and the p-p coupling between Bi and the host atoms. A sizeable magnetic moment is measured by means of x-ray magnetic circular dichroism at the O K-edge, probing directly the spin polarization of the O(2p) states. This result is in agreement with the theoretical predictions and inductive magnetometry measurements. Ab initio calculations of the electronic and magnetic structure of ZnBixO1-x at various doping levels allow to trace the origin of the ferromagnetic character of this material. It appears, that the spin-orbit energy of the heavy ion Bi stabilizes the ferromagnetic phase. Thus, ZnBixO1-x doped with a heavy non-ferromagnetic element, such as Bi, is a credible example of a candidate material for a new class of compounds for spintronics applications, based on the spin polarization of the p states.

  1. Towards a new class of heavy ion doped magnetic semiconductors for room temperature applications

    PubMed Central

    Lee, Juwon; Subramaniam, Nagarajan Ganapathi; Agnieszka Kowalik, Iwona; Nisar, Jawad; Lee, Jaechul; Kwon, Younghae; Lee, Jaechoon; Kang, Taewon; Peng, Xiangyang; Arvanitis, Dimitri; Ahuja, Rajeev

    2015-01-01

    The article presents, using Bi doped ZnO, an example of a heavy ion doped oxide semiconductor, highlighting a novel p-symmetry interaction of the electronic states to stabilize ferromagnetism. The study includes both ab initio theory and experiments, which yield clear evidence for above room temperature ferromagnetism. ZnBixO1−x thin films are grown using the pulsed laser deposition technique. The room temperature ferromagnetism finds its origin in the holes introduced by the Bi doping and the p-p coupling between Bi and the host atoms. A sizeable magnetic moment is measured by means of x-ray magnetic circular dichroism at the O K-edge, probing directly the spin polarization of the O(2p) states. This result is in agreement with the theoretical predictions and inductive magnetometry measurements. Ab initio calculations of the electronic and magnetic structure of ZnBixO1−x at various doping levels allow to trace the origin of the ferromagnetic character of this material. It appears, that the spin-orbit energy of the heavy ion Bi stabilizes the ferromagnetic phase. Thus, ZnBixO1−x doped with a heavy non-ferromagnetic element, such as Bi, is a credible example of a candidate material for a new class of compounds for spintronics applications, based on the spin polarization of the p states. PMID:26592564

  2. High temperature ferromagnetism with a giant magnetic moment in transparent co-doped SnO(2-delta).

    PubMed

    Ogale, S B; Choudhary, R J; Buban, J P; Lofland, S E; Shinde, S R; Kale, S N; Kulkarni, V N; Higgins, J; Lanci, C; Simpson, J R; Browning, N D; Das Sarma, S; Drew, H D; Greene, R L; Venkatesan, T

    2003-08-15

    The occurrence of room temperature ferromagnetism is demonstrated in pulsed laser deposited thin films of Sn(1-x)Co(x)O(2-delta) (x<0.3). Interestingly, films of Sn(0.95)Co(0.05)O(2-delta) grown on R-plane sapphire not only exhibit ferromagnetism with a Curie temperature close to 650 K, but also a giant magnetic moment of 7.5+/-0.5 micro(B)/Co, not yet reported in any diluted magnetic semiconductor system. The films are semiconducting and optically highly transparent.

  3. Remote control of magnetostriction-based nanocontacts at room temperature.

    PubMed

    Jammalamadaka, S Narayana; Kuntz, Sebastian; Berg, Oliver; Kittler, Wolfram; Kannan, U Mohanan; Chelvane, J Arout; Sürgers, Christoph

    2015-09-01

    The remote control of the electrical conductance through nanosized junctions at room temperature will play an important role in future nano-electromechanical systems and electronic devices. This can be achieved by exploiting the magnetostriction effects of ferromagnetic materials. Here we report on the electrical conductance of magnetic nanocontacts obtained from wires of the giant magnetostrictive compound Tb0.3Dy0.7Fe1.95 as an active element in a mechanically controlled break-junction device. The nanocontacts are reproducibly switched at room temperature between "open" (zero conductance) and "closed" (nonzero conductance) states by variation of a magnetic field applied perpendicularly to the long wire axis. Conductance measurements in a magnetic field oriented parallel to the long wire axis exhibit a different behaviour where the conductance switches between both states only in a limited field range close to the coercive field. Investigating the conductance in the regime of electron tunneling by mechanical or magnetostrictive control of the electrode separation enables an estimation of the magnetostriction. The present results pave the way to utilize the material in devices based on nano-electromechanical systems operating at room temperature.

  4. Remote control of magnetostriction-based nanocontacts at room temperature

    PubMed Central

    Jammalamadaka, S. Narayana; Kuntz, Sebastian; Berg, Oliver; Kittler, Wolfram; Kannan, U. Mohanan; Chelvane, J. Arout; Sürgers, Christoph

    2015-01-01

    The remote control of the electrical conductance through nanosized junctions at room temperature will play an important role in future nano-electromechanical systems and electronic devices. This can be achieved by exploiting the magnetostriction effects of ferromagnetic materials. Here we report on the electrical conductance of magnetic nanocontacts obtained from wires of the giant magnetostrictive compound Tb0.3Dy0.7Fe1.95 as an active element in a mechanically controlled break-junction device. The nanocontacts are reproducibly switched at room temperature between “open” (zero conductance) and “closed” (nonzero conductance) states by variation of a magnetic field applied perpendicularly to the long wire axis. Conductance measurements in a magnetic field oriented parallel to the long wire axis exhibit a different behaviour where the conductance switches between both states only in a limited field range close to the coercive field. Investigating the conductance in the regime of electron tunneling by mechanical or magnetostrictive control of the electrode separation enables an estimation of the magnetostriction. The present results pave the way to utilize the material in devices based on nano-electromechanical systems operating at room temperature. PMID:26323326

  5. Structural phase transition, narrow band gap, and room-temperature ferromagnetism in [KNbO{sub 3}]{sub 1−x}[BaNi{sub 1/2}Nb{sub 1/2}O{sub 3−δ}]{sub x} ferroelectrics

    SciTech Connect

    Zhou, Wenliang; Yang, Pingxiong Chu, Junhao; Deng, Hongmei

    2014-09-15

    Structural phase transition, narrow band gap (E{sub g}), and room-temperature ferromagnetism (RTFM) have been observed in the [KNbO{sub 3}]{sub 1−x}[BaNi{sub 1/2}Nb{sub 1/2}O{sub 3−δ}]{sub x} (KBNNO) ceramics. All the samples have single phase perovskite structure, but exhibit a gradual transition behaviour from the orthorhombic to a cubic structure with the increase of x. Raman spectroscopy analysis not only corroborates this doping-induced change in normal structure but also shows the local crystal symmetry for x ≥ 0.1 compositions to deviate from the idealized cubic perovskite structure. A possible mechanism for the observed specific changes in lattice structure is discussed. Moreover, it is noted that KBNNO with compositions x = 0.1–0.3 have quite narrow E{sub g} of below 1.5 eV, much smaller than the 3.2 eV band gap of parent KNbO{sub 3} (KNO), which is due to the increasing Ni 3d electronic states within the gap of KNO. Furthermore, the KBNNO materials present RTFM near a tetragonal to cubic phase boundary. With increasing x from 0 to 0.3, the magnetism of the samples develops from diamagnetism to ferromagnetism and paramagnetism, originating from the ferromagnetic–antiferromagnetic competition. These results are helpful in the deeper understanding of phase transitions, band gap tunability, and magnetism variations in perovskite oxides and show the potential role, such materials can play, in perovskite solar cells and multiferroic applications.

  6. High-Temperature Ferromagnetism in Low-Carrier Density Semimetals

    NASA Astrophysics Data System (ADS)

    Young, David P.

    2000-03-01

    Experimental results are presented on the magnetic and transport properties of lightly-doped alkaline earth hexaborides. At very low doping levels ( ~0.5%) weak ferromagnetism is observed at high temperature, which is an unexpected result considering that none of the constituent elements is normally associated with magnetic ordering. This phenomenon is fairly robust, with a Curie temperature near 600 K, which is also close to the value of the Fermi temperature. Two important aspects of this ferromagnetism are the following: (1)the magnetic ordering is only observed over a small range of doping concentrations, and (2)the maximum magnetic moment is about 0.1 μB per charge carrier. Two different theoretical descriptions have been proposed to explain the ferromagnetism: polarization of the free 3D electron gas at low density and spontaneous magnetization arising from a spin-triplet state in a doped excitonic insulator. This work is due to a collaborative effort with M.E. Torelli, D.W. Hall, A.D. Bianchi, F. Drymiotis, and Z. Fisk, NHMFL and Florida State University, Tallahassee, FL; R. Zysler, CA Bariloche, Argentina; R.G. Goodrich, Louisiana State University, Baton Rouge, LA; S. Oseroff, San Diego State University, San Diego, CA; J.D. Thompson and J.L. Sarrao, LANL, Los Alamos, NM; and H.-R. Ott, ETH, Zurich.

  7. Competing ferromagnetism in high-temperature copper oxide superconductors.

    PubMed

    Kopp, Angela; Ghosal, Amit; Chakravarty, Sudip

    2007-04-10

    The extreme variability of observables across the phase diagram of the cuprate high-temperature superconductors has remained a profound mystery, with no convincing explanation for the superconducting dome. Although much attention has been paid to the underdoped regime of the hole-doped cuprates because of its proximity to a complex Mott insulating phase, little attention has been paid to the overdoped regime. Experiments are beginning to reveal that the phenomenology of the overdoped regime is just as puzzling. For example, the electrons appear to form a Landau Fermi liquid, but this interpretation is problematic; any trace of Mott phenomena, as signified by incommensurate antiferromagnetic fluctuations, is absent, and the uniform spin susceptibility shows a ferromagnetic upturn. Here, we show and justify that many of these puzzles can be resolved if we assume that competing ferromagnetic fluctuations are simultaneously present with superconductivity, and the termination of the superconducting dome in the overdoped regime marks a quantum critical point beyond which there should be a genuine ferromagnetic phase at zero temperature. We propose experiments and make predictions to test our theory and suggest that an effort must be mounted to elucidate the nature of the overdoped regime, if the problem of high-temperature superconductivity is to be solved. Our approach places competing order as the root of the complexity of the cuprate phase diagram.

  8. Competing ferromagnetism in high-temperature copper oxide superconductors

    PubMed Central

    Kopp, Angela; Ghosal, Amit; Chakravarty, Sudip

    2007-01-01

    The extreme variability of observables across the phase diagram of the cuprate high-temperature superconductors has remained a profound mystery, with no convincing explanation for the superconducting dome. Although much attention has been paid to the underdoped regime of the hole-doped cuprates because of its proximity to a complex Mott insulating phase, little attention has been paid to the overdoped regime. Experiments are beginning to reveal that the phenomenology of the overdoped regime is just as puzzling. For example, the electrons appear to form a Landau Fermi liquid, but this interpretation is problematic; any trace of Mott phenomena, as signified by incommensurate antiferromagnetic fluctuations, is absent, and the uniform spin susceptibility shows a ferromagnetic upturn. Here, we show and justify that many of these puzzles can be resolved if we assume that competing ferromagnetic fluctuations are simultaneously present with superconductivity, and the termination of the superconducting dome in the overdoped regime marks a quantum critical point beyond which there should be a genuine ferromagnetic phase at zero temperature. We propose experiments and make predictions to test our theory and suggest that an effort must be mounted to elucidate the nature of the overdoped regime, if the problem of high-temperature superconductivity is to be solved. Our approach places competing order as the root of the complexity of the cuprate phase diagram. PMID:17404239

  9. Electric control of magnetism at room temperature.

    PubMed

    Wang, Liaoyu; Wang, Dunhui; Cao, Qingqi; Zheng, Yuanxia; Xuan, Haicheng; Gao, Jinlong; Du, Youwei

    2012-01-01

    In the single-phase multiferroics, the coupling between electric polarization (P) and magnetization (M) would enable the magnetoelectric (ME) effect, namely M induced and modulated by E, and conversely P by H. Especially, the manipulation of magnetization by an electric field at room-temperature is of great importance in technological applications, such as new information storage technology, four-state logic device, magnetoelectric sensors, low-power magnetoelectric device and so on. Furthermore, it can reduce power consumption and realize device miniaturization, which is very useful for the practical applications. In an M-type hexaferrite SrCo(2)Ti(2)Fe(8)O(19), large magnetization and electric polarization were observed simultaneously at room-temperature. Moreover, large effect of electric field-controlled magnetization was observed even without magnetic bias field. These results illuminate a promising potential to apply in magnetoelectric devices at room temperature and imply plentiful physics behind them.

  10. Electric control of magnetism at room temperature

    PubMed Central

    Wang, Liaoyu; Wang, Dunhui; Cao, Qingqi; Zheng, Yuanxia; Xuan, Haicheng; Gao, Jinlong; Du, Youwei

    2012-01-01

    In the single-phase multiferroics, the coupling between electric polarization (P) and magnetization (M) would enable the magnetoelectric (ME) effect, namely M induced and modulated by E, and conversely P by H. Especially, the manipulation of magnetization by an electric field at room-temperature is of great importance in technological applications, such as new information storage technology, four-state logic device, magnetoelectric sensors, low-power magnetoelectric device and so on. Furthermore, it can reduce power consumption and realize device miniaturization, which is very useful for the practical applications. In an M-type hexaferrite SrCo2Ti2Fe8O19, large magnetization and electric polarization were observed simultaneously at room-temperature. Moreover, large effect of electric field-controlled magnetization was observed even without magnetic bias field. These results illuminate a promising potential to apply in magnetoelectric devices at room temperature and imply plentiful physics behind them. PMID:22355737

  11. Dynamics of Glass Relaxation at Room Temperature

    NASA Astrophysics Data System (ADS)

    Welch, Roger C.; Smith, John R.; Potuzak, Marcel; Guo, Xiaoju; Bowden, Bradley F.; Kiczenski, T. J.; Allan, Douglas C.; King, Ellyn A.; Ellison, Adam J.; Mauro, John C.

    2013-06-01

    The problem of glass relaxation under ambient conditions has intrigued scientists and the general public for centuries, most notably in the legend of flowing cathedral glass windows. Here we report quantitative measurement of glass relaxation at room temperature. We find that Corning® Gorilla® Glass shows measurable and reproducible relaxation at room temperature. Remarkably, this relaxation follows a stretched exponential decay rather than simple exponential relaxation, and the value of the stretching exponent (β=3/7) follows a theoretical prediction made by Phillips for homogeneous glasses.

  12. Widely tunable room temperature semiconductor terahertz source

    SciTech Connect

    Lu, Q. Y.; Slivken, S.; Bandyopadhyay, N.; Bai, Y.; Razeghi, M.

    2014-11-17

    We present a widely tunable, monolithic terahertz source based on intracavity difference frequency generation within a mid-infrared quantum cascade laser at room temperature. A three-section ridge waveguide laser design with two sampled grating sections and a distributed-Bragg section is used to achieve the terahertz (THz) frequency tuning. Room temperature single mode THz emission with a wide tunable frequency range of 2.6–4.2 THz (∼47% of the central frequency) and THz power up to 0.1 mW is demonstrated, making such device an ideal candidate for THz spectroscopy and sensing.

  13. Curie temperature of ultrathin ferromagnetic layer with Dzyaloshinskii-Moriya interaction

    SciTech Connect

    You, Chun-Yeol

    2014-08-07

    We investigate the effect of the Dzyaloshinskii-Moriya interaction (DMI) on the Curie temperature of the ultrathin ferromagnetic layers. It has been known that the Curie temperature of the ferromagnet depends on spin wave excitation energies, and they are affected by DMI. Therefore, the ferromagnetic transition temperature of the ultrathin ferromagnetic layer must be sensitive on the DMI. We find that the Curie temperature depends on the DMI by using the double time Green's function method. Since the DMI is arisen by the inversion symmetry breaking structure, the DMI is always important in the inversion symmetry breaking ultrathin ferromagnetic layers.

  14. Ferromagnetic particles as magnetic resonance imaging temperature sensors

    PubMed Central

    Hankiewicz, J. H.; Celinski, Z.; Stupic, K. F.; Anderson, N. R.; Camley, R. E.

    2016-01-01

    Magnetic resonance imaging is an important technique for identifying different types of tissues in a body or spatial information about composite materials. Because temperature is a fundamental parameter reflecting the biological status of the body and individual tissues, it would be helpful to have temperature maps superimposed on spatial maps. Here we show that small ferromagnetic particles with a strong temperature-dependent magnetization, can be used to produce temperature-dependent images in magnetic resonance imaging with an accuracy of about 1 °C. This technique, when further developed, could be used to identify inflammation or tumours, or to obtain spatial maps of temperature in various medical interventional procedures such as hyperthermia and thermal ablation. This method could also be used to determine temperature profiles inside nonmetallic composite materials. PMID:27503610

  15. Ferromagnetic particles as magnetic resonance imaging temperature sensors

    NASA Astrophysics Data System (ADS)

    Hankiewicz, J. H.; Celinski, Z.; Stupic, K. F.; Anderson, N. R.; Camley, R. E.

    2016-08-01

    Magnetic resonance imaging is an important technique for identifying different types of tissues in a body or spatial information about composite materials. Because temperature is a fundamental parameter reflecting the biological status of the body and individual tissues, it would be helpful to have temperature maps superimposed on spatial maps. Here we show that small ferromagnetic particles with a strong temperature-dependent magnetization, can be used to produce temperature-dependent images in magnetic resonance imaging with an accuracy of about 1 °C. This technique, when further developed, could be used to identify inflammation or tumours, or to obtain spatial maps of temperature in various medical interventional procedures such as hyperthermia and thermal ablation. This method could also be used to determine temperature profiles inside nonmetallic composite materials.

  16. Ferromagnetic particles as magnetic resonance imaging temperature sensors.

    PubMed

    Hankiewicz, J H; Celinski, Z; Stupic, K F; Anderson, N R; Camley, R E

    2016-08-09

    Magnetic resonance imaging is an important technique for identifying different types of tissues in a body or spatial information about composite materials. Because temperature is a fundamental parameter reflecting the biological status of the body and individual tissues, it would be helpful to have temperature maps superimposed on spatial maps. Here we show that small ferromagnetic particles with a strong temperature-dependent magnetization, can be used to produce temperature-dependent images in magnetic resonance imaging with an accuracy of about 1 °C. This technique, when further developed, could be used to identify inflammation or tumours, or to obtain spatial maps of temperature in various medical interventional procedures such as hyperthermia and thermal ablation. This method could also be used to determine temperature profiles inside nonmetallic composite materials.

  17. Imaging spin diffusion in germanium at room temperature

    NASA Astrophysics Data System (ADS)

    Zucchetti, C.; Bottegoni, F.; Vergnaud, C.; Ciccacci, F.; Isella, G.; Ghirardini, L.; Celebrano, M.; Rortais, F.; Ferrari, A.; Marty, A.; Finazzi, M.; Jamet, M.

    2017-07-01

    We report on the nonlocal detection of optically oriented spins in lightly n -doped germanium at room temperature. Localized spin generation is achieved by scanning a circularly polarized laser beam (λ =1550 nm) on an array of lithographically defined Pt microstructures. The in-plane oriented spin generated at the edges of such microstructures, placed at different distances from a spin-detection element, allows for a direct imaging of spin diffusion in the semiconductor, leading to a measured spin diffusion length of about 10 μ m . Two different spin-detection blocks are employed, consisting of either a magnetic tunnel junction or a platinum stripe where the spin current is converted in an electrical signal by the inverse spin-Hall effect. The second solution represents the realization of a nonlocal spin-injection/detection scheme that is completely free from ferromagnetic functional blocks.

  18. Room temperature synthesis of biodiesel using sulfonated ...

    EPA Pesticide Factsheets

    Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature. Prepared for submission to Royal Society of Chemistry (RSC) journal, Green Chemistry as a communication.

  19. High-Curie-temperature ferromagnetism in self-organized Ge1-xMnx nanocolumns.

    PubMed

    Jamet, Matthieu; Barski, André; Devillers, Thibaut; Poydenot, Valier; Dujardin, Romain; Bayle-Guillemaud, Pascale; Rothman, Johan; Bellet-Amalric, Edith; Marty, Alain; Cibert, Joël; Mattana, Richard; Tatarenko, Serge

    2006-08-01

    The emerging field of spintronics would be dramatically boosted if room-temperature ferromagnetism could be added to semiconductor nanostructures that are compatible with silicon technology. Here, we report a high-TC (>400K) ferromagnetic phase of (Ge,Mn) epitaxial layer. The manganese content is 6%, and careful structural and chemical analyses show that the Mn distribution is strongly inhomogeneous: we observe eutectoid growth of well-defined Mn-rich nanocolumns surrounded by a Mn-poor matrix. The average diameter of these nanocolumns is 3nm and their spacing is 10nm. Their composition is close to Ge(2)Mn, which corresponds to an unknown germanium-rich phase, and they have a uniaxially elongated diamond structure. Their Curie temperature is higher than 400K. Magnetotransport reveals a pronounced anomalous Hall effect up to room temperature. A giant positive magnetoresistance is measured from 7,000% at 30K to 200% at 300K and 9T, with no evidence of saturation.

  20. Multi-functional single electron device at room temperature

    NASA Astrophysics Data System (ADS)

    Nguyen, Chieu; Ong, Jason Kee Yang; Saraf, Ravi F.

    2014-03-01

    Smart designs of sub-wavelength structures enable observation of unusual properties of materials as in metamaterials. Typically, Coulomb blockade is observed in array of conducting particles at cryogenic temperature due to local charging of few particles by a single electron in the percolation path. We will report 1-D network of cemented Au nanoparticles in a multi-functional single electron device exhibiting Coulomb blockade at room temperature. The 1-D array is a self-assembled monolayer network spanning between electrodes 10-100 μm apart. It is formed by first bridging the negatively charged 10nm Au NPs with positive ions (Cd2+or Fe3+) followed by cementing with reactive gas to form a robust 2-D network. The network array cemented with CdS and Iron oxide exhibits robust single electron effect at room temperature with electroluminescence (EL) or ferromagnetism, respectively. The nature of EL in this symmetric structure is explained in term of field induced ionization. The EL is specular where the spots are independent of bias magnitude. The magnetic array exhibits ``spin-valve'' behavior with Barkhausen effect. These unique nano materials, fully self-assembled where, properties can be tailored by varying the cement chemistry, have potential applications in solid state lighting.

  1. Electrical creation of spin polarization in silicon at room temperature

    NASA Astrophysics Data System (ADS)

    Jansen, Ron

    2010-03-01

    The integration of magnetism and mainstream semiconductor electronics could impact information technology in ways beyond imagination. A pivotal step is the implementation of spin-based electronic functionality in silicon devices. Much of the interest in silicon derives from its prevalence in semiconductor technology and from the robustness and longevity of spin as it is only weakly coupled to other degrees of freedom in the material. Recently it has become possible to induce and detect spin polarization in otherwise non-magnetic semiconductors (GaAs and Si) using all-electrical structures, but so far at temperatures below 150 K and only in n-type material. The main challenges are: (i) to design fully electrical silicon-based spintronic devices with large spin signals, (ii) to demonstrate device operation at room temperature, (iii) to do so for n-type and p-type material, and (iv) to find ways to manipulate spins and spin flow with a gate electric field. After a brief overview of the state of affairs, our recent advances in these areas are described. In particular, we demonstrate room-temperature electrical injection of spin polarization into n-type and p-type silicon from a ferromagnetic tunnel contact, spin manipulation using the Hanle effect, and the electrical detection of the induced spin accumulation. It is shown that a spin splitting as large as 2.9 meV can be created in Si at room temperature, corresponding to an electron spin polarization of 4.6%. The results open the way to the implementation of spin functionality in complementary silicon devices and electronic circuits operating at ambient temperature, and to the exploration of their prospects as well as the fundamental rules that govern their behavior. [4pt] [1] S.P. Dash, S. Sharma, R.S. Patel, M.P. de Jong and R. Jansen, Nature 462, 491 (2009).

  2. Imprinting bulk amorphous alloy at room temperature

    SciTech Connect

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T.; Lograsso, Thomas A.; Huh, Moo-Young; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

    2015-11-13

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the ability of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. In conclusion, our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment.

  3. Imprinting bulk amorphous alloy at room temperature

    PubMed Central

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T.; Lograsso, Thomas A.; Huh, Moo-Young; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

    2015-01-01

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the ability of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. Our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment. PMID:26563908

  4. Finite-temperature spin polarization in half-metallic ferromagnets

    NASA Astrophysics Data System (ADS)

    Dowben, P. A.; Skomski, R.

    2003-05-01

    The temperature dependence of the spin polarization of half-metallic ferromagnets is investigated. A unitary spinor transformation shows that the corresponding spin mixing goes beyond finite-temperature smearing of the Fermi level, leading to a nonzero density of states in the gap of the insulating spin channel. As a consequence, the resistance ratio of the two spin channels changes from infinity to some finite value and, in a strict sense, half-metallic ferromagnetism is limited to zero temperature. Bloch-type spin waves and crystal imperfections contribute to the density of states in the gap but only partly explain the pronounced changes at about 0.2TC observed in various half-metallic magnets. In the case of NiMnSb, the spin structure depends on a nearly dispersionless transverse optical mode that occurs at about 28 meV. In terms of 3kBT, this corresponds to 103 K—very close to the temperature at which there is a dramatic loss in the Ni and Mn magnetization in NiMnSb. Similar modes exist in other potential half-metallic systems.

  5. Room-temperature semiconductor heterostructure refrigeration

    NASA Astrophysics Data System (ADS)

    Chao, K. A.; Larsson, Magnus; Mal'shukov, A. G.

    2005-07-01

    With the proper design of semiconductor tunneling barrier structures, we can inject low-energy electrons via resonant tunneling, and take out high-energy electrons via a thermionic process. This is the operation principle of our semiconductor heterostructure refrigerator (SHR) without the need of applying a temperature gradient across the device. Even for the bad thermoelectric material AlGaAs, our calculation shows that at room temperature, the SHR can easily lower the temperature by 5-7K. Such devices can be fabricated with the present semiconductor technology. Besides its use as a kitchen refrigerator, the SHR can efficiently cool microelectronic devices.

  6. Room Temperature Electrical Detection of Spin Polarized Currents in Topological Insulators.

    PubMed

    Dankert, André; Geurs, Johannes; Kamalakar, M Venkata; Charpentier, Sophie; Dash, Saroj P

    2015-12-09

    Topological insulators (TIs) are a new class of quantum materials that exhibit a current-induced spin polarization due to spin-momentum locking of massless Dirac Fermions in their surface states. This helical spin polarization in three-dimensional (3D) TIs has been observed using photoemission spectroscopy up to room temperatures. Recently, spin polarized surface currents in 3D TIs were detected electrically by potentiometric measurements using ferromagnetic detector contacts. However, these electric measurements are so far limited to cryogenic temperatures. Here we report the room temperature electrical detection of the spin polarization on the surface of Bi2Se3 by employing spin sensitive ferromagnetic tunnel contacts. The current-induced spin polarization on the Bi2Se3 surface is probed by measuring the magnetoresistance while switching the magnetization direction of the ferromagnetic detector. A spin resistance of up to 70 mΩ is measured at room temperature, which increases linearly with current bias, reverses sign with current direction, and decreases with higher TI thickness. The magnitude of the spin signal, its sign, and control experiments, using different measurement geometries and interface conditions, rule out other known physical effects. These findings provide further information about the electrical detection of current-induced spin polarizations in 3D TIs at ambient temperatures and could lead to innovative spin-based technologies.

  7. Spin Seebeck effect in a weak ferromagnet

    SciTech Connect

    Arboleda, Juan David Arnache Olmos, Oscar; Aguirre, Myriam Haydee; Ibarra, Manuel Ricardo; Ramos, Rafael; Anadon, Alberto

    2016-06-06

    We report the observation of room temperature spin Seebeck effect (SSE) in a weak ferromagnetic normal spinel Zinc Ferrite (ZFO). Despite the weak ferromagnetic behavior, the measurements of the SSE in ZFO show a thermoelectric voltage response comparable with the reported values for other ferromagnetic materials. Our results suggest that SSE might possibly originate from the surface magnetization of the ZFO.

  8. Spin Seebeck effect in a weak ferromagnet

    NASA Astrophysics Data System (ADS)

    Arboleda, Juan David; Arnache Olmos, Oscar; Aguirre, Myriam Haydee; Ramos, Rafael; Anadon, Alberto; Ibarra, Manuel Ricardo

    2016-06-01

    We report the observation of room temperature spin Seebeck effect (SSE) in a weak ferromagnetic normal spinel Zinc Ferrite (ZFO). Despite the weak ferromagnetic behavior, the measurements of the SSE in ZFO show a thermoelectric voltage response comparable with the reported values for other ferromagnetic materials. Our results suggest that SSE might possibly originate from the surface magnetization of the ZFO.

  9. Cubic ideal ferromagnets at low temperature and weak magnetic field

    NASA Astrophysics Data System (ADS)

    Hofmann, Christoph P.

    2017-04-01

    The low-temperature series for the free energy density, pressure, magnetization and susceptibility of cubic ideal ferromagnets in weak external magnetic fields are discussed within the effective Lagrangian framework up to three loops. The structure of the simple, body-centered, and face-centered cubic lattice is taken into account explicitly. The expansion involves integer and half-integer powers of the temperature. The corresponding coefficients depend on the magnetic field and on low-energy effective constants that can be expressed in terms of microscopic quantities. Our formulas may also serve as efficiency or consistency check for other techniques like Green's function methods, where spurious terms in the low-temperature expansion have appeared. We explore the sign and magnitude of the spin-wave interaction in the pressure, magnetization and susceptibility, and emphasize that our effective field theory approach is fully systematic and rigorous.

  10. Energy based model for temperature dependent behavior of ferromagnetic materials

    NASA Astrophysics Data System (ADS)

    Sah, Sanjay; Atulasimha, Jayasimha

    2017-03-01

    An energy based model for temperature dependent anhysteretic magnetization curves of ferromagnetic materials is proposed and benchmarked against experimental data. This is based on the calculation of macroscopic magnetic properties by performing an energy weighted average over all possible orientations of the magnetization vector. Most prior approaches that employ this method are unable to independently account for the effect of both inhomogeneity and temperature in performing the averaging necessary to model experimental data. Here we propose a way to account for both effects simultaneously and benchmark the model against experimental data from 5 K to 300 K for two different materials in both annealed (fewer inhomogeneities) and deformed (more inhomogeneities) samples. This demonstrates that this framework is well suited to simulate temperature dependent experimental magnetic behavior.

  11. High temperature ferromagnetism and optical properties of Co doped ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Pal, Bappaditya; Giri, P. K.

    2010-10-01

    We report on the occurrence of high temperature ferromagnetism (FM) in ZnO nanoparticles (NPs) doped with Co-atoms. ZnO NPs of two different initial sizes are doped with 3% and 5% Co using ball milling and FM is studied at room temperature and above. X-ray diffraction and high-resolution transmission electron microscopy analysis confirm the absence of metallic Co clusters or any other phase different from würtzite-type ZnO. UV-visible absorption studies show change in band structure and photoluminescence studies show green emission band at 520 nm indicating incorporation of Co-atoms and presence of oxygen vacancy defects, respectively in ZnO lattice. Micro-Raman studies of doped samples shows defect related additional bands at 547 and 574 cm-1. XRD and Raman spectra provide clear evidence for strain in the doped ZnO NPs. The field dependence of magnetization (M-H curve) measured at room temperature exhibits the clear FM with saturation magnetization (Ms) and coercive field (Hc) of the order of 3-7 emu/g and 260 Oe, respectively. Temperature dependence of magnetization (M-T) measurement shows sharp ferromagnetic to paramagnetic transition with a high Curie temperature (Tc) of ˜800 K for 3% Co doped ZnO NPs. It is found that doping at 5% and higher concentration does not exhibit a proper magnetic transition. We attempt to fit the observed FM data with the bound magnetic polaron (BMP) model involving localized carriers and magnetic cations. However, calculated concentration of the BMPs is well below the typical percolation threshold in ZnO. We believe that observed high temperature FM is primarily mediated by defects in the strained NPs. ZnO NPs of lower initial size show enhanced FM that may be attributed to size dependent doping effect.

  12. Physical understanding of negative bias temperature instability below room temperature

    NASA Astrophysics Data System (ADS)

    Ji, Xiaoli; Liao, Yiming; Yan, Feng; Zhu, Chenxin; Shi, Yi; Guo, Qiang

    2012-11-01

    The physical mechanism of VT degradations under negative bias temperature stress below room temperature has been studied for SiO2 and plasma nitrided oxide (PNO-based) pMOSFETs. It is found that VT degradations in both devices exhibit strong dependence on the electric field and temperature. The analysis shows that this strong dependence follows multi-phonon field-assisted tunneling theory, which indicates the inelastic hole trapping mechanism in the low temperature negative bias temperature instability (NBTI). On the other hand, by applying a low temperature sweeping technique, the energy distribution of these NBTI-induced hole traps below room temperature is indentified. The energy distribution of hole traps has two obvious peaks, one in the lower and one in the upper half of the silicon band gap. Both peaks gradually develop with increasing the stress time and temperature. We attempt to compare the energy profile for SiO2 and PNO devices to identify the trap precursors in NBTI below room temperature.

  13. Imprinting bulk amorphous alloy at room temperature

    DOE PAGES

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T.; ...

    2015-11-13

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the abilitymore » of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. In conclusion, our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment.« less

  14. Pressure-Temperature-Field Phase Diagram in the Ferromagnet U3P4

    NASA Astrophysics Data System (ADS)

    Araki, Shingo; Hayashida, Minami; Nishiumi, Naoto; Manabe, Hiroki; Ikeda, Yoichi; Kobayashi, Tatsuo C.; Murata, Keizo; Inada, Yoshihiko; Wiśniewski, Piotr; Aoki, Dai; Ōnuki, Yoshichika; Yamamoto, Etsuji; Haga, Yoshinori

    2015-02-01

    The pressure-temperature-field phase diagram and quantum fluctuation effect were investigated in the itinerant ferromagnet U3P4 by resistivity, ac susceptibility, and Hall effect measurements under high pressure. The zero-temperature ferromagnetic-to-paramagnetic transition is located at Pc ˜ 4.0 GPa. The tricritical point exists at P* = 3.8 GPa and T* = 32 K, where the ferromagnetic transition changes from second- to first-order. As a quantum fluctuation effect, the low-temperature resistivity at Pc follows T5/3 dependence, which was theoretically described in the case of a three-dimensional ferromagnet. This result indicates that the ferromagnetic-to-paramagnetic transition at Pc may be considered as weakly first-order. Another critical behavior, the huge enhancement of ρ0 observed at Pc, cannot be interpreted as the ferromagnetic fluctuation effect. The Hall effect measurements suggest that the magnetic structure in the ordered state changes under high pressure.

  15. Robust isothermal electric control of exchange bias at room temperature.

    PubMed

    He, Xi; Wang, Yi; Wu, Ning; Caruso, Anthony N; Vescovo, Elio; Belashchenko, Kirill D; Dowben, Peter A; Binek, Christian

    2010-07-01

    Voltage-controlled spin electronics is crucial for continued progress in information technology. It aims at reduced power consumption, increased integration density and enhanced functionality where non-volatile memory is combined with high-speed logical processing. Promising spintronic device concepts use the electric control of interface and surface magnetization. From the combination of magnetometry, spin-polarized photoemission spectroscopy, symmetry arguments and first-principles calculations, we show that the (0001) surface of magnetoelectric Cr(2)O(3) has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr(2)O(3) single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias field between positive and negative values by reversing the electric field while maintaining a permanent magnetic field. This effect reflects the switching of the bulk antiferromagnetic domain state and the interface magnetization coupled to it. The switchable exchange bias sets in exactly at the bulk Néel temperature.

  16. Robust isothermal electric control of exchange bias at room temperature

    NASA Astrophysics Data System (ADS)

    He, Xi; Wang, Yi; Wu, Ning; Caruso, Anthony N.; Vescovo, Elio; Belashchenko, Kirill D.; Dowben, Peter A.; Binek, Christian

    2010-07-01

    Voltage-controlled spin electronics is crucial for continued progress in information technology. It aims at reduced power consumption, increased integration density and enhanced functionality where non-volatile memory is combined with high-speed logical processing. Promising spintronic device concepts use the electric control of interface and surface magnetization. From the combination of magnetometry, spin-polarized photoemission spectroscopy, symmetry arguments and first-principles calculations, we show that the (0001) surface of magnetoelectric Cr2O3 has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr2O3 single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias field between positive and negative values by reversing the electric field while maintaining a permanent magnetic field. This effect reflects the switching of the bulk antiferromagnetic domain state and the interface magnetization coupled to it. The switchable exchange bias sets in exactly at the bulk Néel temperature.

  17. Robust isothermal electric control of exchange bias at room temperature

    SciTech Connect

    He, X.; Vescovo, E.; Wang, Y.; Caruso, A.N.; Belashchenko, K.D.; Dowben, P.A.; Binek, C.

    2010-06-20

    Voltage-controlled spin electronics is crucial for continued progress in information technology. It aims at reduced power consumption, increased integration density and enhanced functionality where non-volatile memory is combined with high-speed logical processing. Promising spintronic device concepts use the electric control of interface and surface magnetization. From the combination of magnetometry, spin-polarized photoemission spectroscopy, symmetry arguments and first-principles calculations, we show that the (0001) surface of magnetoelectric Cr{sub 2}O{sub 3} has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr{sub 2}O{sub 3} single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias field between positive and negative values by reversing the electric field while maintaining a permanent magnetic field. This effect reflects the switching of the bulk antiferromagnetic domain state and the interface magnetization coupled to it. The switchable exchange bias sets in exactly at the bulk Neel temperature.

  18. Absorber Materials at Room and Cryogenic Temperatures

    SciTech Connect

    F. Marhauser, T.S. Elliott, A.T. Wu, E.P. Chojnacki, E. Savrun

    2011-09-01

    We recently reported on investigations of RF absorber materials at cryogenic temperatures conducted at Jefferson Laboratory (JLab). The work was initiated to find a replacement material for the 2 Kelvin low power waveguide Higher Order Mode (HOM) absorbers employed within the original cavity cryomodules of the Continuous Electron Beam Accelerator Facility (CEBAF). This effort eventually led to suitable candidates as reported in this paper. Furthermore, though constrained by small funds for labor and resources, we have analyzed a variety of lossy ceramic materials, several of which could be usable as HOM absorbers for both normal conducting and superconducting RF structures, e.g. as loads in cavity waveguides and beam tubes either at room or cryogenic temperatures and, depending on cooling measures, low to high operational power levels.

  19. Weak ferromagnetism and temperature dependent dielectric properties of Zn{sub 0.9}Ni{sub 0.1}O diluted magnetic semiconductor

    SciTech Connect

    Ahmed, Raju; Moslehuddin, A.S.M.; Mahmood, Zahid Hasan; Hossain, A.K.M. Akther

    2015-03-15

    Highlights: • Single phase wurtzite structure was confirmed from XRD analysis. • Weak ferromagnetic behaviour at room temperature. • Pure semiconducting properties confirmed from temperature dependent conductivity. • Smaller dielectric properties at higher frequency. • Possible potential application in high frequency spintronic devices. - Abstract: In this study the room temperature ferromagnetic behaviour and dielectric properties of ZnO based diluted magnetic semiconductor (DMS) have been investigated using nominal chemical composition Zn{sub 0.9}Ni{sub 0.1}O. The X-ray diffraction analysis confirmed formation of single phase hexagonal wurtzite structure. An increase in grain size with increasing sintering temperature was observed from scanning electron microscopy. Field dependent DC magnetization values indicated dominant paramagnetic ordering along with a slight ferromagnetic behaviour at room temperature. Frequency dependent complex initial permeability showed some positive values around 12 at room temperature. In dielectric measurement, an increasing trend of complex permittivity, loss tangent and ac conductivity with increasing temperature were observed. The temperature dependent dispersion curves of dielectric properties revealed clear relaxation at higher temperature. Frequency dependent ac conductivity was found to increase with frequency whereas complex permittivity and loss tangent showed an opposite trend.

  20. Dense nanocrystalline yttrium iron garnet films formed at room temperature by aerosol deposition

    SciTech Connect

    Johnson, Scooter D. Glaser, Evan R.; Cheng, Shu-Fan; Hite, Jennifer

    2016-04-15

    Highlights: • We deposit yttrium iron garnet films at room temperature using aerosol deposition. • Films are 96% of theoretical density for yttrium iron garnet. • We report magnetic and structural properties post-deposition and post-annealing. • Low-temperature annealing decreases the FMR linewidth. • We discuss features of the FMR spectra at each anneal temperature. - Abstract: We have employed aerosol deposition to form polycrystalline yttrium iron garnet (YIG) films on sapphire at room temperature that are 90–96% dense. We characterize the structural and dynamic magnetic properties of the dense films using scanning electron microscopy, X-ray diffraction, and ferromagnetic resonance techniques. We find that the as-deposited films are pure single-phase YIG formed of compact polycrystallites ∼20 nm in size. The ferromagnetic resonance mode occurs at 2829 G with a linewidth of 308 G. We perform a series of successive anneals up to 1000 °C on a film to explore heat treatment on the ferromagnetic resonance linewidth. We find the narrowest linewidth of 98 G occurs after a 750 °C anneal.

  1. Room-temperature solid-state maser.

    PubMed

    Oxborrow, Mark; Breeze, Jonathan D; Alford, Neil M

    2012-08-16

    The invention of the laser has resulted in many innovations, and the device has become ubiquitous. However, the maser, which amplifies microwave radiation rather than visible light, has not had as large an impact, despite being instrumental in the laser's birth. The maser's relative obscurity has mainly been due to the inconvenience of the operating conditions needed for its various realizations: atomic and free-electron masers require vacuum chambers and pumping; and solid-state masers, although they excel as low-noise amplifiers and are occasionally incorporated in ultrastable oscillators, typically require cryogenic refrigeration. Most realizations of masers also require strong magnets, magnetic shielding or both. Overcoming these various obstacles would pave the way for improvements such as more-sensitive chemical assays, more-precise determinations of biomolecular structure and function, and more-accurate medical diagnostics (including tomography) based on enhanced magnetic resonance spectrometers incorporating maser amplifiers and oscillators. Here we report the experimental demonstration of a solid-state maser operating at room temperature in pulsed mode. It works on a laboratory bench, in air, in the terrestrial magnetic field and amplifies at around 1.45 gigahertz. In contrast to the cryogenic ruby maser, in our maser the gain medium is an organic mixed molecular crystal, p-terphenyl doped with pentacene, the latter being photo-excited by yellow light. The maser's pumping mechanism exploits spin-selective molecular intersystem crossing into pentacene's triplet ground state. When configured as an oscillator, the solid-state maser's measured output power of around -10 decibel milliwatts is approximately 100 million times greater than that of an atomic hydrogen maser, which oscillates at a similar frequency (about 1.42 gigahertz). By exploiting the high levels of spin polarization readily generated by intersystem crossing in photo-excited pentacene and other

  2. Atomically resolved force microscopy at room temperature

    SciTech Connect

    Morita, Seizo

    2014-04-24

    Atomic force microscopy (AFM) can now not only image individual atoms but also construct atom letters using atom manipulation method even at room temperature (RT). Therefore, the AFM is the second generation atomic tool following the scanning tunneling microscopy (STM). However the AFM can image even insulating atoms, and also directly measure/map the atomic force and potential at the atomic scale. Noting these advantages, we have been developing a bottom-up nanostructuring system at RT based on the AFM. It can identify chemical species of individual atoms and then manipulate selected atom species to the predesigned site one-by-one to assemble complex nanostructures consisted of multi atom species at RT. Here we introduce our results toward atom-by-atom assembly of composite nanostructures based on the AFM at RT including the latest result on atom gating of nano-space for atom-by-atom creation of atom clusters at RT for semiconductor surfaces.

  3. Room-temperature ionic liquid battery electrolytes

    SciTech Connect

    Carlin, R.T.; Fuller, J.

    1997-12-01

    The room-temperature molten salts possess a number of unique properties that make them ideal battery electrolytes. In particular, they are nonflammable, nonvolatile, and chemically inert, and they display wide electrochemical windows, high inherent conductivities, and wide thermal operating ranges. Although the ionic liquids have excellent characteristics, the chemical and electrochemical properties of desirable battery electrode materials are not well understood in these electrolytes. The research has focused on rechargeable electrodes and has included work on metallic lithium and sodium anodes in buffered neutral chloroaluminate melts, graphite-intercalation electrodes in neutral chloroaluminate and non-chloroaluminate melts, and silane-imidazole polymeric cathodes in acidic chloroaluminate melts. This paper will provide an overview of the research in these areas.

  4. Structure of room temperature ionic liquids

    NASA Astrophysics Data System (ADS)

    Yethiraj, Arun

    2016-10-01

    The structure of room temperature ionic liquids is studied using molecular dynamics simulations and integral equation theory. Three ionic liquids 1-alkyl-3-methylimidazolium hexfluorophosphate, [C n MIM] [PF6], for n  =  1, 4, and 8, are studied using a united atom model of the ions. The primary interest is a study of the pair correlation functions and a test of the reference interaction site model theory. There is liquid-like ordering in the liquid that arises from electrostatic attractions and steric packing considerations. The theory is not in quantitative agreement with the simulation results and underestimates the degree of liquid-like order. A pre-peak in the static structure factor is seen in both simulations and theory, suggesting that this is a geometric effect arising from a packing of the alkyl chains.

  5. Room-temperature spin-orbit torque in NiMnSb

    NASA Astrophysics Data System (ADS)

    Ciccarelli, C.; Anderson, L.; Tshitoyan, V.; Ferguson, A. J.; Gerhard, F.; Gould, C.; Molenkamp, L. W.; Gayles, J.; Železný, J.; Šmejkal, L.; Yuan, Z.; Sinova, J.; Freimuth, F.; Jungwirth, T.

    2016-09-01

    Materials that crystallize in diamond-related lattices, with Si and GaAs as their prime examples, are at the foundation of modern electronics. Simultaneously, inversion asymmetries in their crystal structure and relativistic spin-orbit coupling led to discoveries of non-equilibrium spin-polarization phenomena that are now extensively explored as an electrical means for manipulating magnetic moments in a variety of spintronic structures. Current research of these relativistic spin-orbit torques focuses primarily on magnetic transition-metal multilayers. The low-temperature diluted magnetic semiconductor (Ga, Mn)As, in which spin-orbit torques were initially discovered, has so far remained the only example showing the phenomenon among bulk non-centrosymmetric ferromagnets. Here we present a general framework, based on the complete set of crystallographic point groups, for identifying the potential presence and symmetry of spin-orbit torques in non-centrosymmetric crystals. Among the candidate room-temperature ferromagnets we chose to use NiMnSb, which is a member of the broad family of magnetic Heusler compounds. By performing all-electrical ferromagnetic resonance measurements in single-crystal epilayers of NiMnSb we detect room-temperature spin-orbit torques generated by effective fields of the expected symmetry and of a magnitude consistent with our ab initio calculations.

  6. Electrorecovery of actinides at room temperature

    SciTech Connect

    Stoll, Michael E; Oldham, Warren J; Costa, David A

    2008-01-01

    There are a large number of purification and processing operations involving actinide species that rely on high-temperature molten salts as the solvent medium. One such application is the electrorefining of impure actinide metals to provide high purity material for subsequent applications. There are some drawbacks to the electrodeposition of actinides in molten salts including relatively low yields, lack of accurate potential control, maintaining efficiency in a highly corrosive environment, and failed runs. With these issues in mind we have been investigating the electrodeposition of actinide metals, mainly uranium, from room temperature ionic liquids (RTILs) and relatively high-boiling organic solvents. The RTILs we have focused on are comprised of 1,3-dialkylimidazolium or quaternary ammonium cations and mainly the {sup -}N(SO{sub 2}CF{sub 3}){sub 2} anion [bis(trif1uoromethylsulfonyl)imide {equivalent_to} {sup -}NTf{sub 2}]. These materials represent a class of solvents that possess great potential for use in applications employing electrochemical procedures. In order to ascertain the feasibility of using RTILs for bulk electrodeposition of actinide metals our research team has been exploring the electron transfer behavior of simple coordination complexes of uranium dissolved in the RTIL solutions. More recently we have begun some fundamental electrochemical studies on the behavior of uranium and plutonium complexes in the organic solvents N-methylpyrrolidone (NMP) and dimethylsulfoxide (DMSO). Our most recent results concerning electrodeposition will be presented in this account. The electrochemical behavior of U(IV) and U(III) species in RTILs and the relatively low vapor pressure solvents NMP and DMSO is described. These studies have been ongoing in our laboratory to uncover conditions that will lead to the successful bulk electrodeposition of actinide metals at a working electrode surface at room temperature or slightly elevated temperatures. The RTILs we

  7. Sub-room Temperature Magnetic Refrigerator

    NASA Astrophysics Data System (ADS)

    Zimm, Carl

    1998-03-01

    Magnetic refrigeration has been predicted to be an efficient cooling technology because of the highly reversible nature of the magnetocaloric effect for some materials. However, cooling power and efficiency of past devices has been limited because of the difficulties in exchanging heat with the solid magnetic refrigerant. Astronautics in a joint project with Ames DOE Laboratory has constructed a regenerative magnetic refrigerator that provides cooling near room temperature using gadolinium as a refrigerant and water as a heat transfer fluid. Using a superconducting magnet at 5 T, cooling of 500 watts was obtained at coefficients of performance of 5 or more watts of cooling per watt of work input. Cooling of 150 watts was obtained using a 1.5 T field, which can be obtained from permanent magnet sources. The main losses in the present device are magnet AC losses and seal friction, although limits on temperature span may also be imposed by magnetic material properties. We have identified design, magnet, and magnetic material improvements that should reduce such losses, allowing the construction of devices whose efficiency well exceeds that obtainable from conventional technology. The fluid used in such magnetic refrigerators presents no toxicity, ozone depletion or global warming hazard. This talk will include test results and projections of the capabilities and limitations of the technology.

  8. LETTER TO THE EDITOR: Curie temperature suppression of ferromagnetic nanosolids

    NASA Astrophysics Data System (ADS)

    Zhong, W. H.; Sun, Chang Q.; Tay, B. K.; Li, S.; Bai, H. L.; Jiang, E. Y.

    2002-06-01

    Based on the recent bond-order-bond-length-bond-strength correlation mechanism (Sun C Q, Chen T P, Tay B K, Li S, Huang H, Zhang Y B, Pan L K, Lau S P and Sun X W 2001 J. Phys. D: Appl. Phys. 34 3470) and the criterion of thermal-vibration-exchange-interaction energy equilibrium, an atomistic model has been developed for the Curie temperature (TC) suppression of ferromagnetic nanosolids. At TC, the atomic thermal vibration energy (EV) overcomes the atomic cohesive energy (Ecoh), which triggers the order-disorder transition of the spin-spin exchange interaction. Besides, the coordination-number (CN) imperfection at a surface enhances the strength of the bonds of the surface atoms. The CN reduction and bond-strength enhancement modifies the surface atomic Ecoh from that of an atom inside the bulk. As such, the critical EV for an atom at a free surface will be different from the bulk value and, hence, the TC of a nanosolid will change with the portion of surface atoms. Matching between predictions and experimental observations on the TC suppression of Fe, Ni and Co nanofilms evidences the validity of the current premise, in which no assumptions or freely adjustable parameters are involved.

  9. Direct evidence for significant spin-polarization of EuS in Co/EuS multilayers at room temperature

    PubMed Central

    Pappas, S. D.; Poulopoulos, P.; Lewitz, B.; Straub, A.; Goschew, A.; Kapaklis, V.; Wilhelm, F.; Rogalev, A.; Fumagalli, P.

    2013-01-01

    The new era of spintronics promises the development of nanodevices, where the electron spin will be used to store information and charge currents will be replaced by spin currents. For this, ferromagnetic semiconductors at room temperature are needed. We report on significant room-temperature spin polarization of EuS in Co/EuS multilayers recorded by x-ray magnetic circular dichroism (XMCD). The films were found to contain a mixture of divalent and trivalent europium, but only Eu++ is responsible for the ferromagnetic behavior of EuS. The magnetic XMCD signal of Eu at room temperature could unambiguously be assigned to magnetic ordering of EuS and was found to be only one order of magnitude smaller than that at 2.5 K. The room temperature magnetic moment of EuS is as large as the one of bulk ferromagnetic Ni. Our findings pave the path for fabrication of room–temperature spintronic devices using spin polarized EuS layers. PMID:23434820

  10. Controllable ferromagnetism of iron doped topological insulator

    NASA Astrophysics Data System (ADS)

    Qiao, Shan; Liu, Zhen; Ji, Fuhao; Li, Bin; Xi, Fuchun; Kuroda, K.; Ye, Mao; Miyamoto, K.; Kimura, A.

    2012-02-01

    The higher than room temperature ferromagnetism was found in iron doped Bi2Se3. Samples generated by different processes have different magnetic characters. The Curie temperature is independent on iron concentration which against all discovered dilute magnetic systems. EXAFS observations show that the local structure of iron in samples with paramagnetic character is complex. On the contrary, that with ferromagnetic character is very simple that the iron atoms make up small single atom, dimer or trimer structures and these structures randomly distributed in Bi2Se3 crystal. The ferromagnetism can be enhanced or suppressed by the shift of Fermi edge by co-doping of Mg and Fe to Bi2Se3 crystal. The less than 3 atoms small structure cannot have room temperature ferromagnetism, so we believe that the higher than room temperature controllable ferromagnetism is intrinsic character of iron doped topological insulator.

  11. Room-temperature nanowire terahertz photodetectors

    NASA Astrophysics Data System (ADS)

    Romeo, Lorenzo; Coquillant, Dominique; Viti, Leonardo; Ercolani, Daniele; Sorba, Lucia; Knap, Wojciech; Tredicucci, Alessandro; Vitiello, Miriam S.

    2013-01-01

    Semiconductor nanowires (NWs) represent an ideal building block for implementing rectifying diodes or plasma­ wave detectors that could operate well into the THz, thanks to the typical attofarad-order capacitance. Despite the strong effort in developing these nanostructures for a new generation of complementary metal-oxide semi­ conductors (CMOS), memory and photonic devices, their potential as radiation sensors into the Terahertz is just starting to be explored. We report on the development of NW-based field effect transistors operating as high sensitivity THz detectors in the 0.3 - 2.8 THz range. By feeding the radiation field of either an electronic THz source or a quantum cascade laser (QCL) at the gate-source electrodes by means of a wide band dipole antenna, we measured a photovoltage signal corresponding to responsivity values up to 100 V IW, with impressive noise equivalent power levels < 6 x 10-11W/Hz at room temperature and a > 300kHz modulation bandwidth. The potential scalability to even higher frequencies and the technological feasibility of realizing multi-pixel arrays coupled with QCL sources make the proposed technology highly competitive for a future generation of THz detection systems.

  12. Room temperature molecular up conversion in solution

    PubMed Central

    Nonat, Aline; Chan, Chi Fai; Liu, Tao; Platas-Iglesias, Carlos; Liu, Zhenyu; Wong, Wing-Tak; Wong, Wai-Kwok; Wong, Ka-Leung; Charbonnière, Loïc J.

    2016-01-01

    Up conversion is an Anti-Stokes luminescent process by which photons of low energy are piled up to generate light at a higher energy. Here we show that the addition of fluoride anions to a D2O solution of a macrocyclic erbium complex leads to the formation of a supramolecular [(ErL)2F]+ assembly in which fluoride is sandwiched between two complexes, held together by the synergistic interactions of the Er-F-Er bridging bond, four intercomplex hydrogen bonds and two aromatic stacking interactions. Room temperature excitation into the Er absorption bands at 980 nm of a solution of the complex in D2O results in the observation of up converted emission at 525, 550 and 650 nm attributed to Er centred transitions via a two-step excitation. The up conversion signal is dramatically increased upon formation of the [(ErL)2F]+ dimer in the presence of 0.5 equivalents of fluoride anions. PMID:27302144

  13. Room-Temperature Spin Polariton Diode Laser

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Aniruddha; Baten, Md Zunaid; Iorsh, Ivan; Frost, Thomas; Kavokin, Alexey; Bhattacharya, Pallab

    2017-08-01

    A spin-polarized laser offers inherent control of the output circular polarization. We have investigated the output polarization characteristics of a bulk GaN-based microcavity polariton diode laser at room temperature with electrical injection of spin-polarized electrons via a FeCo /MgO spin injector. Polariton laser operation with a spin-polarized current is characterized by a threshold of ˜69 A / cm2 in the light-current characteristics, a significant reduction of the electroluminescence linewidth and blueshift of the emission peak. A degree of output circular polarization of ˜25 % is recorded under remanent magnetization. A second threshold, due to conventional photon lasing, is observed at an injection of ˜7.2 kA /cm2 . The variation of output circular and linear polarization with spin-polarized injection current has been analyzed with the carrier and exciton rate equations and the Gross-Pitaevskii equations for the condensate and there is good agreement between measured and calculated data.

  14. Nonlinear interaction of a ferromagnet with a high-temperature superconductor

    SciTech Connect

    Kashurnikov, V. A. Maksimova, A. N.; Rudnev, I. A. Sotnikova, A. P.

    2013-03-15

    The interaction of an Abrikosov vertex with a ferromagnetic substrate is taken into account in the model of a layered high-temperature superconductor (HTSC). The magnetization reversal loops are calculated by the Monte Carlo method for various values of the magnetic moment of the substrate and at various temperatures. The nonlinearity of the interaction of the superconductor with the ferromagnet is demonstrated. The magnetization of HTSC films on magnetic and nonmagnetic substrates is measured. It is found that the ferromagnetism of the substrate strongly affects the shape and magnitude of the magnetization of the HTSC-substrate composite. Experimental data are found to correlate with the results of calculations.

  15. Temperature dependent magnetic coupling between ferromagnetic FeTaC layers in multilayer thin films

    NASA Astrophysics Data System (ADS)

    Singh, Akhilesh Kumar; Hsu, Jen-Hwa; Perumal, Alagarsamy

    2016-11-01

    We report systematic investigations on temperature dependent magnetic coupling between ferromagnetic FeTaC layers and resulting magnetic properties of multilayer structured [FeTaC (~67 nm)/Ta(x nm)]2/FeTaC(~67 nm)] thin films, which are fabricated directly on thermally oxidized Si substrate. As-deposited amorphous films are post annealed at different annealing temperatures (TA=200, 300 and 400 °C). Structural analyzes reveal that the films annealed at TA≤200 °C exhibit amorphous nature, while the films annealed above 200 °C show nucleation of nanocrystals at TA=300 °C and well-defined α-Fe nanocrystals with size of about 9 nm in amorphous matrix for 400 °C annealed films. Room temperature and temperature dependent magnetic hysteresis (M-H) loops reveal that magnetization reversal behaviors and magnetic properties are strongly depending on spacer layer thickness (x), TA and temperature. A large reduction in coercivity (HC) was observed for the films annealed at 200 °C and correlated to relaxation of stress quenched in during the film deposition. On the other hand, the films annealed at 300 °C exhibit unusual variation of HC(T), i.e., a broad minimum in HC(T) vs T curve. This is caused by change in magnetic coupling between ferromagnetic layers having different microstructure. In addition, the broad minimum in the HC(T) curve shifts from 150 K for x=1 film to 80 K for x=4 film. High-temperature thermomagnetization data show a strong (significant) variation of Curie temperature (TC) with TA (x). The multilayer films annealed at 200 °C exhibit low value of TC with a minimum of 350 K for x=4 film. But, the films annealed at 400 °C show largest TC with a maximum of 869 K for x=1 film. The observed results are discussed on the basis of variations in magnetic couplings between FeTaC layers, which are majorly driven by temperature, spacer layer thickness, annealing temperature and nature of interfaces.

  16. Prediction of near-room-temperature quantum anomalous Hall effect on honeycomb materials.

    PubMed

    Wu, Shu-Chun; Shan, Guangcun; Yan, Binghai

    2014-12-19

    Recently, the long-sough quantum anomalous Hall effect was realized in a magnetic topological insulator. However, the requirement of an extremely low temperature (approximately 30 mK) hinders realistic applications. Based on ab initio band structure calculations, we propose a quantum anomalous Hall platform with a large energy gap of 0.34 and 0.06 eV on honeycomb lattices comprised of Sn and Ge, respectively. The ferromagnetic (FM) order forms in one sublattice of the honeycomb structure by controlling the surface functionalization rather than dilute magnetic doping, which is expected to be visualized by spin polarized STM in experiment. Strong coupling between the inherent quantum spin Hall state and ferromagnetism results in considerable exchange splitting and, consequently, an FM insulator with a large energy gap. The estimated mean-field Curie temperature is 243 and 509 K for Sn and Ge lattices, respectively. The large energy gap and high Curie temperature indicate the feasibility of the quantum anomalous Hall effect in the near-room-temperature and even room-temperature regions.

  17. Compton imager using room temperature silicon detectors

    NASA Astrophysics Data System (ADS)

    Kurfess, James D.; Novikova, Elena I.; Phlips, Bernard F.; Wulf, Eric A.

    2007-08-01

    We have been developing a multi-layer Compton Gamma Ray Imager using position-sensitive, intrinsic silicon detectors. Advantages of this approach include room temperature operation, reduced Doppler broadening, and use of conventional silicon fabrication technologies. We have obtained results on the imaging performance of a multi-layer instrument where each layer consists of a 2×2 array of double-sided strip detectors. Each detector is 63 mm×63 mm×2 mm thick and has 64 strips providing a strip pitch of approximately 0.9 mm. The detectors were fabricated by SINTEF ICT (Oslo Norway) from 100 mm diameter wafers. The use of large arrays of silicon detectors appears especially advantageous for applications that require excellent sensitivity, spectral resolution and imaging such as gamma ray astrophysics, detection of special nuclear materials, and medical imaging. The multiple Compton interactions (three or more) in the low-Z silicon enable the energy and direction of the incident gamma ray to be determined without full deposition of the incident gamma-ray energy in the detector. The performance of large volume instruments for various applications are presented, including an instrument under consideration for NASA's Advanced Compton Telescope (ACT) mission and applications to Homeland Security. Technology developments that could further extend the sensitivity and performance of silicon Compton Imagers are presented, including the use of low-energy (few hundred keV) electron tracking within novel silicon detectors and the potential for a wafer-bonding approach to produce thicker, position-sensitive silicon detectors with an associated reduction of required electronics and instrument cost.

  18. Room temperature micro-hydrogen-generator

    NASA Astrophysics Data System (ADS)

    Gervasio, Don; Tasic, Sonja; Zenhausern, Frederic

    A new compact and cost-effective hydrogen-gas generator has been made that is well suited for supplying hydrogen to a fuel-cell for providing base electrical power to hand-carried appliances. This hydrogen-generator operates at room temperature, ambient pressure and is orientation-independent. The hydrogen-gas is generated by the heterogeneous catalytic hydrolysis of aqueous alkaline borohydride solution as it flows into a micro-reactor. This reactor has a membrane as one wall. Using the membrane keeps the liquid in the reactor, but allows the hydrogen-gas to pass out of the reactor to a fuel-cell anode. Aqueous alkaline 30 wt% borohydride solution is safe and promotes long application life, because this solution is non-toxic, non-flammable, and is a high energy-density (≥2200 W-h per liter or per kilogram) hydrogen-storage solution. The hydrogen is released from this storage-solution only when it passes over the solid catalyst surface in the reactor, so controlling the flow of the solution over the catalyst controls the rate of hydrogen-gas generation. This allows hydrogen generation to be matched to hydrogen consumption in the fuel-cell, so there is virtually no free hydrogen-gas during power generation. A hydrogen-generator scaled for a system to provide about 10 W electrical power is described here. However, the technology is expected to be scalable for systems providing power spanning from 1 W to kW levels.

  19. Designing switchable polarization and magnetization at room temperature in an oxide

    NASA Astrophysics Data System (ADS)

    Mandal, P.; Pitcher, M. J.; Alaria, J.; Niu, H.; Borisov, P.; Stamenov, P.; Claridge, J. B.; Rosseinsky, M. J.

    2015-09-01

    Ferroelectric and ferromagnetic materials exhibit long-range order of atomic-scale electric or magnetic dipoles that can be switched by applying an appropriate electric or magnetic field, respectively. Both switching phenomena form the basis of non-volatile random access memory, but in the ferroelectric case, this involves destructive electrical reading and in the magnetic case, a high writing energy is required. In principle, low-power and high-density information storage that combines fast electrical writing and magnetic reading can be realized with magnetoelectric multiferroic materials. These materials not only simultaneously display ferroelectricity and ferromagnetism, but also enable magnetic moments to be induced by an external electric field, or electric polarization by a magnetic field. However, synthesizing bulk materials with both long-range orders at room temperature in a single crystalline structure is challenging because conventional ferroelectricity requires closed-shell d0 or s2 cations, whereas ferromagnetic order requires open-shell dn configurations with unpaired electrons. These opposing requirements pose considerable difficulties for atomic-scale design strategies such as magnetic ion substitution into ferroelectrics. One material that exhibits both ferroelectric and magnetic order is BiFeO3, but its cycloidal magnetic structure precludes bulk magnetization and linear magnetoelectric coupling. A solid solution of a ferroelectric and a spin-glass perovskite combines switchable polarization with glassy magnetization, although it lacks long-range magnetic order. Crystal engineering of a layered perovskite has recently resulted in room-temperature polar ferromagnets, but the electrical polarization has not been switchable. Here we combine ferroelectricity and ferromagnetism at room temperature in a bulk perovskite oxide, by constructing a percolating network of magnetic ions with strong superexchange interactions within a structural scaffold

  20. SQUID Microscopy: Magnetic Images of Room Temperature Samples

    NASA Astrophysics Data System (ADS)

    Grossman, Helene

    1998-10-01

    We use a microscope based on a high-Tc Superconducting Quantum Interference Device (SQUID) to study room temperature samples. The SQUID, which measures magnetic flux, is mounted on a sapphire rod and maintained at 77 K inside a vacuum chamber. A sample, separated from the vacuum chamber by a window, is placed above the SQUID, and the entire microscope is enclosed within a magnetic shield. The sample can be scanned over the SQUID to obtain a magnetic image. We have used the microscope to study magnetotactic bacteria, which have a permanent magnetic dipole moment of about 1.5 x 10-16 Am^2. The bacteria, suspended in an aqueous medium, are placed in a cell which is separated from the vacuum chamber by a 3 micron thick SiN membrane. The sample is brought as close as 15 micron to the SQUID, and the magnetic flux noise from the motion of the bacteria is measured. Data from non-motile cells, which undergo Brownian motion, give us information about the distribution of lengths of the bacteria. By applying a magnetic field, we can determine the average dipole moment. Noise measurements of the live bacteria give us the rates of flagellar rotation and body-roll, as well as the amplitudes of the vibrational and precessional motions. Another application of the microscope is non-destructive evaluation of steel. We have investigated the effects of both thermal and mechanical stresses on the remnant magnetization of steel. A third application of the microscope is in studying the properties of ferromagnetic nanocrystals of Co and Fe_3O_4.

  1. Spin-Pump-Induced Spin Transport in p-Type Si at Room Temperature

    NASA Astrophysics Data System (ADS)

    Shikoh, Eiji; Ando, Kazuya; Kubo, Kazuki; Saitoh, Eiji; Shinjo, Teruya; Shiraishi, Masashi

    2013-03-01

    A spin battery concept is applied for the dynamical generation of pure spin current and spin transport in p-type silicon (p-Si). Ferromagnetic resonance and effective s-d coupling in Ni80Fe20 results in spin accumulation at the Ni80Fe20/p-Si interface, inducing spin injection and the generation of spin current in the p-Si. The pure spin current is converted to a charge current by the inverse spin Hall effect of Pd evaporated onto the p-Si. This approach demonstrates the generation and transport of pure spin current in p-Si at room temperature.

  2. Spin-pump-induced spin transport in p-type Si at room temperature.

    PubMed

    Shikoh, Eiji; Ando, Kazuya; Kubo, Kazuki; Saitoh, Eiji; Shinjo, Teruya; Shiraishi, Masashi

    2013-03-22

    A spin battery concept is applied for the dynamical generation of pure spin current and spin transport in p-type silicon (p-Si). Ferromagnetic resonance and effective s-d coupling in Ni(80)Fe(20) results in spin accumulation at the Ni(80)Fe(20)/p-Si interface, inducing spin injection and the generation of spin current in the p-Si. The pure spin current is converted to a charge current by the inverse spin Hall effect of Pd evaporated onto the p-Si. This approach demonstrates the generation and transport of pure spin current in p-Si at room temperature.

  3. Monolithic integration of room-temperature multifunctional BaTiO3-CoFe2O4 epitaxial heterostructures on Si(001)

    NASA Astrophysics Data System (ADS)

    Scigaj, Mateusz; Dix, Nico; Gázquez, Jaume; Varela, María; Fina, Ignasi; Domingo, Neus; Herranz, Gervasi; Skumryev, Vassil; Fontcuberta, Josep; Sánchez, Florencio

    2016-08-01

    The multifunctional (ferromagnetic and ferroelectric) response at room temperature that is elusive in single phase multiferroic materials can be achieved in a proper combination of ferroelectric perovskites and ferrimagnetic spinel oxides in horizontal heterostructures. In this work, lead-free CoFe2O4/BaTiO3 bilayers are integrated with Si(001) using LaNiO3/CeO2/YSZ as a tri-layer buffer. They present structural and functional properties close to those achieved on perovskite substrates: the bilayers are fully epitaxial with extremely flat surface, and exhibit robust ferromagnetism and ferroelectricity at room temperature.

  4. Monolithic integration of room-temperature multifunctional BaTiO3-CoFe2O4 epitaxial heterostructures on Si(001)

    PubMed Central

    Scigaj, Mateusz; Dix, Nico; Gázquez, Jaume; Varela, María; Fina, Ignasi; Domingo, Neus; Herranz, Gervasi; Skumryev, Vassil; Fontcuberta, Josep; Sánchez, Florencio

    2016-01-01

    The multifunctional (ferromagnetic and ferroelectric) response at room temperature that is elusive in single phase multiferroic materials can be achieved in a proper combination of ferroelectric perovskites and ferrimagnetic spinel oxides in horizontal heterostructures. In this work, lead-free CoFe2O4/BaTiO3 bilayers are integrated with Si(001) using LaNiO3/CeO2/YSZ as a tri-layer buffer. They present structural and functional properties close to those achieved on perovskite substrates: the bilayers are fully epitaxial with extremely flat surface, and exhibit robust ferromagnetism and ferroelectricity at room temperature. PMID:27550543

  5. Optically Pumped Subwavelength Lasers Operated at Room Temperature

    DTIC Science & Technology

    2012-05-06

    REPORT NACHOS Project Final Report_University of Michigan Optically pumped subwavelength lasers operated at room temperature 14. ABSTRACT 16. SECURITY...28-Feb-2011 NACHOS Project Final Report_University of Michigan Optically pumped subwavelength lasers operated at room temperature Report Title

  6. A simple method to obtain Fe-doped CeO2 nanocrystals at room temperature

    NASA Astrophysics Data System (ADS)

    Almeida, J. M. A.; Santos, P. E. C.; Cardoso, L. P.; Meneses, C. T.

    2013-02-01

    Ce1-xFexO2 nanocrystals (0room temperature using the coprecipitation method. The samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and magnetization measurements as a function of field. The XRD results and Rietveld refinement analysis show that all particles have a crystalline structure isomorphous to the host structure (CeO2), with average size of 9 nm. This information was also confirmed by TEM images in which it is shown that the particles present spherical-like shape. The magnetic measurements indicated that the Fe-doped samples exhibit a weak ferromagnetism at room temperature, which increases with the increasing of the Fe content.

  7. Room-temperature spin transport in n-Ge probed by four-terminal nonlocal measurements

    NASA Astrophysics Data System (ADS)

    Yamada, Michihiro; Tsukahara, Makoto; Fujita, Yuichi; Naito, Takahiro; Yamada, Shinya; Sawano, Kentarou; Hamaya, Kohei

    2017-09-01

    We demonstrate electrical spin injection and detection in n-type Ge (n-Ge) at room temperature using four-terminal nonlocal spin-valve and Hanle-effect measurements in lateral spin-valve (LSV) devices with Heusler-alloy Schottky tunnel contacts. The spin diffusion length (λGe) of the Ge layer used (n ˜ 1 × 1019 cm-3) at 296 K is estimated to be ˜0.44 ± 0.02 µm. Room-temperature spin signals can be observed reproducibly in the low bias voltage range (≤0.7 V) for LSVs with relatively low resistance-area product (RA) values (≤1 kΩ µm2). This means that the Schottky tunnel contacts used here are more suitable than ferromagnet/MgO tunnel contacts (RA ≥ 100 kΩ µm2) for developing Ge spintronic applications.

  8. Advances in methods to obtain and characterise room temperature magnetic ZnO

    SciTech Connect

    Lorite, I.; Kumar, P.; Esquinazi, P.; Straube, B.; Villafuerte, M.; Ohldag, H.; Rodríguez Torres, C. E.; Perez de Heluani, S.; Antonov, V. N.; Bekenov, L. V.; Ernst, A.; and others

    2015-02-23

    We report the existence of magnetic order at room temperature in Li-doped ZnO microwires after low energy H{sup +} implantation. The microwires with diameters between 0.3 and 10 μm were prepared by a carbothermal process. We combine spectroscopy techniques to elucidate the influence of the electronic structure and local environment of Zn, O, and Li and their vacancies on the magnetic response. Ferromagnetism at room temperature is obtained only after implanting H{sup +} in Li-doped ZnO. The overall results indicate that low-energy proton implantation is an effective method to produce the necessary amount of stable Zn vacancies near the Li ions to trigger the magnetic order.

  9. Investigation of magnetic proximity effect in ferromagnet/superconductor thin films by low temperature Magneto Optical Kerr Effect measurement

    NASA Astrophysics Data System (ADS)

    Christiansen, David A.

    A room temperature Magneto Optical Kerr Effect (MOKE) experimental setup was expanded to improve performance and integrated with a liquid Helium cryogenic system. Ferromagnetic/superconductor hybrid systems have recently been intensively studied due to their interesting proximity effect and the possible applications such as a current switching device. Most of previous work focused on the superconducting property change due to the presence of the ferromagnet but not much research of the magnetic property change due to the superconducting transition has been done. Using the extended MOKE setup, magnetization from the top ferromagnetic layer can be measured below and above the critical temperature of the superconducting thin film layer. Temperatures as low as 4.2K were achieved and the magnetization with respect to applied magnetic field of a Permalloy/Niobium (Py/Nb) thin film was measured at 295K, 11K, and 4.2K. Coercivity increased as temperature decreased. A magnetization measurement with constant applied magnetic field was also performed with a temperature sweep passing the superconducting transition. However, due to temperature instability it was difficult to compare the magnetization above and below Tc of the Nb. Both hysteresis loops above and below the superconducting critical temperature were measured to be similar within the measurement error and have a coercivity of 160 ±16 Oe. Reasons for not detecting a magnetization change due to the superconductor could be either due to sample heating, thermometer calibration, the limited accuracy of measuring the coercivity in this sample, or the change due to the SC may be smaller or not exist.

  10. High temperature ferromagnetism in Ni doped ZnO nanoparticles: Milling time dependence

    SciTech Connect

    Pal, Bappaditya Sarkar, D.; Giri, P. K.

    2014-04-24

    We report on the room temperature ferromagnetism (RT FM) in the Zn{sub 1−x}Ni{sub x}O (x = 0, 0.03, and 0.05) nanoparticles (NPs) synthesized by a ball milling technique. X-ray diffraction analysis confirms the single crystalline ZnO wurtzite structure with presence of small intensity secondary phase related peak which disappear with increasing milling time for Ni doped samples. HRTEM lattice images show that the doped NPs are single crystalline with a dspacing of 2.44 Å. Energy-dispersive X-ray spectroscopy analysis confirms the presence of Ni ions in the ZnO matrix. Magnetic measurement (RT) exhibits the hysteresis loop with saturation magnetization (M{sub s}) of 1.6–2.56 (emu/g) and coercive field (H{sub c}) of 296–322 Oe. M-T measurement shows a Curie temperature of the order of 325°C for 3% Ni doped sample. Micro -Raman studies show doping/disorder induced additional modes at ∼510, 547, 572 cm{sup −1} in addition to 437 cm{sup −1} peak of pure ZnO. UV-Vis absorption spectra illustrate band gap shift due to doping. Alteration of M{sub s} value with the variation of doping concentration and milling time has been studied and discussed.

  11. FAST TRACK COMMUNICATION: Reproducible room temperature giant magnetocaloric effect in Fe-Rh

    NASA Astrophysics Data System (ADS)

    Manekar, Meghmalhar; Roy, S. B.

    2008-10-01

    We present the results of magnetocaloric effect (MCE) studies in polycrystalline Fe-Rh alloy over a temperature range of 250-345 K across the first order antiferromagnetic to ferromagnetic transition. By measuring the MCE under various thermomagnetic histories, contrary to the long held belief, we show here explicitly that the giant MCE in Fe-Rh near room temperature does not vanish after the first field cycle. In spite of the fact that the virgin magnetization curve is lost after the first field cycle near room temperature, reproducibility in the MCE under multiple field cycles can be achieved by properly choosing a combination of isothermal and adiabatic field variation cycles in the field-temperature phase space. This reproducible MCE leads to a large effective refrigerant capacity of 324.42 J kg-1, which is larger than that of the well-known magnetocaloric material Gd5Si2Ge2. This information could be important as Fe-Rh has the advantage of having a working temperature of around 300 K, which can be used for room temperature magnetic refrigeration.

  12. Temperature dependence of spin polarization in ferromagnetic metals using lateral spin valves

    NASA Astrophysics Data System (ADS)

    Villamor, Estitxu; Isasa, Miren; Hueso, Luis E.; Casanova, Fèlix

    2013-11-01

    Spin injection properties of ferromagnetic metals are studied and are compared by using highly reproducible cobalt/copper and permalloy/copper lateral spin valves (LSVs) with transparent contacts, fabricated with a careful control of the interface and the purity of copper. Spin polarization of permalloy and cobalt are obtained as a function of temperature. Analysis of the temperature dependence of both the spin polarization and the conductivity of permalloy confirms that the two-channel model for ferromagnetic metals is valid to define the current spin polarization and shows that a correction factor of ˜2 is needed for the values obtained by LSV experiments. The spin transport properties of copper, which also are studied as a function of temperature, are not affected by the used ferromagnetic material. The low-temperature maximum in the spin-diffusion length of copper is attributed to the presence of diluted magnetic impurities intrinsic from the copper.

  13. Room temperature multiferroic properties of (Fex, Sr1-x)TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Kim, Kyoung-Tae; Kim, Cheolbok; Fang, Sheng-Po; Yoon, Yong-Kyu

    2014-09-01

    This letter reports the structural, dielectric, ferroelectric, and magnetic properties of Fe substituted SrTiO3 thin films in room temperature. The structural data obtained from x-ray diffraction indicates that (Fex,Sr1-x)TiO3, the so called FST, transforms from pseudocubic to tetragonal structures with increase of the Fe content in SrTiO3 thin films, featuring the ferroelectricity, while vibrating sample magnetometer measurements show magnetic hysteresis loops for the samples with low iron contents indicating their ferromagnetism. The characterized ferroelectricity and ferromagnetism confirms strong multiferroitism of the single phase FST thin films in room temperature. Also, an FST thin film metal-insulator-metal multiferroic capacitor has been fabricated and characterized in microwave frequencies between 10 MHz and 5 GHz. A capacitor based on Fe0.1Sr0.9TiO3 with a thickness of 260 nm shows a high electric tunability of 18.6% at 10 V and a maximum magnetodielectric value of 1.37% at 0.4 mT with a loss tangent of 0.021 at 1 GHz. This high tuning and low loss makes this material as a good candidate for frequency agile microwave devices such as tunable filters, phase shifters, and antennas.

  14. Room-temperature creation and spin-orbit torque-induced manipulation of skyrmions in thin film

    NASA Astrophysics Data System (ADS)

    Yu, Guoqiang; Upadhyaya, Pramey; Li, Xiang; Li, Wenyuan; Im, Se Kwon K.; Fan, Yabin; Wong, Kin L.; Tserkovnyak, Yaroslav; Amiri, Pedram Khalili; Wang, Kang L.

    Magnetic skyrmions, which are topologically protected spin texture, are promising candidates for ultra-low energy and ultra-high density magnetic data storage and computing applications1, 2. To date, most experiments on skyrmions have been carried out at low temperatures. The choice of materials available is limited and there is a lack of electrical means to control of skyrmions. Here, we experimentally demonstrate a method for creating skyrmion bubbles phase in the ferromagnetic thin film at room temperature. We further demonstrate that the created skyrmion bubbles can be manipulated by electric current. This room-temperature creation and manipulation of skyrmion in thin film is of particular interest for applications, being suitable for room-temperature operation and compatible with existing semiconductor manufacturing tools. 1. Nagaosa, N., Tokura, Y. Nature Nanotechnology 8, 899-911 (2013). 2. Fert, A., et al., Nature Nanotechnology 8, 152-156 (2013).

  15. Room temperature and productivity in office work

    SciTech Connect

    Seppanen, O.; Fisk, W.J.; Lei, Q.H.

    2006-07-01

    Indoor temperature is one of the fundamental characteristics of the indoor environment. It can be controlled with a degree of accuracy dependent on the building and its HVAC system. The indoor temperature affects several human responses, including thermal comfort, perceived air quality, sick building syndrome symptoms and performance at work. In this study, we focused on the effects of temperature on performance at office work. We included those studies that had used objective indicators of performance that are likely to be relevant in office type work, such as text processing, simple calculations (addition, multiplication), length of telephone customer service time, and total handling time per customer for call-center workers. We excluded data from studies of industrial work performance. We calculated from all studies the percentage of performance change per degree increase in temperature, and statistically analyzed measured work performance with temperature. The results show that performance increases with temperature up to 21-22 C, and decreases with temperature above 23-24 C. The highest productivity is at temperature of around 22 C. For example, at the temperature of 30 C, the performance is only 91.1% of the maximum i.e. the reduction in performance is 8.9%.

  16. Oxygen-vacancy-induced room-temperature magnetization in lamellar V2O5 thin films

    NASA Astrophysics Data System (ADS)

    Cezar, A. B.; Graff, I. L.; Varalda, J.; Schreiner, W. H.; Mosca, D. H.

    2014-10-01

    In this work, we study the local atomic and electronic structures as well as oxygen-vacancy-induced magnetic properties of electrodeposited V2O5 films. Unlike stoichiometric V2O5, which is a diamagnetic lamellar semiconductor, our oxygen-defective V2O5 films are ferromagnetic at room-temperature and their saturation magnetization decreases with air exposure time. X-ray absorption spectroscopy was used to monitor the aging effect on these films, revealing that freshly-made samples exhibit only local crystalline order, whereas the aged ones undoubtedly show an enhancement of crystallinity and coordination symmetry. The mean number of oxygen atoms around V tends to increase, indicating a decrease of oxygen vacancies with time. Concurrently with the decrease of oxygen vacancies, a loss of saturation magnetization is also observed. Hence, it can be concluded that the ferromagnetism of the V2O5 films originates from a vacancy-induced mechanism, confirming the universality of this class of ferromagnetism.

  17. High-efficiency resonant amplification of weak magnetic fields for single spin magnetometry at room temperature

    NASA Astrophysics Data System (ADS)

    Trifunovic, Luka; Pedrocchi, Fabio L.; Hoffman, Silas; Maletinsky, Patrick; Yacoby, Amir; Loss, Daniel

    2015-06-01

    Magnetic resonance techniques not only provide powerful imaging tools that have revolutionized medicine, but they have a wide spectrum of applications in other fields of science such as biology, chemistry, neuroscience and physics. However, current state-of-the-art magnetometers are unable to detect a single nuclear spin unless the tip-to-sample separation is made sufficiently small. Here, we demonstrate theoretically that by placing a ferromagnetic particle between a nitrogen-vacancy magnetometer and a target spin, the magnetometer sensitivity is improved dramatically. Using materials and techniques that are already experimentally available, our proposed set-up is sensitive enough to detect a single nuclear spin within ten milliseconds of data acquisition at room temperature. The sensitivity is practically unchanged when the ferromagnet surface to the target spin separation is smaller than the ferromagnet lateral dimensions; typically about a tenth of a micrometre. This scheme further benefits when used for nitrogen-vacancy ensemble measurements, enhancing sensitivity by an additional three orders of magnitude.

  18. Fabrication method for a room temperature hydrogen sensor

    NASA Technical Reports Server (NTRS)

    Seal, Sudipta (Inventor); Shukla, Satyajit V. (Inventor); Ludwig, Lawrence (Inventor); Cho, Hyoung (Inventor)

    2011-01-01

    A sensor for selectively determining the presence and measuring the amount of hydrogen in the vicinity of the sensor. The sensor comprises a MEMS device coated with a nanostructured thin film of indium oxide doped tin oxide with an over layer of nanostructured barium cerate with platinum catalyst nanoparticles. Initial exposure to a UV light source, at room temperature, causes burning of organic residues present on the sensor surface and provides a clean surface for sensing hydrogen at room temperature. A giant room temperature hydrogen sensitivity is observed after making the UV source off. The hydrogen sensor of the invention can be usefully employed for the detection of hydrogen in an environment susceptible to the incursion or generation of hydrogen and may be conveniently used at room temperature.

  19. Room temperature synthesis of biodiesel using sulfonated graphitic carbon nitride

    SciTech Connect

    Baig, R. B. Nasir; Verma, Sanny; Nadagouda, Mallikarjuna N.; Varma, Rajender S.

    2016-12-19

    Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature.

  20. Room temperature synthesis of biodiesel using sulfonated graphitic carbon nitride

    NASA Astrophysics Data System (ADS)

    Baig, R. B. Nasir; Verma, Sanny; Nadagouda, Mallikarjuna N.; Varma, Rajender S.

    2016-12-01

    Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature.

  1. Room temperature synthesis of biodiesel using sulfonated graphitic carbon nitride

    EPA Science Inventory

    Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature.

  2. Room temperature synthesis of biodiesel using sulfonated graphitic carbon nitride

    EPA Science Inventory

    Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature.

  3. Room temperature synthesis of biodiesel using sulfonated graphitic carbon nitride.

    PubMed

    Baig, R B Nasir; Verma, Sanny; Nadagouda, Mallikarjuna N; Varma, Rajender S

    2016-12-19

    Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature.

  4. Room temperature synthesis of biodiesel using sulfonated graphitic carbon nitride

    DOE PAGES

    Baig, R. B. Nasir; Verma, Sanny; Nadagouda, Mallikarjuna N.; ...

    2016-12-01

    Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature.

  5. Room temperature synthesis of biodiesel using sulfonated graphitic carbon nitride

    PubMed Central

    Baig, R. B. Nasir; Verma, Sanny; Nadagouda, Mallikarjuna N.; Varma, Rajender S.

    2016-01-01

    Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature. PMID:27991593

  6. Neutron absorbing room temperature vulcanizable silicone rubber compositions

    DOEpatents

    Zoch, Harold L.

    1979-11-27

    A neutron absorbing composition comprising a one-component room temperature vulcanizable silicone rubber composition or a two-component room temperature vulcanizable silicone rubber composition in which the composition contains from 25 to 300 parts by weight based on the base silanol or vinyl containing diorganopolysiloxane polymer of a boron compound or boron powder as the neutron absorbing ingredient. An especially useful boron compound in this application is boron carbide.

  7. Structural investigations on Co{sub 3-x}Mn{sub x}TeO{sub 6}; (0 < x ≤ 2); High temperature ferromagnetism and enhanced low temperature anti-ferromagnetism

    SciTech Connect

    Singh, Harishchandra; Sinha, A. K. E-mail: hng@rrcat.gov.in; Ghosh, Haranath E-mail: hng@rrcat.gov.in; Singh, M. N.; Rajput, Parasmani; Prajapat, C. L.; Singh, M. R.; Ravikumar, G.

    2014-08-21

    In the quest of materials with high temperature ferromagnetism and low temperature anti-ferromagnetism, we prepare Co{sub 3-x}Mn{sub x}TeO{sub 6}; (0 < x ≤ 2) solid solutions. Room temperature structural investigations on these solid solutions as a function of Mn concentration using Synchrotron X-ray diffraction (SXRD) and X-ray absorption near edge structure measurements in corroboration with magnetism are presented. Phase diagram obtained from Rietveld Refinement on SXRD data as a function of Mn concentration indicates doping disproportionate mixing of both monoclinic (C2/c) and rhombohedral (R 3{sup ¯}) structure for x < 0.5, while only R 3{sup ¯} structure for x ≥ 0.5. Further, it shows increase in both lattice parameters as well as average transition metal-oxygen (Co/Mn-O) bond lengths for x ≥ 0.5. Co and Mn K-edge XANES spectra reveal that both Co and Mn are in mixed oxidation state, Co{sup 2+}/Mn{sup 2+} and Co{sup 3+}/Mn{sup 3+}. Relative ratios of Co{sup 3+}/Co{sup 2+} and Mn{sup 3+}/Mn{sup 2+} obtained using Linear combination fit decrease with increasing x (for x ≥ 0.5). These structural and spectroscopic evidences are used to provide possible interpretation of the observed paramagnetic to ferromagnetic transition at around 185 K followed by an enhanced antiferromagnetic transition ∼45 K for x = 0.5.

  8. A novel ferromagnetic thermo-stent for plaque stabilization that self-regulates the temperature.

    PubMed

    Matsui, Takemi; Matsumura, Kouji; Hagisawa, Kousuke; Ishihara, Masayuki; Ishizuka, Toshiaki; Suzuki, Minoru; Kurita, Akira; Kikuchi, Makoto

    2002-06-01

    The purpose of this study is to investigate the vascular wall with a thermally self-regulating, cylindrical stent made of a low Curie temperature ferromagnetic alloy. Physiologic saline was circulated in the silicone model vessel implanted with the stent. The stent-temperature remained nearly constant for variable saline flows, saline temperatures, and magnetic flux densities. Stent implants of this type in human blood vessels could potentially enable thermotherapy and temperature determination without catheterization.

  9. High temperature ferromagnetism in Cu-doped MoS2 nanosheets

    NASA Astrophysics Data System (ADS)

    Xia, Baorui; Guo, Qing; Gao, Daqiang; Shi, Shoupeng; Tao, Kun

    2016-04-01

    The synthesis of 2D metal chalcogenide based on ferromagnetic nanosheets is in high demand for modern electronics and spintronics applications. Herein, Cu-doped MoS2 nanosheets were successfully prepared by a hydrothermal method. Magnetic measurement results indicate that the doping of Cu ions can introduce ferromagnetism into MoS2 nanosheets, where saturate magnetization increases with increased Cu concentration. Further, the hysteresis curves measured at different temperatures demonstrate a high Curie temperature of 930 K for the Cu-doped MoS2 nanosheets. This result opens a new path to exploring spintronics in pristine 2D nanostructures by non-magnetic atom doping.

  10. High temperature magnetic order in Zn1-x Mn x SnSb2+MnSb nanocomposite ferromagnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Kilanski, L.; Górska, M.; Ślawska-Waniewska, A.; Lewińska, S.; Szymczak, R.; Dynowska, E.; Podgórni, A.; Dobrowolski, W.; Ralević, U.; Gajić, R.; Romčević, N.; Fedorchenko, I. V.; Marenkin, S. F.

    2016-08-01

    We present studies of structural, magnetic, and electrical properties of Zn1-x Mn x SnSb2+MnSb nanocomposite ferromagnetic semiconductors with the average Mn-content, \\bar{x} , changing from 0.027 up to 0.138. The magnetic force microscope imaging done at room temperature shows the presence of a strong signal coming from MnSb clusters. Magnetic properties show the paramagnet-ferromagnet transition with the Curie temperature, T C, equal to about 522 K and the cluster-glass behavior with the transition temperature, T CG, equal to about 465 K, both related to MnSb clusters. The magnetotransport studies show that all investigated samples are p-type semiconductors with high hole concentration, p, changing from 1021 to 1022 cm-3. A large increase in the resistivity as a function of the magnetic field is observed at T  <  10 K and small magnetic fields, |B|<100 mT, for all the studied samples with a maximum amplitude of the magnetoresistance about 460% at T  =  1.4 K. The large increase in the resistivity is most probably caused by the appearance of the superconducting state in the samples at T  <  4.3 K.

  11. Nature of room-temperature photoluminescence in ZnO

    SciTech Connect

    Shan, W.; Walukiewicz, W.; Ager III, J.W.; Yu, K.M.; Yuan, H.B.; Xin, H.P.; Cantwell, G.; Song, J.J.

    2004-11-11

    The temperature dependence of the photoluminescence (PL) transitions associated with various excitons and their phonon replicas in high-purity bulk ZnO has been studied at temperatures from 12 K to above room temperature (320 K). Several strong PL emission lines associated with LO phonon replicas of free and bound excitons are clearly observed. The room temperature PL spectrum is dominated by the phonon replicas of the free exciton transition with the maximum at the first LO phonon replica. The results explain the discrepancy between the transition energy of free exciton determined by reflection measurement and the peak position obtained by the PL measurement.

  12. Control and Room Temperature Optimization of Energy Efficient Buildings

    SciTech Connect

    Djouadi, Seddik M; Kuruganti, Phani Teja

    2012-01-01

    The building sector consumes a large part of the energy used in the United States and is responsible for nearly 40% of greenhouse gas emissions. It is therefore economically and environmentally important to reduce the building energy consumption to realize massive energy savings. In this paper, a method to control room temperature in buildings is proposed. The approach is based on a distributed parameter model represented by a three dimensional (3D) heat equation in a room with heater/cooler located at ceiling. The latter is resolved using finite element methods, and results in a model for room temperature with thousands of states. The latter is not amenable to control design. A reduced order model of only few states is then derived using Proper Orthogonal Decomposition (POD). A Linear Quadratic Regulator (LQR) is computed based on the reduced model, and applied to the full order model to control room temperature.

  13. Room temperature magnetoelectric coupling in Zn1-xCoxO/BaTiO3 bilayer system

    NASA Astrophysics Data System (ADS)

    Sundararaj, Anuraj; Annal Therese, Helen; Ramaswamy, Shivaraman; Chandrasekaran, Gopalakrishnan; Annamalai, Karthigeyan

    2014-09-01

    We report on room temperature magnetoelectric coupling in Zn1-xCoxO/BaTiO3 (x = 0.02, 0.05, and 0.10) bilayer thinfilm multiferroic system (BLS) grown on SrTiO3 (100) substrate. All the BLSs exhibit room temperature ferroelectric response. The BLS with x = 0.02 is paramagnetic, while the BLS with x = 0.05 and 0.10 is weakly ferromagnetic. Increase in Co concentration of the BLS results in reduction of permittivity and electric polarization along with increase of coercive voltage, coercive field, and magnetic moment. The d33 value change from 23 pm/V to 30 pm/V with increase in external magnetic field from 1500 G to 2500 G for BLS with x = 0.05. This shows that Zn1-xCoxO/BaTiO3 is magnetoelectrically coupled at room temperature.

  14. Room Temperature Magnetic Behavior In Nanocrystalline Ni-Doped Zro2 By Microwave-Assisted Polyol Synthesis

    NASA Astrophysics Data System (ADS)

    Parimita Rath, Pragyan; Parhi, Pankaj Kumar; Ranjan Panda, Sirish; Priyadarshini, Barsharani; Ranjan Sahoo, Tapas

    2017-08-01

    This article, deals with a microwave-assisted polyol method to demonstrate a low temperature route < 250°C, to prepare a high temperature cubic zirconia phase. Powder XRD pattern shows broad diffraction peaks suggesting nanometric size of the particles. Magnetic behavior of 1-5 at% Ni doped samples show a threshold for substitutional induced room temperature ferromagnetism up to 3 at% of Ni. TGA data reveals that Ni-doped ZrO2 polyol precursors decompose exothermically below 300°C. IR data confirms the reduction of Zr(OH)4 precipitates to ZrO2, in agreement with the conclusions drawn from the TGA analysis.

  15. Exchange interactions, spin waves, and Curie temperature in zincblende half-metallic sp-electron ferromagnets: the case of CaZ (Z = N, P, As, Sb).

    PubMed

    Laref, A; Saşioglu, E; Galanakis, I

    2011-07-27

    Using first-principle calculations in conjunction with the frozen-magnon technique we have calculated the exchange interactions and spin-wave dispersions in the series of the zincblende half-metallic II-V (CaZ, Z = N, P, As, Sb) ferromagnets. The calculated exchange constants are used to estimate the Curie temperature within the random phase approximation. The large Stoner gap in these alloys gives rise to well-defined undamped spin waves throughout the Brillouin zone. Moreover we show that the spin-wave stiffness constants for the considered systems are among the largest available for local moment ferromagnets. The predicted Curie temperature of half-metallic CaN is noticeably higher than the room temperature with respect to the other compounds, and thus we propose CaN as a promising candidate for future applications in spintronic devices.

  16. Room temperature dual ferroic behaviour of ball mill synthesized NdFeO{sub 3} orthoferrite

    SciTech Connect

    Aparnadevi, N.; Saravana Kumar, K.; Manikandan, M.; Venkateswaran, C.; Paul Joseph, D.

    2016-07-21

    Phase pure NdFeO{sub 3} has been achieved using high energy ball milling of oxide precursors with subsequent sintering. It is established that structural arrangement of NdFeO{sub 3} regulates the multifunctional feature of the material. Rietveld refinement of the room temperature X-ray diffraction pattern shows that the Fe-O-Fe bond angle significantly favors the super exchange interaction, which is predominantly antiferromagnetic in nature. Magnetization measurement illustrates antiferromagnetic behaviour with a weak ferromagnetic component caused by the canted nature of the Fe{sup 3+} spins at room temperature. Absorption bands in the visible ambit, apparent from the UV-Vis diffuse reflectance studies, is found due to the crystal ligand field of octahedral oxygen environment of Fe{sup 3+} ions. The direct band gap is estimated to be 2.39 eV from the diffuse reflectance spectrum. The lossy natured ferroelectric loop having a maximum polarization of 0.23 μC/cm{sup 2} at room temperature is found to be driven by the non-collinear magnetic structure with reverse Dzyaloshinskii–Moriya effect. Magnetic field has influence on the dielectric constant as evident from the impedance spectroscopy, indicating the strong coupling between ferroelectric and the magnetic structure of NdFeO{sub 3}.

  17. Inverse spin Hall effect in the semiconductor (Ga,Mn)As at room temperature

    NASA Astrophysics Data System (ADS)

    Mendes, J. B. S.; Mello, S. L. A.; Alves Santos, O.; Cunha, R. O.; Rodríguez-Suárez, R. L.; Azevedo, A.; Rezende, S. M.

    2017-06-01

    We report experiments demonstrating that a spin current can be converted into a charge current in a film of the paramagnetic semiconductor (Ga,Mn)As at room temperature by means of the inverse spin Hall effect. The spin currents are generated in a thin layer of permalloy (Py) by two different processes: spin-pumping effect (SPE) and spin Seebeck effect (SSE). In the first, we use microwave-driven ferromagnetic resonance of the Py film to generate a SPE spin current that is injected into the (Ga,Mn)As film either in direct contact with Py or through a thin layer of insulating antiferromagnetic NiO. In the second, we use the SSE in the longitudinal configuration in Py with no contamination by the Nernst effect made possible with the use of a thin layer of NiO between the Py and (Ga,Mn)As layers. The results of the two measurements are consistent with each other, and from them, we obtain a spin Hall angle for (Ga,Mn)As at room temperature of θSH=(1.5 ±0.5 ) ×10-3 , which is one order of magnitude larger than the values reported for p -Si and n -Ge at room temperature.

  18. Enabling room temperature sodium metal batteries

    SciTech Connect

    Cao, Ruiguo; Mishra, Kuber; Li, Xiaolin; Qian, Jiangfeng; Engelhard, Mark H.; Bowden, Mark E.; Han, Kee Sung; Mueller, Karl T.; Henderson, Wesley A.; Zhang, Ji-Guang

    2016-12-01

    Rechargeable batteries based upon sodium (Na+) cations are at the core of many new battery chemistries beyond Li-ion batteries. Rather than using carbon or alloy-based anodes, the direct utilization of solid sodium metal as an anode would be highly advantageous, but its use has been highly problematic due to its high reactivity. In this work, however, it is demonstrated that, by tailoring the electrolyte formulation, solid Na metal can be electrochemically plated/stripped at ambient temperature with high efficiency (> 99%) on both copper and inexpensive aluminum current collectors thereby enabling a shift in focus to new battery chemical couples based upon Na metal operating at ambient temperature. These highly concentrated electrolytes has enabled stable cycling of Na metal batteries based on a Na metal anode and Na3V2(PO4)3 cathode at high rates with very high efficiency.

  19. Proposal for a room-temperature diamond maser

    PubMed Central

    Jin, Liang; Pfender, Matthias; Aslam, Nabeel; Neumann, Philipp; Yang, Sen; Wrachtrup, Jörg; Liu, Ren-Bao

    2015-01-01

    The application of masers is limited by its demanding working conditions (high vacuum or low temperature). A room-temperature solid-state maser is highly desirable, but the lifetimes of emitters (electron spins) in solids at room temperature are usually too short (∼ns) for population inversion. Masing from pentacene spins in p-terphenyl crystals, which have a long spin lifetime (∼0.1 ms), has been demonstrated. This maser, however, operates only in the pulsed mode. Here we propose a room-temperature maser based on nitrogen-vacancy centres in diamond, which features the longest known solid-state spin lifetime (∼5 ms) at room temperature, high optical pumping efficiency (∼106 s−1) and material stability. Our numerical simulation demonstrates that a maser with a coherence time of approximately minutes is feasible under readily accessible conditions (cavity Q-factor ∼5 × 104, diamond size ∼3 × 3 × 0.5 mm3 and pump power <10 W). A room-temperature diamond maser may facilitate a broad range of microwave technologies. PMID:26394758

  20. Proposal for a room-temperature diamond maser.

    PubMed

    Jin, Liang; Pfender, Matthias; Aslam, Nabeel; Neumann, Philipp; Yang, Sen; Wrachtrup, Jörg; Liu, Ren-Bao

    2015-09-23

    The application of masers is limited by its demanding working conditions (high vacuum or low temperature). A room-temperature solid-state maser is highly desirable, but the lifetimes of emitters (electron spins) in solids at room temperature are usually too short (∼ns) for population inversion. Masing from pentacene spins in p-terphenyl crystals, which have a long spin lifetime (∼0.1 ms), has been demonstrated. This maser, however, operates only in the pulsed mode. Here we propose a room-temperature maser based on nitrogen-vacancy centres in diamond, which features the longest known solid-state spin lifetime (∼5 ms) at room temperature, high optical pumping efficiency (∼10(6) s(-1)) and material stability. Our numerical simulation demonstrates that a maser with a coherence time of approximately minutes is feasible under readily accessible conditions (cavity Q-factor ∼5 × 10(4), diamond size ∼3 × 3 × 0.5 mm(3) and pump power <10 W). A room-temperature diamond maser may facilitate a broad range of microwave technologies.

  1. Non-magnetic organic/inorganic spin injector at room temperature

    SciTech Connect

    Mathew, Shinto P.; Mondal, Prakash Chandra; Naaman, Ron; Moshe, Hagay; Mastai, Yitzhak

    2014-12-15

    Spin injection into solid-state devices is commonly performed by use of ferromagnetic metal electrodes. Here, we present a spin injector design without permanent magnet; rather, the spin selectivity is determined by a chiral tunneling barrier. The chiral tunneling barrier is composed of an ultrathin Al{sub 2}O{sub 3} layer that is deposited on top of a chiral self-assembled monolayer (SAM), which consists of cysteine or oligopeptide molecules. The experimentally observed magnetoresistance can be up to 20% at room temperature, and it displays an uncommon asymmetric curve as a function of the applied magnetic field. These findings show that the spin injector transmits only one spin orientation, independent of external magnetic field. The sign of the magnetoresistance depends on the handedness of the molecules in the SAM, which act as a spin filter, and the magnitude of the magnetoresistance depends only weakly on temperature.

  2. Large Magnetoelectric Coupling Near Room Temperature in Synthetic Melanostibite Mn2 FeSbO6.

    PubMed

    Dos Santos-García, Antonio J; Solana-Madruga, Elena; Ritter, Clemens; Andrada-Chacón, Adrián; Sánchez-Benítez, Javier; Mompean, Federico J; Garcia-Hernandez, Mar; Sáez-Puche, Regino; Schmidt, Rainer

    2017-04-10

    Multiferroic materials exhibit two or more ferroic orders and have potential applications as multifunctional materials in the electronics industry. A coupling of ferroelectricity and ferromagnetism is hereby particularly promising. We show that the synthetic melanostibite mineral Mn2 FeSbO6 (R3‾ space group) with ilmenite-type structure exhibits cation off-centering that results in alternating modulated displacements, thus allowing antiferroelectricity to occur. Massive magnetoelectric coupling (MEC) and magnetocapacitance effect of up to 4000 % was detected at a record high temperature of 260 K. The multiferroic behavior is based on the imbalance of cationic displacements caused by a magnetostrictive mechanism, which sets up an unprecedented example to pave the way for the development of highly effective MEC devices operational at or near room temperature. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. High-temperature ferromagnetism in Co-doped CeO2 synthesized by the coprecipitation technique.

    PubMed

    Colis, S; Bouaine, A; Schmerber, G; Ulhaq-Bouillet, C; Dinia, A; Choua, S; Turek, P

    2012-05-28

    The aim of the present study is to check the influence of annealing under vacuum and a mixture of N(2)-H(2) atmosphere on the magnetic properties of polycrystalline Co-doped CeO(2) diluted magnetic oxides (DMOs) with Co concentrations of 5 at% synthesized using the coprecipitation technique. X-Ray diffraction (XRD) patterns and transmission electron microscopy (TEM) showed for all samples the expected CeO(2) cubic fluorite-type structure and that Co ions are uniformly distributed inside the samples. Room-temperature Raman and photoluminescence (PL) spectroscopies indicate an increase in the concentration of oxygen vacancies upon Co doping and further annealing. Field dependent magnetization measurements revealed a paramagnetic behavior for as-prepared Co-doped CeO(2), while a ferromagnetic behavior appears when the same samples are annealed under vacuum or N(2)-H(2) atmosphere. Temperature dependent magnetization measurements suggest that the observed ferromagnetism is due to the presence of metallic Co clusters with nanometric size and broad size distribution. These results are supported by electron paramagnetic resonance studies.

  4. Room-temperature bonding of thin plastic sheets

    NASA Technical Reports Server (NTRS)

    Frazer, R. E.

    1979-01-01

    Thin sheets of plastic are bonded together, without heat, by depositing metal films on plastic and applying light pressure. Films are pressed together at room temperature, technique which makes it possible to join organic material without high temperatures necessary for conventional adhesive bonding.

  5. Tunable Curie temperature around room temperature and magnetocaloric effect in ternary Ce-Fe-B amorphous ribbons

    NASA Astrophysics Data System (ADS)

    Li, Zhu-bai; Zhang, Le-le; Zhang, Xue-feng; Li, Yong-feng; Zhao, Qian; Zhao, Tong-yun; Shen, Bao-gen

    2017-01-01

    Ce13-x Fe81+x B6 (x  =  0, 0.5, 1, 1.5, and 2) amorphous magnets were prepared by melt-spinning method. These magnets are magnetically soft at low temperature, and undergo a second-order phase transition from ferromagnetic to paramagnetic state near room temperature with a broad temperature span. The phase-transition temperature is tunable by the variation of the Ce/Fe atomic ratio, which is mainly due to the change of the coordination number of Fe atoms in these ternary Ce-Fe-B amorphous magnets. Though the entropy change is low, the refrigeration capacities are in the ranges of 116-150 J kg-1 and 319-420 J kg-1, respectively, for the magnetic field changes of 0-2 T and 0-5 T, which is comparable with those of conventional magnetic materials for room-temperature refrigeration. Given the low cost of Fe and Ce, Ce-Fe-B amorphous magnets are attractive magnetic refrigerant candidates.

  6. Giant electrocaloric effect in ferroelectric nanotubes near room temperature.

    PubMed

    Liu, Man; Wang, Jie

    2015-01-12

    Ferroelectric perovskite oxides possess large electrocaloric effect, but only at high temperature, which limits their potential as next generation solid state cooling devices. Here, we demonstrate from phase field simulations that a giant adiabatic temperature change exhibits near room temperature in the strained ferroelectric PbTiO₃ nanotubes, which is several times in magnitude larger than that of PbTiO₃ thin films. Such giant adiabatic temperature change is attributed to the extrinsic contribution of unusual domain transition, which involves a dedicated interplay among the electric field, strain, temperature and polarization. Careful selection of external strain allows one to harness the extrinsic contribution to obtain large adiabatic temperature change in ferroelectric nanotubes near room temperature. Our finding provides a novel insight into the electrocaloric response of ferroelectric nanostructures and leads to a new strategy to tailor and improve the electrocaloric properties of ferroelectric materials through domain engineering.

  7. Giant electrocaloric effect in ferroelectric nanotubes near room temperature

    PubMed Central

    Liu, Man; Wang, Jie

    2015-01-01

    Ferroelectric perovskite oxides possess large electrocaloric effect, but only at high temperature, which limits their potential as next generation solid state cooling devices. Here, we demonstrate from phase field simulations that a giant adiabatic temperature change exhibits near room temperature in the strained ferroelectric PbTiO3 nanotubes, which is several times in magnitude larger than that of PbTiO3 thin films. Such giant adiabatic temperature change is attributed to the extrinsic contribution of unusual domain transition, which involves a dedicated interplay among the electric field, strain, temperature and polarization. Careful selection of external strain allows one to harness the extrinsic contribution to obtain large adiabatic temperature change in ferroelectric nanotubes near room temperature. Our finding provides a novel insight into the electrocaloric response of ferroelectric nanostructures and leads to a new strategy to tailor and improve the electrocaloric properties of ferroelectric materials through domain engineering. PMID:25578434

  8. Room Temperature Silicene Field-Effect Transistors

    NASA Astrophysics Data System (ADS)

    Akinwande, Deji

    Silicene, a buckled Si analogue of graphene, holds significant promise for future electronics beyond traditional CMOS. In our predefined experiments via encapsulated delamination with native electrodes approach, silicene devices exhibit an ambipolar charge transport behavior, corroborating theories on Dirac band in Ag-free silicene. Monolayer silicene device has extracted field-effect mobility within the theoretical expectation and ON/OFF ratio greater than monolayer graphene, while multilayer silicene devices show decreased mobility and gate modulation. Air-stability of silicene devices depends on the number of layers of silicene and intrinsic material structure determined by growth temperature. Few or multi-layer silicene devices maintain their ambipolar behavior for days in contrast to minutes time scale for monolayer counterparts under similar conditions. Multilayer silicene grown at different temperatures below 300oC possess different intrinsic structures and yield different electrical property and air-stability. This work suggests a practical prospect to enable more air-stable silicene devices with layer and growth condition control, which can be leveraged for other air-sensitive 2D materials. In addition, we describe quantum and classical transistor device concepts based on silicene and related buckled materials that exploit the 2D topological insulating phenomenon. The transistor device physics offer the potential for ballistic transport that is robust against scattering and can be employed for both charge and spin transport. This work was supported by the ARO.

  9. Temperature dependence of the training effect in exchange coupled ferromagnetic bilayers

    NASA Astrophysics Data System (ADS)

    Polisetty, S.; Sahoo, S.; Berger, A.; Binek, Ch.

    2008-11-01

    The temperature dependence of the training effect is studied in an exchange coupled thin-film bilayer composed of a hard ferromagnetic pinning (CoPtCrB) layer in proximity of a soft ferromagnetic pinned (CoCr) layer. Interlayer exchange shifts the hysteresis loops of the soft layer along the magnetic-field axis. This shift is quantified by the bias field in far reaching analogy to the exchange bias field of conventional antiferromagnetic/ferromagnetic heterostructures. A ferromagnetic domain state induced in the hard layer experiences aging very similar to the training behavior of the antiferromagnetic domain state in conventional exchange bias systems. Training originates from changes in the spin structure of the pinning layer with consecutive magnetization reversals of the pinned layer. Here we perform a detailed investigation of the temperature dependence of the bias field and its training effect. Consecutively cycled hysteresis loops of the soft layer are measured at various temperatures. We also derive a theoretical description of the temperature dependence of the training effect which is in agreement with the experimental data.

  10. Raman evidence for presence of high-temperature ferromagnetic clusters in magnetodielectric compound Ba-doped La2NiMnO6

    NASA Astrophysics Data System (ADS)

    Barbosa, D. A. B.; Paschoal, C. W. A.

    2017-10-01

    Magnetodielectric ferromagnetic semiconductors are key materials because of their applications in spintronic devices; they can be used to control the magnetic properties by applying electric fields. La2NiMnO6 emerged as an important magnetodielectric ferromagnetic semiconductor because of its high Curie temperature near room temperature. Recently Ba doped was successfully used to improve magnetic properties in La2NiMnO6, originating partially ordered systems with different ordering degrees but presenting same Tc = 280 K. However, the influence of Ba doping on the temperature dependent vibrational properties of the system was not investigated. To investigate the Ba doping influence on temperature dependent phonon spectra in La2NiMnO6, we used Raman Spectroscopy to probe the symmetric stretching mode behavior in the range from 10 to 600 K. Remarkable softenings were detected in the phonon behavior due to spin phonon coupling, at several different temperatures, much above Tc. The FWHM dependence with temperature rules out magnetostriction effects. The phonon softenings are the largest reported so far for the RE2NiMnO6 systems and also indicate that Ba doping induces ordering in the Ni/Mn sites. The temperature discordance in characteristic softening onset of the spin phonon coupling are related to ferromagnetic short range clusters due the presence of Ni3 +, Mn3 + oxidation states.

  11. Raman evidence for presence of high-temperature ferromagnetic clusters in magnetodielectric compound Ba-doped La2NiMnO6.

    PubMed

    Barbosa, D A B; Paschoal, C W A

    2017-10-05

    Magnetodielectric ferromagnetic semiconductors are key materials because of their applications in spintronic devices; they can be used to control the magnetic properties by applying electric fields. La2NiMnO6 emerged as an important magnetodielectric ferromagnetic semiconductor because of its high Curie temperature near room temperature. Recently Ba doped was successfully used to improve magnetic properties in La2NiMnO6, originating partially ordered systems with different ordering degrees but presenting same Tc=280K. However, the influence of Ba doping on the temperature dependent vibrational properties of the system was not investigated. To investigate the Ba doping influence on temperature dependent phonon spectra in La2NiMnO6, we used Raman Spectroscopy to probe the symmetric stretching mode behavior in the range from 10 to 600K. Remarkable softenings were detected in the phonon behavior due to spin phonon coupling, at several different temperatures, much above Tc. The FWHM dependence with temperature rules out magnetostriction effects. The phonon softenings are the largest reported so far for the RE2NiMnO6 systems and also indicate that Ba doping induces ordering in the Ni/Mn sites. The temperature discordance in characteristic softening onset of the spin phonon coupling are related to ferromagnetic short range clusters due the presence of Ni(3+), Mn(3+) oxidation states. Copyright © 2017 Elsevier B.V. All rights reserved.

  12. Near-room-temperature Chern insulator and Dirac spin-gapless semiconductor: nickel chloride monolayer.

    PubMed

    He, Junjie; Li, Xiao; Lyu, Pengbo; Nachtigall, Petr

    2017-02-09

    A great obstacle for practical applications of the quantum anomalous Hall (QAH) effect is the lack of suitable QAH materials (Chern insulators) with a large non-trivial band gap, room-temperature magnetic order and high carrier mobility. Based on first-principles calculations it is shown here that a nickel chloride (NiCl3) monolayer has all these characteristics. Thus, the NiCl3 monolayer represents a new class of Dirac materials with Dirac spin-gapless semiconducting properties and high-temperature ferromagnetism (∼400 K). Taking into account the spin-orbit coupling, the NiCl3 monolayer becomes an intrinsic Chern insulator with a large non-trivial band gap of ∼24 meV, corresponding to an operating temperature as high as ∼280 K at which the quantum anomalous Hall effect could be observed. The calculated large non-trivial gap, high Curie temperature and single-spin Dirac states reported herein for the NiCl3 monolayer led us to propose that this material gives a great promise for potential realization of a near-room temperature QAH effect and potential applications in spintronics. Last but not least the calculated Fermi velocities of Dirac fermions of about 4 × 10(5) m s(-1) indicate very high mobility in NiCl3 monolayers.

  13. Interfacial dominated ferromagnetism in nanograined ZnO: a μSR and DFT study

    PubMed Central

    Tietze, Thomas; Audehm, Patrick; Chen, Yu–Chun; Schütz, Gisela; Straumal, Boris B.; Protasova, Svetlana G.; Mazilkin, Andrey A.; Straumal, Petr B.; Prokscha, Thomas; Luetkens, Hubertus; Salman, Zaher; Suter, Andreas; Baretzky, Brigitte; Fink, Karin; Wenzel, Wolfgang; Danilov, Denis; Goering, Eberhard

    2015-01-01

    Diamagnetic oxides can, under certain conditions, become ferromagnetic at room temperature and therefore are promising candidates for future material in spintronic devices. Contrary to early predictions, doping ZnO with uniformly distributed magnetic ions is not essential to obtain ferromagnetic samples. Instead, the nanostructure seems to play the key role, as room temperature ferromagnetism was also found in nanograined, undoped ZnO. However, the origin of room temperature ferromagnetism in primarily non–magnetic oxides like ZnO is still unexplained and a controversial subject within the scientific community. Using low energy muon spin relaxation in combination with SQUID and TEM techniques, we demonstrate that the magnetic volume fraction is strongly related to the sample volume fraction occupied by grain boundaries. With molecular dynamics and density functional theory we find ferromagnetic coupled electron states in ZnO grain boundaries. Our results provide evidence and a microscopic model for room temperature ferromagnetism in oxides. PMID:25747456

  14. Transition-metal embedded carbon nitride monolayers: high-temperature ferromagnetism and half-metallicity

    NASA Astrophysics Data System (ADS)

    Choudhuri, Indrani; Kumar, Sourabh; Mahata, Arup; Rawat, Kuber Singh; Pathak, Biswarup

    2016-07-01

    High-temperature ferromagnetic materials with planar surfaces are promising candidates for spintronics applications. Using state-of-the-art density functional theory (DFT) calculations, transition metal (TM = Cr, Mn, and Fe) incorporated graphitic carbon nitride (TM@gt-C3N4) systems are investigated as possible spintronics devices. Interestingly, ferromagnetism and half-metallicity were observed in all of the TM@gt-C3N4 systems. We find that Cr@gt-C3N4 is a nearly half-metallic ferromagnetic material with a Curie temperature of ~450 K. The calculated Curie temperature is noticeably higher than other planar 2D materials studied to date. Furthermore, it has a steel-like mechanical stability and also possesses remarkable dynamic and thermal (500 K) stability. The calculated magnetic anisotropy energy (MAE) in Cr@gt-C3N4 is as high as 137.26 μeV per Cr. Thereby, such material with a high Curie temperature can be operated at high temperatures for spintronics devices.High-temperature ferromagnetic materials with planar surfaces are promising candidates for spintronics applications. Using state-of-the-art density functional theory (DFT) calculations, transition metal (TM = Cr, Mn, and Fe) incorporated graphitic carbon nitride (TM@gt-C3N4) systems are investigated as possible spintronics devices. Interestingly, ferromagnetism and half-metallicity were observed in all of the TM@gt-C3N4 systems. We find that Cr@gt-C3N4 is a nearly half-metallic ferromagnetic material with a Curie temperature of ~450 K. The calculated Curie temperature is noticeably higher than other planar 2D materials studied to date. Furthermore, it has a steel-like mechanical stability and also possesses remarkable dynamic and thermal (500 K) stability. The calculated magnetic anisotropy energy (MAE) in Cr@gt-C3N4 is as high as 137.26 μeV per Cr. Thereby, such material with a high Curie temperature can be operated at high temperatures for spintronics devices. Electronic supplementary information (ESI

  15. High temperature ferromagnetism in cubic Mn-doped ZrO2 thin films

    NASA Astrophysics Data System (ADS)

    Hong, Nguyen Hoa; Park, Chul-Kwon; Raghavender, A. T.; Ruyter, Antoine; Chikoidze, Ekaterina; Dumont, Yves

    2012-09-01

    Theory has predicted that high temperature ferromagnetism (FM) should be found in cubic fake-diamonds, Mn-doped ZrO2. Experimentally, it is shown that Mn-doped ZrO2 ceramics are not ferromagnetic, but the nanosized Mn-doped ZrO2 thin films grown on LaAlO3 substrates can be ferromagnets with TC above 400 K. The largest saturated magnetic moment (Ms) is huge as of about 230 emu/cm3 for the Mn0.05Zr0.95O2 films, and it decreases as the Mn content increases. The intrinsic FM is strongly associated with the cubic structure of Mn-doped ZrO2, and the Mn-Mn interactions via oxygen intermediates are important. No electrical conductivity is observed. Mn-doped ZrO2 thin films can be truly considered as excellent candidates for spintronic applications.

  16. Modified Spin Wave Analysis of Low Temperature Properties of the Spin-1/2 Frustrated Ferromagnetic Ladder

    NASA Astrophysics Data System (ADS)

    Hida, Kazuo; Iino, Takashi

    2012-03-01

    Low temperature properties of the spin-1/2 frustrated ladder with ferromagnetic rungs and legs, and two different antiferromagnetic next nearest neighbor interactions are investigated using the modified spin wave approximation in the region with ferromagnetic ground states. The temperature dependence of the magnetic susceptibility and magnetic structure factors is calculated. The results are consistent with the numerical exact diagonalization results in the intermediate temperature range. Below this temperature range, the finite size effect is significant in the numerical diagonalization results, while the modified spin wave approximation gives more reliable results. The low temperature properties near the limit of the stability of the ferromagnetic ground state are also discussed.

  17. Room Temperature Crystallization of Hydroxyapatite in Porous Silicon Structures.

    PubMed

    Santana, M; Estevez, J O; Agarwal, V; Herrera-Becerra, R

    2016-12-01

    Porous silicon (PS) substrates, with different pore sizes and morphology, have been used to crystallize hydroxyapatite (HA) nano-fibers by an easy and economical procedure using a co-precipitation method at room temperature. In situ formation of HA nanoparticles, within the meso- and macroporous silicon structure, resulted in the formation of nanometer-sized hydroxyapatite crystals on/within the porous structure. The X-ray diffraction technique was used to determine the tetragonal structure of the crystals. Analysis/characterization demonstrates that under certain synthesis conditions, growth and crystallization of hydroxyapatite layer on/inside PS can be achieved at room temperature. Such composite structures expand the possibility of designing a new bio-composite material based on the hydroxyapatite and silicon synthesized at room temperature.

  18. Giant room-temperature elastocaloric effect in ferroelectric ultrathin films.

    PubMed

    Liu, Yang; Infante, Ingrid C; Lou, Xiaojie; Bellaiche, Laurent; Scott, James F; Dkhil, Brahim

    2014-09-17

    Environmentally friendly ultrathin BaTiO3 capacitors can exhibit a giant stress-induced elastocaloric effect without hysteresis loss or Joule heating. By combining this novel elastocaloric effect with the intrinsic electrocaloric effect, an ideal refrigeration cycle with high performance (temperature change over 10 K with a wide working-temperature window of 60 K) at room temperature is proposed for future cooling applications.

  19. Nanostructured Materials for Room-Temperature Gas Sensors.

    PubMed

    Zhang, Jun; Liu, Xianghong; Neri, Giovanni; Pinna, Nicola

    2016-02-03

    Sensor technology has an important effect on many aspects in our society, and has gained much progress, propelled by the development of nanoscience and nanotechnology. Current research efforts are directed toward developing high-performance gas sensors with low operating temperature at low fabrication costs. A gas sensor working at room temperature is very appealing as it provides very low power consumption and does not require a heater for high-temperature operation, and hence simplifies the fabrication of sensor devices and reduces the operating cost. Nanostructured materials are at the core of the development of any room-temperature sensing platform. The most important advances with regard to fundamental research, sensing mechanisms, and application of nanostructured materials for room-temperature conductometric sensor devices are reviewed here. Particular emphasis is given to the relation between the nanostructure and sensor properties in an attempt to address structure-property correlations. Finally, some future research perspectives and new challenges that the field of room-temperature sensors will have to address are also discussed.

  20. Crystallization of bacteriorhodopsin from bicelle formulations at room temperature.

    PubMed

    Faham, Salem; Boulting, Gabriella L; Massey, Elizabeth A; Yohannan, Sarah; Yang, Dawn; Bowie, James U

    2005-03-01

    We showed previously that high-quality crystals of bacteriorhodopsin (bR) from Halobacterium salinarum can be obtained from bicelle-forming DMPC/CHAPSO mixtures at 37 degrees C. As many membrane proteins are not sufficiently stable for crystallization at this high temperature, we tested whether the bicelle method could be applied at a lower temperature. Here we show that bR can be crystallized at room temperature using two different bicelle-forming compositions: DMPC/CHAPSO and DTPC/CHAPSO. The DTPC/CHAPSO crystals grown at room temperature are essentially identical to the previous, twinned crystals: space group P21 with unit cell dimensions of a = 44.7 A, b = 108.7 A, c = 55.8 A, beta = 113.6 degrees . The room-temperature DMPC/CHAPSO crystals are untwinned, however, and belong to space group C222(1) with the following unit cell dimensions: a = 44.7 A, b = 102.5 A, c = 128.2 A. The bR protein packs into almost identical layers in the two crystal forms, but the layers stack differently. The new untwinned crystal form yielded clear density for a previously unresolved CHAPSO molecule inserted between protein subunits within the layers. The ability to grow crystals at room temperature significantly expands the applicability of bicelle crystallization.

  1. Local electrical control of magnetic order and orientation by ferroelastic domain arrangements just above room temperature

    PubMed Central

    Phillips, L. C.; Cherifi, R. O.; Ivanovskaya, V.; Zobelli, A.; Infante, I. C.; Jacquet, E.; Guiblin, N.; Ünal, A. A.; Kronast, F.; Dkhil, B.; Barthélémy, A.; Bibes, M.; Valencia, S.

    2015-01-01

    Ferroic materials (ferromagnetic, ferroelectric, ferroelastic) usually divide into domains with different orientations of their order parameter. Coupling between different ferroic systems creates new functionalities, for instance the electrical control of macroscopic magnetic properties including magnetization and coercive field. Here we show that ferroelastic domains can be used to control both magnetic order and magnetization direction at the nanoscale with a voltage. We use element-specific X-ray imaging to map the magnetic domains as a function of temperature and voltage in epitaxial FeRh on ferroelastic BaTiO3. Exploiting the nanoscale phase-separation of FeRh, we locally interconvert between ferromagnetic and antiferromagnetic states with a small electric field just above room temperature. Imaging and ab initio calculations show the antiferromagnetic phase of FeRh is favoured by compressive strain on c-oriented BaTiO3 domains, and the resultant magnetoelectric coupling is larger and more reversible than previously reported from macroscopic measurements. Our results emphasize the importance of nanoscale ferroic domain structure and the promise of first-order transition materials to achieve enhanced coupling in artificial multiferroics. PMID:25969926

  2. Ultrahigh magnetoresistance at room temperature in molecular wires.

    PubMed

    Mahato, R N; Lülf, H; Siekman, M H; Kersten, S P; Bobbert, P A; de Jong, M P; De Cola, L; van der Wiel, W G

    2013-07-19

    Systems featuring large magnetoresistance (MR) at room temperature and in small magnetic fields are attractive owing to their potential for applications in magnetic field sensing and data storage. Usually, the magnetic properties of materials are exploited to achieve large MR effects. Here, we report on an exceptionally large (>2000%), room-temperature, small-field (a few millitesla) MR effect in one-dimensional, nonmagnetic systems formed by molecular wires embedded in a zeolite host crystal. This ultrahigh MR effect is ascribed to spin blockade in one-dimensional electron transport. Its generic nature offers very good perspectives to exploit the effect in a wide range of low-dimensional systems.

  3. Room Temperature Nanoimprint Technology Using Hydrogen Silsequioxane (HSQ)

    NASA Astrophysics Data System (ADS)

    Igaku, Yutaka; Matsui, Shinji; Ishigaki, Hiroyuki; Fujita, Jun-ichi; Ishida, Masahiko; Ochiai, Yukinori; Namatsu, Hideo; Komuro, Masanori; Hiroshima, Hiroshi

    2002-06-01

    Room-temperature nanoimprint lithography (RT-NIL) technology has been developed to overcome critical dimensions and pattern placement error due to thermal expansion in the conventional nanoimprint lithography (NIL) process. We propose RT-NIL using hydrogen silsequioxane (HSQ) instead of PMMA used in conventional NIL, and demonstrate HSQ replicated patterns with 90 nm hole diameter and 50 nm linewidth realized by room-temperature replications. We performed step-and-repeat replications using HSQ on a 1.5 in. wafer and evaluated the uniformity of the imprinted HSQ patterns.

  4. Room Temperature Antiferromagnetic Ordering of Nanocrystalline Tb1.90Ni0.10O3

    NASA Astrophysics Data System (ADS)

    Mandal, J.; Dalal, M.; Sarkar, B. J.; Chakrabarti, P. K.

    2017-02-01

    Nanocrystalline Ni-doped terbium oxide (Tb1.90Ni0.10O3) has been synthesized by the co-precipitation method followed by annealing at 700°C for 6 h in vacuum. The crystallographic phase and the substitution of Ni2+ ions in the lattice of Tb2O3 are confirmed by Rietveld analysis of the x-ray diffraction pattern using the software MAUD. High-resolution transmission electron microscopy is also carried out to study the morphology of the sample. Magnetic measurements are carried out at different temperatures from 5 K to 300 K using a superconducting quantum interference device (SQUID) magnetometer. The dependence of the magnetization of Tb1.90Ni0.10O3 as a function of temperature ( M- T) and magnetic field ( M- H) suggests the presence of both paramagnetic and antiferromagnetic phase at room temperature, but antiferromagnetic phase dominates below ˜120 K. The lack of saturation in the M- H curve and good fitting of the M- T curve by the Johnston formula also indicate the presence of both paramagnetic and antiferromagnetic phase at room temperature. Interestingly, an antiferromagnetic to ferromagnetic phase transition is observed below ˜40 K. The result also shows a high value of magnetization at 5 K.

  5. Large anomalous Hall effect in a non-collinear antiferromagnet at room temperature.

    PubMed

    Nakatsuji, Satoru; Kiyohara, Naoki; Higo, Tomoya

    2015-11-12

    In ferromagnetic conductors, an electric current may induce a transverse voltage drop in zero applied magnetic field: this anomalous Hall effect is observed to be proportional to magnetization, and thus is not usually seen in antiferromagnets in zero field. Recent developments in theory and experiment have provided a framework for understanding the anomalous Hall effect using Berry-phase concepts, and this perspective has led to predictions that, under certain conditions, a large anomalous Hall effect may appear in spin liquids and antiferromagnets without net spin magnetization. Although such a spontaneous Hall effect has now been observed in a spin liquid state, a zero-field anomalous Hall effect has hitherto not been reported for antiferromagnets. Here we report empirical evidence for a large anomalous Hall effect in an antiferromagnet that has vanishingly small magnetization. In particular, we find that Mn3Sn, an antiferromagnet that has a non-collinear 120-degree spin order, exhibits a large anomalous Hall conductivity of around 20 per ohm per centimetre at room temperature and more than 100 per ohm per centimetre at low temperatures, reaching the same order of magnitude as in ferromagnetic metals. Notably, the chiral antiferromagnetic state has a very weak and soft ferromagnetic moment of about 0.002 Bohr magnetons per Mn atom (refs 10, 12), allowing us to switch the sign of the Hall effect with a small magnetic field of around a few hundred oersted. This soft response of the large anomalous Hall effect could be useful for various applications including spintronics--for example, to develop a memory device that produces almost no perturbing stray fields.

  6. Room-Temperature-Cured Copolymers for Lithium Battery Gel Electrolytes

    NASA Technical Reports Server (NTRS)

    Meador, Mary Ann B.; Tigelaar, Dean M.

    2009-01-01

    Polyimide-PEO copolymers (PEO signifies polyethylene oxide) that have branched rod-coil molecular structures and that can be cured into film form at room temperature have been invented for use as gel electrolytes for lithium-ion electric-power cells. These copolymers offer an alternative to previously patented branched rod-coil polyimides that have been considered for use as polymer electrolytes and that must be cured at a temperature of 200 C. In order to obtain sufficient conductivity for lithium ions in practical applications at and below room temperature, it is necessary to imbibe such a polymer with a suitable carbonate solvent or ionic liquid, but the high-temperature cure makes it impossible to incorporate and retain such a liquid within the polymer molecular framework. By eliminating the high-temperature cure, the present invention makes it possible to incorporate the required liquid.

  7. Room Temperature Magnetically Ordered Polar Corundum GaFeO3 Displaying Magnetoelectric Coupling.

    PubMed

    Niu, Hongjun; Pitcher, Michael J; Corkett, Alex J; Ling, Sanliang; Mandal, Pranab; Zanella, Marco; Dawson, Karl; Stamenov, Plamen; Batuk, Dmitry; Abakumov, Artem M; Bull, Craig L; Smith, Ronald I; Murray, Claire A; Day, Sarah J; Slater, Ben; Cora, Furio; Claridge, John B; Rosseinsky, Matthew J

    2017-02-01

    The polar corundum structure type offers a route to new room temperature multiferroic materials, as the partial LiNbO3-type cation ordering that breaks inversion symmetry may be combined with long-range magnetic ordering of high spin d(5) cations above room temperature in the AFeO3 system. We report the synthesis of a polar corundum GaFeO3 by a high-pressure, high-temperature route and demonstrate that its polarity arises from partial LiNbO3-type cation ordering by complementary use of neutron, X-ray, and electron diffraction methods. In situ neutron diffraction shows that the polar corundum forms directly from AlFeO3-type GaFeO3 under the synthesis conditions. The A(3+)/Fe(3+) cations are shown to be more ordered in polar corundum GaFeO3 than in isostructural ScFeO3. This is explained by DFT calculations which indicate that the extent of ordering is dependent on the configurational entropy available to each system at the very different synthesis temperatures required to form their corundum structures. Polar corundum GaFeO3 exhibits weak ferromagnetism at room temperature that arises from its Fe2O3-like magnetic ordering, which persists to a temperature of 408 K. We demonstrate that the polarity and magnetization are coupled in this system with a measured linear magnetoelectric coupling coefficient of 0.057 ps/m. Such coupling is a prerequisite for potential applications of polar corundum materials in multiferroic/magnetoelectric devices.

  8. Tunable room-temperature magnetic skyrmions in Ir/Fe/Co/Pt multilayers

    NASA Astrophysics Data System (ADS)

    Soumyanarayanan, Anjan; Raju, M.; Gonzalez Oyarce, A. L.; Tan, Anthony K. C.; Im, Mi-Young; Petrović, A. P.; Ho, Pin; Khoo, K. H.; Tran, M.; Gan, C. K.; Ernult, F.; Panagopoulos, C.

    2017-09-01

    Magnetic skyrmions are nanoscale topological spin structures offering great promise for next-generation information storage technologies. The recent discovery of sub-100-nm room-temperature (RT) skyrmions in several multilayer films has triggered vigorous efforts to modulate their physical properties for their use in devices. Here we present a tunable RT skyrmion platform based on multilayer stacks of Ir/Fe/Co/Pt, which we study using X-ray microscopy, magnetic force microscopy and Hall transport techniques. By varying the ferromagnetic layer composition, we can tailor the magnetic interactions governing skyrmion properties, thereby tuning their thermodynamic stability parameter by an order of magnitude. The skyrmions exhibit a smooth crossover between isolated (metastable) and disordered lattice configurations across samples, while their size and density can be tuned by factors of two and ten, respectively. We thus establish a platform for investigating functional sub-50-nm RT skyrmions, pointing towards the development of skyrmion-based memory devices.

  9. Coulomb blockade and Coulomb staircase behavior observed at room temperature

    NASA Astrophysics Data System (ADS)

    Uky Vivitasari, Pipit; Azuma, Yasuo; Sakamoto, Masanori; Teranishi, Toshiharu; Majima, Yutaka

    2017-02-01

    A single-electron transistor (SET) consists of source, drain, Coulomb island, and gate to modulate the number of electrons and control the current. For practical applications, it is important to operate a SET at room temperature. One proposal towards the ability to operate at room temperature is to decrease Coulomb island size down to a few nanometres. We investigate a SET using Sn-porphyrin (Sn-por) protected gold nanoparticles (AuNPs) with 1.4 nm in core diameter as a Coulomb island. The fabrication method of nanogap electrodes uses the combination of a top-down technique by electron beam lithography (EBL) and a bottom-up process through electroless gold plating (ELGP) as our group have described before. The electrical measurement was conducted at room temperature (300 K). From current-voltage (I d-V d) characteristics, we obtained clear Coulomb blockade phenomena together with a Coulomb staircase due to a Sn-por protected gold NP as a Coulomb island. Experimental results of I d-V d characteristics agree with a theoretical curve based on using the orthodox model. Clear dI d/dV d peaks are observed in the Coulomb staircase at 9 K which suggest the electron transports through excited energy levels of Au NPs. These results are a big step for obtaining SETs that can operate at room temperature.

  10. Required Be Capsule Strength For Room Temperature Transport

    SciTech Connect

    Cook, B

    2005-03-21

    The purpose of this memo is to lay out the criteria for the Be capsule strength necessary for room temperature transport. Ultimately we will test full thickness capsules by sealing high pressures inside, but currently we are limited to both thinner capsules and alternative measures of capsule material strength.

  11. Coherent population trapping in a crystalline solid at room temperature

    SciTech Connect

    Kolesov, Roman

    2005-11-15

    Observation of coherent population trapping (CPT) at ground-state Zeeman sublevels of Cr{sup 3+} ion in ruby at room temperature is reported. A mechanism of CPT, not owing to optical pumping, is revealed in a situation when the optical pulse duration is shorter than the population decay time from the excited optical state.

  12. Experimental epikeratophakia using tissue lathed at room temperature.

    PubMed Central

    Rostron, C. K.; Sandford-Smith, J. H.; Morton, D. B.

    1988-01-01

    This report presents for the first time the results of carrying out epikeratophakia with tissue lathed at room temperature. Using an experimental model of epikeratophakia in the rabbit, we evaluated tissue handling techniques for the preparation of donor lenticules. Details of the technique are described and the in-vivo and histopathological findings reported. Images PMID:3293653

  13. Room-Temperature Ionic Liquids for Electrochemical Capacitors

    NASA Technical Reports Server (NTRS)

    Fireman, Heather; Yowell, Leonard; Moloney, Padraig G.; Arepalli, Sivaram; Nikolaev, P.; Huffman, C.; Ready, Jud; Higgins, C.D.; Turano, S. P.; Kohl, P.A.; Kim, K.

    2009-01-01

    A document discusses room-temperature ionic liquids (RTILs) used as electrolytes in carbon-nanotube-based, electrochemical, double-layer capacitors. Unlike the previous electrolyte (EtNB4 in acetonitrile), the RTIL used here does not produce cyanide upon thermal decomposition and does not have a moisture sensitivity.

  14. Amination of allylic alcohols in water at room temperature.

    PubMed

    Nishikata, Takashi; Lipshutz, Bruce H

    2009-06-04

    The "trick" to carrying out regiocontrolled aminations of allylic alcohols in water as the only medium is use of a nanomicelle's interior as the organic reaction solvent. When HCO(2)Me is present, along with the proper base and source of catalytic Pd, allylic amines are cleanly formed at room temperature.

  15. Giant tunnelling magnetoresistance at room temperature with MgO (100) tunnel barriers.

    PubMed

    Parkin, Stuart S P; Kaiser, Christian; Panchula, Alex; Rice, Philip M; Hughes, Brian; Samant, Mahesh; Yang, See-Hun

    2004-12-01

    Magnetically engineered magnetic tunnel junctions (MTJs) show promise as non-volatile storage cells in high-performance solid-state magnetic random access memories (MRAM). The performance of these devices is currently limited by the modest (< approximately 70%) room-temperature tunnelling magnetoresistance (TMR) of technologically relevant MTJs. Much higher TMR values have been theoretically predicted for perfectly ordered (100) oriented single-crystalline Fe/MgO/Fe MTJs. Here we show that sputter-deposited polycrystalline MTJs grown on an amorphous underlayer, but with highly oriented (100) MgO tunnel barriers and CoFe electrodes, exhibit TMR values of up to approximately 220% at room temperature and approximately 300% at low temperatures. Consistent with these high TMR values, superconducting tunnelling spectroscopy experiments indicate that the tunnelling current has a very high spin polarization of approximately 85%, which rivals that previously observed only using half-metallic ferromagnets. Such high values of spin polarization and TMR in readily manufactureable and highly thermally stable devices (up to 400 degrees C) will accelerate the development of new families of spintronic devices.

  16. Electronic spin transport and spin precession in single graphene layers at room temperature

    NASA Astrophysics Data System (ADS)

    Tombros, Nikolaos; Jozsa, Csaba; Popinciuc, Mihaita; Jonkman, Harry T.; van Wees, Bart J.

    2007-08-01

    Electronic transport in single or a few layers of graphene is the subject of intense interest at present. The specific band structure of graphene, with its unique valley structure and Dirac neutrality point separating hole states from electron states, has led to the observation of new electronic transport phenomena such as anomalously quantized Hall effects, absence of weak localization and the existence of a minimum conductivity. In addition to dissipative transport, supercurrent transport has also been observed. Graphene might also be a promising material for spintronics and related applications, such as the realization of spin qubits, owing to the low intrinsic spin orbit interaction, as well as the low hyperfine interaction of the electron spins with the carbon nuclei. Here we report the observation of spin transport, as well as Larmor spin precession, over micrometre-scale distances in single graphene layers. The `non-local' spin valve geometry was used in these experiments, employing four-terminal contact geometries with ferromagnetic cobalt electrodes making contact with the graphene sheet through a thin oxide layer. We observe clear bipolar (changing from positive to negative sign) spin signals that reflect the magnetization direction of all four electrodes, indicating that spin coherence extends underneath all of the contacts. No significant changes in the spin signals occur between 4.2K, 77K and room temperature. We extract a spin relaxation length between 1.5 and 2μm at room temperature, only weakly dependent on charge density. The spin polarization of the ferromagnetic contacts is calculated from the measurements to be around ten per cent.

  17. Observation of anharmonicity for copper thin film near room temperatures.

    PubMed

    Yang, D S

    2001-03-01

    The fluorescence EXAFS spectra for a copper thin film with a thickness of 3000A measured at 300K, 350K and 400K were analyzed by the regularization method to directly obtain the radial distribution. The pair distribution was almost symmetric for 300K but asymmetric for 350K and 400K. This indicates that the atoms in copper vibrate anharmonically near room temperatures. The anharmonicity and the skewness of the asymmetric distribu-tion increases as temperature increases.

  18. Evaluation of Ceramic Honeycomb Core Compression Behavior at Room Temperature

    NASA Technical Reports Server (NTRS)

    Bird, Richard K.; Lapointe, Thomas S.

    2013-01-01

    Room temperature flatwise compression tests were conducted on two varieties of ceramic honeycomb core specimens that have potential for high-temperature structural applications. One set of specimens was fabricated using strips of a commercially-available thin-gage "ceramic paper" sheet molded into a hexagonal core configuration. The other set was fabricated by machining honeycomb core directly from a commercially available rigid insulation tile material. This paper summarizes the results from these tests.

  19. Assembling non-ferromagnetic materials to ferromagnetic architectures using metal-semiconductor interfaces

    NASA Astrophysics Data System (ADS)

    Ma, Ji; Liu, Chunting; Chen, Kezheng

    2016-09-01

    In this work, a facile and versatile solution route was used to fabricate room-temperature ferromagnetic fish bone-like, pteridophyte-like, poplar flower-like, cotton-like Cu@Cu2O architectures and golfball-like Cu@ZnO architecture. The ferromagnetic origins in these architectures were found to be around metal-semiconductor interfaces and defects, and the root cause for their ferromagnetism lay in charge transfer processes from metal Cu to semiconductors Cu2O and ZnO. Owing to different metallization at their interfaces, these architectures exhibited different ferromagnetic behaviors, including coercivity, saturation magnetization as well as magnetic interactions.

  20. Assembling non-ferromagnetic materials to ferromagnetic architectures using metal-semiconductor interfaces

    PubMed Central

    Ma, Ji; Liu, Chunting; Chen, Kezheng

    2016-01-01

    In this work, a facile and versatile solution route was used to fabricate room-temperature ferromagnetic fish bone-like, pteridophyte-like, poplar flower-like, cotton-like Cu@Cu2O architectures and golfball-like Cu@ZnO architecture. The ferromagnetic origins in these architectures were found to be around metal-semiconductor interfaces and defects, and the root cause for their ferromagnetism lay in charge transfer processes from metal Cu to semiconductors Cu2O and ZnO. Owing to different metallization at their interfaces, these architectures exhibited different ferromagnetic behaviors, including coercivity, saturation magnetization as well as magnetic interactions. PMID:27680286

  1. Low-temperature ferromagnetic properties in Co-doped Ag{sub 2}Se nanoparticles

    SciTech Connect

    Yang, Fengxia E-mail: xia9020@hust.edu.cn; Yu, Gen; Han, Chong; Liu, Tingting; Zhang, Duanming; Xia, Zhengcai E-mail: xia9020@hust.edu.cn

    2014-01-06

    β-Ag{sub 2}Se is a topologically nontrivial insulator. The magnetic properties of Co-doped Ag{sub 2}Se nanoparticles with Co concentrations up to 40% were investigated. The cusp of zero-field-cooling magnetization curves and the low-temperature hysteresis loops were observed. With increasing concentration of Co{sup 2+} ions mainly substituting Ag{sub I} sites in the Ag{sub 2}Se structure, the resistivity, Curie temperature T{sub c}, and magnetization increased. At 10 T, a sharp drop of resistance near T{sub c} was detected due to Co dopants. The ferromagnetic behavior in Co-doped Ag{sub 2}Se might result from the intra-layer ferromagnetic coupling and surface spin. This magnetic semiconductor is a promising candidate in electronics and spintronics.

  2. Room-temperature magnetoelectric multiferroic thin films and applications thereof

    SciTech Connect

    Katiyar, Ram S; Kuman, Ashok; Scott, James F.

    2014-08-12

    The invention provides a novel class of room-temperature, single-phase, magnetoelectric multiferroic (PbFe.sub.0.67W.sub.0.33O.sub.3).sub.x (PbZr.sub.0.53Ti.sub.0.47O.sub.3).sub.1-x (0.2.ltoreq.x.ltoreq.0.8) (PFW.sub.x-PZT.sub.1-x) thin films that exhibit high dielectric constants, high polarization, weak saturation magnetization, broad dielectric temperature peak, high-frequency dispersion, low dielectric loss and low leakage current. These properties render them to be suitable candidates for room-temperature multiferroic devices. Methods of preparation are also provided.

  3. Micromachined room-temperature microbolometers for millimeter-wave detection

    NASA Astrophysics Data System (ADS)

    Rahman, Arifur; de Lange, Gert; Hu, Qing

    1996-04-01

    We have combined silicon micromachining technology with planar circuits to fabricate room-temperature niobium microbolometers for millimeter-wave detection. In this type of detector, a thin niobium film, with a dimension much smaller than the wavelength and fabricated on a 1 μm thick Si3N4 membrane, acts both as a radiation absorber and temperature sensor. Incident radiation is coupled into the microbolometer by a 0.37λ dipole antenna of center frequency 95 GHz with a 3 dB bandwidth of 15%, which is impedance matched with the Nb film. An electrical noise equivalent power (NEP) of 4.5×10-10 W/√Hz has been achieved. This is comparable to the best commercial room-temperature millimeter-wave detectors.

  4. Room-temperature chiral charge pumping in Dirac semimetals

    PubMed Central

    Zhang, Cheng; Zhang, Enze; Wang, Weiyi; Liu, Yanwen; Chen, Zhi-Gang; Lu, Shiheng; Liang, Sihang; Cao, Junzhi; Yuan, Xiang; Tang, Lei; Li, Qian; Zhou, Chao; Gu, Teng; Wu, Yizheng; Zou, Jin; Xiu, Faxian

    2017-01-01

    Chiral anomaly, a non-conservation of chiral charge pumped by the topological nontrivial gauge fields, has been predicted to exist in Weyl semimetals. However, until now, the experimental signature of this effect exclusively relies on the observation of negative longitudinal magnetoresistance at low temperatures. Here, we report the field-modulated chiral charge pumping process and valley diffusion in Cd3As2. Apart from the conventional negative magnetoresistance, we observe an unusual nonlocal response with negative field dependence up to room temperature, originating from the diffusion of valley polarization. Furthermore, a large magneto-optic Kerr effect generated by parallel electric and magnetic fields is detected. These new experimental approaches provide a quantitative analysis of the chiral anomaly phenomenon which was inaccessible previously. The ability to manipulate the valley polarization in topological semimetal at room temperature opens up a route towards understanding its fundamental properties and utilizing the chiral fermions. PMID:28067234

  5. Room-temperature chiral charge pumping in Dirac semimetals

    NASA Astrophysics Data System (ADS)

    Zhang, Cheng; Zhang, Enze; Wang, Weiyi; Liu, Yanwen; Chen, Zhi-Gang; Lu, Shiheng; Liang, Sihang; Cao, Junzhi; Yuan, Xiang; Tang, Lei; Li, Qian; Zhou, Chao; Gu, Teng; Wu, Yizheng; Zou, Jin; Xiu, Faxian

    2017-01-01

    Chiral anomaly, a non-conservation of chiral charge pumped by the topological nontrivial gauge fields, has been predicted to exist in Weyl semimetals. However, until now, the experimental signature of this effect exclusively relies on the observation of negative longitudinal magnetoresistance at low temperatures. Here, we report the field-modulated chiral charge pumping process and valley diffusion in Cd3As2. Apart from the conventional negative magnetoresistance, we observe an unusual nonlocal response with negative field dependence up to room temperature, originating from the diffusion of valley polarization. Furthermore, a large magneto-optic Kerr effect generated by parallel electric and magnetic fields is detected. These new experimental approaches provide a quantitative analysis of the chiral anomaly phenomenon which was inaccessible previously. The ability to manipulate the valley polarization in topological semimetal at room temperature opens up a route towards understanding its fundamental properties and utilizing the chiral fermions.

  6. Room Temperature Characterization of a Magnetic Bearing for Turbomachinery

    NASA Technical Reports Server (NTRS)

    Montague, Gerald; Jansen, Mark; Provenza, Andrew; Jansen, Ralph; Ebihara, Ben; Palazzolo, Alan

    2002-01-01

    Open loop, experimental force and power measurements of a three-axis, radial, heteropolar magnetic bearing at room temperature for rotor speeds up to 20,000 RPM are presented in this paper. The bearing, NASA Glenn Research Center's and Texas A&M's third generation high temperature magnetic bearing, was designed to operate in a 1000 F (540 C) environment and was primarily optimized for maximum load capacity. The experimentally measured force produced by one C-core of this bearing was 630 lb. (2.8 kN) at 16 A, while a load of 650 lbs (2.89 kN) was predicted at 16 A using 1D circuit analysis. The maximum predicted radial load for one of the three axes is 1,440 lbs (6.41 kN) at room temperature. The maximum measured load of an axis was 1050 lbs. (4.73 kN). Results of test under rotating conditions showed that rotor speed has a negligible effect on the bearing's load capacity. A single C-core required approximately 70 W of power to generate 300 lb (1.34 kN) of magnetic force. The room temperature data presented was measured after three thermal cycles up to 1000 F (540 C), totaling six hours at elevated temperatures.

  7. Four high-temperature ferromagnets in the Hf-Fe-Sn system.

    SciTech Connect

    Calta, Nicholas P.; Francisco, Melanie C.; Malliakas, Christos D.; Schlueter, John A.; Kanatzidis, Mercouri G.

    2014-12-09

    We report the synthesis and characterization of four new ferromagnetic compounds discovered using Sn flux: Hf1.823(16)Fe5Sn3.815(14), HfFe2-xSnx, and two polymorphs of Hf1-xFe2Snx. All are closely related to HfFe2 Laves phase parent structures. HfFe2-xSnx (x approximate to 0.3-0.4) adopts the MgZn2-type (C14) crystal structure, whereas Hf1-xFe2Snx (x approximate to 0.1-0.4) adopts both the MgCu2-type (C15), and MgNi2-type (C36) structures. They crystallize in P6(3)/mmc, Fd3m, and P6(3)/mmc, respectively, with measured unit-cell parameters of a = 4.9238(7) angstrom and c = 7.9643(12) angstrom; a = 7.068(2) angstrom; and a = 4.9944(4) angstrom and c = 16.2604(15) angstrom, although phase width leads to a range of unit cell edge lengths. Hf1.823(16)Fe5Sn3.815(14) adopts a more complicated, incommensurately modulated structure in the superspace group Xmmm(00 gamma)000 with an orthorhombic subcell a = 9.7034(12) angstrom, b = 16.823(2) angstrom, and c = 8.4473(10) angstrom, three centering vectors of (1/2 0 0 1/2), (0 1/2 0 1/2), and (1/2 1/2 0 0), and a single-component modulation vector q = 0.2768(8)c*. The structure is composed of alternating slabs of the Fe-bonded Kagome nets observed in the HfFe2 parent structures alternated with Sn-rich Th2Zn17-type slabs, with Hf atoms primarily occurring at the interfaces between the slabs. All four compounds are ferromagnetic metals at room temperature, with Curie temperatures ranging from 467(2) to 658(2) K. Their coercive fields are remarkably low, between 2(1) and 15(2) Oe. Interestingly, in two of three cases the addition of nonmagnetic Sn atoms in place of magnetic Hf or Fe atoms in the HfFe2 structure seems to strengthen rather than weaken magnetic coupling and increase TC. Fits to electrical resistivity data for the compound suggest that electron scattering in the Laves phase polymorphs shows substantial contributions from electron-magnon and/or electron-electron scattering, while the electrical behavior of Hf1.823(16)Fe

  8. Uniqueness of Translation-Covariant Zero-Temperature Metastate in Disordered Ising Ferromagnets

    NASA Astrophysics Data System (ADS)

    Wehr, Jan; Wasielak, Aramian

    2016-01-01

    We study ground states of Ising models with random ferromagnetic couplings, proving the triviality of all zero-temperature metastates. This result sheds a new light on the properties of these systems, putting strong restrictions on their possible ground state structure. Open problems related to existence of interface-supporting ground states are stated and an interpretation of the main result in terms of first-passage and random surface models in a random environment is presented.

  9. A novel perovskite oxide chemically designed to show multiferroic phase boundary with room-temperature magnetoelectricity

    NASA Astrophysics Data System (ADS)

    Fernández-Posada, Carmen M.; Castro, Alicia; Kiat, Jean-Michel; Porcher, Florence; Peña, Octavio; Algueró, Miguel; Amorín, Harvey

    2016-09-01

    There is a growing activity in the search of novel single-phase multiferroics that could finally provide distinctive magnetoelectric responses at room temperature, for they would enable a range of potentially disruptive technologies, making use of the ability of controlling polarization with a magnetic field or magnetism with an electric one (for example, voltage-tunable spintronic devices, uncooled magnetic sensors and the long-searched magnetoelectric memory). A very promising novel material concept could be to make use of phase-change phenomena at structural instabilities of a multiferroic state. Indeed, large phase-change magnetoelectric response has been anticipated by a first-principles investigation of the perovskite BiFeO3-BiCoO3 solid solution, specifically at its morphotropic phase boundary between multiferroic polymorphs of rhombohedral and tetragonal symmetries. Here, we report a novel perovskite oxide that belongs to the BiFeO3-BiMnO3-PbTiO3 ternary system, chemically designed to present such multiferroic phase boundary with enhanced ferroelectricity and canted ferromagnetism, which shows distinctive room-temperature magnetoelectric responses.

  10. A novel perovskite oxide chemically designed to show multiferroic phase boundary with room-temperature magnetoelectricity.

    PubMed

    Fernández-Posada, Carmen M; Castro, Alicia; Kiat, Jean-Michel; Porcher, Florence; Peña, Octavio; Algueró, Miguel; Amorín, Harvey

    2016-09-28

    There is a growing activity in the search of novel single-phase multiferroics that could finally provide distinctive magnetoelectric responses at room temperature, for they would enable a range of potentially disruptive technologies, making use of the ability of controlling polarization with a magnetic field or magnetism with an electric one (for example, voltage-tunable spintronic devices, uncooled magnetic sensors and the long-searched magnetoelectric memory). A very promising novel material concept could be to make use of phase-change phenomena at structural instabilities of a multiferroic state. Indeed, large phase-change magnetoelectric response has been anticipated by a first-principles investigation of the perovskite BiFeO3-BiCoO3 solid solution, specifically at its morphotropic phase boundary between multiferroic polymorphs of rhombohedral and tetragonal symmetries. Here, we report a novel perovskite oxide that belongs to the BiFeO3-BiMnO3-PbTiO3 ternary system, chemically designed to present such multiferroic phase boundary with enhanced ferroelectricity and canted ferromagnetism, which shows distinctive room-temperature magnetoelectric responses.

  11. A novel perovskite oxide chemically designed to show multiferroic phase boundary with room-temperature magnetoelectricity

    PubMed Central

    Fernández-Posada, Carmen M.; Castro, Alicia; Kiat, Jean-Michel; Porcher, Florence; Peña, Octavio; Algueró, Miguel; Amorín, Harvey

    2016-01-01

    There is a growing activity in the search of novel single-phase multiferroics that could finally provide distinctive magnetoelectric responses at room temperature, for they would enable a range of potentially disruptive technologies, making use of the ability of controlling polarization with a magnetic field or magnetism with an electric one (for example, voltage-tunable spintronic devices, uncooled magnetic sensors and the long-searched magnetoelectric memory). A very promising novel material concept could be to make use of phase-change phenomena at structural instabilities of a multiferroic state. Indeed, large phase-change magnetoelectric response has been anticipated by a first-principles investigation of the perovskite BiFeO3–BiCoO3 solid solution, specifically at its morphotropic phase boundary between multiferroic polymorphs of rhombohedral and tetragonal symmetries. Here, we report a novel perovskite oxide that belongs to the BiFeO3–BiMnO3–PbTiO3 ternary system, chemically designed to present such multiferroic phase boundary with enhanced ferroelectricity and canted ferromagnetism, which shows distinctive room-temperature magnetoelectric responses. PMID:27677353

  12. Large Conductance Switching in a Single-Molecule Device through Room Temperature Spin-Dependent Transport.

    PubMed

    Aragonès, Albert C; Aravena, Daniel; Cerdá, Jorge I; Acís-Castillo, Zulema; Li, Haipeng; Real, José Antonio; Sanz, Fausto; Hihath, Josh; Ruiz, Eliseo; Díez-Pérez, Ismael

    2016-01-13

    Controlling the spin of electrons in nanoscale electronic devices is one of the most promising topics aiming at developing devices with rapid and high density information storage capabilities. The interface magnetism or spinterface resulting from the interaction between a magnetic molecule and a metal surface, or vice versa, has become a key ingredient in creating nanoscale molecular devices with novel functionalities. Here, we present a single-molecule wire that displays large (>10000%) conductance switching by controlling the spin-dependent transport under ambient conditions (room temperature in a liquid cell). The molecular wire is built by trapping individual spin crossover Fe(II) complexes between one Au electrode and one ferromagnetic Ni electrode in an organic liquid medium. Large changes in the single-molecule conductance (>100-fold) are measured when the electrons flow from the Au electrode to either an α-up or a β-down spin-polarized Ni electrode. Our calculations show that the current flowing through such an interface appears to be strongly spin-polarized, thus resulting in the observed switching of the single-molecule wire conductance. The observation of such a high spin-dependent conductance switching in a single-molecule wire opens up a new door for the design and control of spin-polarized transport in nanoscale molecular devices at room temperature.

  13. Metal-Controlled Magnetoresistance at Room Temperature in Single-Molecule Devices.

    PubMed

    Aragonès, Albert C; Aravena, Daniel; Valverde-Muñoz, Francisco J; Real, José Antonio; Sanz, Fausto; Díez-Pérez, Ismael; Ruiz, Eliseo

    2017-03-03

    The appropriate choice of the transition metal complex and metal surface electronic structure opens the possibility to control the spin of the charge carriers through the resulting hybrid molecule/metal spinterface in a single-molecule electrical contact at room temperature. The single-molecule conductance of a Au/molecule/Ni junction can be switched by flipping the magnetization direction of the ferromagnetic electrode. The requirements of the molecule include not just the presence of unpaired electrons: the electronic configuration of the metal center has to provide occupied or empty orbitals that strongly interact with the junction metal electrodes and that are close in energy to their Fermi levels for one of the electronic spins only. The key ingredient for the metal surface is to provide an efficient spin texture induced by the spin-orbit coupling in the topological surface states that results in an efficient spin-dependent interaction with the orbitals of the molecule. The strong magnetoresistance effect found in this kind of single-molecule wire opens a new approach for the design of room-temperature nanoscale devices based on spin-polarized currents controlled at molecular level.

  14. Nanoscale structural modulation and enhanced room-temperature multiferroic properties

    NASA Astrophysics Data System (ADS)

    Sun, Shujie; Huang, Yan; Wang, Guopeng; Wang, Jianlin; Fu, Zhengping; Peng, Ranran; Knize, Randy J.; Lu, Yalin

    2014-10-01

    Availability of a single-phase multiferroic material functional at room temperature poses a big challenge, although it is very important to both fundamental physics and application development. Recently, layered Aurivillius oxide materials, one of the most promising candidates, have attracted considerable interest. In this work, we investigated the nanoscale structural evolution of the six-layer Bi7Fe3-xCoxTi3O21 when substituting excessive Co. Nanoscale structural modulation (NSM) occurred at the boundaries when changing the material gradually from the originally designed six-layer nanoscale architecture down to five and then four, when increasing the Co content, inducing a previously unidentified analogous morphotropic transformation (AMT) effect. The AMT's net contribution to the enhanced intrinsic multiferroic properties at room temperature was confirmed by quantifying and deducting the contribution from the existing impurity phase using derivative thermo-magneto-gravimetry measurements (DTMG). Significantly, this new AMT effect may be caused by a possible coupling contribution from co-existing NSM phases, indicating a potential method for realizing multiferroic materials that function at room temperature.Availability of a single-phase multiferroic material functional at room temperature poses a big challenge, although it is very important to both fundamental physics and application development. Recently, layered Aurivillius oxide materials, one of the most promising candidates, have attracted considerable interest. In this work, we investigated the nanoscale structural evolution of the six-layer Bi7Fe3-xCoxTi3O21 when substituting excessive Co. Nanoscale structural modulation (NSM) occurred at the boundaries when changing the material gradually from the originally designed six-layer nanoscale architecture down to five and then four, when increasing the Co content, inducing a previously unidentified analogous morphotropic transformation (AMT) effect. The AMT

  15. Room temperature recrystallization of 99. 999 PCT aluminum

    SciTech Connect

    Changhee Choi; Changseok, Oh; Dong Nyung Lee . Dept. of Metallurgical Engineering); Jaehan Jeong )

    1994-02-01

    It has been known that recrystallization of metals can be accelerated by a combined effect of high purity and a heavy deformation. There is an increasing interest in deformation and recrystallization behaviors of high purity aluminum, because of the sensitivity of its recrystallization temperature to impurities. Room temperature recrystallization of high purity aluminum is a typical example of this sensitivity and has been found and displayed in an earlier work. This result has been thought to occur statically, because aluminum was only known to undergo dynamic recovery (DRV) as a restoration mechanism due to a high stacking fault energy. However, some recent studies suggested the occurrence of dynamic recrystallization (DRX) in room temperature compression tests of 99.999 pct aluminum. Thus, the restoration mechanism of 99.999 pct aluminum during deformation is in dispute. The purpose of this study is to clarify whether or not DRX can occur in 99.999 pct aluminum that is subjected to plastic deformation at room temperature.

  16. Zero-temperature relaxation of three-dimensional Ising ferromagnets

    NASA Astrophysics Data System (ADS)

    Olejarz, J.; Krapivsky, P. L.; Redner, S.

    2011-05-01

    We investigate the properties of the Ising-Glauber model on a periodic cubic lattice of linear dimension L after a quench to zero temperature. The resulting evolution is extremely slow, with long periods of wandering on constant energy plateaus, punctuated by occasional energy-decreasing spin-flip events. The characteristic time scale τ for this relaxation grows exponentially with the system size; we provide a heuristic and numerical evidence that τ~exp(L2). For all but the smallest-size systems, the long-time state is almost never static. Instead, the system contains a small number of “blinker” spins that continue to flip forever with no energy cost. Thus, the system wanders ad infinitum on a connected set of equal-energy blinker states. These states are composed of two topologically complex interwoven domains of opposite phases. The average genus gL of the domains scales as Lγ, with γ≈1.7; thus, domains typically have many holes, leading to a “plumber’s nightmare” geometry.

  17. Induced spin-polarization of EuS at room temperature in Ni/EuS multilayers

    SciTech Connect

    Poulopoulos, P.; Goschew, A.; Straub, A.; Fumagalli, P.; Kapaklis, V.; Wolff, M.; Delimitis, A.; Wilhelm, F.; Rogalev, A.; Pappas, S. D.

    2014-03-17

    Ni/EuS multilayers with excellent multilayer sequencing are deposited via e-beam evaporation on the native oxide of Si(100) wafers at 4 × 10{sup −9} millibars. The samples have very small surface and interface roughness and show sharp interfaces. Ni layers are nanocrystalline 4–8 nm thick and EuS layers are 2–4 nm thick and are either amorphous or nanocrystalline. Unlike for Co/EuS multilayers, all Eu ions are in divalent (ferromagnetic) state. We show a direct antiferromagnetic coupling between EuS and Ni layers. At room temperature, the EuS layers are spin-polarized due to the proximity of Ni. Therefore, Ni/EuS is a candidate for room-temperature spintronics applications.

  18. Outrunning free radicals in room-temperature macromolecular crystallography

    PubMed Central

    Owen, Robin L.; Axford, Danny; Nettleship, Joanne E.; Owens, Raymond J.; Robinson, James I.; Morgan, Ann W.; Doré, Andrew S.; Lebon, Guillaume; Tate, Christopher G.; Fry, Elizabeth E.; Ren, Jingshan; Stuart, David I.; Evans, Gwyndaf

    2012-01-01

    A significant increase in the lifetime of room-temperature macromolecular crystals is reported through the use of a high-brilliance X-ray beam, reduced exposure times and a fast-readout detector. This is attributed to the ability to collect diffraction data before hydroxyl radicals can propagate through the crystal, fatally disrupting the lattice. Hydroxyl radicals are shown to be trapped in amorphous solutions at 100 K. The trend in crystal lifetime was observed in crystals of a soluble protein (immunoglobulin γ Fc receptor IIIa), a virus (bovine enterovirus serotype 2) and a membrane protein (human A2A adenosine G-protein coupled receptor). The observation of a similar effect in all three systems provides clear evidence for a common optimal strategy for room-temperature data collection and will inform the design of future synchrotron beamlines and detectors for macro­molecular crystallography. PMID:22751666

  19. Nanostructured ZnO Films for Room Temperature Ammonia Sensing

    NASA Astrophysics Data System (ADS)

    Dhivya Ponnusamy; Sridharan Madanagurusamy

    2014-09-01

    Zinc oxide (ZnO) thin films have been deposited by a reactive dc magnetron sputtering technique onto a thoroughly cleaned glass substrate at room temperature. X-ray diffraction revealed that the deposited film was polycrystalline in nature. The field emission scanning electron micrograph (FE-SEM) showed the uniform formation of a rugby ball-shaped ZnO nanostructure. Energy dispersive x-ray analysis (EDX) confirmed that the film was stoichiometric and the direct band gap of the film, determined using UV-Vis spectroscopy, was 3.29 eV. The ZnO nanostructured film exhibited better sensing towards ammonia (NH3) at room temperature (˜30°C). The fabricated ZnO film based sensor was capable of detecting NH3 at as low as 5 ppm, and its parameters, such as response, selectivity, stability, and response/recovery time, were also investigated.

  20. Room Temperature Creep Of SiC/SiC Composites

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Gyekenyesi, Andrew; Levine, Stanley (Technical Monitor)

    2001-01-01

    During a recent experimental study, time dependent deformation was observed for a damaged Hi-Nicalon reinforced, BN interphase, chemically vapor infiltrated SiC matrix composites subjected to static loading at room temperature. The static load curves resembled primary creep curves. In addition, acoustic emission was monitored during the test and significant AE activity was recorded while maintaining a constant load, which suggested matrix cracking or interfacial sliding. For similar composites with carbon interphases, little or no time dependent deformation was observed. Evidently, exposure of the BN interphase to the ambient environment resulted in a reduction in the interfacial mechanical properties, i.e. interfacial shear strength and/or debond energy. These results were in qualitative agreement with observations made by Eldridge of a reduction in interfacial shear stress with time at room temperature as measured by fiber push-in experiments.

  1. Broadband room temperature strong coupling between quantum dots and metamaterials.

    PubMed

    Indukuri, Chaitanya; Yadav, Ravindra Kumar; Basu, J K

    2017-08-17

    Herein, we report the first demonstration of room temperature enhanced light-matter coupling in the visible regime for metamaterials using cooperative coupled quasi two dimensional quantum dot assemblies located at precise distances from the hyperbolic metamaterial (HMM) templates. The non-monotonic variation of the magnitude of strong coupling, manifested in terms of strong splitting of the photoluminescence of quantum dots, can be explained in terms of enhanced LDOS near the surface of such metamaterials as well as the plasmon mediated super-radiance of closely spaced quantum dots (QDs). Our methodology of enhancing broadband, room temperature, light-matter coupling in the visible regime for metamaterials opens up new possibilities of utilising these materials for a wide range of applications including QD based thresholdless nanolasers and novel metamaterial based integrated photonic devices.

  2. Primary and secondary room temperature molten salt electrochemical cells

    NASA Astrophysics Data System (ADS)

    Reynolds, G. F.; Dymek, C. J., Jr.

    1985-07-01

    Three novel primary cells which use room temperature molten salt electrolytes are examined and found to have high open circuit potentials in the 1.75-2.19 V range, by comparison with the Al/AlCl3-MEICl concentration cell; their cathodes were of FeCl3-MEICl, WCl6-MEICl, and Br2/reticulated vitreous carbon together with Pt. Also, secondary electrochemical cell candidates were examined which combined the reversible Al/AlCl3-MEICl electrode with reversible zinc and cadmium molten salt electrodes to yield open circuit potentials of about 0.7 and 1.0 V, respectively. Room temperature molten salts' half-cell reduction potentials are given.

  3. Tribochemical Decomposition of Light Ionic Hydrides at Room Temperature.

    PubMed

    Nevshupa, Roman; Ares, Jose Ramón; Fernández, Jose Francisco; Del Campo, Adolfo; Roman, Elisa

    2015-07-16

    Tribochemical decomposition of magnesium hydride (MgH2) induced by deformation at room temperature was studied on a micrometric scale, in situ and in real time. During deformation, a near-full depletion of hydrogen in the micrometric affected zone is observed through an instantaneous (t < 1 s) and huge release of hydrogen (3-50 nmol/s). H release is related to a nonthermal decomposition process. After deformation, the remaining hydride is thermally decomposed at room temperature, exhibiting a much slower rate than during deformation. Confocal-microRaman spectroscopy of the mechanically affected zone was used to characterize the decomposition products. Decomposition was enhanced through the formation of the distorted structure of MgH2 with reduced crystal size by mechanical deformation.

  4. Room temperature electrodeposition of actinides from ionic solutions

    DOEpatents

    Hatchett, David W.; Czerwinski, Kenneth R.; Droessler, Janelle; Kinyanjui, John

    2017-04-25

    Uranic and transuranic metals and metal oxides are first dissolved in ozone compositions. The resulting solution in ozone can be further dissolved in ionic liquids to form a second solution. The metals in the second solution are then electrochemically deposited from the second solutions as room temperature ionic liquid (RTIL), tri-methyl-n-butyl ammonium n-bis(trifluoromethansulfonylimide) [Me.sub.3N.sup.nBu][TFSI] providing an alternative non-aqueous system for the extraction and reclamation of actinides from reprocessed fuel materials. Deposition of U metal is achieved using TFSI complexes of U(III) and U(IV) containing the anion common to the RTIL. TFSI complexes of uranium were produced to ensure solubility of the species in the ionic liquid. The methods provide a first measure of the thermodynamic properties of U metal deposition using Uranium complexes with different oxidation states from RTIL solution at room temperature.

  5. Enhanced magnetic Purcell effect in room-temperature masers

    PubMed Central

    Breeze, Jonathan; Tan, Ke-Jie; Richards, Benjamin; Sathian, Juna; Oxborrow, Mark; Alford, Neil McN

    2015-01-01

    Recently, the world’s first room-temperature maser was demonstrated. The maser consisted of a sapphire ring housing a crystal of pentacene-doped p-terphenyl, pumped by a pulsed rhodamine-dye laser. Stimulated emission of microwaves was aided by the high quality factor and small magnetic mode volume of the maser cavity yet the peak optical pumping power was 1.4 kW. Here we report dramatic miniaturization and 2 orders of magnitude reduction in optical pumping power for a room-temperature maser by coupling a strontium titanate resonator with the spin-polarized population inversion provided by triplet states in an optically excited pentacene-doped p-terphenyl crystal. We observe maser emission in a thimble-sized resonator using a xenon flash lamp as an optical pump source with peak optical power of 70 W. This is a significant step towards the goal of continuous maser operation. PMID:25698634

  6. Irreconcilable room temperature magnetotransport properties of polypyrrole nanoparticles and nanorods

    NASA Astrophysics Data System (ADS)

    Rehman Sagar, Rizwan Ur; Stadler, Florian J.; Navale, Sachin T.; Mane, Rajaram S.; Nazir, Adnan; Nabi, Ghulam

    2017-09-01

    The morphology of nanostructures plays a vital role in determining the conductivity of specimens and, consequently, affects the efficiency of magnetoelectronic devices such as magnetic field sensors. Herein, nanoparticles (NPs) and nanorods (NRs) of conducting polymer polypyrrole have been synthesized at room temperature via the chemical oxidative polymerization method. The positive and negative magnetoresistance signatures are respectively obtained in NPs and NRs morphology, respectively. Both morphologies have conduction in the variable range-hopping regime with the average charge carrier hopping length being highly influenced by the sign of magnetoresistance. This morphology dependence is not only interesting for fundamental research but it also allows for tuning magnetic field sensor materials to be usable at room temperature for the desired characteristics.

  7. Quantum correlations from a room-temperature optomechanical cavity

    NASA Astrophysics Data System (ADS)

    Purdy, T. P.; Grutter, K. E.; Srinivasan, K.; Taylor, J. M.

    2017-06-01

    The act of position measurement alters the motion of an object being measured. This quantum measurement backaction is typically much smaller than the thermal motion of a room-temperature object and thus difficult to observe. By shining laser light through a nanomechanical beam, we measure the beam’s thermally driven vibrations and perturb its motion with optical force fluctuations at a level dictated by the Heisenberg measurement-disturbance uncertainty relation. We demonstrate a cross-correlation technique to distinguish optically driven motion from thermally driven motion, observing this quantum backaction signature up to room temperature. We use the scale of the quantum correlations, which is determined by fundamental constants, to gauge the size of thermal motion, demonstrating a path toward absolute thermometry with quantum mechanically calibrated ticks.

  8. Room Temperature Source of Single Photons of Definite Polarization

    SciTech Connect

    Lukishova, S.G.; Schmid, A.W.; Knox, R.; Freivald, P.; Bissel, L.J.; Boyd, R.W.; Stroud, Jr., C.R.; Marshall, K.L.

    2007-02-12

    A definite polarization in fluorescence from single emitters (dye molecules) at room temperature is demonstrated. A planar-aligned, nematic liquid-crystal host provides definite alignment of single dye molecules in a preferred direction. Well-defined polarized fluorescence from single-emitters (single photon source) is important for applications in photonic quantum information. Polarized single-photon sources based on single-emitters, for example, are key hardware elements both for absolutely secure quantum communication and quantum computation systems.

  9. A Room Temperature Low-Threshold Ultraviolet Plasmonic Nanolaser

    DTIC Science & Technology

    2014-09-23

    Here we demonstrate the first strong room temperature ultraviolet (B370 nm) SP polariton laser with an extremely low threshold (B3.5MWcm 2). We find...localized surface plasmon and propagating surface plasmon polariton (SPP), has been demonstrated in metal nanosphere cavities6, metal-cladding...Quantum plasmonics. Nat. Phys. 9, 329–340 (2013). 4. Berini, P. & De Leon, I. Surface plasmon- polariton amplifiers and lasers. Nat. Photon. 6, 16–24 (2012

  10. Rapid Methods of Staining Bacterial Spores at Room Temperature

    PubMed Central

    Lechtman, M. D.; Bartholomew, J. W.; Phillips, A.; Russo, M.

    1965-01-01

    Lechtman, M. D. (University of Southern California, Los Angeles), J. W. Bartholomew, A. Phillips, and M. Russo. Rapid methods of staining bacterial spores at room temperature. J. Bacteriol. 89:848–854. 1965.—Spores of Bacillus subtilis var. niger were stained in 2 min at room temperature, after suitable pretreatment, with a dye reagent composed of 2% crystal violet in 1% phenol and 26% ethanol. Pretreatments included heat fixation to 260 C, mechanical rupture, and hydrolysis at room temperature in 44 n H3PO4 for 5 min, 33.4 n H3PO4 for 10 min, 12 n HCl for 5 sec, 6 n HCl for 2 min, 12 n HNO3 for 5 sec, and 6 n HNO3 for 60 sec. Acid hydrolysis at 60 C enabled the lowering of both acid concentration and time: 33.4 n H3PO4 for 15 sec, 25.9 n H3PO4 for 60 sec, 2 n HCl for 30 sec, 1 n HCl for 30 sec, 2 n HNO3 for 15 sec, and 1 n HNO3 for 30 sec. After acid treatment, 1 n NaOH was used as a neutralization agent. The cytological manifestations of these pretreatments, examined in an electron microscope after replication, showed definite degradation of spore coats, which probably explains the increase in dye permeability. The pretreatments were evaluated for use in a differential staining procedure for spores and vegetative cells. They were found to be too drastic in that they resulted in replacement of the primary dye by the 0.25% safranine counter stain in both vegetative cells and endospores. Less drastic pretreatments, such as 6 n HNO3 for 10 sec at room temperature, gave good differential stains, but failed to stain some free spores. The staining techniques above were evaluated with six species of Bacillus and were found to apply to all. Images PMID:14273671

  11. Experimental observation of negative capacitance in ferroelectrics at room temperature.

    PubMed

    Appleby, Daniel J R; Ponon, Nikhil K; Kwa, Kelvin S K; Zou, Bin; Petrov, Peter K; Wang, Tianle; Alford, Neil M; O'Neill, Anthony

    2014-07-09

    Effective negative capacitance has been postulated in ferroelectrics because there is a hysteresis in plots of polarization-electric field. Compelling experimental evidence of effective negative capacitance is presented here at room temperature in engineered devices, where it is stabilized by the presence of a paraelectric material. In future integrated circuits, the incorporation of such negative capacitance into MOSFET gate stacks would reduce the subthreshold slope, enabling low power operation and reduced self-heating.

  12. Mercuric iodine room temperature gamma-ray detectors

    NASA Technical Reports Server (NTRS)

    Patt, Bradley E.; Markakis, Jeffrey M.; Gerrish, Vernon M.; Haymes, Robert C.; Trombka, Jacob I.

    1990-01-01

    high resolution mercuric iodide room temperature gamma-ray detectors have excellent potential as an essential component of space instruments to be used for high energy astrophysics. Mercuric iodide detectors are being developed both as photodetectors used in combination with scintillation crystals to detect gamma-rays, and as direct gamma-ray detectors. These detectors are highly radiation damage resistant. The list of applications includes gamma-ray burst detection, gamma-ray line astronomy, solar flare studies, and elemental analysis.

  13. Silicon photodiodes with high photoconductive gain at room temperature.

    PubMed

    Li, X; Carey, J E; Sickler, J W; Pralle, M U; Palsule, C; Vineis, C J

    2012-02-27

    Silicon photodiodes with high photoconductive gain are demonstrated. The photodiodes are fabricated in a complementary metal-oxide-semiconductor (CMOS)-compatible process. The typical room temperature responsivity at 940 nm is >20 A/W and the dark current density is ≈ 100 nA/cm2 at 5 V reverse bias, yielding a detectivity of ≈ 10(14) Jones. These photodiodes are good candidates for applications that require high detection sensitivity and low bias operation.

  14. Room Temperature Hydrosilylation of Silicon Nanocrystals with Bifunctional Terminal Alkenes

    PubMed Central

    Yu, Yixuan; Hessel, Colin M.; Bogart, Timothy; Panthani, Matthew G.; Rasch, Michael R.; Korgel, Brian A.

    2013-01-01

    H-terminated Si nanocrystals undergo room temperature hydrosilylation with bifunctional alkenes with distal polar moieties—ethyl-, methyl-ester or carboxylic acids—without the aid of light or added catalyst. The passivated Si nanocrystals exhibit bright photoluminescence (PL) and disperse in polar solvents, including water. We propose a reaction mechanism in which ester or carboxylic acid groups facilitate direct nucleophilic attack of the highly curved Si surface of the nanocrystals by the alkene. PMID:23312033

  15. Mercuric iodine room temperature gamma-ray detectors

    NASA Technical Reports Server (NTRS)

    Patt, Bradley E.; Markakis, Jeffrey M.; Gerrish, Vernon M.; Haymes, Robert C.; Trombka, Jacob I.

    1990-01-01

    high resolution mercuric iodide room temperature gamma-ray detectors have excellent potential as an essential component of space instruments to be used for high energy astrophysics. Mercuric iodide detectors are being developed both as photodetectors used in combination with scintillation crystals to detect gamma-rays, and as direct gamma-ray detectors. These detectors are highly radiation damage resistant. The list of applications includes gamma-ray burst detection, gamma-ray line astronomy, solar flare studies, and elemental analysis.

  16. Chemoselective reductions of nitroaromatics in water at room temperature.

    PubMed

    Kelly, Sean M; Lipshutz, Bruce H

    2014-01-03

    A robust and green protocol for the reduction of functionalized nitroarenes to the corresponding primary amines has been developed. It relies on inexpensive zinc dust in water containing nanomicelles derived from the commercially available designer surfactant TPGS-750-M. This mild process takes place at room temperature and tolerates a wide range of functionalities. Highly selective reductions can also be achieved in the presence of common protecting groups.

  17. Room-temperature direct alkynylation of arenes with copper acetylides.

    PubMed

    Theunissen, Cédric; Evano, Gwilherm

    2014-09-05

    C-H bond in azoles and polyhalogenated arenes can be smoothly activated by copper acetylides to give the corresponding alkynylated (hetero)arenes by simple reaction at room temperature in the presence of phenanthroline and lithium tert-butoxide under an oxygen atmosphere. These stable, unreactive, and readily available polymers act as especially efficient and practical reagents for the introduction of an alkyne group to a wide number of arenes under remarkably mild conditions.

  18. Spontaneous Polarization Buildup in a Room-Temperature Polariton Laser

    SciTech Connect

    Baumberg, J. J.; Christopoulos, S.; Kavokin, A. V.; Grundy, A. J. D.; Baldassarri Hoeger von Hoegersthal, G.; Butte, R.; Christmann, G.; Feltin, E.; Carlin, J.-F.; Grandjean, N.; Solnyshkov, D. D.; Malpuech, G.

    2008-09-26

    We observe the buildup of strong ({approx}50%) spontaneous vector polarization in emission from a GaN-based polariton laser excited by short optical pulses at room temperature. The Stokes vector of emitted light changes its orientation randomly from one excitation pulse to another, so that the time-integrated polarization remains zero. This behavior is completely different from any previous laser. We interpret this observation in terms of the spontaneous symmetry breaking in a Bose-Einstein condensate of exciton polaritons.

  19. Room-temperature Formation of Hollow Cu2O Nanoparticles

    SciTech Connect

    Hung, Ling-I; Tsung, Chia-Kuang; Huang, Wenyu; Yang, Peidong

    2010-01-18

    Monodisperse Cu and Cu2O nanoparticles (NPs) are synthesized using tetradecylphosphonic acid as a capping agent. Dispersing the NPs in chloroform and hexane at room temperature results in the formation of hollow Cu2O NPs and Cu@Cu2O core/shell NPs, respectively. The monodisperse Cu2O NPs are used to fabricate hybrid solar cells with efficiency of 0.14percent under AM 1.5 and 1 Sun illumination.

  20. The Effect of Planar Magnetic Inhomogeneities on the Critical Temperature of Ferromagnet-Superconductor Systems

    NASA Astrophysics Data System (ADS)

    Tumanov, V. A.; Proshin, Yu. N.

    2016-12-01

    We study superconducting systems with the inhomogeneous effective exchange field background. A model of magnetic superconductor which takes into account the collectivized electrons interaction with the inhomogeneous effective exchange field is used. With local unitary rotation in spinor space we rewrite the Hamiltonian in a new basis where this interaction is diagonal. The problem is reduced to the one with a uniform exchange field but the effective tensor field appears. This method allows us to simplify the Gor'kov, Eilenberger, and Usadel equations in many symmetric cases. We calculate the critical temperature of the superconductor/ferromagnet proximity system in the dirty limit where the ferromagnet has periodic domain structure with planar domain walls.

  1. Temperature dependence of ferromagnet-antiferromagnet spin alignment and coercivity in epitaxial micromagnet bilayers

    DOE PAGES

    Lee, Michael S.; Wynn, Thomas A.; Folven, Erik; ...

    2017-06-26

    In this paper, soft x-ray photoemission electron microscopy with an in situ magnetic field has been used to study the relationship between ferromagnetic and antiferromagnetic spin alignment and the switching/reversal field of epitaxial micromagnetic structures. We investigated a model system consisting of a bilayer of ferromagnetic La0.7Sr0.3MnO3 and antiferromagnetic LaFeO3 where the spin axes in each layer can be driven from mutually perpendicular (spin-flop) to parallel alignment by varying the temperature between 30 and 300 K. Results show that not only does this spin alignment noticeably influence the bilayer micromagnet coercivity compared to La0.7Sr0.3MnO3 single-layer micromagnets, but the coercivity withinmore » this materials system can be tuned over a wide range by careful balance of material properties.« less

  2. A highly reversible room-temperature sodium metal anode

    DOE PAGES

    Seh, Zhi Wei; Sun, Jie; Sun, Yongming; ...

    2015-11-02

    Owing to its low cost and high natural abundance, sodium metal is among the most promising anode materials for energy storage technologies beyond lithium ion batteries. However, room-temperature sodium metal anodes suffer from poor reversibility during long-term plating and stripping, mainly due to formation of nonuniform solid electrolyte interphase as well as dendritic growth of sodium metal. Herein we report for the first time that a simple liquid electrolyte, sodium hexafluorophosphate in glymes (mono-, di-, and tetraglyme), can enable highly reversible and nondendritic plating–stripping of sodium metal anodes at room temperature. High average Coulombic efficiencies of 99.9% were achieved overmore » 300 plating–stripping cycles at 0.5 mA cm–2. In this study, the long-term reversibility was found to arise from the formation of a uniform, inorganic solid electrolyte interphase made of sodium oxide and sodium fluoride, which is highly impermeable to electrolyte solvent and conducive to nondendritic growth. As a proof of concept, we also demonstrate a room-temperature sodium–sulfur battery using this class of electrolytes, paving the way for the development of next-generation, sodium-based energy storage technologies.« less

  3. A Highly Reversible Room-Temperature Sodium Metal Anode

    PubMed Central

    2015-01-01

    Owing to its low cost and high natural abundance, sodium metal is among the most promising anode materials for energy storage technologies beyond lithium ion batteries. However, room-temperature sodium metal anodes suffer from poor reversibility during long-term plating and stripping, mainly due to formation of nonuniform solid electrolyte interphase as well as dendritic growth of sodium metal. Herein we report for the first time that a simple liquid electrolyte, sodium hexafluorophosphate in glymes (mono-, di-, and tetraglyme), can enable highly reversible and nondendritic plating–stripping of sodium metal anodes at room temperature. High average Coulombic efficiencies of 99.9% were achieved over 300 plating–stripping cycles at 0.5 mA cm–2. The long-term reversibility was found to arise from the formation of a uniform, inorganic solid electrolyte interphase made of sodium oxide and sodium fluoride, which is highly impermeable to electrolyte solvent and conducive to nondendritic growth. As a proof of concept, we also demonstrate a room-temperature sodium–sulfur battery using this class of electrolytes, paving the way for the development of next-generation, sodium-based energy storage technologies. PMID:27163006

  4. Highly Directional Room-Temperature Single Photon Device.

    PubMed

    Livneh, Nitzan; Harats, Moshe G; Istrati, Daniel; Eisenberg, Hagai S; Rapaport, Ronen

    2016-04-13

    One of the most important challenges in modern quantum optical applications is the demonstration of efficient, scalable, on-chip single photon sources, which can operate at room temperature. In this paper we demonstrate a room-temperature single photon source based on a single colloidal nanocrystal quantum dot positioned inside a circular bulls-eye shaped hybrid metal-dielectric nanoantenna. Experimental results show that 20% of the photons are emitted into a very low numerical aperture (NA < 0.25), a 20-fold improvement over a free-standing quantum dot, and with a probability of more than 70% for a single photon emission. With an NA = 0.65 more than 35% of the single photon emission is collected. The single photon purity is limited only by emission from the metal, an obstacle that can be bypassed with careful design and fabrication. The concept presented here can be extended to many other types of quantum emitters. Such a device paves a promising route for a high purity, high efficiency, on-chip single photon source operating at room temperature.

  5. A Na+ Superionic Conductor for Room-Temperature Sodium Batteries

    NASA Astrophysics Data System (ADS)

    Song, Shufeng; Duong, Hai M.; Korsunsky, Alexander M.; Hu, Ning; Lu, Li

    2016-08-01

    Rechargeable lithium ion batteries have ruled the consumer electronics market for the past 20 years and have great significance in the growing number of electric vehicles and stationary energy storage applications. However, in addition to concerns about electrochemical performance, the limited availability of lithium is gradually becoming an important issue for further continued use and development of lithium ion batteries. Therefore, a significant shift in attention has been taking place towards new types of rechargeable batteries such as sodium-based systems that have low cost. Another important aspect of sodium battery is its potential compatibility with the all-solid-state design where solid electrolyte is used to replace liquid one, leading to simple battery design, long life span, and excellent safety. The key to the success of all-solid-state battery design is the challenge of finding solid electrolytes possessing acceptable high ionic conductivities at room temperature. Herein, we report a novel sodium superionic conductor with NASICON structure, Na3.1Zr1.95Mg0.05Si2PO12 that shows high room-temperature ionic conductivity of 3.5 × 10-3 S cm-1. We also report successful fabrication of a room-temperature solid-state Na-S cell using this conductor.

  6. A Na+ Superionic Conductor for Room-Temperature Sodium Batteries

    PubMed Central

    Song, Shufeng; Duong, Hai M.; Korsunsky, Alexander M.; Hu, Ning; Lu, Li

    2016-01-01

    Rechargeable lithium ion batteries have ruled the consumer electronics market for the past 20 years and have great significance in the growing number of electric vehicles and stationary energy storage applications. However, in addition to concerns about electrochemical performance, the limited availability of lithium is gradually becoming an important issue for further continued use and development of lithium ion batteries. Therefore, a significant shift in attention has been taking place towards new types of rechargeable batteries such as sodium-based systems that have low cost. Another important aspect of sodium battery is its potential compatibility with the all-solid-state design where solid electrolyte is used to replace liquid one, leading to simple battery design, long life span, and excellent safety. The key to the success of all-solid-state battery design is the challenge of finding solid electrolytes possessing acceptable high ionic conductivities at room temperature. Herein, we report a novel sodium superionic conductor with NASICON structure, Na3.1Zr1.95Mg0.05Si2PO12 that shows high room-temperature ionic conductivity of 3.5 × 10−3 S cm−1. We also report successful fabrication of a room-temperature solid-state Na-S cell using this conductor. PMID:27572915

  7. Noninvasive liver iron measurements with a room-temperature susceptometer

    PubMed Central

    Avrin, W F; Kumar, S

    2011-01-01

    Magnetic susceptibility measurements on the liver can quantify iron overload accurately and noninvasively. However, established susceptometer designs, using Superconducting QUantum Interference Devices (SQUIDs) that work in liquid helium, have been too expensive for widespread use. This paper presents a less expensive liver susceptometer that works at room temperature. This system uses oscillating magnetic fields, which are produced and detected by copper coils. The coil design cancels the signal from the applied field, eliminating noise from fluctuations of the source-coil current and sensor gain. The coil unit moves toward and away from the patient at 1 Hz, cancelling drifts due to thermal expansion of the coils. Measurements on a water phantom indicated instrumental errors less than 30 μg of iron per gram of wet liver tissue, which is small compared with other errors due to the response of the patient’s body. Liver iron measurements on eight thalassemia patients yielded a correlation coefficient r=0.98 between the room-temperature susceptometer and an existing SQUID. These results indicate that the fundamental accuracy limits of the room-temperature susceptometer are similar to those of the SQUID. PMID:17395991

  8. Outrunning free radicals in room-temperature macromolecular crystallography

    SciTech Connect

    Owen, Robin L. Axford, Danny; Nettleship, Joanne E.; Owens, Raymond J.; Robinson, James I.; Morgan, Ann W.; Doré, Andrew S.; Lebon, Guillaume; Tate, Christopher G.; Fry, Elizabeth E.; Ren, Jingshan; Stuart, David I.; Evans, Gwyndaf

    2012-06-15

    A systematic increase in lifetime is observed in room-temperature protein and virus crystals through the use of reduced exposure times and a fast detector. A significant increase in the lifetime of room-temperature macromolecular crystals is reported through the use of a high-brilliance X-ray beam, reduced exposure times and a fast-readout detector. This is attributed to the ability to collect diffraction data before hydroxyl radicals can propagate through the crystal, fatally disrupting the lattice. Hydroxyl radicals are shown to be trapped in amorphous solutions at 100 K. The trend in crystal lifetime was observed in crystals of a soluble protein (immunoglobulin γ Fc receptor IIIa), a virus (bovine enterovirus serotype 2) and a membrane protein (human A{sub 2A} adenosine G-protein coupled receptor). The observation of a similar effect in all three systems provides clear evidence for a common optimal strategy for room-temperature data collection and will inform the design of future synchrotron beamlines and detectors for macromolecular crystallography.

  9. Temperature dependent ferromagnetic relaxation and gyromagnetic ratio in Ni80Fe20 / Gd thin films

    NASA Astrophysics Data System (ADS)

    Khodadadi, Behrouz; Mohammadi, Jamileh; Mewes, Claudia; Mewes, Tim; Eggers, Tatiana; Miller, Casey; MINT Center Team; Rochester Institute of Technology Team

    2015-03-01

    We report on the temperature dependence of the magnetization dynamics of NiFe thin films (5nm & 10nm) capped with a 3nm Gd layer using broadband ferromagnetic resonance. We observe that the effective Gilbert damping parameter determined from the broadband measurements increases as the temperature approaches the Curie-temperature of the Gd layer. Part of the enhancement can be explained by an increase of the spin-pumping contribution to the relaxation as the temperature approaches the Curie temperature of Gd. We also measure a strong increase of the gyromagnetic ratio with decreasing temperature which resembles the increase of the gyromagnetic ratio in rare earth containing transition metals near the compensation point. This increase in the gyromagnetic ratio is expected to lead to an increased Gilbert type damping due to spin-orbit interaction, that likely also contributes to the increase in damping. NSF-CAREER Award No. 0952929 and NSF-ECCS-1231929.

  10. Interlayer Exchange Coupling in Asymmetric Co -Fe /Ru /Co -Fe Trilayers Investigated with Broadband Temperature-Dependent Ferromagnetic Resonance

    NASA Astrophysics Data System (ADS)

    Khodadadi, Behrouz; Mohammadi, Jamileh Beik; Jones, Joshua Michael; Srivastava, Abhishek; Mewes, Claudia; Mewes, Tim; Kaiser, Christian

    2017-07-01

    We report on a comprehensive study of the interlayer exchange coupling in Co -Fe (5 nm )/Ru (t )/Co -Fe (8 nm ) trilayers (t =0.8 ,…,2.8 nm ) using broadband ferromagnetic resonance. A systematic frequency dependence of the field separation between the acoustic and optic modes is found, which is caused by different effective magnetizations of the two ferromagnetic layers. Hence, it is shown that the broadband measurements are vital for reducing the systematic error margins in the determination of interlayer exchange coupling using ferromagnetic resonance. We also investigate the temperature dependence of the interlayer exchange coupling and compare our results with existing theories. It is shown that models which take into account the temperature dependence due to thermal excitations of spin waves within the ferromagnetic layers have a considerably better agreement with the experiment than models solely based on spacer and interface contributions to the temperature dependence.

  11. Electric-field manipulation of magnetization rotation and tunneling magnetoresistance of magnetic tunnel junctions at room temperature

    NASA Astrophysics Data System (ADS)

    Chen, Aitian; Li, Peisen; Li, Dalai; Zhao, Yonggang; Zhang, Sen; Yang, Lifeng; Liu, Yan; Zhu, Meihong; Zhang, Huiyun; Han, Xiufeng

    2015-03-01

    Recent studies on the electric-field control of tunneling magnetoresistance (TMR) have attracted considerable attention for low power consumption. So far two methods have been demonstrated for electric-field control of TMR. One method uses ferroelectric or multiferroic barriers, which is limited by low temperature. The other is nanoscale thin film magnetic tunnel junction (MTJ), but the assistance of a magnetic field is required. Therefore, electric-field control of TMR at room temperature without a magnetic field is highly desired. One promising way is to employ strain-mediated coupling in ferromagnetic/piezoelectric structure. Though MTJs/piezoelectric has been predicted by theory, experiment work is still lacking. We deposited CoFeB/AlOx/CoFeB on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) ferroelectric single crystal. Under external electric fields, PMN-PT will produce a piezostrain due to piezoelectric effect, and the piezostrain transfers to ferromagnetic film to change the magnetic anisotropy. We demonstrate a reversible, continuous magnetization rotation and manipulation of TMR at room temperature by electric fields without the assistance of a magnetic field.

  12. Aging of ceramic carbonized hydroxyapatite at room temperature

    NASA Astrophysics Data System (ADS)

    Tkachenko, M. V.; Kamzin, A. S.

    2016-08-01

    The process of aging of ceramic carbonized hydroxyapatite (CHA) produced in a dry carbon dioxide atmosphere at temperatures of 800-1200°C has been studied by chemical and X-ray structural analysis, infrared spectroscopy, and scanning electron microscopy methods. The phase composition and structure of initial prepared ceramics samples and those aged for a year have been compared. It has been shown that relaxation of internal stresses occurring during pressed sample sintering causes plastic deformation of crystallites at room temperature, accompanied by redistribution of carbonate ions between A1, A2, B1, and B2 sites and CHA decomposition with the formation of CaO separations.

  13. Observation of a huge polaron gyrotropic response near room temperature in manganite thin films

    NASA Astrophysics Data System (ADS)

    Herranz, Gervasi; Casals, Blai; Cichelero, Rafael; Pesquera, David; Campoy, Mariano; Sanchez, Florencio; Fontcuberta, Josep; Garcia Fernandez, Pablo; Junquera, Javier

    Magnetic materials induce rotation and ellipticity in the polarization of light. This phenomenon is exploited, e.g., to control the flux of light along optical fibers. In the pursuit for increased magneto-optic responses, strategies so far have been based on photonic or plasmonic effects. Here we uncover a novel physical mechanism by which the gyrotropic activity is hugely enhanced around the Curie temperature in optimally doped ferromagnetic manganites. This phenomenon is observed only for a narrow range of wavelengths and temperatures and is strongly dependent on the angle of incidence and polarization. We understand such an outstanding response as the result of the interplay between Jahn-Teller distortions and spin-orbit coupling in narrow-band manganites. The showcased material is La2/3Ca1/3MnO3, for which the extraordinary gyrotropic response is seen near room temperature. This raises the possibility of optimizing the stoichiometric composition to drive the effect to higher temperatures. The observed phenomenon gives an added functionality -unseen previously in any manganite or other magnetic oxides- and puts a new perspective on the use of these materials for optical data storage and retrieval.

  14. Room-temperature superfluidity in a polariton condensate

    NASA Astrophysics Data System (ADS)

    Lerario, Giovanni; Fieramosca, Antonio; Barachati, Fábio; Ballarini, Dario; Daskalakis, Konstantinos S.; Dominici, Lorenzo; de Giorgi, Milena; Maier, Stefan A.; Gigli, Giuseppe; Kéna-Cohen, Stéphane; Sanvitto, Daniele

    2017-09-01

    Superfluidity--the suppression of scattering in a quantum fluid at velocities below a critical value--is one of the most striking manifestations of the collective behaviour typical of Bose-Einstein condensates. This phenomenon, akin to superconductivity in metals, has until now been observed only at prohibitively low cryogenic temperatures. For atoms, this limit is imposed by the small thermal de Broglie wavelength, which is inversely related to the particle mass. Even in the case of ultralight quasiparticles such as exciton-polaritons, superfluidity has been demonstrated only at liquid helium temperatures. In this case, the limit is not imposed by the mass, but instead by the small binding energy of Wannier-Mott excitons, which sets the upper temperature limit. Here we demonstrate a transition from supersonic to superfluid flow in a polariton condensate under ambient conditions. This is achieved by using an organic microcavity supporting stable Frenkel exciton-polaritons at room temperature. This result paves the way not only for tabletop studies of quantum hydrodynamics, but also for room-temperature polariton devices that can be robustly protected from scattering.

  15. Intrinsic ferromagnetism in hexagonal boron nitride nanosheets

    SciTech Connect

    Si, M. S.; Gao, Daqiang E-mail: xueds@lzu.edu.cn; Yang, Dezheng; Peng, Yong; Zhang, Z. Y.; Xue, Desheng E-mail: xueds@lzu.edu.cn; Liu, Yushen; Deng, Xiaohui; Zhang, G. P.

    2014-05-28

    Understanding the mechanism of ferromagnetism in hexagonal boron nitride nanosheets, which possess only s and p electrons in comparison with normal ferromagnets based on localized d or f electrons, is a current challenge. In this work, we report an experimental finding that the ferromagnetic coupling is an intrinsic property of hexagonal boron nitride nanosheets, which has never been reported before. Moreover, we further confirm it from ab initio calculations. We show that the measured ferromagnetism should be attributed to the localized π states at edges, where the electron-electron interaction plays the role in this ferromagnetic ordering. More importantly, we demonstrate such edge-induced ferromagnetism causes a high Curie temperature well above room temperature. Our systematical work, including experimental measurements and theoretical confirmation, proves that such unusual room temperature ferromagnetism in hexagonal boron nitride nanosheets is edge-dependent, similar to widely reported graphene-based materials. It is believed that this work will open new perspectives for hexagonal boron nitride spintronic devices.

  16. Intrinsic ferromagnetism in hexagonal boron nitride nanosheets.

    PubMed

    Si, M S; Gao, Daqiang; Yang, Dezheng; Peng, Yong; Zhang, Z Y; Xue, Desheng; Liu, Yushen; Deng, Xiaohui; Zhang, G P

    2014-05-28

    Understanding the mechanism of ferromagnetism in hexagonal boron nitride nanosheets, which possess only s and p electrons in comparison with normal ferromagnets based on localized d or f electrons, is a current challenge. In this work, we report an experimental finding that the ferromagnetic coupling is an intrinsic property of hexagonal boron nitride nanosheets, which has never been reported before. Moreover, we further confirm it from ab initio calculations. We show that the measured ferromagnetism should be attributed to the localized π states at edges, where the electron-electron interaction plays the role in this ferromagnetic ordering. More importantly, we demonstrate such edge-induced ferromagnetism causes a high Curie temperature well above room temperature. Our systematical work, including experimental measurements and theoretical confirmation, proves that such unusual room temperature ferromagnetism in hexagonal boron nitride nanosheets is edge-dependent, similar to widely reported graphene-based materials. It is believed that this work will open new perspectives for hexagonal boron nitride spintronic devices.

  17. Intrinsic ferromagnetism in hexagonal boron nitride nanosheets

    NASA Astrophysics Data System (ADS)

    Si, M. S.; Gao, Daqiang; Yang, Dezheng; Peng, Yong; Zhang, Z. Y.; Xue, Desheng; Liu, Yushen; Deng, Xiaohui; Zhang, G. P.

    2014-05-01

    Understanding the mechanism of ferromagnetism in hexagonal boron nitride nanosheets, which possess only s and p electrons in comparison with normal ferromagnets based on localized d or f electrons, is a current challenge. In this work, we report an experimental finding that the ferromagnetic coupling is an intrinsic property of hexagonal boron nitride nanosheets, which has never been reported before. Moreover, we further confirm it from ab initio calculations. We show that the measured ferromagnetism should be attributed to the localized π states at edges, where the electron-electron interaction plays the role in this ferromagnetic ordering. More importantly, we demonstrate such edge-induced ferromagnetism causes a high Curie temperature well above room temperature. Our systematical work, including experimental measurements and theoretical confirmation, proves that such unusual room temperature ferromagnetism in hexagonal boron nitride nanosheets is edge-dependent, similar to widely reported graphene-based materials. It is believed that this work will open new perspectives for hexagonal boron nitride spintronic devices.

  18. Room Temperature Chemical Oxidation of Delafossite-Type Oxides

    NASA Astrophysics Data System (ADS)

    Trari, M.; Töpfer, J.; Doumerc, J. P.; Pouchard, M.; Ammar, A.; Hagenmuller, P.

    1994-07-01

    Examination of the delafossite-type structure of CuLaO 2 and CuYO 2 suggests that there is room enough to accomodate intercalated oxide ions and the charge compensation resulting simply from the oxidation of an equivalent amount of Cu + into Cu 2+. Reaction with hypohalites in an aqueous solution leads to color change. Evidence of the formation of Cu 2+ is given by TGA, iodometric titration, and magnetic (static and EPR) measurements. The obtained La and Y compounds seem to behave in a different way: whereas CuLaO 2+ x appears as a single phase, CuYO 2+ x corresponds to a two-phase mixture, with respectively low and high x values, the latter being isostructural with the thermally oxidized compound recently reported by Cava et al. Comparison is stressed between the oxides obtained by oxidation at room and those obtained at higher temperatures.

  19. Atomically engineered ferroic layers yield a room-temperature magnetoelectric multiferroic

    NASA Astrophysics Data System (ADS)

    Mundy, Julia A.; Brooks, Charles M.; Holtz, Megan E.; Moyer, Jarrett A.; Das, Hena; Rébola, Alejandro F.; Heron, John T.; Clarkson, James D.; Disseler, Steven M.; Liu, Zhiqi; Farhan, Alan; Held, Rainer; Hovden, Robert; Padgett, Elliot; Mao, Qingyun; Paik, Hanjong; Misra, Rajiv; Kourkoutis, Lena F.; Arenholz, Elke; Scholl, Andreas; Borchers, Julie A.; Ratcliff, William D.; Ramesh, Ramamoorthy; Fennie, Craig J.; Schiffer, Peter; Muller, David A.; Schlom, Darrell G.

    2016-09-01

    Materials that exhibit simultaneous order in their electric and magnetic ground states hold promise for use in next-generation memory devices in which electric fields control magnetism. Such materials are exceedingly rare, however, owing to competing requirements for displacive ferroelectricity and magnetism. Despite the recent identification of several new multiferroic materials and magnetoelectric coupling mechanisms, known single-phase multiferroics remain limited by antiferromagnetic or weak ferromagnetic alignments, by a lack of coupling between the order parameters, or by having properties that emerge only well below room temperature, precluding device applications. Here we present a methodology for constructing single-phase multiferroic materials in which ferroelectricity and strong magnetic ordering are coupled near room temperature. Starting with hexagonal LuFeO3—the geometric ferroelectric with the greatest known planar rumpling—we introduce individual monolayers of FeO during growth to construct formula-unit-thick syntactic layers of ferrimagnetic LuFe2O4 (refs 17, 18) within the LuFeO3 matrix, that is, (LuFeO3)m/(LuFe2O4)1 superlattices. The severe rumpling imposed by the neighbouring LuFeO3 drives the ferrimagnetic LuFe2O4 into a simultaneously ferroelectric state, while also reducing the LuFe2O4 spin frustration. This increases the magnetic transition temperature substantially—from 240 kelvin for LuFe2O4 (ref. 18) to 281 kelvin for (LuFeO3)9/(LuFe2O4)1. Moreover, the ferroelectric order couples to the ferrimagnetism, enabling direct electric-field control of magnetism at 200 kelvin. Our results demonstrate a design methodology for creating higher-temperature magnetoelectric multiferroics by exploiting a combination of geometric frustration, lattice distortions and epitaxial engineering.

  20. Atomically engineered ferroic layers yield a room-temperature magnetoelectric multiferroic.

    PubMed

    Mundy, Julia A; Brooks, Charles M; Holtz, Megan E; Moyer, Jarrett A; Das, Hena; Rébola, Alejandro F; Heron, John T; Clarkson, James D; Disseler, Steven M; Liu, Zhiqi; Farhan, Alan; Held, Rainer; Hovden, Robert; Padgett, Elliot; Mao, Qingyun; Paik, Hanjong; Misra, Rajiv; Kourkoutis, Lena F; Arenholz, Elke; Scholl, Andreas; Borchers, Julie A; Ratcliff, William D; Ramesh, Ramamoorthy; Fennie, Craig J; Schiffer, Peter; Muller, David A; Schlom, Darrell G

    2016-09-22

    Materials that exhibit simultaneous order in their electric and magnetic ground states hold promise for use in next-generation memory devices in which electric fields control magnetism. Such materials are exceedingly rare, however, owing to competing requirements for displacive ferroelectricity and magnetism. Despite the recent identification of several new multiferroic materials and magnetoelectric coupling mechanisms, known single-phase multiferroics remain limited by antiferromagnetic or weak ferromagnetic alignments, by a lack of coupling between the order parameters, or by having properties that emerge only well below room temperature, precluding device applications. Here we present a methodology for constructing single-phase multiferroic materials in which ferroelectricity and strong magnetic ordering are coupled near room temperature. Starting with hexagonal LuFeO3-the geometric ferroelectric with the greatest known planar rumpling-we introduce individual monolayers of FeO during growth to construct formula-unit-thick syntactic layers of ferrimagnetic LuFe2O4 (refs 17, 18) within the LuFeO3 matrix, that is, (LuFeO3)m/(LuFe2O4)1 superlattices. The severe rumpling imposed by the neighbouring LuFeO3 drives the ferrimagnetic LuFe2O4 into a simultaneously ferroelectric state, while also reducing the LuFe2O4 spin frustration. This increases the magnetic transition temperature substantially-from 240 kelvin for LuFe2O4 (ref. 18) to 281 kelvin for (LuFeO3)9/(LuFe2O4)1. Moreover, the ferroelectric order couples to the ferrimagnetism, enabling direct electric-field control of magnetism at 200 kelvin. Our results demonstrate a design methodology for creating higher-temperature magnetoelectric multiferroics by exploiting a combination of geometric frustration, lattice distortions and epitaxial engineering.

  1. Room-temperature resonant quantum tunneling transport of macroscopic systems.

    PubMed

    Xiong, Zhengwei; Wang, Xuemin; Yan, Dawei; Wu, Weidong; Peng, Liping; Li, Weihua; Zhao, Yan; Wang, Xinmin; An, Xinyou; Xiao, Tingting; Zhan, Zhiqiang; Wang, Zhuo; Chen, Xiangrong

    2014-11-21

    A self-assembled quantum dots array (QDA) is a low dimensional electron system applied to various quantum devices. This QDA, if embedded in a single crystal matrix, could be advantageous for quantum information science and technology. However, the quantum tunneling effect has been difficult to observe around room temperature thus far, because it occurs in a microcosmic and low temperature condition. Herein, we show a designed a quasi-periodic Ni QDA embedded in a single crystal BaTiO3 matrix and demonstrate novel quantum resonant tunneling transport properties around room-temperature according to theoretical calculation and experiments. The quantum tunneling process could be effectively modulated by changing the Ni QDA concentration. The major reason was that an applied weak electric field (∼10(2) V cm(-1)) could be enhanced by three orders of magnitude (∼10(5) V cm(-1)) between the Ni QDA because of the higher permittivity of BaTiO3 and the 'hot spots' of the Ni QDA. Compared with the pure BaTiO3 films, the samples with embedded Ni QDA displayed a stepped conductivity and temperature (σ-T curves) construction.

  2. Energy-filtered cold electron transport at room temperature

    PubMed Central

    Bhadrachalam, Pradeep; Subramanian, Ramkumar; Ray, Vishva; Ma, Liang-Chieh; Wang, Weichao; Kim, Jiyoung; Cho, Kyeongjae; Koh, Seong Jin

    2014-01-01

    Fermi-Dirac electron thermal excitation is an intrinsic phenomenon that limits functionality of various electron systems. Efforts to manipulate electron thermal excitation have been successful when the entire system is cooled to cryogenic temperatures, typically <1 K. Here we show that electron thermal excitation can be effectively suppressed at room temperature, and energy-suppressed electrons, whose energy distribution corresponds to an effective electron temperature of ~45 K, can be transported throughout device components without external cooling. This is accomplished using a discrete level of a quantum well, which filters out thermally excited electrons and permits only energy-suppressed electrons to participate in electron transport. The quantum well (~2 nm of Cr2O3) is formed between source (Cr) and tunnelling barrier (SiO2) in a double-barrier-tunnelling-junction structure having a quantum dot as the central island. Cold electron transport is detected from extremely narrow differential conductance peaks in electron tunnelling through CdSe quantum dots, with full widths at half maximum of only ~15 mV at room temperature. PMID:25204839

  3. Single-molecule spectroscopy and dynamics at room temperature

    SciTech Connect

    Xie, X.S.

    1996-12-01

    The spirit of studying single-molecule behaviors dates back to the turn of the century. In addition to Einstein`s well-known work on Brownian motion, there has been a tradition for studying single {open_quotes}macromolecules{close_quotes} or a small number of molecules either by light scattering or by fluorescence using an optical microscope. Modern computers have allowed detailed studies of single-molecule behaviors in condensed media through molecular dynamics simulations. Optical spectroscopy offers a wealth of information on the structure, interaction, and dynamics of molecular species. With the motivation of removing {open_quotes}inhomogeneous broadening{close_quotes}, spectroscopic techniques have evolved from spectral hole burning, fluorescence line narrowing, and photo-echo to the recent pioneering work on single-molecule spectroscopy in solids at cryogenic temperatures. High-resolution spectroscopic work on single molecules relies on zero phonon lines which appear at cryogenic temperatures, and have narrow line widths and large absorption cross sections. Recent advances in near-field and confocal fluorescence have allowed not only fluorescence imaging of single molecules with high spatial resolutions but also single-molecule spectroscopy at room temperature. In this Account, the author provides a physical chemist`s perspective on experimental and theoretical developments on room-temperature single-molecule spectroscopy and dynamics, with the emphasis on the information obtainable from single-molecule experiments. 61 refs., 9 figs.

  4. Ferromagnetism in Co-doped (La,Sr)TiO3

    SciTech Connect

    Fix, T.; Liberati, M.; Aubriet, H.; Sahonta, S.-L.; Bali, R.; Becker, C.; Ruch, D.; MacManus-Driscoll, J.L.; Arenholz, E.; Blamire, M.G.

    2009-04-21

    The origin of ferromagnetism in Co-doped (La,Sr)TiO{sub 3} epitaxial thin films is discussed. While the as-grown samples are not ferromagnetic at room temperature or at 10 K, ferromagnetism at room temperature appears after annealing the films in reducing conditions and disappears after annealing in oxidizing conditions. Magnetic measurements, x-ray absorption spectroscopy, x-ray photoemission spectroscopy and transmission electron microscopy experiments indicate that within the resolution of the instruments the activation of the ferromagnetism is not due to the presence of pure Co.

  5. Does the electric power grid need a room temperature superconductor?

    NASA Astrophysics Data System (ADS)

    Malozemoff, A. P.

    2013-11-01

    Superconductivity can revolutionize electric power grids, for example with high power underground cables to open urban power bottlenecks and fault current limiters to solve growing fault currents problems. Technology based on high temperature superconductor (HTS) wire is beginning to meet these critical needs. Wire performance is continually improving. For example, American Superconductor has recently demonstrated long wires with up to 500 A/cm-width at 77 K, almost doubling its previous production performance. But refrigeration, even at 77 K, is a complication, driving interest in discovering room temperature superconductors (RTS). Unfortunately, short coherence lengths and accelerated flux creep will make RTS applications unlikely. Existing HTS technology, in fact, offers a good compromise of relatively high operating temperature but not so high as to incur coherence-length and flux-creep limitations. So - no, power grids do not need RTS; existing HTS wire is proving to be what grids really need.

  6. Terahertz pulsed photogenerated current in microdiodes at room temperature

    SciTech Connect

    Ilkov, Marjan; Torfason, Kristinn; Manolescu, Andrei Valfells, Ágúst

    2015-11-16

    Space-charge modulation of the current in a vacuum diode under photoemission leads to the formation of beamlets with time periodicity corresponding to THz frequencies. We investigate the effect of the emitter temperature and internal space-charge forces on the formation and persistence of the beamlets. We find that temperature effects are most important for beam degradation at low values of the applied electric field, whereas at higher fields, intra-beamlet space-charge forces are dominant. The current modulation is most robust when there is only one beamlet present in the diode gap at a time, corresponding to a macroscopic version of the Coulomb blockade. It is shown that a vacuum microdiode can operate quite well as a tunable THz oscillator at room temperature with an applied electric field above 10 MV/m and a diode gap of the order of 100 nm.

  7. Large electrocaloric effect in ferroelectric polymers near room temperature.

    PubMed

    Neese, Bret; Chu, Baojin; Lu, Sheng-Guo; Wang, Yong; Furman, E; Zhang, Q M

    2008-08-08

    Applying an electrical field to a polar polymer may induce a large change in the dipolar ordering, and if the associated entropy changes are large, they can be explored in cooling applications. With the use of the Maxwell relation between the pyroelectric coefficient and the electrocaloric effect (ECE), it was determined that a large ECE can be realized in the ferroelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer at temperatures above the ferroelectric-paraelectric transition (above 70 degrees C), where an isothermal entropy change of more than 55 joules per kilogram per kelvin degree and adiabatic temperature change of more than 12 degrees C were observed. We further showed that a similar level of ECE near room temperature can be achieved by working with the relaxor ferroelectric polymer of P(VDF-TrFE-chlorofluoroethylene).

  8. Large Electrocaloric Effect in Ferroelectric Polymers Near Room Temperature

    NASA Astrophysics Data System (ADS)

    Neese, Bret; Chu, Baojin; Lu, Sheng-Guo; Wang, Yong; Furman, E.; Zhang, Q. M.

    2008-08-01

    Applying an electrical field to a polar polymer may induce a large change in the dipolar ordering, and if the associated entropy changes are large, they can be explored in cooling applications. With the use of the Maxwell relation between the pyroelectric coefficient and the electrocaloric effect (ECE), it was determined that a large ECE can be realized in the ferroelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer at temperatures above the ferroelectric-paraelectric transition (above 70°C), where an isothermal entropy change of more than 55 joules per kilogram per kelvin degree and adiabatic temperature change of more than 12°C were observed. We further showed that a similar level of ECE near room temperature can be achieved by working with the relaxor ferroelectric polymer of P(VDF-TrFE-chlorofluoroethylene).

  9. Multi-scale modeling of ferromagnetism in bcc Fe as a function of pressure and temperature

    NASA Astrophysics Data System (ADS)

    Sha, Xianwei; Cohen, R. E.

    2007-03-01

    We investigate the magnetic properties of bcc Fe as functions of pressure and temperature using multi-scale modeling techniques. We employ a first-principles fitted tight-binding total-energy model in the generalized-gradient approximation to examine bcc Fe at numerous ferromagnetic, antiferromagnetic and spin spiral states, and fit the tight-binding data to a generalized Heisenberg Hamiltonian which includes both the on-site and local exchange energy to describe the magnetic energy for any arbitrary magnetic configuration. We obtain the Curie temperature, magnetization curve, and other finite-temperature magnetic properties through extensive Monte Carlo simulations, which have been further applied to examine the influence of the magnetic fluctuations on the free energy and thermal equation of state properties of bcc Fe at high temperatures. This work was supported by US Department of Energy ASCI/ASAP subcontract to Caltech, Grant DOE W-7405-ENG-48 (to REC).

  10. Low-temperature transport and ferromagnetism in GaAs-based structures with Mn

    SciTech Connect

    Kulbachinskii, V. A. Gurin, P. V.; Danilov, Yu. A.; Malysheva, E. I.; Horikoshi, Y.; Onomitsu, K.

    2007-07-15

    GaAs structures with implanted Mn and, additionally, with Mg for increasing the hole concentration in the implanted Mn layer are synthesized and investigated. SQUID magnetometer measurements revealed the existence of ferromagnetism in the temperature range 4.2 K {<=} T < 400 K, which is associated with the formation of the Ga{sub 1-x}Mn{sub x}As solid solution and MnAs and Ga{sub 1-y}Mn{sub y} clusters in the sample as a result of rapid high-temperature annealing. At temperatures from 4.2 to approximately 200 K, the anomalous Hall effect associated with additional magnetization of the sample is observed. As the temperature increases from 4.2 K, the colossal negative magnetoresistance is transformed into a positive magnetoresistance at T {approx} 35 K.

  11. Temperature dependence of magnetic susceptibility in the vicinity of martensitic transformation in ferromagnetic shape memory alloys.

    PubMed

    Zablotskii, V; Pérez-Landazábal, J I; Recarte, V; Gómez-Polo, C

    2010-08-11

    Temperature dependences of low-field quasistatic magnetic susceptibility in the vicinity of martensitic transitions in an NiFeGa alloy are studied both by experiment and analytically. Pronounced reversible jumps of the magnetic susceptibility were observed near the martensitic transition temperature. A general description of the temperature dependences of the susceptibility in ferromagnetic austenite and martensite phases and the susceptibility jump at the transition is suggested. As a result, the main factors governing the temperature dependences of the magnetic susceptibility in the magnetic shape memory alloys are revealed. The magnetic susceptibility jump value is found to be related to changes of: (i) magnetic anisotropy; (ii) magnetic domain wall geometrical constraints (those determined by the alignment and size of twin variants) and (iii) mean magnetic domain spacing.

  12. Exhaled breath temperature in healthy children is influenced by room temperature and lung volume.

    PubMed

    Logie, Karla M; Kusel, Merci M H; Sly, Peter D; Hall, Graham L

    2011-11-01

    Exhaled breath temperature (EBT) has been proposed for the non-invasive assessment of airway inflammation. Previous studies have not examined the influence of room temperature or lung size on the EBT. This study aimed to address these issues in healthy children. We assessed the effects of room temperature and lung volume in 60 healthy children aged 9-11 years (mean age 10.3 years, 33 male). Static lung volumes were assessed using multiple breath nitrogen washout. Questionnaire and skin prick tests were also used to establish respiratory health in the children. We obtained the EBT parameters of slope, end plateau temperature (PLET) and normalized plateau temperature (nPLET; plateau temperature minus inspired air temperature), and ascertained physiological factors influencing EBT. End plateau temperature was shown to be proportionally affected by room temperature (r = 0.532, P < 0.001) whereas slope and nPLET decreased with increasing room temperature (r = -0.392 P < 0.02 and r = -0.507 P = 0.002). After adjusting for room temperature, height and age, the total lung capacity (r(2)  = 0.435, P = 0.006) and slow vital capacity (SVC; r(2)  = 0.44, P = 0.005) were found to be the strongest predictors of end PLET in healthy children. When all factors were included in a multiple regression model, SVC and room temperature were the only predictors of plateau and nPLET. Slope was only influenced by room temperature. Exhaled breath temperature measurements are highly feasible in children with a 95% success rate in this healthy population. Room temperature and SVC significantly influence EBT variables in healthy children. Further studies are required to investigate the ability of EBT to assess airway inflammation in children with respiratory disease. Pediatr. Pulmonol. 2011; 46:1062-1068. © 2011 Wiley Periodicals, Inc. Copyright © 2011 Wiley Periodicals, Inc.

  13. In vitro comparison of output fluid temperatures for room temperature and prewarmed fluids.

    PubMed

    Soto, N; Towle Millard, H A; Lee, R A; Weng, H Y

    2014-08-01

    To determine if prewarmed intravenous fluids produce superior fluid output temperatures compared with room temperature fluids at common anaesthetic fluid rates for small animal patients. A prospective, randomised, in vitro fluid line test-vein study was performed. Nine flow rates were analysed (10, 20, 60, 100, 140, 180, 220, 260 and 300 mL/hour) for room temperature fluids (21°C) and for five prewarmed fluids (40, 45, 50, 55 and 60°C). For each flow rate tested, room temperature fluids never exceeded 25°C at any time point for each trial (range 18 to 25°C). For each flow rate tested, prewarmed fluids never exceeded 25 · 5°C at any time point for each trial (range 18 to 25 · 5°C). The mean output fluid temperature of prewarmed fluids was significantly warmer than room temperature fluids only at 300 mL/hour for 40°C (P = 0 · 0012), 45°C (P = 0 · 004), 50°C (P = 0 · 0002), 55°C (P = 0 · 0001) and 60°C (P < 0 · 0001). There was no thermodynamic benefit to utilising prewarmed intravenous fluids (up to 60°C) compared with room temperature intravenous fluids at common anaesthetic fluid rates for small animals. © 2014 British Small Animal Veterinary Association.

  14. Xenon Recovery at Room Temperature using Metal-Organic Frameworks.

    PubMed

    Elsaidi, Sameh K; Ongari, Daniele; Xu, Wenqian; Mohamed, Mona H; Haranczyk, Maciej; Thallapally, Praveen K

    2017-08-10

    Xenon is known to be a very efficient anesthetic gas, but its cost prohibits the wider use in medical industry and other potential applications. It has been shown that Xe recovery and recycling from anesthetic gas mixtures can significantly reduce its cost as anesthetic. The current technology uses series of adsorbent columns followed by low-temperature distillation to recover Xe; this method is expensive to use in medical facilities. Herein, we propose a much simpler and more efficient system to recover and recycle Xe from exhaled anesthetic gas mixtures at room temperature using metal-organic frameworks (MOFs). Among the MOFs tested, PCN-12 exhibits unprecedented performance with high Xe capacity and Xe/O2 , Xe/N2 and Xe/CO2 selectivity at room temperature. The in situ synchrotron measurements suggest that Xe is occupies the small pockets of PCN-12 compared to unsaturated metal centers (UMCs). Computational modeling of adsorption further supports our experimental observation of Xe binding sites in PCN-12. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Magnetic properties of stainless steels at room and cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Oxley, Paul; Goodell, Jennifer; Molt, Robert

    2009-07-01

    The magnetic properties of ten types of ferritic and martensitic stainless steels have been measured at room temperature and at 77 K. The steel samples studied were in the annealed state as received from the manufacturer. Our room temperature measurements indicate significantly harder magnetic properties than those quoted in the ASM International Handbook, which studied fully annealed stainless steel samples. Despite having harder magnetic properties than fully annealed steels some of the as-received steels still display soft magnetic properties adequate for magnetic applications. The carbon content of the steels was found to affect the permeability and coercive force, with lower-carbon steels displaying significantly higher permeability and lower coercive force. The decrease in coercive force with reduced carbon content is attributed to fewer carbide inclusions which inhibit domain wall motion. Cooling to 77 K resulted in harder magnetic properties. Averaged over the ten steels tested the maximum permeability decreased by 8%, the coercive force increased by 14%, and the residual and saturation flux densities increased by 4% and 3%, respectively. The change in coercive force when cooled is comparable to the theoretical prediction for iron, based on a model of domain wall motion inhibited by inclusions. The modest changes of the magnetic properties indicate that the stainless steels can still be used in magnetic applications at very low temperatures.

  16. Magnetic refrigeration-towards room-temperature applications

    NASA Astrophysics Data System (ADS)

    Brück, E.; Tegus, O.; Li, X. W.; de Boer, F. R.; Buschow, K. H. J.

    2003-04-01

    Modern society relies very much on readily available cooling. Magnetic refrigeration based on the magneto-caloric effect (MCE) has become a promising competitive technology for the conventional gas-compression/expansion technique in use today. Recently, there have been two breakthroughs in magnetic-refrigeration research: one is that American scientists demonstrated the world's first room-temperature, permanent-magnet, magnetic refrigerator; the other one is that we discovered a new class of magnetic refrigerant materials for room-temperature applications. The new materials are manganese-iron-phosphorus-arsenic (MnFe(P,As)) compounds. This new material has important advantages over existing magnetic coolants: it exhibits a huge MCE, which is larger than that of Gd metal; and its operating temperature can be tuned from about 150 to about 335 K by adjusting the P/As ratio. Here we report on further improvement of the materials by increasing the Mn content. The large entropy change is attributed to a field-induced first-order phase transition enhancing the effect of the applied magnetic field. Addition of Mn reduces the thermal hysteresis, which is intrinsic to the first-order transition. This implies that already moderate applied magnetic fields of below 2 T may suffice.

  17. Xenon Recovery at Room Temperature using Metal Organic Frameworks

    SciTech Connect

    Elsaidi, Sameh K.; Ongari, Daniele; Xu, Wenqian; Mohamed, Mona H.; Haranczyk, Maciej; Thallapally, Praveen K.

    2017-01-01

    Xenon is known to be a very efficient anesthetic gas but its cost prohibits the wider use in medical industry and other potential applications. It has been shown that Xe recovery and recycle from anesthetic gas mixture can significantly reduce its cost as anesthetic. The current technology uses series of adsorbent columns followed by low temperature distillation to recover Xe, which is expensive to use in medical facilities. Herein, we propose much efficient and simpler system to recover and recycle Xe from simulant exhale anesthetic gas mixture at room temperature using metal organic frameworks. Among the MOFs tested, PCN-12 exhibits unprecedented performance with high Xe capacity, Xe/O2, Xe/N2 and Xe/CO2 selectivity at room temperature. The in-situ synchrotron measurements suggest the Xe is occupied in the small pockets of PCN-12 compared to unsaturated metal centers (UMCs). Computational modeling of adsorption further supports our experimental observation of Xe binding sites in PCN-12.

  18. Conformation of protonated glutamic acid at room and cryogenic temperatures.

    PubMed

    Bouchet, Aude; Klyne, Johanna; Ishiuchi, Shun-Ichi; Fujii, Masaaki; Dopfer, Otto

    2017-05-03

    Recognition properties of biologically relevant molecules depend on their conformation. Herein, the conformation of protonated glutamic acid (H(+)Glu) isolated in quadruple ion traps is characterized by vibrational spectroscopy at room and cryogenic temperatures and dispersion-corrected density functional theory calculations at the B3LYP-D3/aug-cc-pVTZ level. The infrared multiple photon dissociation (IRMPD) spectrum recorded in the fingerprint range at room temperature using an IR free electron laser is attributed to the two most stable and nearly isoenergetic conformations (1-cc and 2-cc) with roughly equal population (ΔG298 = 0.0 kJ mol(-1)). Both have bridging C[double bond, length as m-dash]O(HNH)(+)O[double bond, length as m-dash]C ionic H-bonds of rather different strengths but cannot be distinguished by their similar IRMPD spectra. In contrast, the higher-resolution single-photon IRPD spectrum of H2-tagged H(+)Glu recorded in the conformation-sensitive X-H stretch range in a trap held at 10 K distinguishes both conformers. At low temperature, 1-cc is roughly twice more abundant than 2-cc, in line with its slightly lower calculated energy (ΔE0 = 0.5 kJ mol(-1)). This example illustrates the importance of cryogenic cooling, single-photon absorption conditions, and the consideration of the X-H stretch range for the identification of biomolecular conformations involving hydrogen bonds.

  19. Giant room temperature magnetoelectric response in strain controlled nanocomposites

    NASA Astrophysics Data System (ADS)

    Rafique, Mohsin; Herklotz, Andreas; Dörr, Kathrin; Manzoor, Sadia

    2017-05-01

    We report giant magnetoelectric coupling at room temperature in a self-assembled nanocomposite of BiFeO3-CoFe2O4 (BFO-CFO) grown on a BaTiO3 (BTO) crystal. The nanocomposite consisting of CFO nanopillars embedded in a BFO matrix exhibits weak perpendicular magnetic anisotropy due to a small out-of-plane compression (˜0.3%) of the magnetostrictive (CFO) phase, enabling magnetization rotation under moderate in-plane compression. Temperature dependent magnetization measurements demonstrate strong magnetoelastic coupling between the BaTiO3 substrate and the nanocomposite film, which has been exploited to produce a large magnetoelectric response in the sample. The reorientation of ferroelectric domains in the BTO crystal upon the application of an electric field (E) alters the strain state of the nanocomposite film, thus enabling control of its magnetic anisotropy. The strain mediated magnetoelectric coupling coefficient α = μ o d M / d E calculated from remnant magnetization at room temperature is 2.6 × 10-7 s m-1 and 1.5 × 10-7 s m-1 for the out-of-plane and in-plane orientations, respectively.

  20. A room temperature low-threshold ultraviolet plasmonic nanolaser.

    PubMed

    Zhang, Qing; Li, Guangyuan; Liu, Xinfeng; Qian, Fang; Li, Yat; Sum, Tze Chien; Lieber, Charles M; Xiong, Qihua

    2014-09-23

    Constrained by large ohmic and radiation losses, plasmonic nanolasers operated at visible regime are usually achieved either with a high threshold (10(2)-10(4) MW cm(-2)) or at cryogenic temperatures (4-120 K). Particularly, the bending-back effect of surface plasmon (SP) dispersion at high energy makes the SP lasing below 450 nm more challenging. Here we demonstrate the first strong room temperature ultraviolet (~370 nm) SP polariton laser with an extremely low threshold (~3.5 MW cm(-2)). We find that a closed-contact planar semiconductor-insulator-metal interface greatly lessens the scattering loss, and more importantly, efficiently promotes the exciton-SP energy transfer thus furnishes adequate optical gain to compensate the loss. An excitation polarization-dependent lasing action is observed and interpreted with a microscopic energy-transfer process from excitons to SPs. Our work advances the fundamental understanding of hybrid plasmonic waveguide laser and provides a solution of realizing room temperature UV nanolasers for biological applications and information technologies.

  1. A room temperature low-threshold ultraviolet plasmonic nanolaser

    NASA Astrophysics Data System (ADS)

    Zhang, Qing; Li, Guangyuan; Liu, Xinfeng; Qian, Fang; Li, Yat; Sum, Tze Chien; Lieber, Charles M.; Xiong, Qihua

    2014-09-01

    Constrained by large ohmic and radiation losses, plasmonic nanolasers operated at visible regime are usually achieved either with a high threshold (102-104 MW cm-2) or at cryogenic temperatures (4-120 K). Particularly, the bending-back effect of surface plasmon (SP) dispersion at high energy makes the SP lasing below 450 nm more challenging. Here we demonstrate the first strong room temperature ultraviolet (~370 nm) SP polariton laser with an extremely low threshold (~3.5 MW cm-2). We find that a closed-contact planar semiconductor-insulator-metal interface greatly lessens the scattering loss, and more importantly, efficiently promotes the exciton-SP energy transfer thus furnishes adequate optical gain to compensate the loss. An excitation polarization-dependent lasing action is observed and interpreted with a microscopic energy-transfer process from excitons to SPs. Our work advances the fundamental understanding of hybrid plasmonic waveguide laser and provides a solution of realizing room temperature UV nanolasers for biological applications and information technologies.

  2. Directional molecular sliding at room temperature on a silicon runway.

    PubMed

    Bouju, Xavier; Chérioux, Frédéric; Coget, Sébastien; Rapenne, Gwénaël; Palmino, Frank

    2013-08-07

    The design of working nanovehicles is a key challenge for the development of new devices. In this context, 1D controlled sliding of molecules on a silicon-based surface is successfully achieved by using an optimized molecule-substrate pair. Even though the molecule and surface are compatible, the molecule-substrate interaction provides a 1D template effect to guide molecular sliding along a preferential surface orientation. Molecular motion is monitored by STM experiments under ultra-high vacuum at room temperature. Molecule-surface interactions are elucidated by semi-empirical calculations.

  3. Laser phosphoroscope and applications to room-temperature phosphorescence.

    PubMed

    Payne, Sarah J; Zhang, Guoqing; Demas, James N; Fraser, Cassandra L; Degraff, Ben A

    2011-11-01

    A simple phosphoroscope with no moving parts is described. In one scan the total luminescence, the long-lived phosphorescence, and the short-lived fluorescence can be determined. A 50% duty cycle excitation from a diode laser is used to excite the sample, and from the digitized waveform the phosphorescence is extracted from the off period, the total emission from the full cycle, and the fluorescence from the on period corrected for the phosphorescence contribution. The performance of the system is demonstrated using room-temperature phosphorescence of organic dyes in boric acid glasses, a multi-emissive boron-polymer dye, and a europium chelate.

  4. Room-temperature phonon boundary scattering below the Casimir limit

    SciTech Connect

    Sadhu, J; Sinha, S

    2011-09-26

    Thermal conductivity data for rough surface silicon nanowires suggest the breakdown of the Casimir limit which assumes completely diffuse phonon boundary scattering. We show that coherent effects in phonon transport at room temperature indeed lead to such breakdown. Correlated multiple scattering of phonons off the rough surface lead to a reduced thermal conductivity that is dependent not only on the roughness amplitude but more importantly on the roughness correlation length. A correlation length less than the diameter of the wire is typically necessary for lowering the thermal conductivity below the Casimir limit. Our model explains seeming anomalies in data reported for electrolessly etched and electron beam lithography defined nanowires.

  5. Development of bulk GaAs room temperature radiation detectors

    SciTech Connect

    McGregor, D.S.; Knoll, G.F. . Dept. of Nuclear Engineering); Eisen, Y. . Soreq Nuclear Research Center); Brake, R. )

    1992-10-01

    This paper reports on GaAs, a wide band gap semiconductor with potential use as a room temperature radiation detector. Various configurations of Schottky diode detectors were fabricated with bulk crystals of liquid encapsulated Czochralski (LEC) semi-insulating undoped GaAs material. Basic detector construction utilized one Ti/Au Schottky contact and one Au/Ge/Ni alloyed ohmic contact. Pulsed X-ray analysis indicated pulse decay times dependent on bias voltage. Pulse height analysis disclosed non-uniform electric field distributions across the detectors tentatively explained as a consequence of native deep level donors (EL2) in the crystal.

  6. Ultrafast excitonic room temperature nonlinearity in neutron irradiated quantum wells

    SciTech Connect

    Ten, S.; Williams, J.G.; Guerreiro, P.T.; Khitrova, G.; Peyghambarian, N.

    1997-01-01

    Sharp room temperature exciton features and complete recovery of the excitonic absorption with 21 ps time constant are demonstrated in neutron irradiated (Ga,Al)As/GaAs multiple quantum wells. Carrier lifetime reduction is consistent with the EL2 midgap defect which is efficiently generated by fast neutrons. Influence of gamma rays accompanying neutron irradiation is discussed. Neutron irradiation provides a straightforward way to control carrier lifetime in semiconductor heterostructures with minor deterioration of their excitonic properties. {copyright} {ital 1997 American Institute of Physics.}

  7. Room temperature peierls distortion in small diameter nanotubes.

    PubMed

    Connétable, D; Rignanese, G-M; Charlier, J-C; Blase, X

    2005-01-14

    By means of ab initio simulations, we investigate the phonon band structure and electron-phonon coupling in small 4-A diameter nanotubes. We show that both the C(5,0) and C(3,3) tubes undergo above room temperature a Peierls transition mediated by an acoustical long wavelength and an optical q=2k(F) phonon, respectively. In the armchair geometry, we verify that the electron-phonon coupling parameter lambda originates mainly from phonons at q=2k(F) and is strongly enhanced when the diameter decreases. These results question the origin of superconductivity in small diameter nanotubes.

  8. Mobile Neel skyrmions at room temperature: Status and future

    DOE PAGES

    Jiang, Wanjun; Zhang, Wei; Yu, Guoqiang; ...

    2016-03-07

    Magnetic skyrmions are topologically protected spin textures that exhibit many fascinating features. As compared to the well-studied cryogenic Bloch skyrmions in bulk materials, we focus on the room- temperature Néel skyrmions in thin-film systems with an interfacial broken inversion symmetry in this article. Specifically, we show the stabilization, the creation, and the implementation of Néel skyrmions that are enabled by the electrical current-induced spin-orbit torques. As a result, towards the nanoscale Néel skyrmions, we further discuss the challenges from both material optimization and imaging characterization perspectives.

  9. Oxygen-vacancy-induced room-temperature magnetization in lamellar V{sub 2}O{sub 5} thin films

    SciTech Connect

    Cezar, A. B.; Graff, I. L. Varalda, J.; Schreiner, W. H.; Mosca, D. H.

    2014-10-28

    In this work, we study the local atomic and electronic structures as well as oxygen-vacancy-induced magnetic properties of electrodeposited V{sub 2}O{sub 5} films. Unlike stoichiometric V{sub 2}O{sub 5}, which is a diamagnetic lamellar semiconductor, our oxygen-defective V{sub 2}O{sub 5} films are ferromagnetic at room-temperature and their saturation magnetization decreases with air exposure time. X-ray absorption spectroscopy was used to monitor the aging effect on these films, revealing that freshly-made samples exhibit only local crystalline order, whereas the aged ones undoubtedly show an enhancement of crystallinity and coordination symmetry. The mean number of oxygen atoms around V tends to increase, indicating a decrease of oxygen vacancies with time. Concurrently with the decrease of oxygen vacancies, a loss of saturation magnetization is also observed. Hence, it can be concluded that the ferromagnetism of the V{sub 2}O{sub 5} films originates from a vacancy-induced mechanism, confirming the universality of this class of ferromagnetism.

  10. Room temperature homogeneous flow in a bulk metallic glass with low glass transition temperature

    SciTech Connect

    Zhao, K.; Xia, X. X.; Bai, H. Y.; Zhao, D. Q.; Wang, W. H.

    2011-04-04

    We report a high entropy metallic glass of Zn{sub 20}Ca{sub 20}Sr{sub 20}Yb{sub 20}(Li{sub 0.55}Mg{sub 0.45}){sub 20} via composition design that exhibiting remarkable homogeneous deformation without shear banding under stress at room temperature. The glass also shows properties such as low glass transition temperature (323 K) approaching room temperature, low density and high specific strength, good conductivity, polymerlike thermoplastic manufacturability, and ultralow elastic moduli comparable to that of bones. The alloy is thermally and chemically stable.

  11. Curie temperature and NMR of 53Cr nuclei in doped ferromagnetic cadmium chromium selenide semiconductors

    NASA Astrophysics Data System (ADS)

    Kuz'min, E. V.; Polulyakh, S. N.; Berzhansky, V. N.; Abelyashev, G. N.; Aminov, T. G.

    2008-10-01

    The effect of alien-valence substitution on exchange interactions in ferromagnetic cadmium chromium selenide spinel is studied both experimentally and theoretically. The Curie temperature is calculated within the molecular field approximation. From comparing the calculated results with experimental dependences of the Curie temperature on impurity concentration and variation in NMR chromium spectra with temperature, a conclusion is drawn in favor of the model of magnetic clusters. The model suggests that, during the alien-valence substitution for nonmagnetic cations, the valence is compensated by a change in the valence state of chromium ions. The excess charge carriers hop between equivalent ions surrounding the impurity. By analogy with the double-exchange model, a detailed description of this hopping and its influence on the exchange interaction of magnetic ions is given.

  12. Room-Temperature Equation of State for CO2-I

    NASA Astrophysics Data System (ADS)

    Scott, H. P.; Kinney, T. W.; Frank, M. R.; Lin, J.

    2010-12-01

    We have measured the room-temperature bulk modulus (K0T) and its pressure derivative (K') for solid carbon dioxide in its relatively low-pressure phase I (space group: Pa3; CO2-I) between 0.9 and 9 GPa. This pressure range closely matches the actual room-temperature stability field for this phase. The motivation for our investigation is to address an apparent discrepancy in two earlier publications and provide a complete and internally consistent set of equation of state (EoS) parameters for future investigators to conveniently predict the diffraction peak positions for CO2-I at elevated pressures. We note that there is much interest in the chemical reactivity of CO2 at elevated pressures and temperatures and anticipate that this will be a useful addition to the literature. Because the solid phase is unquenchable at room temperature, we used the estimated zero-pressure volume extrapolated to 300 K from lower temperatures by Olinger (1982) and held this value fixed: V0 = 197.9 Å3/unit cell. We performed fits with both the Vinet (K0T = 3.1 ± 0.1 GPa, K' = 9.1 ± 0.2) and Birch-Murnaghan (K0T = 2.5 ± 0.2 GPa, K' = 13.0 ± 0.9) EoS models. The observed difference is not surprising given the very high compressibility of this phase and the inherent covariance between K0T and K'. Although we note that both sets of EoS parameters produce acceptable fits to our data, we favor the Vinet values, especially in terms of determining a realistic value for K', because the phase is so compressible. However, many workers utilize software with built-in routines for calculating peak positions at high pressures, and these often assume a Birch Murnaghan EoS. To facilitate the usage of our results with such programs, we have also performed a Birch-Murnaghan fit for which the K' value from the Vinet fit was held fixed and K0T was the only fit parameter. Accordingly, we present the following EoS parameters for the convenient calculation of expected peak positions for CO2-I at high

  13. Dynamics and structure of room temperature ionic liquids

    NASA Astrophysics Data System (ADS)

    Fayer, Michael D.

    2014-11-01

    Room temperature ionic liquids (RTIL) are intrinsically interesting because they simultaneously have properties that are similar to organic liquids and liquid salts. In addition, RTILs are increasingly being considered for and used in technological applications. RTILs are usually composed of an organic cation and an inorganic anion. The organic cation, such as imidazolium, has alkyl chains of various lengths. The disorder in the liquid produced by the presence of the alkyl groups lowers the temperature for crystallization below room temperature and can also result in supercooling and glass formation rather than crystallization. The presence of the alkyl moieties also results in a segregation of the liquid into ionic and organic regions. In this article, experiments are presented that address the relationship between RTIL dynamics and structure. Time resolved fluorescence anisotropy measurements were employed to study the local environments in the organic and ionic regions of RTILs using a nonpolar chromophore that locates in the organic regions and an ionic chromophore that locates in the ionic regions. In the alkyl regions, the in plane and out of plane orientational friction coefficients change in different manners as the alkyl chains get longer. Both friction coefficients converge toward those of a long chain length hydrocarbon as the RTIL chains increase in length, which demonstrates that for sufficiently long alkyl chains the RTIL organic regions have properties similar to a hydrocarbon. However, putting Li+ in the ionic regions changes the friction coefficients in the alkyl regions, which demonstrates that changes of the ion structural organization influences the organization of the alkyl chains. Optical heterodyne detected optical Kerr effect (OHD-OKE) experiments were used to examine the orientational relaxation dynamics of RTILs over times scales of a hundred femtoseconds to a hundred nanoseconds. Detailed temperature dependent studies in the liquid and

  14. Airway narrowing measured by spirometry and impulse oscillometry following room temperature and cold temperature exercise.

    PubMed

    Evans, Tina M; Rundell, Kenneth W; Beck, Kenneth C; Levine, Alan M; Baumann, Jennifer M

    2005-10-01

    The efficacy of using impulse oscillometry (IOS) as an indirect measure of airflow obstruction compared to spirometry after exercise challenges in the evaluation of exercise-induced bronchoconstriction (EIB) has not been fully appreciated. The objective was to compare airway responses following room temperature and cold temperature exercise challenges, and to compare whether IOS variables relate to spirometry variables. Spirometry and IOS were performed at baseline and for 20 min after challenge at 5-min intervals. Two 6-min exercise challenges, inhaling either room temperature (22.0 degrees C) or cold temperature (- 1 degrees C) dry medical-grade bottled air. At least 48 h was observed between these randomly assigned challenges. Twenty-two physically active individuals (12 women and 10 men) with probable EIB. Subjects performed 6 min of stationary cycle ergometry while breathing either cold or room temperature medical-grade dry bottled air. Subjects were instructed to exercise at the highest intensity sustainable for the duration of the challenge. Heart rate and kilojoules of work performed were documented to verify exercise intensity. Strong correlations were observed within testing modalities for post-room temperature and post-cold temperature exercise spirometry and IOS values. Spirometry revealed no differences in postexercise peak falls in lung function between conditions; however, IOS identified significant differences in respiratory resistance (p < 0.05), with room temperature-inspired air being more potent than cold temperature-inspired air. Correlations were found between spirometric and IOS measures of change in airway function for both exercise challenges, indicating close equivalency of the methods. The challenges appeared to elicit the EIB response by a similar mechanism of water loss, and cold temperature did not have an additive effect. IOS detected a difference in degree of response between the temperatures, whereas spirometry indicated no

  15. Current-Induced Nucleation and Annihilation of Magnetic Skyrmions at Room Temperature in a Chiral Magnet.

    PubMed

    Yu, Xiuzhen; Morikawa, Daisuke; Tokunaga, Yusuke; Kubota, Masashi; Kurumaji, Takashi; Oike, Hiroshi; Nakamura, Masao; Kagawa, Fumitaka; Taguchi, Yasujiro; Arima, Taka-Hisa; Kawasaki, Masashi; Tokura, Yoshinori

    2017-06-01

    A magnetic skyrmion is a nanometer-scale magnetic vortex carrying an integer topological charge. Skyrmions show a promise for potential application in low-power-consumption and high-density memory devices. To promote their use in applications, it is attempted to control the existence of skyrmions using low electric currents at room temperature (RT). This study presents real-space observations for the current-induced formation and annihilation of a skyrmion lattice (SkL) as well as isolated skyrmions in a microdevice composed of a thin chiral magnet Co8 Zn9 Mn3 with a Curie temperature, TC ≈ 325 K, above RT. It is found that the critical current for the manipulation of Bloch-type skyrmions is on the order of 10(8) A m(-2) , approximately three orders of magnitude lower than that needed for the creation and drive of ferromagnetic (FM) domain walls in thin FM films. The in situ real-space imaging also demonstrates the dynamical topological transition from a helical or conical structure to a SkL induced by the flow of DC current, thus paving the way for the electrical control of magnetic skyrmions. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Investigation of the room temperature annealing peak in ionomers

    SciTech Connect

    Goddard, R.J.; Grady, B.P.; Cooper, S.L.

    1993-12-31

    A number of studies appearing in the literature have documented an endothermic peak in differential scanning calorimetry (DSC) scans for ethylene-methacrylic acid copolymer ionomers which appears only upon annealing at room temperature. This peak has been attributed to either polyethylene crystallites, ionic crystallite, or water absorption. In a novel polyurethane cationomer with a quarternized amine contained in hard segment, the same phenomena has been found in DSC scans when the neutralizing anion is bromine or iodine. Since this material does not crystallize, the authors were able to conclusively eliminate crystallization as the cause of the endotherm. The extended x-ray absorption fine structure (EXAFS) of bromine has been measured to differentiate between water absorption and ionic crystallites. Spectra were collected above and below the temperature corresponding to the endothermic peak. The results of the EXAFS analysis will be presented.

  17. New Flexible Channels for Room Temperature Tunneling Field Effect Transistors

    SciTech Connect

    Hao, Boyi; Asthana, Anjana; Hazaveh, Paniz Khanmohammadi; Bergstrom, Paul L.; Banyai, Douglas; Savaikar, Madhusudan A.; Jaszczak, John A.; Yap, Yoke Khin

    2016-02-05

    Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues of Si based transistors, such as short channel effect, finite leakage current, and high contact resistance. Unfortunately, most if not all TFETs are operational only at cryogenic temperatures. Here we report that iron (Fe) quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) can be used as the flexible tunneling channels of TFETs at room temperatures. The electrical insulating BNNTs are used as the one-dimensional (1D) substrates to confine the uniform formation of Fe QDs on their surface as the flexible tunneling channel. Consistent semiconductor-like transport behaviors under various bending conditions are detected by scanning tunneling spectroscopy in a transmission electron microscopy system (insitu STM-TEM). Ultimately, as suggested by computer simulation, the uniform distribution of Fe QDs enable an averaging effect on the possible electron tunneling pathways, which is responsible for the consistent transport properties that are not sensitive to bending.

  18. Airtight metallic sealing at room temperature under small mechanical pressure

    NASA Astrophysics Data System (ADS)

    Stagon, Stephen P.; Huang, Hanchen

    2013-10-01

    Metallic seals can be resistant to air leakage, resistant to degradation under heat, and capable of carrying mechanical loads. Various technologies - such as organic solar cells and organic light emitting diodes - need, at least benefit from, such metallic seals. However, these technologies involve polymeric materials and can tolerate neither the high-temperature nor the high-pressure processes of conventional metallic sealing. Recent progress in nanorod growth opens the door to metallic sealing for these technologies. Here, we report a process of metallic sealing using small well-separated Ag nanorods; the process is at room temperature, under a small mechanical pressure of 9.0 MPa, and also in ambient. The metallic seals have an air leak rate of 1.1 × 10-3 cm3atm/m2/day, and a mechanical shear strength higher than 8.9 MPa. This leak rate meets the requirements of organic solar cells and organic light emitting diodes.

  19. Room-temperature metastability of multilayer graphene oxide films.

    PubMed

    Kim, Suenne; Zhou, Si; Hu, Yike; Acik, Muge; Chabal, Yves J; Berger, Claire; de Heer, Walt; Bongiorno, Angelo; Riedo, Elisa

    2012-05-06

    Graphene oxide potentially has multiple applications. The chemistry of graphene oxide and its response to external stimuli such as temperature and light are not well understood and only approximately controlled. This understanding is crucial to enable future applications of this material. Here, a combined experimental and density functional theory study shows that multilayer graphene oxide produced by oxidizing epitaxial graphene through the Hummers method is a metastable material whose structure and chemistry evolve at room temperature with a characteristic relaxation time of about one month. At the quasi-equilibrium, graphene oxide reaches a nearly stable reduced O/C ratio, and exhibits a structure deprived of epoxide groups and enriched in hydroxyl groups. Our calculations show that the structural and chemical changes are driven by the availability of hydrogen in the oxidized graphitic sheets, which favours the reduction of epoxide groups and the formation of water molecules.

  20. Room temperature quantum coherence in a potential molecular qubit

    NASA Astrophysics Data System (ADS)

    Bader, Katharina; Dengler, Dominik; Lenz, Samuel; Endeward, Burkhard; Jiang, Shang-Da; Neugebauer, Petr; van Slageren, Joris

    2014-10-01

    The successful development of a quantum computer would change the world, and current internet encryption methods would cease to function. However, no working quantum computer that even begins to rival conventional computers has been developed yet, which is due to the lack of suitable quantum bits. A key characteristic of a quantum bit is the coherence time. Transition metal complexes are very promising quantum bits, owing to their facile surface deposition and their chemical tunability. However, reported quantum coherence times have been unimpressive. Here we report very long quantum coherence times for a transition metal complex of 68 μs at low temperature (qubit figure of merit QM=3,400) and 1 μs at room temperature, much higher than previously reported values for such systems. We show that this achievement is because of the rigidity of the lattice as well as removal of nuclear spins from the vicinity of the magnetic ion.

  1. Generation of coherent terahertz pulses in ruby at room temperature

    SciTech Connect

    Kuznetsova, Elena; Rostovtsev, Yuri; Kalugin, Nikolai G.; Kolesov, Roman; Kocharovskaya, Olga; Scully, Marlan O.

    2006-08-15

    We have shown that a coherently driven solid state medium can potentially produce strong controllable short pulses of THz radiation. The high efficiency of the technique is based on excitation of maximal THz coherence by applying resonant optical pulses to the medium. The excited coherence in the medium is connected to macroscopic polarization coupled to THz radiation. We have performed detailed simulations by solving the coupled density matrix and Maxwell equations. By using a simple V-type energy scheme for ruby, we have demonstrated that the energy of generated THz pulses ranges from hundreds of pico-Joules to nano-Joules at room temperature and micro-Joules at liquid helium temperature, with pulse durations from picoseconds to tens of nanoseconds. We have also suggested a coherent ruby source that lases on two optical wavelengths and simultaneously generates THz radiation. We discussed also possibilities of extension of the technique to different solid-state materials.

  2. Room temperature skyrmion ground state stabilized through interlayer exchange coupling

    SciTech Connect

    Chen, Gong Schmid, Andreas K.; Mascaraque, Arantzazu; N'Diaye, Alpha T.

    2015-06-15

    Possible magnetic skyrmion device applications motivate the search for structures that extend the stability of skyrmion spin textures to ambient temperature. Here, we demonstrate an experimental approach to stabilize a room temperature skyrmion ground state in chiral magnetic films via exchange coupling across non-magnetic spacer layers. Using spin polarized low-energy electron microscopy to measure all three Cartesian components of the magnetization vector, we image the spin textures in Fe/Ni films. We show how tuning the thickness of a copper spacer layer between chiral Fe/Ni films and perpendicularly magnetized Ni layers permits stabilization of a chiral stripe phase, a skyrmion phase, and a single domain phase. This strategy to stabilize skyrmion ground states can be extended to other magnetic thin film systems and may be useful for designing skyrmion based spintronics devices.

  3. Cadmium selenide: a promising novel room temperature radiation detector

    SciTech Connect

    Burger, A.; Schieber, M.; Shilo, I.

    1983-02-01

    Large single crystals of CdSe weighing about 30g were grown by the vertical unseeded vapor growth technique at a linear growth rate of 5mm/day and a temperature gradient of 10/sup 0/C/cm. Crystal perfection and homogeneity were evaluated by Laue X-ray diffraction, etch pit density, SEM and microprobe analysis methods. The dark resistivity of the as-grown and the heat treated crystal was about 1..cap omega..cm and 10/sup 12/..cap omega..cm respectively. Slices were used to fabricate room temperature detectors for nuclear radiation energy. The detectors showed high efficiency and stability as a function of time for radiation sources from 10KeV to 660KeV.

  4. Room temperature quantum coherence in a potential molecular qubit.

    PubMed

    Bader, Katharina; Dengler, Dominik; Lenz, Samuel; Endeward, Burkhard; Jiang, Shang-Da; Neugebauer, Petr; van Slageren, Joris

    2014-10-20

    The successful development of a quantum computer would change the world, and current internet encryption methods would cease to function. However, no working quantum computer that even begins to rival conventional computers has been developed yet, which is due to the lack of suitable quantum bits. A key characteristic of a quantum bit is the coherence time. Transition metal complexes are very promising quantum bits, owing to their facile surface deposition and their chemical tunability. However, reported quantum coherence times have been unimpressive. Here we report very long quantum coherence times for a transition metal complex of 68 μs at low temperature (qubit figure of merit QM=3,400) and 1 μs at room temperature, much higher than previously reported values for such systems. We show that this achievement is because of the rigidity of the lattice as well as removal of nuclear spins from the vicinity of the magnetic ion.

  5. Magnesium Electrorefining in Non-Aqueous Electrolyte at Room Temperature

    NASA Astrophysics Data System (ADS)

    Kwon, Kyungjung; Park, Jesik; Kusumah, Priyandi; Dilasari, Bonita; Kim, Hansu; Lee, Churl Kyoung

    Magnesium, of which application is often limited by its poor corrosion resistance, is more vulnerable to corrosion with existence of metal impurities such as Fe. Therefore, for the refining and recycling of magnesium, high temperature electrolysis using molten salts has been frequently adopted. In this report, the purification of magnesium scrap by electrolysis at room temperature is investigated with non-aqueous electrolytes. An aprotic solvent of tetrahydrofuran (THF) was used as a solvent of the electrolyte. Magnesium scrap was used as anode materials and ethyl magnesium bromide (EtMgBr) was dissolved in THF for magnesium source. The purified magnesium can be uniformly electrodeposited on copper electrode under potentiostatic conditions. The deposits were confirmed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analysis.

  6. New Flexible Channels for Room Temperature Tunneling Field Effect Transistors.

    PubMed

    Hao, Boyi; Asthana, Anjana; Hazaveh, Paniz Khanmohammadi; Bergstrom, Paul L; Banyai, Douglas; Savaikar, Madhusudan A; Jaszczak, John A; Yap, Yoke Khin

    2016-02-05

    Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues of Si based transistors, such as short channel effect, finite leakage current, and high contact resistance. Unfortunately, most if not all TFETs are operational only at cryogenic temperatures. Here we report that iron (Fe) quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) can be used as the flexible tunneling channels of TFETs at room temperatures. The electrical insulating BNNTs are used as the one-dimensional (1D) substrates to confine the uniform formation of Fe QDs on their surface as the flexible tunneling channel. Consistent semiconductor-like transport behaviors under various bending conditions are detected by scanning tunneling spectroscopy in a transmission electron microscopy system (in-situ STM-TEM). As suggested by computer simulation, the uniform distribution of Fe QDs enable an averaging effect on the possible electron tunneling pathways, which is responsible for the consistent transport properties that are not sensitive to bending.

  7. Silicon Nanowires Light Emitting Devices at Room Temperature

    NASA Astrophysics Data System (ADS)

    Artoni, Pietro; Irrera, A.; Franzò', G.; Fazio, B.; Galli, M.; Pecora, E.; Iacona, F.; Priolo, F.

    Group-IV semiconductor nanowires (NWs) are attracting interest among the scientific community as building blocks for a wide range of future nanoscaled devices. Vapor-liquid-Solid (VLS) is the most used technique for semiconductor NWs growth. Si NWs are promising as building blocks for photovoltaic elements, sensors and high-performance batteries; however, Si NWs are less explored for photonic applications, probably since there are many drawbacks due to the NW structure obtained by VLS. In fact, there is a minimum obtainable size which reduces the possibility to have quantum confinement effects without high temperature oxidation processes; metal used as a catalyst may be incorporated inside the NW thus affecting its electrical and optical properties. Moreover, by VLS method the doping is no easily controllable because of the segregation of the dopants at the NWs interface. Indeed, the possibility of obtaining light from silicon at room temperature under optical and electrical pumping is strategic for the communication technology.

  8. Room temperature ferroelectricity in continuous croconic acid thin films

    SciTech Connect

    Jiang, Xuanyuan; Lu, Haidong; Yin, Yuewei; Ahmadi, Zahra; Costa, Paulo S.; Zhang, Xiaozhe; Wang, Xiao; Yu, Le; Cheng, Xuemei; DiChiara, Anthony D.; Gruverman, Alexei E-mail: a.enders@me.com Enders, Axel E-mail: a.enders@me.com Xu, Xiaoshan E-mail: a.enders@me.com

    2016-09-05

    Ferroelectricity at room temperature has been demonstrated in nanometer-thin quasi 2D croconic acid thin films, by the polarization hysteresis loop measurements in macroscopic capacitor geometry, along with observation and manipulation of the nanoscale domain structure by piezoresponse force microscopy. The fabrication of continuous thin films of the hydrogen-bonded croconic acid was achieved by the suppression of the thermal decomposition using low evaporation temperatures in high vacuum, combined with growth conditions far from thermal equilibrium. For nominal coverages ≥20 nm, quasi 2D and polycrystalline films, with an average grain size of 50–100 nm and 3.5 nm roughness, can be obtained. Spontaneous ferroelectric domain structures of the thin films have been observed and appear to correlate with the grain patterns. The application of this solvent-free growth protocol may be a key to the development of flexible organic ferroelectric thin films for electronic applications.

  9. Room temperature ferroelectricity in continuous croconic acid thin films

    NASA Astrophysics Data System (ADS)

    Jiang, Xuanyuan; Lu, Haidong; Yin, Yuewei; Zhang, Xiaozhe; Wang, Xiao; Yu, Le; Ahmadi, Zahra; Costa, Paulo S.; DiChiara, Anthony D.; Cheng, Xuemei; Gruverman, Alexei; Enders, Axel; Xu, Xiaoshan

    2016-09-01

    Ferroelectricity at room temperature has been demonstrated in nanometer-thin quasi 2D croconic acid thin films, by the polarization hysteresis loop measurements in macroscopic capacitor geometry, along with observation and manipulation of the nanoscale domain structure by piezoresponse force microscopy. The fabrication of continuous thin films of the hydrogen-bonded croconic acid was achieved by the suppression of the thermal decomposition using low evaporation temperatures in high vacuum, combined with growth conditions far from thermal equilibrium. For nominal coverages ≥20 nm, quasi 2D and polycrystalline films, with an average grain size of 50-100 nm and 3.5 nm roughness, can be obtained. Spontaneous ferroelectric domain structures of the thin films have been observed and appear to correlate with the grain patterns. The application of this solvent-free growth protocol may be a key to the development of flexible organic ferroelectric thin films for electronic applications.

  10. A stable room-temperature sodium–sulfur battery

    PubMed Central

    Wei, Shuya; Xu, Shaomao; Agrawral, Akanksha; Choudhury, Snehashis; Lu, Yingying; Tu, Zhengyuan; Ma, Lin; Archer, Lynden A.

    2016-01-01

    High-energy rechargeable batteries based on earth-abundant materials are important for mobile and stationary storage technologies. Rechargeable sodium–sulfur batteries able to operate stably at room temperature are among the most sought-after platforms because such cells take advantage of a two-electron-redox process to achieve high storage capacity from inexpensive electrode materials. Here we report a room-temperature sodium–sulfur battery that uses a microporous carbon–sulfur composite cathode, and a liquid carbonate electrolyte containing the ionic liquid 1-methyl-3-propylimidazolium-chlorate tethered to SiO2 nanoparticles. We show that these cells can cycle stably at a rate of 0.5 C (1 C=1675, mAh g−1) with 600 mAh g−1 reversible capacity and nearly 100% Coulombic efficiency. By means of spectroscopic and electrochemical analysis, we find that the particles form a sodium-ion conductive film on the anode, which stabilizes deposition of sodium. We also find that sulfur remains interred in the carbon pores and undergo solid-state electrochemical reactions with sodium ions. PMID:27277345

  11. Unconditional polarization qubit quantum memory at room temperature

    NASA Astrophysics Data System (ADS)

    Namazi, Mehdi; Kupchak, Connor; Jordaan, Bertus; Shahrokhshahi, Reihaneh; Figueroa, Eden

    2016-05-01

    The creation of global quantum key distribution and quantum communication networks requires multiple operational quantum memories. Achieving a considerable reduction in experimental and cost overhead in these implementations is thus a major challenge. Here we present a polarization qubit quantum memory fully-operational at 330K, an unheard frontier in the development of useful qubit quantum technology. This result is achieved through extensive study of how optical response of cold atomic medium is transformed by the motion of atoms at room temperature leading to an optimal characterization of room temperature quantum light-matter interfaces. Our quantum memory shows an average fidelity of 86.6 +/- 0.6% for optical pulses containing on average 1 photon per pulse, thereby defeating any classical strategy exploiting the non-unitary character of the memory efficiency. Our system significantly decreases the technological overhead required to achieve quantum memory operation and will serve as a building block for scalable and technologically simpler many-memory quantum machines. The work was supported by the US-Navy Office of Naval Research, Grant Number N00141410801 and the Simons Foundation, Grant Number SBF241180. B. J. acknowledges financial assistance of the National Research Foundation (NRF) of South Africa.

  12. A stable room-temperature sodium-sulfur battery

    NASA Astrophysics Data System (ADS)

    Wei, Shuya; Xu, Shaomao; Agrawral, Akanksha; Choudhury, Snehashis; Lu, Yingying; Tu, Zhengyuan; Ma, Lin; Archer, Lynden A.

    2016-06-01

    High-energy rechargeable batteries based on earth-abundant materials are important for mobile and stationary storage technologies. Rechargeable sodium-sulfur batteries able to operate stably at room temperature are among the most sought-after platforms because such cells take advantage of a two-electron-redox process to achieve high storage capacity from inexpensive electrode materials. Here we report a room-temperature sodium-sulfur battery that uses a microporous carbon-sulfur composite cathode, and a liquid carbonate electrolyte containing the ionic liquid 1-methyl-3-propylimidazolium-chlorate tethered to SiO2 nanoparticles. We show that these cells can cycle stably at a rate of 0.5 C (1 C=1675, mAh g-1) with 600 mAh g-1 reversible capacity and nearly 100% Coulombic efficiency. By means of spectroscopic and electrochemical analysis, we find that the particles form a sodium-ion conductive film on the anode, which stabilizes deposition of sodium. We also find that sulfur remains interred in the carbon pores and undergo solid-state electrochemical reactions with sodium ions.

  13. Room-temperature Magnetic Ordering in Functionalized Graphene

    PubMed Central

    Hong, Jeongmin; Bekyarova, Elena; Liang, Ping; de Heer, Walt A.; Haddon, Robert C.; Khizroev, Sakhrat

    2012-01-01

    Despite theoretical predictions, the question of room-temperature magnetic order in graphene must be conclusively resolved before graphene can fully achieve its potential as a spintronic medium. Through scanning tunneling microscopy (STM) and point I-V measurements, the current study reveals that unlike pristine samples, graphene nanostructures, when functionalized with aryl radicals, can sustain magnetic order. STM images show 1-D and 2-D periodic super-lattices originating from the functionalization of a single sub-lattice of the bipartite graphene structure. Field-dependent super-lattices in 3-nm wide “zigzag” nanoribbons indicate local moments with parallel and anti-parallel ordering along and across the edges, respectively. Anti-parallel ordering is observed in 2-D segments with sizes of over 20 nm. The field dependence of STM images and point I-V curves indicates a spin polarized local density of states (LDOS), an out-of-plane anisotropy field of less than 10 Oe, and an exchange coupling field of 100 Oe at room temperature. PMID:22953045

  14. [Preservation and stability of corn tortillas at room temperature].

    PubMed

    Higuera-Ciapara, I; Nieblas, J M

    1995-06-01

    Three treatments with chemical preservative (sodium propionate, potassium sorbate-methylparaben and hydrogen peroxidemethyl paraben) were tested to delay microbial spoilage and extend shelf-life of corn tortillas at room temperature (25 degrees C). The treatment with the best results was selected for further studies using two types of packaging: Paper and high density polyethylene. Quality of corn tortillas during storage was assessed by measuring water content, microbial analysis (Total Plate Count, molds and yeast) and throguh sensory evaluation. Results were analyzed by covariance analysis and slope contrast between packaging materials at p<0.05. Spoilage of tortilla without preservative occurred within 24 hours due to a large number of gram negative bacteria, molds and yeasts, which were responsible for offensive odors. Only the combination of hydrogen peroxide-methyl paraben had a significant effect on retarding bacterial yeast spoilage. In addition, hydrogen peroxide residues could not [correction of no] be chemically detected after 2 days of storage. Results from this study show that tortilla can be kept for up to six days at room temperature with acceptable sensory properties with proper preservative treatment and packaging.

  15. Experiments on room temperature optical fiber-fiber direct bonding

    NASA Astrophysics Data System (ADS)

    Hao, Jinping; Yan, Ping; Xiao, Qirong; Wang, Yaping; Gong, Mali

    2012-08-01

    High quality permanent connection between optical fibers is a significant issue in optics and communication. Studies on room temperature optical large diameter fiber-fiber direct bonding, which is essentially surface interactions of glass material, are presented here. Bonded fiber pairs are obtained for the first time through the bonding technics illustrated here. Two different kinds of bonding technics are provided-fresh surface (freshly grinded and polished) bonding and hydrophobic surface (activated by H2SO4 and HF) bonding. By means of fresh surface bonding, a bonded fiber pair with light transmitting efficiency of 98.1% and bond strength of 21.2 N is obtained. Besides, in the bonding process, chemical surface treatment of fibers' end surfaces is an important step. Therefore, various ways of surface treatment are analyzed and compared, based on atomic force microscopy force curves of differently disposed surfaces. According to the comparison, fresh surfaces are suggested as the prior choice in room temperature optical fiber-fiber bonding, owing to their larger adhesive force, attractive force, attractive distance, and adhesive range.

  16. Optically pumped room-temperature GaAs nanowire lasers

    NASA Astrophysics Data System (ADS)

    Saxena, Dhruv; Mokkapati, Sudha; Parkinson, Patrick; Jiang, Nian; Gao, Qiang; Tan, Hark Hoe; Jagadish, Chennupati

    2013-12-01

    Near-infrared lasers are important for optical data communication, spectroscopy and medical diagnosis. Semiconductor nanowires offer the possibility of reducing the footprint of devices for three-dimensional device integration and hence are being extensively studied in the context of optoelectronic devices. Although visible and ultraviolet nanowire lasers have been demonstrated widely, progress towards room-temperature infrared nanowire lasers has been limited because of material quality issues and Auger recombination. (Al)GaAs is an important material system for infrared lasers that is extensively used for conventional lasers. GaAs has a very large surface recombination velocity, which is a serious issue for nanowire devices because of their large surface-to-volume ratio. Here, we demonstrate room-temperature lasing in core-shell-cap GaAs/AlGaAs/GaAs nanowires by properly designing the Fabry-Pérot cavity, optimizing the material quality and minimizing surface recombination. Our demonstration is a major step towards incorporating (Al)GaAs nanowire lasers into the design of nanoscale optoelectronic devices operating at near-infrared wavelengths.

  17. Exfoliated black phosphorus gas sensing properties at room temperature

    NASA Astrophysics Data System (ADS)

    Donarelli, M.; Ottaviano, L.; Giancaterini, L.; Fioravanti, G.; Perrozzi, F.; Cantalini, C.

    2016-06-01

    Room temperature gas sensing properties of chemically exfoliated black phosphorus (BP) to oxidizing (NO2, CO2) and reducing (NH3, H2, CO) gases in a dry air carrier have been reported. To study the gas sensing properties of BP, chemically exfoliated BP flakes have been drop casted on Si3N4 substrates provided with Pt comb-type interdigitated electrodes in N2 atmosphere. Scanning electron microscopy and x-ray photoelectron spectroscopy characterizations show respectively the occurrence of a mixed structure, composed of BP coarse aggregates dispersed on BP exfoliated few layer flakes bridging the electrodes, and a clear 2p doublet belonging to BP, which excludes the occurrence of surface oxidation. Room temperature electrical tests in dry air show a p-type response of multilayer BP with measured detection limits of 20 ppb and 10 ppm to NO2 and NH3 respectively. No response to CO and CO2 has been detected, while a slight but steady sensitivity to H2 has been recorded. The reported results confirm, on an experimental basis, what was previously theoretically predicted, demonstrating the promising sensing properties of exfoliated BP.

  18. Identifying multiexcitons in Mo S2 monolayers at room temperature

    NASA Astrophysics Data System (ADS)

    Lee, Hyun Seok; Kim, Min Su; Kim, Hyun; Lee, Young Hee

    2016-04-01

    One of the unique features of atomically thin two-dimensional materials is strong Coulomb interactions due to the reduced dielectric screening effect; this feature enables the study of many-body phenomena such as excitons, trions, and biexcitons. However, identification of biexcitons remains unresolved owing to their broad peak feature at room temperature. Here, we investigate multiexcitons in monolayer Mo S2 using both electrical and optical doping and identify the transition energies for each exciton. The binding energy of the assigned biexciton is twice that of the trion, in quantitative agreement with theoretical predictions. The biexciton population is predominant under optical doping but negligible under electrical doping. The biexciton population is quadratically proportional to the exciton population, obeying the mass-action theory. Our results illustrate the stable formation of not only trions but also biexcitons due to strong Coulomb interaction even at room temperature; therefore, these results provide a deeper understanding of the complex excitonic behaviors in two-dimensional semiconductors.

  19. Self-transducing silicon nanowire electromechanical systems at room temperature.

    PubMed

    He, Rongrui; Feng, X L; Roukes, M L; Yang, Peidong

    2008-06-01

    Electronic readout of the motions of genuinely nanoscale mechanical devices at room temperature imposes an important challenge for the integration and application of nanoelectromechanical systems (NEMS). Here, we report the first experiments on piezoresistively transduced very high frequency Si nanowire (SiNW) resonators with on-chip electronic actuation at room temperature. We have demonstrated that, for very thin (~90 nm down to ~30 nm) SiNWs, their time-varying strain can be exploited for self-transducing the devices' resonant motions at frequencies as high as approximately 100 MHz. The strain of wire elongation, which is only second-order in doubly clamped structures, enables efficient displacement transducer because of the enhanced piezoresistance effect in these SiNWs. This intrinsically integrated transducer is uniquely suited for a class of very thin wires and beams where metallization and multilayer complex patterning on devices become impractical. The 30 nm thin SiNW NEMS offer exceptional mass sensitivities in the subzeptogram range. This demonstration makes it promising to advance toward NEMS sensors based on ultrathin and even molecular-scale SiNWs, and their monolithic integration with microelectronics on the same chip.

  20. A stable room-temperature sodium-sulfur battery.

    PubMed

    Wei, Shuya; Xu, Shaomao; Agrawral, Akanksha; Choudhury, Snehashis; Lu, Yingying; Tu, Zhengyuan; Ma, Lin; Archer, Lynden A

    2016-06-09

    High-energy rechargeable batteries based on earth-abundant materials are important for mobile and stationary storage technologies. Rechargeable sodium-sulfur batteries able to operate stably at room temperature are among the most sought-after platforms because such cells take advantage of a two-electron-redox process to achieve high storage capacity from inexpensive electrode materials. Here we report a room-temperature sodium-sulfur battery that uses a microporous carbon-sulfur composite cathode, and a liquid carbonate electrolyte containing the ionic liquid 1-methyl-3-propylimidazolium-chlorate tethered to SiO2 nanoparticles. We show that these cells can cycle stably at a rate of 0.5 C (1 C=1675, mAh g(-1)) with 600 mAh g(-1) reversible capacity and nearly 100% Coulombic efficiency. By means of spectroscopic and electrochemical analysis, we find that the particles form a sodium-ion conductive film on the anode, which stabilizes deposition of sodium. We also find that sulfur remains interred in the carbon pores and undergo solid-state electrochemical reactions with sodium ions.

  1. The heat is on: room temperature affects laboratory equipment--an observational study.

    PubMed

    Butler, Julia M; Johnson, Jane E; Boone, William R

    2013-10-01

    To evaluate the effect of ambient room temperature on equipment typically used in in vitro fertilization (IVF). We set the control temperature of the room to 20 °C (+/-0.3) and used CIMScan probes to record temperatures of the following equipment: six microscope heating stages, four incubators, five slide warmers and three heating blocks. We then increased the room temperature to 26 °C (+/-0.3) or decreased it to 17 °C (+/-0.3) and monitored the same equipment again. We wanted to determine what role, if any, changing room temperature has on equipment temperature fluctuation. There was a direct relationship between room temperature and equipment temperature stability. When room temperature increased or decreased, equipment temperature reacted in a corresponding manner. Statistical differences between equipment were found when the room temperature changed. What is also noteworthy is that temperature of equipment responded within 5 min to a change in room temperature. Clearly, it is necessary to be aware of the affect of room temperature on equipment when performing assisted reproductive procedures. Room and equipment temperatures should be monitored faithfully and adjusted as frequently as needed, so that consistent culture conditions can be maintained. If more stringent temperature control can be achieved, human assisted reproduction success rates may improve.

  2. Characterization of ZnO:Co particles prepared by hydrothermal method for room temperature magnetism

    NASA Astrophysics Data System (ADS)

    Peng, Yingzi; Huo, Dexuan; He, Haiping; Li, Yuan; Li, Lingwei; Wang, Huawen; Qian, Zhenghong

    2012-03-01

    ZnO based diluted magnetic semiconductor particles (ZnO:Co) have been grown using a hydrothermal method with good crystallinity. The atomic percentage of Co presented in the specimen is about 0.01. Based on the x-ray diffraction and high-resolution transition electron, Co is found to be incorporated into ZnO lattice without evidence of obvious Co precipitates. However, from photoluminescence (PL) spectra in the range of 1.94 -3.45 eV, a strong broad emission centered around 600 nm (2.07 eV) in the visible range as well as a relatively weak peak at 2.81 eV are observed, indicating the presence of Co impurities. Moreover, intrinsic emissions such as DOX suggest that at least some Co have been doped into ZnO lattice, substituting for Zn2+ ions. The PL results further confirm the substitution of Zn2+ ions by Co, which leads to the changes of the electronic band structures. Magnetism could be realized at room temperature for the ZnO:Co nanoparticles under our experimental conditions although with low coercivity. The field-cooled and zero-field-cooled curves can be explained as a result of competition between the ferromagnetic and the antiferromagnetic ordering in the ZnO:Co nanoparticles. Combining the results from PL and magnetism characterization, it is reasonable to think that both doped Co in the ZnO lattice and Co impurities contribute to magnetism in ZnO:Co nanoparticles at room temperature.

  3. Advances in materials for room temperature hydrogen sensors.

    PubMed

    Arya, Sunil K; Krishnan, Subramanian; Silva, Hayde; Jean, Sheila; Bhansali, Shekhar

    2012-06-21

    Hydrogen (H(2)), as a source of energy, continues to be a compelling choice in applications ranging from fuel cells and propulsion systems to feedstock for chemical, metallurgical and other industrial processes. H(2), being a clean, reliable, and affordable source, is finding ever increasing use in distributed electric power generation and H(2) fuelled cars. Although still under 0.1%, the distributed use of H(2) is the fastest growing area. In distributed H(2) storage, distribution, and consumption, safety continues to be a critical aspect. Affordable safety systems for distributed H(2) applications are critical for the H(2) economy to take hold. Advances in H(2) sensors are driven by specificity, reliability, repeatability, stability, cost, size, response time, recovery time, operating temperature, humidity range, and power consumption. Ambient temperature sensors for H(2) detection are increasingly being explored as they offer specificity, stability and robustness of high temperature sensors with lower operational costs and significantly longer operational lifetimes. This review summarizes and highlights recent developments in room temperature H(2) sensors.

  4. Nearly ferromagnetic Fermi-liquid behaviour in YFe2Zn20 and high-temperature ferromagnetism of GdFe2Zn20

    NASA Astrophysics Data System (ADS)

    Jia, S.; Bud'Ko, S. L.; Samolyuk, G. D.; Canfield, P. C.

    2007-05-01

    One of the historic goals of alchemy was to turn base elements into precious ones. Although the practice of alchemy has been superseded by chemistry and solid-state physics, the desire to dramatically change or tune the properties of a compound, preferably through small changes in stoichiometry or composition, remains. This desire becomes even more compelling for compounds that can be tuned to extremes in behaviour. Here, we report that the RT2Zn20 (R=rare earth and T=transition metal) family of compounds manifests exactly this type of versatility, even though they are more than 85% Zn. By tuning T, we find that YFe2Zn20 is closer to ferromagnetism than elemental Pd, the classic example of a nearly ferromagnetic Fermi liquid. By submerging Gd in this highly polarizable Fermi liquid, we tune the system to a remarkably high-temperature ferromagnetic (TC=86K) state for a compound with less than 5% Gd. Although this is not quite turning lead into gold, it is essentially tuning Zn to become a variety of model compounds.

  5. Insight into the temperature dependent properties of the ferromagnetic Kondo lattice YbNiSn

    NASA Astrophysics Data System (ADS)

    Generalov, A.; Sokolov, D. A.; Chikina, A.; Kucherenko, Yu.; Antonov, V. N.; Bekenov, L. V.; Patil, S.; Huxley, A. D.; Allen, J. W.; Matho, K.; Kummer, K.; Vyalikh, D. V.; Laubschat, C.

    2017-05-01

    Analyzing temperature dependent photoemission (PE) data of the ferromagnetic Kondo-lattice (KL) system YbNiSn in the light of the periodic Anderson model (PAM) we show that the KL behavior is not limited to temperatures below a temperature T¯K, defined empirically from resistivity and specific heat measurements. As characteristic for weakly hybridized Ce and Yb systems, the PE spectra reveal a 4 f -derived Fermi level peak, which reflects contributions from the Kondo resonance and its crystal electric field (CEF) satellites. In YbNiSn this peak has an unusual temperature dependence: With decreasing temperature a steady linear increase of intensity is observed which extends over a large interval ranging from 100 K down to 1 K without showing any peculiarities in the region of T¯K˜TC=5.6 K. In the light of the single-impurity Anderson model (SIAM) this intensity variation reflects a linear increase of 4 f occupancy with decreasing temperature, indicating an onset of Kondo screening at temperatures above 100 K. Within the PAM this phenomenon could be described by a non-Fermi-liquid-like T - linear damping of the self-energy which accounts phenomenologically for the feedback from the closely spaced CEF states.

  6. Coexistence of ferromagnetism and superconductivity in YBCO nanoparticles.

    PubMed

    Zhu, Zhonghua; Gao, Daqiang; Dong, Chunhui; Yang, Guijin; Zhang, Jing; Zhang, Jinlin; Shi, Zhenhua; Gao, Hua; Luo, Honggang; Xue, Desheng

    2012-03-21

    Nanoparticles of superconducting YBa(2)Cu(3)O(7-δ) were synthesized via a citrate pyrolysis technique. Room temperature ferromagnetism was revealed in the samples by a vibrating sample magnetometer. Electron spin resonance spectra at selected temperatures indicated that there is a transition from the normal to the superconducting state at temperatures below 100 K. The M-T curves with various applied magnetic fields showed that the superconducting transition temperatures are 92 K and 55 K for the air-annealed and the post-annealed samples, respectively. Compared to the air-annealed sample, the saturation magnetization of the sample by reheating the air-annealed one in argon atmosphere is enhanced but its superconductivity is weakened, which implies that the ferromagnetism maybe originates from the surface oxygen defects. By superconducting quantum interference device measurements, we further confirmed the ferromagnetic behavior at high temperatures and interesting upturns in field cooling magnetization curves within the superconducting region are found. We attributed the upturn phenomena to the coexistence of ferromagnetism and superconductivity at low temperatures. Room temperature ferromagnetism of superconducting YBa(2)Cu(3)O(7-δ) nanoparticles has been observed in some previous related studies, but the issue of the coexistence of ferromagnetism and superconductivity within the superconducting region is still unclear. In the present work, it will be addressed in detail. The cooperation phenomena found in the spin-singlet superconductors will help us to understand the nature of superconductivity and ferromagnetism in more depth.

  7. Tuning structural instability toward enhanced magnetocaloric effect around room temperature in MnCo1-xZnxGe

    NASA Astrophysics Data System (ADS)

    Choudhury, D.; Suzuki, T.; Tokura, Y.; Taguchi, Y.

    2014-12-01

    Magnetocaloric effect is the phenomenon that temperature change of a magnetic material is induced by application of a magnetic field. This effect can be applied to environmentally-benign magnetic refrigeration technology. Here we show a key role of magnetic-field-induced structural instability in enhancing the magnetocaloric effect for MnCo1-xZnxGe alloys (x = 0-0.05). The increase in x rapidly reduces the martensitic transition temperature while keeping the ferromagnetic transition around room temperature. Fine tuning of x around x = 0.03 leads to the concomitant structural and ferromagnetic transition in a cooling process, giving rise to enhanced magnetocaloric effect as well as magnetic-field-induced structural transition. Analyses of the structural phase diagrams in the T-H plane in terms of Landau free-energy phenomenology accounts for the characteristic x-dependence of the observed magnetocaloric effect, pointing to the importance of the magnetostructural coupling for the design of high-performance magnetocalorics.

  8. Tuning structural instability toward enhanced magnetocaloric effect around room temperature in MnCo1−xZnxGe

    PubMed Central

    Choudhury, D.; Suzuki, T.; Tokura, Y.; Taguchi, Y.

    2014-01-01

    Magnetocaloric effect is the phenomenon that temperature change of a magnetic material is induced by application of a magnetic field. This effect can be applied to environmentally-benign magnetic refrigeration technology. Here we show a key role of magnetic-field-induced structural instability in enhancing the magnetocaloric effect for MnCo1−xZnxGe alloys (x = 0–0.05). The increase in x rapidly reduces the martensitic transition temperature while keeping the ferromagnetic transition around room temperature. Fine tuning of x around x = 0.03 leads to the concomitant structural and ferromagnetic transition in a cooling process, giving rise to enhanced magnetocaloric effect as well as magnetic-field-induced structural transition. Analyses of the structural phase diagrams in the T-H plane in terms of Landau free-energy phenomenology accounts for the characteristic x-dependence of the observed magnetocaloric effect, pointing to the importance of the magnetostructural coupling for the design of high-performance magnetocalorics. PMID:25519919

  9. Evidence for Stable High Temperature Ferromagnetism in Fluorine Treated C60 (Preprint)

    DTIC Science & Technology

    2013-01-02

    Gauss showing a small hysteresis . Figure 4 presents the temperature dependence of the magnetization above room temperature measured in a 3000 Gauss...through the center of the microwave cavity. The magnetization was obtained by measuring the magnetic field dependence of the AC susceptibility at 350...which is proportional to the change in susceptibility, is measured as a function of dc magnetic field strength using a HP 5314 frequency counter. The

  10. Room-temperature effects of UV radiation in KBr:? crystals

    NASA Astrophysics Data System (ADS)

    Pérez-Salas, R.; Meléndrez, R.; Aceves, R.; Rodriguez, R.; Barboza-Flores, M.

    1996-07-01

    Thermoluminescence and optical absorption measurements have been carried out in KBr:0953-8984/8/27/009/img9 crystals irradiated with monochromatic UV light (200 - 300 nm) and x-rays at room temperature. For UV- and x-irradiated crystals strong similarities between the thermoluminescence glow curves have been found, suggesting that the low-energy UV radiation produces the same defects as produced by x-irradiation in this material. The thermoluminescence glow curves are composed of six glow peaks located at 337, 383, 403, 435, 475 and 509 K. Thermal annealing experiments in previously irradiated crystals show clearly a correlation between the glow peak located at 383 K and the F-centre thermal bleaching process. Also, the excitation spectrum for each thermoluminescence glow peak has been investigated, showing that the low-energy radiation induces the formation of F centres.

  11. Quantum memory, entanglement and sensing with room temperature atoms

    NASA Astrophysics Data System (ADS)

    Jensen, K.; Wasilewski, W.; Krauter, H.; Fernholz, T.; Nielsen, B. M.; Petersen, J. M.; Renema, J. J.; Balabas, M. V.; Owari, M.; Plenio, M. B.; Serafini, A.; Wolf, M. M.; Muschik, C. A.; Cirac, J. I.; Müller, J. H.; Polzik, E. S.

    2011-01-01

    Room temperature atomic ensembles in a spin-protected environment are useful systems both for quantum information science and metrology. Here we utilize a setup consisting of two atomic ensembles as a memory for quantum information initially encoded in the polarization state of two entangled light modes. We also use the ensembles as a radio frequency entanglement-assisted magnetometer with projection noise limited sensitivity below femtoTesla/. The performance of the quantum memory as well as the magnetometer was improved by spin-squeezed or entangled atomic states generated by quantum non demolition measurements. Finally, we present preliminary results of long lived entangled atomic states generated by dissipation. With the method presented, one should be able to generate an entangled steady state.

  12. Pressure-responsive mesoscopic structures in room temperature ionic liquids.

    PubMed

    Russina, Olga; Lo Celso, Fabrizio; Triolo, Alessandro

    2015-11-28

    Among the most spectacular peculiarities of room temperature ionic liquids, their mesoscopically segregated structural organization keeps on attracting attention, due to its major consequences for the bulk macroscopic properties. Herein we use molecular dynamics simulations to explore the nm-scale architecture in 1-octyl-3-methylimidazolium tetrafluoroborate, as a function of pressure. This study reveals an intriguing new feature: the mesoscopic segregation in ionic liquids is characterized by a high level of pressure-responsiveness, which progressively vanishes upon application of high enough pressure. These results are in agreement with recent X-ray scattering data and are interpreted in terms of the microscopic organization. This new feature might lead to new methods of developing designer solvents for enhanced solvation capabilities and selectivity.

  13. Mesoscopic structural organization in triphilic room temperature ionic liquids.

    PubMed

    Russina, Olga; Lo Celso, Fabrizio; Di Michiel, Marco; Passerini, Stefano; Appetecchi, Giovanni Battista; Castiglione, Franca; Mele, Andrea; Caminiti, Ruggero; Triolo, Alessandro

    2013-01-01

    Room temperature ionic liquids are one of the most exciting classes of materials in the last decade. The interest for these low melting, ionic compounds stems from both their technological impact and the stimulating plethora of structural and dynamic peculiarities in the mesoscopic space-time scales. It is nowadays well-established that they are characterised by an enhanced degree of mesoscopic order originating from their inherent amphiphilicity. In this contribution we highlight the existence of a further degree of mesoscopic complexity when dealing with RTILs bearing a medium length fluorous tail: such triphilic materials (they simultaneously contain polar, hydrophobic and fluorophilic moieties that mutually segregate from each other) turn out to be highly structurally compartmentalised at the mesoscopic level, thus paving the way to new smart applications for this new class of RTILs.

  14. Cavity-Enhanced Room-Temperature Broadband Raman Memory

    NASA Astrophysics Data System (ADS)

    Saunders, D. J.; Munns, J. H. D.; Champion, T. F. M.; Qiu, C.; Kaczmarek, K. T.; Poem, E.; Ledingham, P. M.; Walmsley, I. A.; Nunn, J.

    2016-03-01

    Broadband quantum memories hold great promise as multiplexing elements in future photonic quantum information protocols. Alkali-vapor Raman memories combine high-bandwidth storage, on-demand readout, and operation at room temperature without collisional fluorescence noise. However, previous implementations have required large control pulse energies and have suffered from four-wave-mixing noise. Here, we present a Raman memory where the storage interaction is enhanced by a low-finesse birefringent cavity tuned into simultaneous resonance with the signal and control fields, dramatically reducing the energy required to drive the memory. By engineering antiresonance for the anti-Stokes field, we also suppress the four-wave-mixing noise and report the lowest unconditional noise floor yet achieved in a Raman-type warm vapor memory, (15 ±2 )×10-3 photons per pulse, with a total efficiency of (9.5 ±0.5 )%.

  15. Realization of a flux-driven memtranstor at room temperature

    NASA Astrophysics Data System (ADS)

    Shi-Peng, Shen; Da-Shan, Shang; Yi-Sheng, Chai; Young, Sun

    2016-02-01

    The memtranstor has been proposed to be the fourth fundamental circuit memelement in addition to the memristor, memcapacitor, and meminductor. Here, we demonstrate the memtranstor behavior at room temperature in a device made of the magnetoelectric hexaferrite (Ba0.5Sr1.5Co2Fe11AlO22) where the electric polarization is tunable by external magnetic field. This device shows a nonlinear q-φ relationship with a butterfly-shaped hysteresis loop, in agreement with the anticipated memtranstor behavior. The memtranstor, like other memelements, has a great potential in developing more advanced circuit functionalities. Project supported by the National Natural Science Foundation of China (Grants Nos. 11227405, 11534015, 11274363, and 11374347) and the Natural Science Foundation from the Chinese Academy of Sciences (Grant No. XDB07030200).

  16. Using room temperature current noise to characterize single molecular spectra.

    PubMed

    Vasudevan, Smitha; Ghosh, Avik W

    2014-03-25

    We propose a way to use room temperature random telegraph noise to characterize single molecules adsorbed on a backgated silicon field-effect transistor. The overlap of molecule and silicon electronic wave functions generates a set of trap levels that impose their unique scattering signatures on the voltage-dependent current noise spectrum. Our results are based on numerical modeling of the current noise, obtained by coupling a density functional treatment of the trap placement within the silicon band gap, a quantum kinetic treatment of the output current, and a Monte Carlo evaluation of the trap occupancy under resonance. As an illustrative example, we show how we can extract molecule-specific "fingerprints" of four benzene-based molecules directly from a frequency-voltage colormap of the noise statistics. We argue that such a colormap carries detailed information about the trap dynamics at the Fermi energy, including the presence of correlated interactions, observed experimentally in backgated carbon nanotubes.

  17. Thermoelectricity in atom-sized junctions at room temperatures

    PubMed Central

    Tsutsui, Makusu; Morikawa, Takanori; Arima, Akihide; Taniguchi, Masateru

    2013-01-01

    Atomic and molecular junctions are an emerging class of thermoelectric materials that exploit quantum confinement effects to obtain an enhanced figure of merit. An important feature in such nanoscale systems is that the electron and heat transport become highly sensitive to the atomic configurations. Here we report the characterization of geometry-sensitive thermoelectricity in atom-sized junctions at room temperatures. We measured the electrical conductance and thermoelectric power of gold nanocontacts simultaneously down to the single atom size. We found junction conductance dependent thermoelectric voltage oscillations with period 2e2/h. We also observed quantum suppression of thermovoltage fluctuations in fully-transparent contacts. These quantum confinement effects appeared only statistically due to the geometry-sensitive nature of thermoelectricity in the atom-sized junctions. The present method can be applied to various nanomaterials including single-molecules or nanoparticles and thus may be used as a useful platform for developing low-dimensional thermoelectric building blocks. PMID:24270238

  18. Ratcheting fatigue behavior of Zircaloy-2 at room temperature

    NASA Astrophysics Data System (ADS)

    Rajpurohit, R. S.; Sudhakar Rao, G.; Chattopadhyay, K.; Santhi Srinivas, N. C.; Singh, Vakil

    2016-08-01

    Nuclear core components of zirconium alloys experience asymmetric stress or strain cycling during service which leads to plastic strain accumulation and drastic reduction in fatigue life as well as dimensional instability of the component. Variables like loading rate, mean stress, and stress amplitude affect the influence of asymmetric loading. In the present investigation asymmetric stress controlled fatigue tests were conducted with mean stress from 80 to 150 MPa, stress amplitude from 270 to 340 MPa and stress rate from 30 to 750 MPa/s to study the process of plastic strain accumulation and its effect on fatigue life of Zircaloy-2 at room temperature. It was observed that with increase in mean stress and stress amplitude accumulation of ratcheting strain was increased and fatigue life was reduced. However, increase in stress rate led to improvement in fatigue life due to less accumulation of ratcheting strain.

  19. Microstructure of room temperature ionic liquids at stepped graphite electrodes

    SciTech Connect

    Feng, Guang; Li, Song; Zhao, Wei; Cummings, Peter T.

    2015-07-14

    Molecular dynamics simulations of room temperature ionic liquid (RTIL) [emim][TFSI] at stepped graphite electrodes were performed to investigate the influence of the thickness of the electrode surface step on the microstructure of interfacial RTILs. A strong correlation was observed between the interfacial RTIL structure and the step thickness in electrode surface as well as the ion size. Specifically, when the step thickness is commensurate with ion size, the interfacial layering of cation/anion is more evident; whereas, the layering tends to be less defined when the step thickness is close to the half of ion size. Furthermore, two-dimensional microstructure of ion layers exhibits different patterns and alignments of counter-ion/co-ion lattice at neutral and charged electrodes. As the cation/anion layering could impose considerable effects on ion diffusion, the detailed information of interfacial RTILs at stepped graphite presented here would help to understand the molecular mechanism of RTIL-electrode interfaces in supercapacitors.

  20. Room-temperature spin-photon interface for quantum networks

    NASA Astrophysics Data System (ADS)

    Hong, Fang-Yu; Fu, Jing-Li; Wu, Yan; Zhu, Zhi-Yan

    2017-02-01

    Although remarkable progress has been achieved recently, to construct an optical cavity where a nitrogen-vacancy (NV) colour centre in diamond is coupled to an optical field in the strong coupling regime is rather difficult. We propose an architecture for a scalable quantum interface capable of interconverting photonic and NV spin qubits, which can work well without the strong coupling requirement. The dynamics of the interface applies an adiabatic passage to sufficiently reduce the decoherence from an excited state of a NV colour centre in diamond. This quantum interface can accomplish many quantum network operations like state transfer and entanglement distribution between qubits at distant nodes. Exact numerical simulations show that high-fidelity quantum interface operations can be achieved under room-temperature and realistic experimental conditions.