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Sample records for room temperature magnetic

  1. 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

  2. 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

  3. Room-temperature chiral magnetic skyrmions in ultrathin magnetic nanostructures

    NASA Astrophysics Data System (ADS)

    Boulle, Olivier; Vogel, Jan; Yang, Hongxin; Pizzini, Stefania; de Souza Chaves, Dayane; Locatelli, Andrea; Menteş, Tevfik Onur; Sala, Alessandro; Buda-Prejbeanu, Liliana D.; Klein, Olivier; Belmeguenai, Mohamed; Roussigné, Yves; Stashkevich, Andrey; Chérif, Salim Mourad; Aballe, Lucia; Foerster, Michael; Chshiev, Mairbek; Auffret, Stéphane; Miron, Ioan Mihai; Gaudin, Gilles

    2016-05-01

    Magnetic skyrmions are chiral spin structures with a whirling configuration. Their topological properties, nanometre size and the fact that they can be moved by small current densities have opened a new paradigm for the manipulation of magnetization at the nanoscale. Chiral skyrmion structures have so far been experimentally demonstrated only in bulk materials and in epitaxial ultrathin films, and under an external magnetic field or at low temperature. Here, we report on the observation of stable skyrmions in sputtered ultrathin Pt/Co/MgO nanostructures at room temperature and zero external magnetic field. We use high lateral resolution X-ray magnetic circular dichroism microscopy to image their chiral Néel internal structure, which we explain as due to the large strength of the Dzyaloshinskii–Moriya interaction as revealed by spin wave spectroscopy measurements. Our results are substantiated by micromagnetic simulations and numerical models, which allow the identification of the physical mechanisms governing the size and stability of the skyrmions.

  4. Room Temperature Magnetic Barrier Layers in Magnetic Tunnel Junctions

    SciTech Connect

    Nelson-Cheeseman, B. B.; Wong, F. J.; Chopdekar, R. V.; Arenholz, E.; Suzuki, Y.

    2010-03-09

    We investigate the spin transport and interfacial magnetism of magnetic tunnel junctions with highly spin polarized LSMO and Fe3O4 electrodes and a ferrimagnetic NiFe2O4 (NFO) barrier layer. The spin dependent transport can be understood in terms of magnon-assisted spin dependent tunneling where the magnons are excited in the barrier layer itself. The NFO/Fe3O4 interface displays strong magnetic coupling, while the LSMO/NFO interface exhibits clear decoupling as determined by a combination of X-ray absorption spectroscopy and X-ray magnetic circular dichroism. This decoupling allows for distinct parallel and antiparallel electrode states in this all-magnetic trilayer. The spin transport of these devices, dominated by the NFO barrier layer magnetism, leads to a symmetric bias dependence of the junction magnetoresistance at all temperatures.

  5. 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.

  6. 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

  7. Room-temperature and near-room-temperature molecule-based magnets.

    PubMed

    Harvey, Mark D; Crawford, T Daniel; Yee, Gordon T

    2008-07-01

    Additional members of the family of high- T c molecule-based magnets, V[acceptor] 2. yCH 2Cl 2 have been discovered in which the acceptor is a fluorophenyltricyanoethylene. Varying the number and position of the fluorine substitutions around the phenyl ring results in materials with significantly different magnetic ordering temperatures ( T c's) ranging from 160 to 300 K. Density functional theory calculations were performed on the neutral and anionic forms of the acceptors that reveal modest correlation between T c and three calculated quantities: the gas-phase electron affinity, the dihedral angle between the phenyl ring and the olefin, and the Mulliken spin densities on the nitrogen atoms. The electrochemistry of the acceptors has also been examined.

  8. Mn,Cd-metallothionein-2: a room temperature magnetic protein.

    PubMed

    Chang, Chia-Ching; Lee, Shang-Fan; Sun, Kein-Wen; Ho, Chien-Chang; Chen, Yu-Ting; Chang, Cheng-Hung; Kan, Lou-Sing

    2006-02-24

    Naturally occurring metallothionein (MT) is a metal binding protein, which binds to seven Zn2+ through 20 conserved cysteines and forms two metal binding clusters with a Zinc-Blende structure. We demonstrate that the MT, when substituting the Zn2+ ions by Mn2+ and Cd2+, exhibits magnetic hysteresis loop observable by SQUID from 10 to 330 K. The magnetic moment may have originated from the bridging effect of the sulfur atoms between the metal ions that leads to the alignment of the electron spins of the Mn2+ ions inside the clusters. The protein backbone may restrain the net spin moment of Mn2+ ions from thermal fluctuation. The modified magnetic-metallothionein is a novel approach to creating molecular magnets with operating temperatures up to 330 K. PMID:16403435

  9. Room-temperature simultaneously enhanced magnetization and electric polarization in BiFeO3 ceramic synthesized by magnetic annealing

    NASA Astrophysics Data System (ADS)

    Luo, Wanju; Wang, Dongliang; Wang, Fangwei; Liu, Tao; Cai, Jianwang; Zhang, Liyan; Liu, Yulong

    2009-05-01

    Multiferroic BiFeO3 ceramics were synthesized by high temperature magnetic annealing using nanosized precursor powders prepared through microwave combustion. Simultaneously enhanced magnetization and electric polarization were observed at room temperature in the sample annealed under an external magnetic field of 10 T. These enhanced properties might be originated from a spin structure severely modulated or the low temperature magnetic phase driven up to room temperature and above by the large external annealing magnetic fields. These results demonstrate that the strong magnetic annealing method is an alternative way to synthesize high performance BiFeO3 materials.

  10. Magnetic switching of ferroelectric domains at room temperature in multiferroic PZTFT

    PubMed Central

    Evans, D.M.; Schilling, A.; Kumar, Ashok; Sanchez, D.; Ortega, N.; Arredondo, M.; Katiyar, R.S.; Gregg, J.M.; Scott, J.F.

    2013-01-01

    Single-phase magnetoelectric multiferroics are ferroelectric materials that display some form of magnetism. In addition, magnetic and ferroelectric order parameters are not independent of one another. Thus, the application of either an electric or magnetic field simultaneously alters both the electrical dipole configuration and the magnetic state of the material. The technological possibilities that could arise from magnetoelectric multiferroics are considerable and a range of functional devices has already been envisioned. Realising these devices, however, requires coupling effects to be significant and to occur at room temperature. Although such characteristics can be created in piezoelectric-magnetostrictive composites, to date they have only been weakly evident in single-phase multiferroics. Here in a newly discovered room temperature multiferroic, we demonstrate significant room temperature coupling by monitoring changes in ferroelectric domain patterns induced by magnetic fields. An order of magnitude estimate of the effective coupling coefficient suggests a value of ~1 × 10−7 sm−1. PMID:23443562

  11. Exchange bias and room-temperature magnetic order in molecular layers.

    PubMed

    Gruber, Manuel; Ibrahim, Fatima; Boukari, Samy; Isshiki, Hironari; Joly, Loïc; Peter, Moritz; Studniarek, Michał; Da Costa, Victor; Jabbar, Hashim; Davesne, Vincent; Halisdemir, Ufuk; Chen, Jinjie; Arabski, Jacek; Otero, Edwige; Choueikani, Fadi; Chen, Kai; Ohresser, Philippe; Wulfhekel, Wulf; Scheurer, Fabrice; Weber, Wolfgang; Alouani, Mebarek; Beaurepaire, Eric; Bowen, Martin

    2015-10-01

    Molecular semiconductors may exhibit antiferromagnetic correlations well below room temperature. Although inorganic antiferromagnetic layers may exchange bias single-molecule magnets, the reciprocal effect of an antiferromagnetic molecular layer magnetically pinning an inorganic ferromagnetic layer through exchange bias has so far not been observed. We report on the magnetic interplay, extending beyond the interface, between a cobalt ferromagnetic layer and a paramagnetic organic manganese phthalocyanine (MnPc) layer. These ferromagnetic/organic interfaces are called spinterfaces because spin polarization arises on them. The robust magnetism of the Co/MnPc spinterface stabilizes antiferromagnetic ordering at room temperature within subsequent MnPc monolayers away from the interface. The inferred magnetic coupling strength is much larger than that found in similar bulk, thin or ultrathin systems. In addition, at lower temperature, the antiferromagnetic MnPc layer induces an exchange bias on the Co film, which is magnetically pinned. These findings create new routes towards designing organic spintronic devices.

  12. Low and room temperature magnetic features of the traffic related urban airborne PM

    NASA Astrophysics Data System (ADS)

    Winkler, A.; Sagnotti, L.

    2012-04-01

    We used magnetic measurements and analyses - such as hysteresis loops and FORCs both at room temperature and at 10K, isothermal remanent magnetization (IRM) vs temperature curves (from 10K to 293K) and IRM vs time decay curves - to characterize the magnetic properties of the traffic related airborne particulate matter (PM) in Rome. This study was specifically addressed to the identification of the ultrafine superparamagnetic (SP) particles, which are particularly sensitive to thermal relaxation effects, and on the eventual detection of low temperature phase transitions which may affect various magnetic minerals. We compared the magnetic properties at 10K and at room temperature of Quercus ilex leaves, disk brakes, diesel and gasoline exhaust pipes powders collected from vehicles circulating in Rome. The magnetic properties of the investigated powders significantly change upon cooling, and no clear phase transition occurs, suggesting that the thermal dependence is mainly triggered by the widespread presence of ultrafine SP particles. The contribution of the SP fraction to the total remanence of traffic related PM samples was quantified at room temperature measuring the decay of a IRM 100 s after the application of a saturation magnetic field. This same method has been also tested at 10K to investigate the temperature dependence of the observed time decay.

  13. Nanostructure and magnetic properties of the MnZnO system, a room temperature magnetic semiconductor?

    PubMed

    Costa-Krämer, J L; Briones, F; Fernández, J F; Caballero, A C; Villegas, M; Díaz, M; García, M A; Hernando, A

    2005-02-01

    The magnetic properties of the system MnZnO prepared by conventional ceramic procedures using ZnO and MnO(2) starting powders are studied and related to the nanostructure. Thermal treatment at 500 °C produces a ferromagnetic phase, although this temperature is not high enough to promote proper sintering; thus the thermally treated compact shows brittle characteristics of unreacted and poorly densified ceramic samples. Scanning electron microscopy and x-ray analysis reveal the appearance of a new phase, most probably related to the diffusion of Zn into MnO(2) oxide nanocrystals. The magnetic properties deviate considerably from what would be expected of an unreacted mixture of ZnO (diamagnetic) and MnO(2) particles (paramagnetic above 100 K and anti-ferromagnetic below that temperature), exhibiting a ferromagnetic like behaviour from 5 to 300 K and beyond mixed with a paramagnetic component. The ferromagnetic phase seems to be originated by diffusion at the nanoscale of Zn into MnO(2) grains. The Curie temperature of the ferromagnetic phase, once the paramagnetic component has been subtracted from the hysteresis loops, is measured to be 450 K. EPR resonance experiments from 100 to 600 K confirm a ferromagnetic to paramagnetic like transition above room temperature for these materials.

  14. Room temperature ferromagnetism in ZnO using non-magnetic dopants

    NASA Astrophysics Data System (ADS)

    Ali, Nasir; Atri, Asha; Singh, Budhi; Ghosh, Subhasis

    2016-05-01

    We studied the magnetic properties of Ag and Cu doped ZnO thin films deposited by magnetron sputtering. Robust room temperature ferromagnetism is observed in the films. Comparative to Cu doped films Ag doped films shows significant increase in ferromagnetism. Spectroscopic ellipsometry studies are also done to see the change in band structure with different metal doping content.

  15. Optical multichannel room temperature magnetic field imaging system for clinical application

    PubMed Central

    Lembke, G.; Erné, S. N.; Nowak, H.; Menhorn, B.; Pasquarelli, A.

    2014-01-01

    Optically pumped magnetometers (OPM) are a very promising alternative to the superconducting quantum interference devices (SQUIDs) used nowadays for Magnetic Field Imaging (MFI), a new method of diagnosis based on the measurement of the magnetic field of the human heart. We present a first measurement combining a multichannel OPM-sensor with an existing MFI-system resulting in a fully functional room temperature MFI-system. PMID:24688820

  16. Room temperature ferromagnetism in non-magnetic doped TiO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Gómez-Polo, C.; Larumbe, S.; Pastor, J. M.

    2013-05-01

    Room-temperature ferromagnetism in non-magnetic doped TiO2 semiconductor nanoparticles is analyzed in the present work. Undoped and N-doped TiO2 nanoparticles were obtained employing sol-gel procedure using urea as the nitrogen source. The obtained gels were first dried at 70 °C and afterwards calcined in air at 300 °C. A residual carbon concentration was retained in the samples as a consequence of the organic decomposition process. Post-annealing treatments at 300 °C under air and vacuum conditions were also performed. The crystallographic structure of nanoparticles was analyzed by X-ray diffraction, obtaining a single anatase crystalline phase after the calcinations (mean nanoparticle diameters around 5-8 nm). SQUID magnetometry was employed to analyze the magnetic response of the samples. Whereas for the undoped samples synthesized with hydrolysis rate h = 6, paramagnetic like behavior is observed at room temperature, the N-doped nanoparticles (h = 3) show a weak ferromagnetic response (saturation magnetization ≈10-3 emu/g). Moreover, a clear reinforcement of the room-temperature ferromagnetism response is found with the post-annealing treatments, in particular that performed in vacuum. Thus, the results indicate the dominant role of the oxygen stoichiometry and the oxygen vacancies in the room temperature ferromagnetic response of these TiO2 nanoparticles.

  17. 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.

  18. Room temperature optical and magnetic properties of polyvinylpyrrolidone capped ZnO nanoparticles

    SciTech Connect

    Chakrabarti, Mahuya; Chakrabarti, Keka R.; Sanyal, D.; Chakrabarti, A.

    2009-09-15

    Defect induced room temperature ferromagnetic properties of polyvinylpyrrolidone (PVP) capped nanocrystalline ZnO samples have been studied. Crystal phase and the lattice parameter of the synthesized nanocrystalline samples have been determined from X-ray diffraction spectra (XRD) and high-resolution transmission electron micrographs (HR-TEM). Room temperature photoluminescence (PL) spectrum for the bare ZnO sample shows a strong band at {approx} 379 nm and another band at {approx} 525 nm. The PL spectra also revealed that the number of oxygen vacancies in the uncapped sample is more than the PVP capped sample. Both sample exhibit ferromagnetic property at room temperature when annealed at 500 deg. C for 3 h, due to the formation of adequate oxygen vacancy related defects. The saturation magnetization for the annealed PVP capped sample is found to be larger compared to that for the uncapped sample.

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

    PubMed

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

    2015-09-17

    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 d(0) or s(2) cations, whereas ferromagnetic order requires open-shell d(n) 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

  1. Room-temperature perpendicular magnetic anisotropy of MgO/Fe/MgO ultrathin films

    SciTech Connect

    Kozioł-Rachwał, A.; Ślęzak, T.; Przewoźnik, J.; Skowroński, W.; Stobiecki, T.; Wilgocka-Ślęzak, D.; Qin, Q. H.; Dijken, S. van; Korecki, J.

    2013-12-14

    We used the anomalous Hall effect to study the magnetic properties of MgO/Fe(t)/MgO(001) structures in which the Fe thickness t ranged from 4 Å to 14 Å. For the iron deposited at 140 K, we obtained perpendicular magnetization at room temperature below the critical thickness of t{sub c} = (9 ± 1) Å. In the vicinity of t{sub c}, the easy magnetization axis switched from an out-of-plane orientation to an in-plane orientation, and the observed spin-reorientation transition was considered in terms of the competition among different anisotropies. The perpendicular magnetization direction was attributed to magnetoelastic anisotropy. Finally, the temperature-dependent spin-reorientation transition was analyzed for Fe thicknesses close to t{sub c}.

  2. Room-temperature magnetism on the zigzag edges of phosphorene nanoribbons

    NASA Astrophysics Data System (ADS)

    Yang, Guang; Xu, Shenglong; Zhang, Wei; Ma, Tianxing; Wu, Congjun

    2016-08-01

    Searching for room-temperature ferromagnetic semiconductors has evolved into a broad field of material science and spintronics for decades, nevertheless, these novel states remain rare. Phosphorene, a monolayer black phosphorus with a puckered honeycomb lattice structure possessing a finite band gap and high carrier mobility, has been synthesized recently. Here we show, by means of two different large-scale quantum Monte Carlo methods, that relatively weak interactions can lead to remarkable edge magnetism in the phosphorene nanoribbons. The ground state constrained path quantum Monte Carlo simulations reveal strong ferromagnetic correlations along the zigzag edges, and the finite temperature determinant quantum Monte Carlo calculations show a high Curie temperature up to room temperature.

  3. A new class of chiral materials hosting magnetic skyrmions beyond room temperature

    NASA Astrophysics Data System (ADS)

    Tokunaga, Y.; Yu, X. Z.; White, J. S.; Rønnow, H. M.; Morikawa, D.; Taguchi, Y.; Tokura, Y.

    2015-07-01

    Skyrmions, topologically protected vortex-like nanometric spin textures in magnets, have been attracting increasing attention for emergent electromagnetic responses and possible technological applications for spintronics. In particular, metallic magnets with chiral and cubic/tetragonal crystal structure may have high potential to host skyrmions that can be driven by low electrical current excitation. However, experimental observations of skyrmions have been limited to below room temperature for the metallic chiral magnets, specifically for the MnSi-type B20 compounds. Towards technological applications, transcending this limitation is crucial. Here we demonstrate the formation of skyrmions with unique spin helicity both at and above room temperature in a family of cubic chiral magnets: β-Mn-type Co-Zn-Mn alloys with a different chiral space group from that of B20 compounds. Lorentz transmission electron microscopy, magnetization and small-angle neutron scattering measurements unambiguously reveal formation of a skyrmion crystal under application of a magnetic field in both thin-plate and bulk forms.

  4. A new class of chiral materials hosting magnetic skyrmions beyond room temperature

    PubMed Central

    Tokunaga, Y.; Yu, X. Z.; White, J. S.; Rønnow, H. M.; Morikawa, D.; Taguchi, Y.; Tokura, Y.

    2015-01-01

    Skyrmions, topologically protected vortex-like nanometric spin textures in magnets, have been attracting increasing attention for emergent electromagnetic responses and possible technological applications for spintronics. In particular, metallic magnets with chiral and cubic/tetragonal crystal structure may have high potential to host skyrmions that can be driven by low electrical current excitation. However, experimental observations of skyrmions have been limited to below room temperature for the metallic chiral magnets, specifically for the MnSi-type B20 compounds. Towards technological applications, transcending this limitation is crucial. Here we demonstrate the formation of skyrmions with unique spin helicity both at and above room temperature in a family of cubic chiral magnets: β-Mn-type Co-Zn-Mn alloys with a different chiral space group from that of B20 compounds. Lorentz transmission electron microscopy, magnetization and small-angle neutron scattering measurements unambiguously reveal formation of a skyrmion crystal under application of a magnetic field in both thin-plate and bulk forms. PMID:26134284

  5. Performance predictions for a room temperature, Ericsson cycle, magnetic heat pump

    NASA Astrophysics Data System (ADS)

    Purnell, J. G.

    1982-05-01

    The performance potential of a room temperature magnetic heat pump utilizing Gadolinium and operating on an Ericsson Cycle was investigated at magnetic flux densities of 2 and 7-Tesla which represent the upper limits of conventional and superconducting electromagnetics, respectively. At a coefficient of performance of 5, a 7-Tesla system would provide a cooling capacity of at best 1200 BTU per hour per pound of Gadolinium while a 2-Tesla system would operate at approximately 130 BTU per hour per pound of Gadolinium. Magnetic circuit efficiency was not determined but must be high (95-percent or better) in order for the magnetic heat pump performance to compete with conventional cooling systems. It is unlikely the magnetic heat pump investigated could approach the performance and compactness of the conventional cooling systems unless field strengths much greater than 7-Tesla are possible.

  6. On the magnetic field signal radiated by an atmospheric pressure room temperature plasma jet

    SciTech Connect

    Wu, S.; Huang, Q.; Wang, Z.; Lu, X.

    2013-01-28

    In this paper, the magnetic field signal radiated from an atmospheric pressure room temperature plasma plume is measured. It's found that the magnetic field signal has similar waveform as the current carried by the plasma plume. By calibration of the magnetic field signal, the plasma plume current is obtained by measuring the magnetic field signal radiated by the plasma plume. In addition, it is found that, when gas flow modes changes from laminar regime to turbulence regime, the magnetic field signal waveforms appears different, it changes from a smooth curve to a curve with multiple spikes. Furthermore, it is confirmed that the plasma plume generated by a single electrode (without ground electrode) plasma jet device carries higher current than that with ground electrode.

  7. Metastable gamma-Iron Nickel Nanostructures for Magnetic Refrigeration Near Room Temperature

    NASA Astrophysics Data System (ADS)

    Ucar, Huseyin

    The observation of a giant magnetocaloric effect in Gd5Ge 1.9Si2Fe0.1 has stimulated the magnetocaloric research in the last two decades. However, the high price of Gd and its proclivity to corrosion of these compounds have prevented their commercial use. To reduce raw materials cost, transition metal-based alloys are investigated to replace rare earth-based materials. Environmental considerations, substitution for scarce and strategic elements, and cost considerations all speak to potential contributions of these new materials to sustainability. Efforts in improving the refrigeration capacity (RC) of refrigerants mainly rely on broadening the magnetic entropy change. One promising technique is to couple two phases of magnetic materials with desirable properties. Second is the investigation of nanoparticle synthesis routes, with ball milling being the most widely used one. The motivation for the nanoparticles synthesis is rooted in their inherent tendency to have distributed exchange coupling, which will broaden the magnetic entropy curve. As proven with the cost analysis, the focus is believed to shift from improving the RC of refrigerants toward finding the most economically advantageous magnetic refrigerant with the highest performance. Mechanically alloyed Fe70Ni30 and Fe72Ni 28 alloys were characterized in terms of their structural and magnetic properties. Previous studies showed that single phase FCC gamma-FeNi alloys with 26-30 at. % Ni have Curie temperatures, TC, near room temperature. Having TC near room temperatures along with large magnetization makes gamma-FeNi alloys attractive for room temperature magnetocaloric cooling technologies. To obtain a single gamma-phase, particles were solution annealed in the gamma-phase field and water quenched. The preferential oxidation of Fe during ball milling was used as a means to tune the TC of the alloy. Refrigeration capacities, RCFWHM, of the Fe70Ni30 and the Fe72Ni28 alloys were calculated to be 470 J/kg and

  8. 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.

  9. 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.

  10. 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

  11. Magnetic refrigeration: an eco-friendly technology for the refrigeration at room temperature

    NASA Astrophysics Data System (ADS)

    Aprea, C.; Greco, A.; Maiorino, A.; Masselli, C.

    2015-11-01

    Magnetic refrigeration is an emerging, environment-friendly technology based on a magnetic solid that acts as a refrigerant by magneto-caloric effect (MCE). In the case of ferromagnetic materials MCE is a warming as the magnetic moments of the atom are aligned by the application of a magnetic field, and the corresponding cooling upon removal of the magnetic field. There are two types of magnetic phase changes that may occur at the Curie point: first order magnetic transition (FOMT) and second order magnetic transition (SOMT). The reference cycle for magnetic refrigeration is AMR (Active Magnetic Regenerative cycle) where the magnetic material matrix works both as a refrigerating medium and as a heat regenerating medium, while the fluid flowing in the porous matrix works as a heat transfer medium. Regeneration can be accomplished by blowing a heat transfer fluid in a reciprocating fashion through the regenerator made of magnetocaloric material that is alternately magnetized and demagnetized. In this paper, attention is directed towards the near room-temperature range. We compare the energetic performance of a commercial R134a refrigeration plant to that of a magnetic refrigerator working with an AMR cycle. Attention is devoted to the evaluation of the environmental impact in terms of a greenhouse effect. The comparison is performed in term of TEWI index (Total Equivalent Warming Impact) that takes into account both direct and indirect contributions to global warming. In this paper the AMR cycle works with different magnetic refrigerants: pure gadolinium, second order phase magnetic transition (Pr0.45Sr0.35MnO3) and first order phase magnetic transition alloys (Gd5Si2Ge2, LaFe11.384Mn0.356Si1.26H1.52, LaFe1105Co0.94Si110 and MnFeP0.45As0.55). The comparison, carried out by means of a mathematical model, clearly shows that GdSi2Ge2 and LaFe11.384Mn0.356Si1.26H1.52 has a TEWI index always lower than that of a vapor compression plant. Furthermore, the TEWI of the AMR

  12. Room-temperature magnetic order on zigzag edges of narrow graphene nanoribbons.

    PubMed

    Magda, Gábor Zsolt; Jin, Xiaozhan; Hagymási, Imre; Vancsó, Péter; Osváth, Zoltán; Nemes-Incze, Péter; Hwang, Chanyong; Biró, László P; Tapasztó, Levente

    2014-10-30

    The possibility that non-magnetic materials such as carbon could exhibit a novel type of s-p electron magnetism has attracted much attention over the years, not least because such magnetic order is predicted to be stable at high temperatures. It has been demonstrated that atomic-scale structural defects of graphene can host unpaired spins, but it remains unclear under what conditions long-range magnetic order can emerge from such defect-bound magnetic moments. Here we propose that, in contrast to random defect distributions, atomic-scale engineering of graphene edges with specific crystallographic orientation--comprising edge atoms from only one sub-lattice of the bipartite graphene lattice--can give rise to a robust magnetic order. We use a nanofabrication technique based on scanning tunnelling microscopy to define graphene nanoribbons with nanometre precision and well-defined crystallographic edge orientations. Although so-called 'armchair' ribbons display quantum confinement gaps, ribbons with the 'zigzag' edge structure that are narrower than 7 nanometres exhibit an electronic bandgap of about 0.2-0.3 electronvolts, which can be identified as a signature of interaction-induced spin ordering along their edges. Moreover, upon increasing the ribbon width, a semiconductor-to-metal transition is revealed, indicating the switching of the magnetic coupling between opposite ribbon edges from the antiferromagnetic to the ferromagnetic configuration. We found that the magnetic order on graphene edges of controlled zigzag orientation can be stable even at room temperature, raising hopes of graphene-based spintronic devices operating under ambient conditions.

  13. Design of dilute magnetic semiconductors with room temperature ferromagnetism by controlling spinodal decompostion

    NASA Astrophysics Data System (ADS)

    Sato, Kazunori

    2008-03-01

    Owing to the recent development of the first-principles method for calculating magnetic properties of dilute magnetic semiconductors (DMS), it has been recognized that the magnetic percolation effect is disastrous to the high temperature ferromagnetism in DMS in particular for low concentrations [1]. The exchange interactions calculated from first-principles are strong for nearest neighbors, but those interactions are short ranged and can not play an important role for realizing high- TC because the solubility of magnetic impurities into DMS is too low to achieve magnetic percolation. To overcome this difficulty and realize room temperature ferromagnetism, we focus on the spinodal decomposition in DMS, and suggest that by controlling the spinodal decomposition high blocking temperature can be realized leading to ferromagnetic behaviour at high temperature [2]. We calculate electronic structure of DMS from first-principles by using the Korringa- Kohn-Rostoker coherent potential approximation (KKR-CPA) method. Then, chemical pair interactions and magnetic exchange interactions between magnetic are calculated. We use the Monte Carlo techniques to simulate spinodal decomposition of DMS and to estimate the magnetic properties of them [3]. The computer simulations for the magnetization process of the decomposition phases indicate that we can control super-paramagnetic blocking temperature by optimizing the size of the clusters by changing the crystal growth condition. This simulation suggests the material design of high blocking temperature DMS by controlling the spinodal decomposition [2].As another approach for realizing high-Tc DMS we propose co-doping method to increase solubility limit of transition metal impurities in DMS [4]. This work is based on the collaboration with H. Katayama-Yoshida and T. Fukushima. [1] L. Bergqvist et al, Phys. Rev. Lett. 93, 137202 (2004), K. Sato et al., Phys. Rev. B 70, 201202 (2004) [2] K. Sato et al., Jpn. J. Appl. Phys. 46, L682

  14. Lateral spin transfer torque induced magnetic switching at room temperature demonstrated by x-ray microscopy.

    PubMed

    Buhl, M; Erbe, A; Grebing, J; Wintz, S; Raabe, J; Fassbender, J

    2013-01-01

    Changing and detecting the orientation of nanomagnetic structures, which can be used for durable information storage, needs to be developed towards true nanoscale dimensions for keeping up the miniaturization speed of modern nanoelectronic components. Therefore, new concepts for controlling the state of nanomagnets are currently in the focus of research in the field of nanoelectronics. Here, we demonstrate reproducible switching of a purely metallic nanopillar placed on a lead that conducts a spin-polarized current at room temperature. Spin diffusion across the metal-metal (Cu to CoFe) interface between the pillar and the lead causes spin accumulation in the pillar, which may then be used to set the magnetic orientation of the pillar. In our experiments, the detection of the magnetic state of the nanopillar is performed by direct imaging via scanning transmission x-ray microscopy (STXM).

  15. Lateral spin transfer torque induced magnetic switching at room temperature demonstrated by x-ray microscopy

    PubMed Central

    Buhl, M.; Erbe, A.; Grebing, J.; Wintz, S.; Raabe, J.; Fassbender, J.

    2013-01-01

    Changing and detecting the orientation of nanomagnetic structures, which can be used for durable information storage, needs to be developed towards true nanoscale dimensions for keeping up the miniaturization speed of modern nanoelectronic components. Therefore, new concepts for controlling the state of nanomagnets are currently in the focus of research in the field of nanoelectronics. Here, we demonstrate reproducible switching of a purely metallic nanopillar placed on a lead that conducts a spin-polarized current at room temperature. Spin diffusion across the metal-metal (Cu to CoFe) interface between the pillar and the lead causes spin accumulation in the pillar, which may then be used to set the magnetic orientation of the pillar. In our experiments, the detection of the magnetic state of the nanopillar is performed by direct imaging via scanning transmission x-ray microscopy (STXM). PMID:24126435

  16. Spatial resolution of SQUID magnetometers and comparison with low noise room temperature magnetic sensors

    NASA Astrophysics Data System (ADS)

    Dolabdjian, C.; Qasimi, A.; Bloyet, D.; Mosser, V.

    2002-03-01

    Any magnetic sensor placed in a spatially inhomogeneous magnetic field delivers a signal proportional the mean field value taken over an effective area or volume which depends on the type of sensor considered. In the case of the field produced by a magnetic dipole and detected by a square or circular planar sensor, the overall measured spatial resolution ideally depends on the ratio of the mean dipole-sensor distance z0 to the square root of the effective sensor area AE. For Z 0/ A E≪1 , the spatial resolution is limited by the size of the sensor, whereas for z 0/ A E≫1 the dipole-sensor distance is the predominant factor. To compare various low noise magnetic sensors operating either at low temperature or at room temperature, we have measured their sensitivities and spatial responses to the field produced by a magnetic moment having the form of a tiny circular current loop. The sensors could be moved in all directions with respect to the current loop. The transfer of each sensor to the magnetic dipole field was compared to their response in a homogeneous field so as to deduce their effective area and compare this area to that deduced from independent spatial resolution measurements. We report the experimental results given by four types of sensors namely a dc-SQUID, a Hall effect sensor, a giant magneto-resistive sensor and a flux-gate sensor and discuss them by mean of a “figure of merit” criterion combining their spatial resolution and their sensitivity.

  17. Magnetic memory based on magnetic alignment of a paramagnetic ionic liquid near room temperature.

    PubMed

    Funasako, Yusuke; Mochida, Tomoyuki; Inagaki, Takashi; Sakurai, Takahiro; Ohta, Hitoshi; Furukawa, Ko; Nakamura, Toshikazu

    2011-04-21

    A paramagnetic ferrocenium-based ionic liquid that exhibits a magnetic memory effect coupled with a liquid-solid phase transformation has been developed. Based on field alignment of the magnetically anisotropic ferrocenium cation, the magnetic susceptibility in the solid state can be tuned by the weak magnetic fields (<1 T) of permanent magnets.

  18. Induction heating studies of magnetite nanospheres synthesized at room temperature for magnetic hyperthermia

    NASA Astrophysics Data System (ADS)

    Rashad, M. M.; El-Sayed, H. M.; Rasly, M.; Nasr, M. I.

    2012-11-01

    An investigation of the synthesis of Fe3O4 nanopowders by the co-precipitation method is reported from aqueous and ethanol mediums. X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer are utilized to study the effect of variation of synthesis conditions on the crystal structure, crystallite size, microstructure and magnetic properties of the formed powders. The XRD analysis showed that the crystalline Fe3O4 phase was formed at Fe3+/Fe2+ molar ratio 2.0 prepared at room temperature for 1 h at pH 10. The crystallite size was in the range between 8 and 11 nm. TEM micrographs showed that the particles appeared as nanospheres. Superparamagnetic nanoparticles with low coercivity and remanence magnetization were achieved. Heating properties of the nanosphere samples in an alternating magnetic field at 160 KHz were evaluated. An excellent heating efficiency for the sample prepared in ethanol medium is a result of more relaxation losses occurring due to its small particle size.

  19. 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.

  20. Room-temperature magnetic properties of SiC based nanowires synthesized via microwave heating method

    NASA Astrophysics Data System (ADS)

    Liu, Song; Wang, Jigang

    2016-07-01

    Two kinds of ferromagnetic SiC based nanowires with and without Ni catalyst were successfully synthesized by employing microwave heating method. The comprehensive characterizations and vibrating sample magnetometer (VSM) have been applied to investigate the micro-structures and magnetic properties of as-grown nanowires. For the nanowires synthesized without using Ni catalyst, the diameters and lengths are in the range of 20-60 nm and dozens of micrometers, respectively. Particularly, the results of transmission electron microscopy (TEM) show that the nanowires consist of SiC core and SiOx shell. The SiC/SiOx coaxial nanowires exhibit room-temperature ferromagnetism with saturation magnetization (Ms) of 0.2 emu/g. As to the nanowires obtained using Ni catalyst, the scanning electron microscopy (SEM) results indicate that the Ni catalyzed nanowires have a nano-particle attached on the tip and a uniform diameter of approximately 50 nm. The vapor-liquid-solid (VLS) growth mechanism can be used to explain the formation of the Ni catalyzed nanowires. The detection result of VSM indicates that the Ni catalyzed nanowires possess the paramagnetism and the ferromagnetism, simultaneously. The enhancement of the ferromagnetism, compared with the SiC/SiOx coaxial nanowires, could be attributed to the Ni2Si and NiSi phases.

  1. Atomic magnetic gradiometer for room temperature high sensitivity magnetic field detection

    DOEpatents

    Xu,Shoujun; Lowery, Thomas L.; Budker, Dmitry; Yashchuk, Valeriy V.; Wemmer, David E.; Pines, Alexander

    2009-08-11

    A laser-based atomic magnetometer (LBAM) apparatus measures magnetic fields, comprising: a plurality of polarization detector cells to detect magnetic fields; a laser source optically coupled to the polarization detector cells; and a signal detector that measures the laser source after being coupled to the polarization detector cells, which may be alkali cells. A single polarization cell may be used for nuclear magnetic resonance (NMR) by prepolarizing the nuclear spins of an analyte, encoding spectroscopic and/or spatial information, and detecting NMR signals from the analyte with a laser-based atomic magnetometer to form NMR spectra and/or magnetic resonance images (MRI). There is no need of a magnetic field or cryogenics in the detection step, as it is detected through the LBAM.

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

    PubMed

    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.

  3. 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.

  4. Near fifty percent sodium substituted lanthanum manganites—A potential magnetic refrigerant for room temperature applications

    SciTech Connect

    Sethulakshmi, N.; Anantharaman, M. R.; Al-Omari, I. A.; Suresh, K. G.

    2014-03-03

    Nearly half of lanthanum sites in lanthanum manganites were substituted with monovalent ion-sodium and the compound possessed distorted orthorhombic structure. Ferromagnetic ordering at 300 K and the magnetic isotherms at different temperature ranges were analyzed for estimating magnetic entropy variation. Magnetic entropy change of 1.5 J·kg{sup −1}·K{sup −1} was observed near 300 K. An appreciable magnetocaloric effect was also observed for a wide range of temperatures near 300 K for small magnetic field variation. Heat capacity was measured for temperatures lower than 300 K and the adiabatic temperature change increases with increase in temperature with a maximum of 0.62 K at 280 K.

  5. Structure, electrical and magnetic properties, and the origin of the room temperature ferromagnetism in Mn-implanted Si

    NASA Astrophysics Data System (ADS)

    Orlov, A. F.; Granovsky, A. B.; Balagurov, L. A.; Kulemanov, I. V.; Parkhomenko, Yu. N.; Perov, N. S.; Gan'shina, E. A.; Bublik, V. T.; Shcherbachev, K. D.; Kartavykh, A. V.; Vdovin, V. I.; Sapelkin, A.; Saraikin, V. V.; Agafonov, Yu. A.; Zinenko, V. I.; Rogalev, A.; Smekhova, A.

    2009-10-01

    The structure and the electrical and magnetic properties of Mn-implanted Si, which exhibits ferromagnetic ordering at room temperature, are studied. Single-crystal n- and p-type Si wafers with high and low electrical resistivities are implanted by manganese ions to a dose of 5 × 1016 cm-2. After implantation and subsequent vacuum annealing at 850°C, the implanted samples are examined by various methods. The Mn impurity that exhibits an electric activity and is incorporated into the Si lattice in interstitial sites is found to account for only a few percent of the total Mn content. The main part of Mn is fixed in Mn15Si26 nanoprecipitates in the Si matrix. The magnetization of implanted Si is found to be independent of the electrical resistivity and the conductivity type of silicon and the type of implanted impurity. The magnetization of implanted Si increases slightly upon short-term postimplantation annealing and disappears completely upon vacuum annealing at 1000°C for 5 h. The Mn impurity in Si is shown to have no significant magnetic moment at room temperature. These results indicate that the room temperature ferromagnetism in Mn-implanted Si is likely to be caused by implantation-induced defects in the silicon lattice rather than by a Mn impurity.

  6. 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

  7. Room-temperature photomagnetism in the spinel ferrite (Mn,Zn,Fe)3O4 as seen via soft x-ray magnetic circular dichroism

    SciTech Connect

    Bettinger, J.S.; Piamonteze, C.; Chopdekar, R.V.; Liberati, M.; Arenholz, E.; Suzuki, Y.

    2009-08-01

    We have used X-ray magnetic circular dichroism (XMCD) in conjunction with multiplet simulations to directly probe the origin of photomagnetism in nanocrystalline (Mn,Zn,Fe){sub 3}O{sub 4}. A photomagnetic effect at room temperature has been observed in these films with HeNe illumination. We have verified an intervalence charge transfer among octahedral Fe cations to account for the increase in magnetization observed at and above room temperature in small magnetic fields. Using XMCD, we demonstrate that the dichroism of Fe in octahedral sites increases by 18% at room temperature while the dichroism of Fe in tetrahedral sites does not change.

  8. 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.

  9. Improved room-temperature-selectivity between Nd and Fe in Nd recovery from Nd-Fe-B magnet

    NASA Astrophysics Data System (ADS)

    Kataoka, Y.; Ono, T.; Tsubota, M.; Kitagawa, J.

    2015-11-01

    The sustainable society requires the recycling of rare metals. Rare earth Nd is one of rare metals, accompanying huge consumption especially in Nd-Fe-B magnets. Although the wet process using acid is in practical use in the in-plant recycle of sludge, higher selectivity between Nd and Fe at room temperature is desired. We have proposed a pretreatment of corrosion before the dissolution into HCl and the oxalic acid precipitation. The corrosion produces γ-FeOOH and a Nd hydroxide, which have high selectivity for HCl solution at room temperature. Nd can be recovered as Mn2O3-type Nd2O3. The estimated recovery-ratio of Nd reaches to 97%.

  10. Improved room-temperature-selectivity between Nd and Fe in Nd recovery from Nd-Fe-B magnet

    SciTech Connect

    Kataoka, Y.; Kitagawa, J.; Ono, T.; Tsubota, M.

    2015-11-15

    The sustainable society requires the recycling of rare metals. Rare earth Nd is one of rare metals, accompanying huge consumption especially in Nd-Fe-B magnets. Although the wet process using acid is in practical use in the in-plant recycle of sludge, higher selectivity between Nd and Fe at room temperature is desired. We have proposed a pretreatment of corrosion before the dissolution into HCl and the oxalic acid precipitation. The corrosion produces γ-FeOOH and a Nd hydroxide, which have high selectivity for HCl solution at room temperature. Nd can be recovered as Mn{sub 2}O{sub 3}-type Nd{sub 2}O{sub 3}. The estimated recovery-ratio of Nd reaches to 97%.

  11. Room temperature magnetic and dielectric properties of cobalt doped CaCu3Ti4O12 ceramics

    NASA Astrophysics Data System (ADS)

    Mu, Chunhong; Song, Yuanqiang; Wang, Haibin; Wang, Xiaoning

    2015-05-01

    CaCu3Ti4-xCoxO12 (x = 0, 0.2, 0.4) ceramics were prepared by a conventional solid state reaction, and the effects of cobalt doping on the room temperature magnetic and dielectric properties were investigated. Both X-ray diffraction and energy dispersive X-ray spectroscopy confirmed the presence of Cu and Co rich phase at grain boundaries of Co-doped ceramics. Scanning electron microscopy micrographs of Co-doped samples showed a striking change from regular polyhedral particle type in pure CaCu3Ti4O12 (CCTO) to sheet-like grains with certain growth orientation. Undoped CaCu3Ti4O12 is well known for its colossal dielectric constant in a broad temperature and frequency range. The dielectric constant value was slightly changed by 5 at. % and 10 at. % Co doping, whereas the second relaxation process was clearly separated in low frequency region at room temperature. A multirelaxation mechanism was proposed to be the origin of the colossal dielectric constant. In addition, the permeability spectra measurements indicated Co-doped CCTO with good magnetic properties, showing the initial permeability (μ') as high as 5.5 and low magnetic loss (μ″ < 0.2) below 3 MHz. And the interesting ferromagnetic superexchange coupling in Co-doped CaCu3Ti4O12 was discussed.

  12. Room-temperature ferromagnetism with high magnetic moment in Cu-doped AlN single crystal whiskers

    NASA Astrophysics Data System (ADS)

    Jiang, Liang-Bao; Liu, Yu; Zuo, Si-Bin; Wang, Wen-Jun

    2015-02-01

    Ferromagnetism is investigated in high-quality Cu-doped AlN single crystal whiskers. The whiskers exhibit room-temperature ferromagnetism with a magnetic moment close to the results from first-principles calculations. High crystallinity and low Cu concentrations are found to be indispensable for high magnetic moments. The difference between the experimental and theoretical moment values is explored in terms of the influence of nitrogen vacancies. The calculated results demonstrate that nitrogen vacancies can reduce the magnetic moments of Cu atom. Project supported by the National Basic Research Program of China (Grant No. 2013CB932901), the National Natural Science Foundation of China (Grant Nos. 51372267, 51210105026, and 51172270), the Funds from the Chinese Academy of Sciences, the International Centre for Diffraction Data, USA (2013 Ludo Frevel Crystallography Scholarship Award), and the Funds from the Ministry of Education of China (2012 Academic Scholarship Award for Doctoral Candidates).

  13. Highly Efficient Extraction of Phenolic Compounds by Use of Magnetic Room Temperature Ionic Liquids for Environmental Remediation

    PubMed Central

    Deng, Ning; Li, Min; Zhao, Lijie; Lu, Chengfei; de Rooy, Sergio L.; Warner, Isiah M.

    2011-01-01

    A hydrophobic magnetic room temperature ionic liquid (MRTIL), trihexyltetradecylphosphonium tetrachloroferrate(III) ([3C6PC14][FeCl4]), was synthesized from trihexyltetradecylphosphonium chloride and FeCl3·6H2O. This MRTIL was investigated as a possible separation agent for solvent extraction of phenolic compounds from aqueous solution. Due to its strong paramagnetism, [3C6PC14][FeCl4] responds to an external neodymium magnet, which was employed in the design of a novel magnetic extraction technique. The conditions for extraction, including extraction time, volume ratio between MRTIL and aqueous phase, pH of aqueous solution, and structures of phenolic compounds were investigated and optimized. The magnetic extraction of phenols achieved equilibrium in 20 min and the phenolic compounds were found to have higher distribution ratios under acidic conditions. In addition, it was observed that phenols containing a greater number of chlorine or nitro substitutents exhibited higher distribution ratios. For example, the distribution ratio of phenol (DPh) was 107. In contrast, 3,5-dichlorophenol distribution ratio (D3,5-DCP) had a much higher value of 6372 under identical extraction conditions. When compared with four selected traditional non-magnetic room temperature ionic liquids, our [3C6PC14][FeCl4] exhibited significantly higher extraction efficiency under the same experimental conditions used in this work. Pentachlorophenol, a major component in the contaminated soil sample obtained from a superfund site, was successfully extracted and removed by use of [3C6PC14][FeCl4] with high extraction efficiency. Pentachlorophenol concentration was dramatically reduced from 7.8 μg.mL−1 to 0.2 μg.mL−1 after the magnetic extraction by use of [3C6PC14][FeCl4]. PMID:21783320

  14. Magnetic properties measurement and discussion of an amorphous power transformer core at room and liquid nitrogen temperature

    NASA Astrophysics Data System (ADS)

    Pronto, A. G.; Maurício, A.; Pina, J. M.

    2014-05-01

    In energy generation, transmission and distribution systems, power transformers are one of the most common and important components. Consequently, the performance of these transformers is crucial to global efficiency of the systems. To optimize transformers efficiency, the selection of an adequate ferromagnetic material is very important. For example, the use of amorphous ferromagnetic materials in transformer cores, replacing crystalline electrical steels, decreases total magnetic losses of the device. Other possible solution to increase energy systems efficiency, is the installation of high temperature superconducting power transformers (HTS transformers), normally cooled by liquid nitrogen at 77 K. In order to contribute to HTS transformer efficiency improvement, a 562.5 VA transformer with an amorphous ferromagnetic core was designed and built. For this core, the most important magnetic properties are measured at room and cryogenic temperature, and then compared with those of a typical crystalline grain-oriented electrical steel. Amorphous material magnetic losses (static and dynamic) at room and 77K are also presented and discussed.

  15. Carboxylate-based molecular magnet: One path toward achieving stable quantum correlations at room temperature

    NASA Astrophysics Data System (ADS)

    Cruz, C.; Soares-Pinto, D. O.; Brandão, P.; dos Santos, A. M.; Reis, M. S.

    2016-02-01

    The control of quantum correlations in solid-state systems by means of material engineering is a broad avenue to be explored, since it makes possible steps toward the limits of quantum mechanics and the design of novel materials with applications on emerging quantum technologies. In this context, this letter explores the potential of molecular magnets to be prototypes of materials for quantum information technology. More precisely, we engineered a material and from its geometric quantum discord we found significant quantum correlations up to 9540 K (even without entanglement); and, in addition, a pure singlet state occupied up to around 80 K (above liquid nitrogen temperature). These results could only be achieved due to the carboxylate group promoting a metal-to-metal huge magnetic interaction.

  16. 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.

  17. Electric field control of magnetization in Cu2O/porous anodic alumina hybrid structures at room temperature

    NASA Astrophysics Data System (ADS)

    Qi, L. Q.; Liu, H. Y.; Sun, H. Y.; Liu, L. H.; Han, R. S.

    2016-04-01

    Cu2O nanoporous films are deposited on porous anodic alumina (PAA) substrates by DC-reactive magnetron sputtering. This paper focuses on voltage driven magnetization switching in Cu2O/PAA (CP) composite films prepared by DC-reactive magnetron sputtering. By applying a dc electric field, the magnetization of the CP composite films can be controlled in a reversible and reproducible way and shows an analogous on-off behavior. The magnitude of the change in the magnetization was about 75 emu/cm3 as the electric field was switched on and off. Resistive switching behavior was also observed in as-prepared CP composite films. Further analysis indicated that the formation/rupture of conducting filaments composed of oxygen vacancies is likely responsible for the changes in the magnetization as well as in the resistivity. Such reversible change of magnetization controlled by an electric field at room temperature may have applications in spintronics and power efficient data storage technologies.

  18. 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

    2016-01-01

    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

  19. 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

  20. 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.

  1. Magnetic circular dichroism studies of myoglobin, hemoglobin and peroxidase at room and low temperatures. Ferrous high spin derivatives.

    PubMed

    Sharonov, Y A; Mineyev, A P; Livshitz, M A; Sharonova, N A; Zhurkin, V B; Lysov, Y P

    1978-04-13

    The magnetic circular dichroism spectra (MCD) recorded for the visible and near-UV regions of high-spin ferrous derivatives of myoglobin, hemoglobin, hemoglobin dimers and isolated chains as well as of horseradish peroxidase at pH 6.8 and 11.4 have been compared at the room and liquid nitrogen temperatures. The MCD of the Q00- and QV-bands have been shown to be sensitive to structural differences in the heme environment of these hemoproteins. The room temperature visible MCD of native hemoglobin differs from that of myoglobin, hemoglobin dimers and isolated chains as well as from that of model pentacoordinated complex. The MCD of hemoglobin is characterized by the greater value of the MCD intensity ratio of derivative shape A-term in the Q00-band to the A-term in the QV-band. The evidneces are presented for the existence of two pH-dependent forms of ferroperoxidase, the neutral peroxidase shows the "hemoglobin-like" MCD, while the alkaline ferroperoxidase is characterized by the "myoglobin-like" MCD spectrum in the visible region. The differences in the MCD of deoxyhemoglobin and neutral ferroperoxidase as compared with other high-spin ferrous hemoproteins are considered to result from the constraints on heme group imposed by quaternary and/or tertiary protein structure. The differences between hemoporteins which are seen at the room temperature become more pronounced at liquid nitrogen temperature. Except the peak at approximately 580 nm in the MCD of deoxymyoglobin and reduced peroxidase at pH 11.4 the visible MCD does not show appreciable temperature dependent C-terms. The nature of the temperature dependent effect at approximately 580 nm is not clear. The Soret MCD of all hemoproteins studied are similar and are predominantly composed of the derivative-shaped C-terms as revealed by the increase of the MCD peaks approximately in accordance with Boltzmann distribution. The interpretation of temperature-dependent MCD observed for the Soret band has been made in

  2. Room Temperature Multiferroicity of Charge Transfer Crystals.

    PubMed

    Qin, Wei; Chen, Xiaomin; Li, Huashan; Gong, Maogang; Yuan, Guoliang; Grossman, Jeffrey C; Wuttig, Manfred; Ren, Shenqiang

    2015-09-22

    Room temperature multiferroics has been a frontier research field by manipulating spin-driven ferroelectricity or charge-order-driven magnetism. Charge-transfer crystals based on electron donor and acceptor assembly, exhibiting simultaneous spin ordering, are drawing significant interests for the development of all-organic magnetoelectric multiferroics. Here, we report that a remarkable anisotropic magnetization and room temperature multiferroicity can be achieved through assembly of thiophene donor and fullerene acceptor. The crystal motif directs the dimensional and compositional control of charge-transfer networks that could switch magnetization under external stimuli, thereby opening up an attractive class of all-organic nanoferronics.

  3. Preparation of Soft Magnetic Fe-Ni-Pb-B Alloy Nanoparticles by Room Temperature Solid-Solid Reaction

    PubMed Central

    Zhong, Qin

    2013-01-01

    The Fe-Ni-Pb-B alloy nanoparticles was prepared by a solid-solid chemical reaction of ferric trichloride, nickel chloride, lead acetate, and potassium borohydride powders at room temperature. The research results of the ICP and thermal analysis indicate that the resultants are composed of iron, nickel, lead, boron, and PVP, and the component of the alloy is connected with the mole ratio of potassium borohydride and the metal salts. The TEM images show that the resultants are ultrafine and spherical particles, and the particle size is about a diameter of 25 nm. The largest saturation magnetization value of the 21.18 emu g−1 is obtained in the Fe-Ni-Pb-B alloy. The mechanism of the preparation reaction for the Fe-Ni-Pb-B multicomponent alloys is discussed. PMID:24348196

  4. Room-temperature antiferromagnetic memory resistor.

    PubMed

    Marti, X; Fina, I; Frontera, C; Liu, Jian; Wadley, P; He, Q; Paull, R J; Clarkson, J D; Kudrnovský, J; Turek, I; Kuneš, J; Yi, D; Chu, J-H; Nelson, C T; You, L; Arenholz, E; Salahuddin, S; Fontcuberta, J; Jungwirth, T; Ramesh, R

    2014-04-01

    The bistability of ordered spin states in ferromagnets provides the basis for magnetic memory functionality. The latest generation of magnetic random access memories rely on an efficient approach in which magnetic fields are replaced by electrical means for writing and reading the information in ferromagnets. This concept may eventually reduce the sensitivity of ferromagnets to magnetic field perturbations to being a weakness for data retention and the ferromagnetic stray fields to an obstacle for high-density memory integration. Here we report a room-temperature bistable antiferromagnetic (AFM) memory that produces negligible stray fields and is insensitive to strong magnetic fields. We use a resistor made of a FeRh AFM, which orders ferromagnetically roughly 100 K above room temperature, and therefore allows us to set different collective directions for the Fe moments by applied magnetic field. On cooling to room temperature, AFM order sets in with the direction of the AFM moments predetermined by the field and moment direction in the high-temperature ferromagnetic state. For electrical reading, we use an AFM analogue of the anisotropic magnetoresistance. Our microscopic theory modelling confirms that this archetypical spintronic effect, discovered more than 150 years ago in ferromagnets, is also present in AFMs. Our work demonstrates the feasibility of fabricating room-temperature spintronic memories with AFMs, which in turn expands the base of available magnetic materials for devices with properties that cannot be achieved with ferromagnets.

  5. Room-temperature antiferromagnetic memory resistor

    NASA Astrophysics Data System (ADS)

    Marti, X.; Fina, I.; Frontera, C.; Liu, Jian; Wadley, P.; He, Q.; Paull, R. J.; Clarkson, J. D.; Kudrnovský, J.; Turek, I.; Kuneš, J.; Yi, D.; Chu, J.-H.; Nelson, C. T.; You, L.; Arenholz, E.; Salahuddin, S.; Fontcuberta, J.; Jungwirth, T.; Ramesh, R.

    2014-04-01

    The bistability of ordered spin states in ferromagnets provides the basis for magnetic memory functionality. The latest generation of magnetic random access memories rely on an efficient approach in which magnetic fields are replaced by electrical means for writing and reading the information in ferromagnets. This concept may eventually reduce the sensitivity of ferromagnets to magnetic field perturbations to being a weakness for data retention and the ferromagnetic stray fields to an obstacle for high-density memory integration. Here we report a room-temperature bistable antiferromagnetic (AFM) memory that produces negligible stray fields and is insensitive to strong magnetic fields. We use a resistor made of a FeRh AFM, which orders ferromagnetically roughly 100 K above room temperature, and therefore allows us to set different collective directions for the Fe moments by applied magnetic field. On cooling to room temperature, AFM order sets in with the direction of the AFM moments predetermined by the field and moment direction in the high-temperature ferromagnetic state. For electrical reading, we use an AFM analogue of the anisotropic magnetoresistance. Our microscopic theory modelling confirms that this archetypical spintronic effect, discovered more than 150 years ago in ferromagnets, is also present in AFMs. Our work demonstrates the feasibility of fabricating room-temperature spintronic memories with AFMs, which in turn expands the base of available magnetic materials for devices with properties that cannot be achieved with ferromagnets.

  6. 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.

  7. InAs quantum well Hall devices for room-temperature detection of single magnetic biomolecular labels.

    SciTech Connect

    Mihajlovic, G.; Xiong, P.; von Molnar, S.; Field, M.; Sullivan, G. J.; Materials Science Division; Florida State Univ.; Teledyne Scientific Co. LLC

    2007-08-01

    Hall sensors with cross width of {approx}1 {micro}m were fabricated from InAs/AlSb quantum well semiconductor heterostructures containing two-dimensional electron gas. The room-temperature device characteristics were examined by Hall effect and electronic noise measurements along with analytical calculations. In the low-frequency range, from 20 Hz to 1.6 kHz, the noise-equivalent magnetic field resolution was found to be limited by 1/f and generation-recombination noise from 22 to 3.5 {micro}T/{radical}Hz. The corresponding noise-equivalent magnetic moment resolution reached 10{sub {mu}{sub B}}{sup 6}/{radical}Hz at {approx}700 Hz and was even lower at higher frequencies. Using a phase-sensitive measurement technique, detection of a single 1.2 {micro}m diameter bead, suitable for biological applications, was achieved with a signal to noise ratio of {approx}33.3 dB, as well as detection of six 250 nm beads with a signal to noise of {approx}2.3 dB per bead. The work demonstrates the efficacy of InAs quantum well Hall devices for application in high sensitivity detection of single magnetic biomolecular labels.

  8. Study of dielectric, magnetic, ferroelectric and magnetoelectric properties in the PbMn(x)Ti(1-x)O(3) system at room temperature.

    PubMed

    Kumar, Manoj; Yadav, K L

    2007-06-20

    We report magnetoelectric coupling at room temperature between ferroelectric and magnetic order parameters in Mn-doped PbTiO(3) compounds prepared by a solid-state reaction method. X-ray diffraction showed that PbMn(x)Ti(1-x)O(3) (x = 0.1, 0.3 and 0.5) compounds were single phase. The Mn substitution reduced the lattice distortion, i.e., the c/a ratio, and hence the ferroelectric Curie temperature (T(C)) decreased with increasing Mn content. High-temperature magnetization measurements showed that the ferromagnetic Curie temperature (T(M)) decreases with increasing Mn in PbMn(x)Ti(1-x)O(3). An anomaly in the dielectric constant (ε) was observed in the vicinity of the ferromagnetic transition temperature. These samples exhibited magnetism and ferroelectricity simultaneously at room temperature, which was evidenced from the coexistence of saturated magnetization and polarization hysteresis loops. An enhancement in saturation polarization after poling the samples in the magnetic field was evidence of magnetoelectric coupling at room temperature. An enhancement of 11-13% in polarization was observed after poling the samples in a magnetic field at 1.2 T. PMID:21694032

  9. Dynamic in situ observation of voltage-driven repeatable magnetization reversal at room temperature.

    PubMed

    Gao, Ya; Hu, Jia-Mian; Nelson, C T; Yang, T N; Shen, Y; Chen, L Q; Ramesh, R; Nan, C W

    2016-03-31

    Purely voltage-driven, repeatable magnetization reversal provides a tantalizing potential for the development of spintronic devices with a minimum amount of power consumption. Substantial progress has been made in this subject especially on magnetic/ferroelectric heterostructures. Here, we report the in situ observation of such phenomenon in a NiFe thin film grown directly on a rhombohedral Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PMN-PT) ferroelectric crystal. Under a cyclic voltage applied perpendicular to the PMN-PT without a magnetic field, the local magnetization of NiFe can be repetitively reversed through an out-of-plane excursion and then back into the plane. Using phase field simulations we interpret magnetization reversal as a synergistic effect of the metastable ferroelastic switching in the PMN-PT and an electrically rotatable local exchange bias field arising from the heterogeneously distributed NiO clusters at the interface.

  10. Dynamic in situ observation of voltage-driven repeatable magnetization reversal at room temperature

    NASA Astrophysics Data System (ADS)

    Gao, Ya; Hu, Jia-Mian; Nelson, C. T.; Yang, T. N.; Shen, Y.; Chen, L. Q.; Ramesh, R.; Nan, C. W.

    2016-03-01

    Purely voltage-driven, repeatable magnetization reversal provides a tantalizing potential for the development of spintronic devices with a minimum amount of power consumption. Substantial progress has been made in this subject especially on magnetic/ferroelectric heterostructures. Here, we report the in situ observation of such phenomenon in a NiFe thin film grown directly on a rhombohedral Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PMN-PT) ferroelectric crystal. Under a cyclic voltage applied perpendicular to the PMN-PT without a magnetic field, the local magnetization of NiFe can be repetitively reversed through an out-of-plane excursion and then back into the plane. Using phase field simulations we interpret magnetization reversal as a synergistic effect of the metastable ferroelastic switching in the PMN-PT and an electrically rotatable local exchange bias field arising from the heterogeneously distributed NiO clusters at the interface.

  11. Dynamic in situ observation of voltage-driven repeatable magnetization reversal at room temperature.

    PubMed

    Gao, Ya; Hu, Jia-Mian; Nelson, C T; Yang, T N; Shen, Y; Chen, L Q; Ramesh, R; Nan, C W

    2016-01-01

    Purely voltage-driven, repeatable magnetization reversal provides a tantalizing potential for the development of spintronic devices with a minimum amount of power consumption. Substantial progress has been made in this subject especially on magnetic/ferroelectric heterostructures. Here, we report the in situ observation of such phenomenon in a NiFe thin film grown directly on a rhombohedral Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PMN-PT) ferroelectric crystal. Under a cyclic voltage applied perpendicular to the PMN-PT without a magnetic field, the local magnetization of NiFe can be repetitively reversed through an out-of-plane excursion and then back into the plane. Using phase field simulations we interpret magnetization reversal as a synergistic effect of the metastable ferroelastic switching in the PMN-PT and an electrically rotatable local exchange bias field arising from the heterogeneously distributed NiO clusters at the interface. PMID:27029464

  12. Dynamic in situ observation of voltage-driven repeatable magnetization reversal at room temperature

    PubMed Central

    Gao, Ya; Hu, Jia-Mian; Nelson, C. T.; Yang, T. N.; Shen, Y.; Chen, L. Q.; Ramesh, R.; Nan, C. W.

    2016-01-01

    Purely voltage-driven, repeatable magnetization reversal provides a tantalizing potential for the development of spintronic devices with a minimum amount of power consumption. Substantial progress has been made in this subject especially on magnetic/ferroelectric heterostructures. Here, we report the in situ observation of such phenomenon in a NiFe thin film grown directly on a rhombohedral Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PMN-PT) ferroelectric crystal. Under a cyclic voltage applied perpendicular to the PMN-PT without a magnetic field, the local magnetization of NiFe can be repetitively reversed through an out-of-plane excursion and then back into the plane. Using phase field simulations we interpret magnetization reversal as a synergistic effect of the metastable ferroelastic switching in the PMN-PT and an electrically rotatable local exchange bias field arising from the heterogeneously distributed NiO clusters at the interface. PMID:27029464

  13. Cobalt nanoparticles doped emaraldine salt of polyaniline: A promising room temperature magnetic semiconductor

    NASA Astrophysics Data System (ADS)

    Hatamie, Shadie; Kulkarni, M. V.; Kulkarni, S. D.; Ningthoujam, R. S.; Vatsa, R. K.; Kale, S. N.

    2010-12-01

    Incorporation of magnetic nanoparticles in polymers with organic functional groups working as semiconducting substrate is of immense interest in the field of dilute magnetic semiconductors (DMS) and spintronics. In this article we report on synthesis and evaluation of dilutely doped (0-10 wt%) cobalt nanoparticles in emaraldine salt (ES) of polyaniline in the presence of dodecyl benzene sulfonic acid (DBSA) and p-toluene sulfonic acid (p-TSA) using a sonochemical-assisted-reduction approach as a possible DMS candidate. The X-ray diffraction pattern and high resolution transmission electron microscopy (HRTEM) image show the ES to be polycrystalline, in which 10 nm sized Co nanoparticles get embedded in its FCC structural form. From Fourier transform infrared (FT-IR) and UV-visible (UV-vis) spectroscopy studies, it is predicted that cobalt particles get electrostatically bound to the specific SO3- ion sites of ES, thereby modifying torsional degrees of freedom of the system. The applied field dependent magnetization study shows that the sample exhibits hysteresis loop with a minimal doping of 3 wt% of Co nanoparticles and increases with the amount of Co nanoparticles in ES due to dipolar interaction. The electron transport data show that with increase in Co wt% there is a gradual shift from ohmic to non-ohmic response to the sample bias, accompanied by opening of electrical hysteresis and an increased resistance. The non-linear response of higher doped systems has been attributed to the combination of direct and Fowler-Nordheim tunneling phenomena in these systems. Persistence of optical and transport properties of the polymer, with an introduction of magnetic moment in the system, envisages the system to be a fine magnetic semiconductor.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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.

  15. Effect of Yb substitution on room temperature magnetic and dielectric properties of bismuth ferrite nanoparticles

    NASA Astrophysics Data System (ADS)

    Remya, K. P.; Amirthapandian, S.; Manivel Raja, M.; Viswanathan, C.; Ponpandian, N.

    2016-10-01

    Effect of the Yb dopant on the structural, magnetic, and electrical properties of the multiferroic BiFeO3 have been studied. The structural properties of sol-gel derived Bi1-xYbxFeO3 (x = 0.0, 0.1, and 0.2) nanoparticles reveal the formation of a rhombohedrally distorted perovskite in XRD and a reduction in the average grain size have been observed with an increase in the Yb concentration. Microstructural studies exhibited the formation of sphere like morphology with decreasing particle size with increase in the dopant concentration. The effective doping also resulted in larger magnetization as well as coercivity with the maximum of 257 Oe and 1.76 emu/g in the Bi0.8Yb0.2FeO3 nanoparticles. Ferroelectric as well as dielectric properties of the nanoparticles were also improved on doping. The best results were obtained for the BiFeO3 nanoparticles having Yb concentration x = 0.2.

  16. 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.

  17. Electric field-induced tuning of magnetism in PbFe{sub 0.5}Nb{sub 0.5}O{sub 3} at room temperature

    SciTech Connect

    Rayaprol, S. E-mail: brangadi@gmail.com; Mukherjee, S.; Kaushik, S. D.; Matteppanavar, S.; Angadi, B. E-mail: brangadi@gmail.com

    2015-08-07

    We study the influence of electrical poling, carried out at room temperature, on the structure and magnetism of Pb(Fe{sub 0.5}Nb{sub 0.5})O{sub 3} by analyzing the differences observed in structural and magnetic properties before and after the electrical poling. The changes observed in magnetization of Pb(Fe{sub 0.5}Nb{sub 0.5})O{sub 3} before and after electrical poling exhibit considerably strong converse magnetoelectric effect at room temperature. In addition, the strengthening of Fe/Nb-O bond due to electrical poling is discussed on the basis of Raman spectral studies and analysis of neutron diffraction patterns. The potential tunability of magnetization with electrical poling can be an ideal tool for realization of application potential of this multiferroic material.

  18. Fast Room Temperature Very Low Field-Magnetic Resonance Imaging System Compatible with MagnetoEncephaloGraphy Environment.

    PubMed

    Galante, Angelo; Sinibaldi, Raffaele; Conti, Allegra; De Luca, Cinzia; Catallo, Nadia; Sebastiani, Piero; Pizzella, Vittorio; Romani, Gian Luca; Sotgiu, Antonello; Della Penna, Stefania

    2015-01-01

    In recent years, ultra-low field (ULF)-MRI is being given more and more attention, due to the possibility of integrating ULF-MRI and Magnetoencephalography (MEG) in the same device. Despite the signal-to-noise ratio (SNR) reduction, there are several advantages to operating at ULF, including increased tissue contrast, reduced cost and weight of the scanners, the potential to image patients that are not compatible with clinical scanners, and the opportunity to integrate different imaging modalities. The majority of ULF-MRI systems are based, until now, on magnetic field pulsed techniques for increasing SNR, using SQUID based detectors with Larmor frequencies in the kHz range. Although promising results were recently obtained with such systems, it is an open question whether similar SNR and reduced acquisition time can be achieved with simpler devices. In this work a room-temperature, MEG-compatible very-low field (VLF)-MRI device working in the range of several hundred kHz without sample pre-polarization is presented. This preserves many advantages of ULF-MRI, but for equivalent imaging conditions and SNR we achieve reduced imaging time based on preliminary results using phantoms and ex-vivo rabbits heads.

  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. Fast Room Temperature Very Low Field-Magnetic Resonance Imaging System Compatible with MagnetoEncephaloGraphy Environment

    PubMed Central

    Galante, Angelo; Sinibaldi, Raffaele; Conti, Allegra; De Luca, Cinzia; Catallo, Nadia; Sebastiani, Piero; Pizzella, Vittorio; Romani, Gian Luca; Sotgiu, Antonello; Della Penna, Stefania

    2015-01-01

    In recent years, ultra-low field (ULF)-MRI is being given more and more attention, due to the possibility of integrating ULF-MRI and Magnetoencephalography (MEG) in the same device. Despite the signal-to-noise ratio (SNR) reduction, there are several advantages to operating at ULF, including increased tissue contrast, reduced cost and weight of the scanners, the potential to image patients that are not compatible with clinical scanners, and the opportunity to integrate different imaging modalities. The majority of ULF-MRI systems are based, until now, on magnetic field pulsed techniques for increasing SNR, using SQUID based detectors with Larmor frequencies in the kHz range. Although promising results were recently obtained with such systems, it is an open question whether similar SNR and reduced acquisition time can be achieved with simpler devices. In this work a room-temperature, MEG-compatible very-low field (VLF)-MRI device working in the range of several hundred kHz without sample pre-polarization is presented. This preserves many advantages of ULF-MRI, but for equivalent imaging conditions and SNR we achieve reduced imaging time based on preliminary results using phantoms and ex-vivo rabbits heads. PMID:26630172

  1. Corneal storage at room temperature.

    PubMed

    Sachs, U; Goldman, K; Valenti, J; Kaufman, H E

    1978-06-01

    Short-term eye banking is based mainly on moist chamber and McCarey-Kaufman medium (M-K medium) preservation. Both involve a controlled 4 C temperature for storage. Warming the cornea to room temperature, however, drastically affects the endothelial viability. On enzymatic staining and histological study, the M-K medium-stored rabbit corneas had more normal endothelium than did "moist chamber" eyes when storage was prolonged for seven days at room temperature. In human corneas that were kept at 4 C for 24 hours and then exposed to a temperature of 25 C, destruction of organelles had occurred by six hours and was increased by 12 hours. Corneas that were kept in M-K medium had relatively intact endothelium after four days, but cell disruption and vacuolation was present by the seventh day. The M-K medium, therefore, affords protection to tissue warmed to room temperature, where metabolic activity is resumed. PMID:350203

  2. Room-temperature switching of magnetic hysteresis by reversible single-crystal-to-single-crystal solvent exchange in imidazole-inspired Fe(ii) complexes.

    PubMed

    Huang, Wei; Shen, Fuxing; Zhang, Ming; Wu, Dayu; Pan, Feifei; Sato, Osamu

    2016-10-14

    The recent upsurge in molecular magnetism reflects its application in the areas of sensors and molecular switches. Thermal hysteresis is crucial to the molecular bistability and information storage, a wide hysteresis near room temperature is expected to be of practical sense for the molecular compound. In this work, spin crossover iron(ii) complexes [Fe(Liq)2](BF4)2·(CH3CH2)2O (1-Et2O) and [Fe(Liq)2](BF4)2·3H2O (1-3H2O) were prepared and structurally and magnetically analysed. The single-crystal-to-single-crystal (SCSC) solvation transformation and the influence on the crystal structures and magnetic hysteresis were investigated in an etherification-hydration cycle. At room temperature, X-ray diffraction experiments indicated a transformation from one crystal (1-Et2O, P21212) to another crystal (1-3H2O, P212121) upon humidity exposure and reversible recovery of its crystallinity upon exposure to ether vapor. The etherified phase 1-Et2O exhibits room temperature spin crossover (T1/2 = 305 K) but negligible thermal hysteresis, however the hydrated phase 1-3H2O exhibits the apparent hysteresis loop (T1/2↑ = 346 K, T1/2↓ = 326 K) which expands to room temperature. This effect is associated with the change of intermolecular cooperativity in the etherification-hydration recyclability. PMID:27477547

  3. Room-temperature switching of magnetic hysteresis by reversible single-crystal-to-single-crystal solvent exchange in imidazole-inspired Fe(ii) complexes.

    PubMed

    Huang, Wei; Shen, Fuxing; Zhang, Ming; Wu, Dayu; Pan, Feifei; Sato, Osamu

    2016-10-14

    The recent upsurge in molecular magnetism reflects its application in the areas of sensors and molecular switches. Thermal hysteresis is crucial to the molecular bistability and information storage, a wide hysteresis near room temperature is expected to be of practical sense for the molecular compound. In this work, spin crossover iron(ii) complexes [Fe(Liq)2](BF4)2·(CH3CH2)2O (1-Et2O) and [Fe(Liq)2](BF4)2·3H2O (1-3H2O) were prepared and structurally and magnetically analysed. The single-crystal-to-single-crystal (SCSC) solvation transformation and the influence on the crystal structures and magnetic hysteresis were investigated in an etherification-hydration cycle. At room temperature, X-ray diffraction experiments indicated a transformation from one crystal (1-Et2O, P21212) to another crystal (1-3H2O, P212121) upon humidity exposure and reversible recovery of its crystallinity upon exposure to ether vapor. The etherified phase 1-Et2O exhibits room temperature spin crossover (T1/2 = 305 K) but negligible thermal hysteresis, however the hydrated phase 1-3H2O exhibits the apparent hysteresis loop (T1/2↑ = 346 K, T1/2↓ = 326 K) which expands to room temperature. This effect is associated with the change of intermolecular cooperativity in the etherification-hydration recyclability.

  4. Novel room-temperature spin-valve-like magnetoresistance in magnetically coupled nano-column Fe3O4/Ni heterostructure.

    PubMed

    Xiao, Wen; Song, Wendong; Herng, Tun Seng; Qin, Qing; Yang, Yong; Zheng, Ming; Hong, Xiaoliang; Feng, Yuan Ping; Ding, Jun

    2016-08-25

    Herein, we design a room-temperature spin-valve-like magnetoresistance in a nano-column Fe3O4/Ni heterostructure without using a non-magnetic spacer or pinning layer. An Fe3O4 nano-column film is self-assembled on a Ni underlayer by the thermal decomposition method. The wet-chemical self-assembly is facile, economical and scalable. The magnetoresistance (MR) response of the Ni underlayer in the heterostructure under positive and negative out-of-plane magnetic fields differ by ∼0.25 at room temperature and ∼0.43 at 100 K. We attribute the spin-valve-like magnetoresistance to the unidirectional magnetic anisotropy of the Ni underlayer when being magnetically coupled by the Fe3O4 nano-column film. The out-of-plane negative-field magnetization is higher than the positive-field magnetization, affirming the unidirectional magnetic anisotropy of the Fe3O4/Ni heterostructure. Temperature-dependent magnetic and resistivity studies illustrate a close correlation between the magnetization transition of Fe3O4 and resistivity transition of Ni and prove a magnetic coupling between the Fe3O4 and Ni. First-principles calculations reveal that the Fe3O4/Ni model under a negative magnetic field is energetically more stable than that under a positive magnetic field. Furthermore, partial density of states (PDOS) analysis demonstrates the unidirectional magnetic anisotropy of the Ni 3d orbital. This is induced by the strong ferromagnetic coupling between Fe3O4 and Ni via oxygen-mediated Fe 3d-O 2p-Ni 3d hybridizations. PMID:27526860

  5. Room temperature magnetism and metal to semiconducting transition in dilute Fe doped Sb1-xSex semiconducting alloy thin films

    NASA Astrophysics Data System (ADS)

    Agrawal, Naveen; Sarkar, Mitesh; Chawda, Mukesh; Ganesan, V.; Bodas, Dhananjay

    2015-02-01

    The magnetism was observed in very dilute Fe doped alloy thin film Fe0.008Sb1-xSex, for x = 0.01 to 0.10. These thin films were grown on silicon substrate using thermal evaporation technique. Structural, electrical, optical, charge carrier concentration measurement, surface morphology and magnetic properties were observed using glancing incidence x-ray diffraction (GIXRD), four probe resistivity, photoluminescence, Hall measurement, atomic force microscopy (AFM) and magnetic force microscopy (MFM) techniques, respectively. No peaks of iron were seen in GIXRD. The resistivity results show that activation energy increases with increase in selenium (Se) concentration. The Arrhenius plot reveals metallic behavior below room temperature. The low temperature conduction is explained by variable range-hopping mechanism, which fits very well in the temperature range 150-300 K. The decrease in density of states has been observed with increasing selenium concentration (x = 0.01 to 0.10). There is a metal-to-semiconductor phase transition observed above room temperature. This transition temperature is Se concentration dependent. The particle size distribution ˜47-61 nm is evaluated using AFM images. These thin films exhibit ferromagnetic interactions at room temperature.

  6. A new perspective on self-reversed thermo-remanent magnetization and room-temperature magnetic exchange bias in quenched and annealed ferri-ilmenite solid solutions

    NASA Astrophysics Data System (ADS)

    Robinson, P.; Harrison, R. J.; Fabian, K.; McEnroe, S. A.; Miyajima, N.

    2012-04-01

    kinds of regions, one dominated by A-ordering containing smaller regions of B-ordering and the other dominated by B-ordering with smaller regions of A-ordering. The key feature for self-reversal is that small and shrinking domains became progressively Fe-enriched compared to their larger neighbors, and the elusive "x-phase" is explained as a less strongly ordered Fe-enriched phase near APBs during coarsening. We pursued these studies further with TEM of the APB's and demonstrating chemical phase separation in a synthetic composition FeTiO3 = 0.61. Subsequent annealing of this sample showed self-reversed TRM and room-temperature magnetic exchange bias. Analysis of charge balance across APB's showed the significant role of contact layers and disordered layers. Monte Carlo simulations demonstrated the necessity for Fe-enrichment in the diminishing phase. A theoretical approach to the ferri-ilmenite phase diagram showed potential for metastable chemical phase separation over a wide composition range, related to the order parameter Q, at temperatures well above phase separation over a limited composition range related to a chemical solvus. A key feature of the new perspective is the recognition of simple antiferromagnetic coupling across the APBs. Evidence suggests negative magnetic (antiferromagnetic) coupling required for magnetic self-reversal can only be maintained when the antiphase domains are smaller than ~ 50 nm.

  7. Irradiation induced ferromagnetism at room temperature in TiO{sub 2} thin films: X-ray magnetic circular dichroism characterizations

    SciTech Connect

    Thakur, Hardeep; Sharma, K. K.; Thakur, P.; Brookes, N. B.; Kumar, Ravi; Singh, A. P.; Kumar, Yogesh; Gautam, S.; Chae, K. H.

    2011-05-09

    We report on the room temperature ferromagnetism in the swift heavy ion (SHI) irradiated TiO{sub 2} thin films by x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) experiments at the O K and Ti L{sub 3,2} absorption edges. The XAS/XMCD measurements provide direct evidence of magnetic polarization of the O 2p and Ti 3d orbitals. The unquenched orbital magnetic moment within the O 2p shell is ferromagnetically coupled to the neighboring Ti moments, which illustrates the intense hybridization of the O 2p and Ti 3d orbitals induced by SHI irradiation.

  8. 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.

  9. 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.

  10. 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

  11. 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.

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

    PubMed

    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

  13. 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.

  14. Large magnetic response in (Bi4Nd)Ti3(Fe0.5Co0.5)O15 ceramic at room-temperature

    NASA Astrophysics Data System (ADS)

    Yang, F. J.; Su, P.; Wei, C.; Chen, X. Q.; Yang, C. P.; Cao, W. Q.

    2011-12-01

    Ceramics of Nd/Co co-substituted Bi5Ti3FeO15, i.e., (Bi4Nd)Ti3(Fe0.5Co0.5)O15 were prepared by the conventional solid-state reaction method. The X-ray diffraction pattern demonstrates that the sample of the layered perovskite phase was successfully obtained, even if little Bi-deficient pyrochlore Bi2Ti2O7 also existed. The ferroelectric and magnetic Curie temperatures were determined to be 1077 K and 497 K, respectively. The multiferroic property of the sample at room temperature was demonstrated by ferroelectric and magnetic measurements. Remarkably, by Nd/Co co-substituting, the sample exhibited large magnetic response with 2Mr = 330 memu/g and 2Hc = 562 Oe at applied magnetic field of 8 kOe at room temperature. The present work suggests the possibility of doped Bi5Ti3FeO15 as a potential multiferroic.

  15. Verification of antiferromagnetic exchange coupling at room temperature using polar magneto-optic Kerr effect in thin EuS/Co multilayers with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Goschew, A.; Scott, M.; Fumagalli, P.

    2016-08-01

    We report on magneto-optic Kerr measurements in polar geometry carried out on a series of thin Co/EuS multilayers on suitable Co/Pd-multilayer substrates. Thin Co/EuS multilayers of a few nanometers individual layer thickness usually have their magnetization in plane. Co/Pd multilayers introduce a perpendicular magnetic anisotropy in the Co/EuS layers deposited on top, thus making it possible to measure magneto-optic signals in the polar geometry in remanence in order to study exchange coupling. Magneto-optic Kerr-effect spectra and hysteresis loops were recorded in the visible and ultraviolet photon-energy range at room temperature. The EuS contribution to the magneto-optic signal is extracted at 4.1 eV by combining hysteresis loops measured at different photon energies with polar magneto-optic Kerr-effect spectra recorded in remanence and in an applied magnetic field of 2.2 T. The extracted EuS signal shows clear signs of antiferromagnetic coupling of the Eu magnetic moments to the Co layers. This implies that the ordering temperature of at least a fraction of the EuS layers is above room temperature proving that magneto-optic Kerr-effect spectroscopy can be used here as a quasi-element-specific method.

  16. Room-temperature ferromagnetism of Cu-doped ZnO films probed by soft X-ray magnetic circular dichroism.

    PubMed

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

    2010-11-12

    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 Cu2+ ions present in all the samples. We find that a sufficient amount of both oxygen vacancies (V(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(O) are mediated by the large-sized vacancy orbitals.

  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. 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.

  19. Room temperature magnetoresistance in CoFeB/SrTiO{sub 3}/CoFeB magnetic tunnel junctions deposited by ion beam sputtering

    SciTech Connect

    Hassen, E. M. J.; Viala, B.; Cyrille, M. C.; Cartier, M.; Redon, O.; Lima, P.; Belhadji, B.; Yang, H. X.; Chshiev, M.; Velev, J.

    2012-04-01

    Room temperature transport properties are reported in polycrystalline SrTiO{sub 3}-based magnetic tunnel junctions deposited by ion beam sputtering. The junctions comprise CoFeB electrodes and the SrTiO{sub 3} barrier with thickness varied between 0.9 and 1.9 nm. Resistance area product values between 3 {Omega}.{mu}m{sup 2} and 22 k{Omega}.{mu}m{sup 2} have been measured with a tunnel magnetoresistance ratio ranging from 3.1 to 13% at room temperature. At low barrier thickness (1.2 nm), ferromagnetic coupling between electrodes is observed, indicating the presence of defects in the structure. A post-oxidation step was found to improve transport properties at lower barrier thickness.

  20. Evidence for room temperature ferromagnetism in CuxZn1-xO from magnetic studies in CuxZn1-xO/CuO composite

    NASA Astrophysics Data System (ADS)

    Seehra, M. S.; Dutta, P.; Singh, V.; Zhang, Y.; Wender, I.

    2007-05-01

    Magnetic studies in bulk 57% CuxZn1-xO/43% CuO composite prepared chemically with x =0.10 (0.03) are reported. Temperature dependence of the magnetic susceptibility shows clear signature of the Néel temperature TN≃230K for pure CuO. Hysteresis loop studies in the zero-field-cooled sample show room-temperature ferromagnetism with coercivity Hc≃50Oe at 300K with strong temperature dependence for T <300K. A negative exchange bias He at 5K is observed when the sample is cooled from RT in H =20kOe, and its temperature dependence yields He→0 at TN=230K of CuO. These results and the temperature dependence of remanence Mr provide strong evidence that the CuxZn1-xO phase with x ≃0.10 is a ferromagnet with Tc≃400K. An electron magnetic resonance signal due to Cu2+ substituting for Zn2+ in CuxZn1-xO is also observed.

  1. A new partially deprotonated mixed-valence manganese(II,III) hydroxide-arsenate with electronic conductivity: magnetic properties of high- and room-temperature sarkinite.

    PubMed

    de Pedro, Imanol; Rojo, Jose M; Rius, Jordi; Vallcorba, Oriol; Ruiz de Larramendi, Idoia; Rodríguez Fernández, Jesús; Lezama, Luis; Rojo, Teofilo

    2012-05-01

    A new three-dimensional hydroxide-arsenate compound called compound 2 has been synthesized by heating (in air) of the sarkinite phase, Mn(2)(OH)AsO(4) (compound 1), with temperature and time control. The crystal structure of this high-temperature compound has been solved by Patterson-function direct methods. A relevant feature of this new material is that it is actually the first member of the adamite-type family with mixed-valence manganese(II,III) and electronic conductivity. Crystal data: a = 6.7367(5) Å, b = 7.5220(6) Å, c = 9.8117(6) Å, α = 92.410(4)°, β = 109.840(4)°, γ = 115.946(4)°, P1̅. The unit cell content derived from Rietveld refinement is Mn(8)(O(4)H(x))(AsO(4))(4). Its framework, projected along [111], is characterized by rings of eight Mn atoms with the OH(-)/O(2-) inside the rings. These rings form an almost perfect hexagonal arrangement with the AsO(4) groups placed in between. Bond-valence analysis indicates both partial deprotonation (x ≅ 3) and the presence of Mn in two different oxidation states (II and III), which is consistent with the electronic conductivity above 300 °C from electrochemical measurements. The electron paramagnetic resonance spectra of compound 1 and of its high-temperature form compound 2 show the presence of antiferromagnetic interactions with stronger magnetic coupling for the high-temperature phase. Magnetization measurements of room-temperature compound 1 show a complex magnetic behavior, with a three-dimensional antiferromagnetic ordering and magnetic anomalies at low temperatures, whereas for compound 2, an ordered state is not reached. Magnetostructural correlations indicate that superexchange interactions via oxygen are present in both compounds. The values of the magnetic exchange pathways [Mn-O-Mn] are characteristic of antiferromagnetic couplings. Notwithstanding, the existence of competition between different magnetic interactions through superexchange pathways can cause the complex magnetic

  2. Nuclear magnetic resonance on room temperature samples in nanotesla fields using a two-stage dc superconducting quantum interference device sensor

    NASA Astrophysics Data System (ADS)

    Körber, R.; Casey, A.; Shibahara, A.; Piscitelli, M.; Cowan, B. P.; Lusher, C. P.; Saunders, J.; Drung, D.; Schurig, Th.

    2007-10-01

    We describe a compact system for pulsed nuclear magnetic resonance at ultralow magnetic fields on small liquid samples (˜0.14ml) at room temperature. The broadband spectrometer employs an integrated two-stage superconducting quantum interference device current sensor with a coupled energy sensitivity of 50h, in the white noise limit. Environmental noise is screened using a compact arrangement of mu-metal and a superconducting shield. Proton signals in water have been observed down to 93nT (a Larmor frequency of 4.0Hz), with a minimum linewidth of 0.16Hz measured at ˜40Hz. Two-component free induction decays were observed from oil/water mixtures between 275 and 300K.

  3. Room temperature magnetic and dielectric properties of cobalt doped CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics

    SciTech Connect

    Mu, Chunhong; Song, Yuanqiang Wang, Xiaoning; Wang, Haibin

    2015-05-07

    CaCu{sub 3}Ti{sub 4−x}Co{sub x}O{sub 12} (x = 0, 0.2, 0.4) ceramics were prepared by a conventional solid state reaction, and the effects of cobalt doping on the room temperature magnetic and dielectric properties were investigated. Both X-ray diffraction and energy dispersive X-ray spectroscopy confirmed the presence of Cu and Co rich phase at grain boundaries of Co-doped ceramics. Scanning electron microscopy micrographs of Co-doped samples showed a striking change from regular polyhedral particle type in pure CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) to sheet-like grains with certain growth orientation. Undoped CaCu{sub 3}Ti{sub 4}O{sub 12} is well known for its colossal dielectric constant in a broad temperature and frequency range. The dielectric constant value was slightly changed by 5 at. % and 10 at. % Co doping, whereas the second relaxation process was clearly separated in low frequency region at room temperature. A multirelaxation mechanism was proposed to be the origin of the colossal dielectric constant. In addition, the permeability spectra measurements indicated Co-doped CCTO with good magnetic properties, showing the initial permeability (μ′) as high as 5.5 and low magnetic loss (μ″ < 0.2) below 3 MHz. And the interesting ferromagnetic superexchange coupling in Co-doped CaCu{sub 3}Ti{sub 4}O{sub 12} was discussed.

  4. A finite element analysis of room temperature silicon crystals for the Advanced Photon Source bending-magnet and insertion-device beams

    SciTech Connect

    Assoufid, L.; Lee, W.K.; Mills, D.M.

    1994-08-01

    The third generation of synchrotron radiation sources, such as the Advanced Photon Source (APS), will provide users with a high brilliance x-ray beam with high power and power densities. In many cases, the first optical component to intercept the x-ray beam is a silicon-crystal monochromator. Due to extreme heat loading, the photon throughput and brilliance will be severely degraded if the monochromator is not properly designed (or cooled). This document describes a series of finite element analyses performed on room temperature silicon for the three standard APS sources, namely, the bending magnet, Wiggler A, and Undulator A. The modeling is performed with the silicon cooled directly with water or liquid gallium through rectangular channels. The temperature distributions and thermally induced deformations are presented.

  5. Manipulation of magnetism in perpendicularly magnetized Heusler alloy Co2FeAl0.5Si0.5 by electric-field at room temperature

    NASA Astrophysics Data System (ADS)

    Wang, H. L.; Wu, Y.; Yu, H. J.; Jiang, Y.; Zhao, J. H.

    2016-09-01

    The electrical manipulation of magnetic properties in perpendicularly magnetized Co2FeAl0.5Si0.5 ultra-thin films has been investigated. An electric-field is applied by utilizing either a solid-state dielectric HfO2 film or an ionic gel film as the gate insulator in the form of a field effect parallel capacitor. Obvious changes of the coercive field and Curie temperature (˜24 K) by gating voltage are observed for a 0.8 nm thick film, while a clear change of the magnetic anisotropy is obtained for the 1.1 nm thick one. The experimental results have been attributed to both the electric-field-induced modulation of carrier density near the interface and the oxidation-reduction effect inside the magnetic films.

  6. 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.

  7. Investigation of local structural environments and room-temperature ferromagnetism in (Fe,Cu)-codoped In2O3 diluted magnetic oxide films.

    PubMed

    An, Yukai; Xing, Yaya; Pan, Fei; Wu, Zhonghua; Liu, Jiwen

    2016-05-11

    The local structural, optical, magnetic and transport properties of (In0.95-xFexCu0.05)2O3 (0.06 ≤ x ≤ 0.20) films deposited by RF-magnetron sputtering have been systemically studied by different experimental techniques. Detailed structural analyses using XRD, XPS, EXAFS and full multiple-scattering ab initio theoretical calculations of Fe K-edge XANES show that the (In0.95-xFexCu0.05)2O3 films have the same cubic bixbyite structure as pure In2O3. The doped Fe ions exist at both +2 and +3 oxidation states, substituting for the In(3+) sites in the In2O3 lattice and forming a FeIn + 2VO complex with the O vacancy in the first coordination shell of Fe. However, the co-doped Cu atoms are not incorporated into the In2O3 lattice and form the Cu metal clusters due to high ionization energy. UV-Vis measurements show that the optical band gap Eg decreases monotonically with the increase of Fe concentration, implying an increasing s-pd exchange interaction in the films. All the films display intrinsic room-temperature (RT) ferromagnetism and the saturated magnetization (Ms) increases monotonically with Fe doping. The temperature dependence of the resistivity data suggests the conduction mechanism of Mott variable-range hopping (VRH) at low temperature, confirming that the carriers are localized. It can be concluded that the observed RT ferromagnetism in the films originates from the overlapping of polarons mediated by oxygen vacancies based on the bound magnetic polaron (BMP) model. The variation of the localization effect of carriers with Fe doping can obviously adjust the magnetic exchange interaction in the (In0.95-xFexCu0.05)2O3 films. PMID:27139011

  8. Investigation of local structural environments and room-temperature ferromagnetism in (Fe,Cu)-codoped In2O3 diluted magnetic oxide films.

    PubMed

    An, Yukai; Xing, Yaya; Pan, Fei; Wu, Zhonghua; Liu, Jiwen

    2016-05-11

    The local structural, optical, magnetic and transport properties of (In0.95-xFexCu0.05)2O3 (0.06 ≤ x ≤ 0.20) films deposited by RF-magnetron sputtering have been systemically studied by different experimental techniques. Detailed structural analyses using XRD, XPS, EXAFS and full multiple-scattering ab initio theoretical calculations of Fe K-edge XANES show that the (In0.95-xFexCu0.05)2O3 films have the same cubic bixbyite structure as pure In2O3. The doped Fe ions exist at both +2 and +3 oxidation states, substituting for the In(3+) sites in the In2O3 lattice and forming a FeIn + 2VO complex with the O vacancy in the first coordination shell of Fe. However, the co-doped Cu atoms are not incorporated into the In2O3 lattice and form the Cu metal clusters due to high ionization energy. UV-Vis measurements show that the optical band gap Eg decreases monotonically with the increase of Fe concentration, implying an increasing s-pd exchange interaction in the films. All the films display intrinsic room-temperature (RT) ferromagnetism and the saturated magnetization (Ms) increases monotonically with Fe doping. The temperature dependence of the resistivity data suggests the conduction mechanism of Mott variable-range hopping (VRH) at low temperature, confirming that the carriers are localized. It can be concluded that the observed RT ferromagnetism in the films originates from the overlapping of polarons mediated by oxygen vacancies based on the bound magnetic polaron (BMP) model. The variation of the localization effect of carriers with Fe doping can obviously adjust the magnetic exchange interaction in the (In0.95-xFexCu0.05)2O3 films.

  9. Super-giant magnetoresistance at room-temperature in copper nanowires due to magnetic field modulation of potential barrier heights at nanowire-contact interfaces.

    PubMed

    Hossain, Md I; Maksud, M; Palapati, N K R; Subramanian, A; Atulasimha, J; Bandyopadhyay, S

    2016-07-29

    We have observed a super-giant (∼10 000 000%) negative magnetoresistance at 39 mT field in Cu nanowires contacted with Au contact pads. In these nanowires, potential barriers form at the two Cu/Au interfaces because of Cu oxidation that results in an ultrathin copper oxide layer forming between Cu and Au. Current flows when electrons tunnel through, and/or thermionically emit over, these barriers. A magnetic field applied transverse to the direction of current flow along the wire deflects electrons toward one edge of the wire because of the Lorentz force, causing electron accumulation at that edge and depletion at the other. This lowers the potential barrier at the accumulated edge and raises it at the depleted edge, causing a super-giant magnetoresistance at room temperature.

  10. Giant tunneling magnetoresistance up to 330% at room temperature in sputter deposited Co{sub 2}FeAl/MgO/CoFe magnetic tunnel junctions

    SciTech Connect

    Wang Wenhong; Sukegawa, Hiroaki; Shan, Rong; Mitani, Seiji; Inomata, Koichiro

    2009-11-02

    Magnetoresistance ratio up to 330% at room temperature (700% at 10 K) has been obtained in a spin-valve-type magnetic tunnel junction (MTJ) consisting of a full-Heusler alloy Co{sub 2}FeAl electrode and a MgO tunnel barrier fabricated on a single crystal MgO (001) substrate by sputtering method. The output voltage of the MTJ at one-half of the zero-bias value was found to be as high as 425 mV, which is the largest reported to date in MTJs using Heusler alloy electrodes. The present finding suggests that Co{sub 2}FeAl may be one of the most promising candidates for future spintronics devices applications.

  11. Indication of intrinsic room-temperature ferromagnetism in Ti1-xCoxO2-δ thin film: An x-ray magnetic circular dichroism study

    NASA Astrophysics Data System (ADS)

    Mamiya, K.; Koide, T.; Fujimori, A.; Tokano, H.; Manaka, H.; Tanaka, A.; Toyosaki, H.; Fukumura, T.; Kawasaki, M.

    2006-08-01

    Soft x-ray magnetic circular dichroism (XMCD) measurements at the Co L2,3 edges of Co-doped rutile TiO2 at room temperature revealed clear multiplet features characteristic of ferromagnetic Co2+ ions coordinated by O2- ions, being in sharp contrast to the featureless XMCD spectrum of Co metal or metallic clusters. The absorption and XMCD spectra agree well with a full atomic-multiplet calculation for the Co2+ high-spin state in the D2h-symmetry crystal field at the Ti site in rutile TiO2. The results indicate that the ferromagnetism arises from the Co2+ ions substituting the Ti4+ ions.

  12. Room temperature ferromagnetic (Fe₁-xCox)₃BO₅ nanorods.

    PubMed

    He, Shuli; Zhang, Hongwang; Xing, Hui; Li, Kai; Cui, Hongfei; Yang, Chenguang; Sun, Shouheng; Zeng, Hao

    2014-07-01

    Cobalt-doped ferroferriborate ((Fe1-xCox)3BO5) nanorods (NRs) are synthesized by a one-pot high-temperature organic-solution-phase method. The aspect ratios of the NRs are tuned by the heating rate. These NRs form via anisotropic growth along twin boundaries of the multiply twinned nuclei. Magnetic properties are dramatically modified by Co substitutional doping, changing from antiferromagnetic order at low temperatures to ferromagnetic above room temperature, with a greatly enhanced magnetic ordering temperature. These anisotropic ferromagnetic NRs with a high ordering temperature may provide a new platform for understanding nanomagnetism and for magnetic applications. PMID:24905634

  13. Magnetic properties of epitaxial Fe{sub 3}O{sub 4} films with various crystal orientations and tunnel magnetoresistance effect at room temperature

    SciTech Connect

    Nagahama, Taro Matsuda, Yuya; Tate, Kazuya; Kawai, Tomohiro; Takahashi, Nozomi; Hiratani, Shungo; Watanabe, Yusuke; Yanase, Takashi; Shimada, Toshihiro

    2014-09-08

    Fe{sub 3}O{sub 4} is a ferrimagnetic spinel ferrite that exhibits electric conductivity at room temperature (RT). Although the material has been predicted to be a half metal according to ab-initio calculations, magnetic tunnel junctions (MTJs) with Fe{sub 3}O{sub 4} electrodes have demonstrated a small tunnel magnetoresistance (TMR) effect. Not even the sign of the tunnel magnetoresistance ratio has been experimentally established. Here, we report on the magnetic properties of epitaxial Fe{sub 3}O{sub 4} films with various crystal orientations. The films exhibited apparent crystal orientation dependence on hysteresis curves. In particular, Fe{sub 3}O{sub 4}(110) films exhibited in-plane uniaxial magnetic anisotropy. With respect to the squareness of hysteresis, Fe{sub 3}O{sub 4} (111) demonstrated the largest squareness. Furthermore, we fabricated MTJs with Fe{sub 3}O{sub 4}(110) electrodes and obtained a TMR effect of −12% at RT. The negative TMR ratio corresponded to the negative spin polarization of Fe{sub 3}O{sub 4} predicted from band calculations.

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

    DOE PAGES

    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.; et al

    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

  15. 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.

  16. 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...

  17. 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.

  18. Self-assembly of imidazolium-based surfactants in magnetic room-temperature ionic liquids: binary mixtures.

    PubMed

    Klee, Andreas; Prevost, Sylvain; Gradzielski, Michael

    2014-12-15

    The phase behaviour of binary mixtures of ionic surfactants (1-alkyl-3-imidazolium chloride, C(n)mimCl with n=14, 16 and 18) and imidazolium-based ionic liquids (1-alkyl-3-methylimidazolium tetrachloroferrate, C(n)mimFeCl4, with n=2 and 4) over a broad temperature range and the complete range of compositions is described. By using many complementary methods including differential scanning calorimetry (DSC), polarised microscopy, small-angle neutron and X-ray scattering (SANS/SAXS), and surface tension, the ability of this model system to support self-assembly is described quantitatively and this behaviour is compared with common water systems. The existence of micelles swollen by the solvent can be deduced from SANS experiments and represent a possible model for aggregates, which has barely been considered for ionic-liquid systems until now, and can be ascribed to the rather low solvophobicity of the surfactants. Our investigation shows that, in general, C(n)mimCl is a rather weak amphiphile in these ionic liquids. The amphiphilic strength increases systematically with the length of the alkyl chain, as seen from the phase behaviour, the critical micelle concentration, and also the level of definition of the aggregates formed.

  19. 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.

  20. Preparation of Pd/Fe3O4 nanoparticles by use of Euphorbia stracheyi Boiss root extract: A magnetically recoverable catalyst for one-pot reductive amination of aldehydes at room temperature.

    PubMed

    Nasrollahzadeh, Mahmoud; Sajadi, S Mohammad

    2016-02-15

    We describe a method for supporting palladium nanoparticles on magnetic nanoparticles using Euphorbia stracheyi Boiss root extract as the natural source of reducing and stabilizing agent. The progress of the reaction was monitored using UV-visible spectroscopy. The nanocatalyst was characterized by FE-SEM, TEM, XRD, EDS, FT-IR spectroscopy and ICP. The nanocatalyst was applied as an efficient, magnetically recoverable, highly reusable and heterogeneous catalyst for one-pot reductive amination of aldehydes at room temperature. The nanocatalyst was easily recovered by applying an external magnet and reused several times without considerable loss of activity.

  1. 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.

  2. 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.

  3. Studies of the Room-Temperature Multiferroic Pb(Fe0.5Ta0.5)0.4(Zr0.53Ti0.47)0.6O3: Resonant Ultrasound Spectroscopy, Dielectric, and Magnetic Phenomena

    PubMed Central

    Schiemer, J; Carpenter, M A; Evans, D M; Gregg, J M; Schilling, A; Arredondo, M; Alexe, M; Sanchez, D; Ortega, N; Katiyar, R S; Echizen, M; Colliver, E; Dutton, S; Scott, J F

    2014-01-01

    Recently, lead iron tantalate/lead zirconium titanate (PZTFT) was demonstrated to possess large, but unreliable, magnetoelectric coupling at room temperature. Such large coupling would be desirable for device applications but reproducibility would also be critical. To better understand the coupling, the properties of all 3 ferroic order parameters, elastic, electric, and magnetic, believed to be present in the material across a range of temperatures, are investigated. In high temperature elastic data, an anomaly is observed at the orthorhombic mm2 to tetragonal 4mm transition, Tot = 475 K, and a softening trend is observed as the temperature is increased toward 1300 K, where the material is known to become cubic. Thermal degradation makes it impossible to measure elastic behavior up to this temperature, however. In the low temperature region, there are elastic anomalies near ≈40 K and in the range 160–245 K. The former is interpreted as being due to a magnetic ordering transition and the latter is interpreted as a hysteretic regime of mixed rhombohedral and orthorhombic structures. Electrical and magnetic data collected below room temperature show anomalies at remarkably similar temperature ranges to the elastic data. These observations are used to suggest that the three order parameters in PZTFT are strongly coupled. PMID:25844085

  4. 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.

  5. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Temperature-Dependent Transport Properties in Oxide p n Junction above Room Temperature

    NASA Astrophysics Data System (ADS)

    Liu, Guo-Zhen; Jin, Kui-Juan; He, Meng; Qiu, Jie; Xing, Jie; Hui-Bin; Yang, Guo-Zhen

    2008-06-01

    Oxide p - n junctions of p -SrIn0.1Ti0.9O3/n-SrNb0.01Ti0.99O3 (SITO/SNTO) are fabricated by laser molecular beam epitaxy. The current-voltage characteristics of the SITO/SNTO p - n junction are investigated mainly in the temperature range of 300-400 K. The SITO/SNTO junction exhibited good rectifying behaviour over the whole temperature range. Our results indicate a possibility of application of oxide p - n junction in higher temperatures in future electronic devices.

  6. 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

  7. Imprinting bulk amorphous alloy at room temperature.

    PubMed

    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

  8. Imprinting bulk amorphous alloy at room temperature

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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.

  9. 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.

  10. Individual room temperature control: A peaceful solution to thermostat wars

    SciTech Connect

    Pieper, C.A. )

    1994-01-01

    This article addresses the problem of maintaining thermal comfort in individual rooms using an individual room temperature control concept to provide greater occupant comfort and potentially reduce energy consumption. The topics of the article include occupant temperature control methods, multi-room zone control, HVAC system operation, computer simulation, and the results of using individual room temperature control.

  11. Large magnetic response in (Bi{sub 4}Nd)Ti{sub 3}(Fe{sub 0.5}Co{sub 0.5})O{sub 15} ceramic at room-temperature

    SciTech Connect

    Yang, F. J.; Su, P.; Wei, C.; Chen, X. Q.; Yang, C. P.; Cao, W. Q.

    2011-12-15

    Ceramics of Nd/Co co-substituted Bi{sub 5}Ti{sub 3}FeO{sub 15}, i.e., (Bi{sub 4}Nd)Ti{sub 3}(Fe{sub 0.5}Co{sub 0.5})O{sub 15} were prepared by the conventional solid-state reaction method. The X-ray diffraction pattern demonstrates that the sample of the layered perovskite phase was successfully obtained, even if little Bi-deficient pyrochlore Bi{sub 2}Ti{sub 2}O{sub 7} also existed. The ferroelectric and magnetic Curie temperatures were determined to be 1077 K and 497 K, respectively. The multiferroic property of the sample at room temperature was demonstrated by ferroelectric and magnetic measurements. Remarkably, by Nd/Co co-substituting, the sample exhibited large magnetic response with 2M{sub r} = 330 memu/g and 2H{sub c} = 562 Oe at applied magnetic field of 8 kOe at room temperature. The present work suggests the possibility of doped Bi{sub 5}Ti{sub 3}FeO{sub 15} as a potential multiferroic.

  12. 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

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

    NASA Astrophysics Data System (ADS)

    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.

  14. 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

    2015-01-01

    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

  15. Room-Temperature Liquid Crystal Blue Phases

    NASA Astrophysics Data System (ADS)

    Taushanoff, Stefanie; van Le, Khoa; Twieg, Robert; Jakli, Antal

    2009-03-01

    The ``blue phases'' of a highly chiral liquid crystal are defect-studded structures of double-twist cylinders that are laced together. The three phases, BPI*, BPII* and BPIII* differ only in the packing of the double-twist cylinders. Until recently, blue phases were of limited practical use because they appeared for only a very narrow temperature range. Mixtures that show BPI* and BPII* phases for wide temperature ranges at or around room temperature are now available [1]. Relatively wide temperature BPIII (the blue fog) phase so far was available only at very high temperatures [2]. Here we present mixtures with room-temperature wide range BPIII* phase and compare the ability of chiral dopants to form the different blue phases in a base nematic mixture. PDLC films cast with blue-phase material are also examined.[3pt] [1] H. Coles and M. Pivnenko, Nature 2005 436-18 997-1000 [0pt] [2] C. V. Yelamaggad, I. S. Shashikala, G. Liao, D.S. Shankar Rao, S. K. Prasad , Q. Li A. Jakli, Chem. Mater Comm, 2006, 18, 6100-6102

  16. Room-temperature magnetoelectric multiferroic thin films and applications thereof

    DOEpatents

    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.

  17. Multiple magnetic transitions and associated room temperature magneto-functionality in Ni2.048Mn1.312In0.64

    NASA Astrophysics Data System (ADS)

    Pramanick, S.; Dutta, P.; Chatterjee, S.; Giri, S.; Majumdar, S.

    2016-05-01

    Present work reports on the observation of multiple magnetic transitions in a Ni-excess ferromagnetic shape memory alloy with nominal composition Ni2.048Mn1.312In0.64. The magnetization data reveal two distinct thermal hystereses associated with two different phase transitions at different temperature regions. The high temperature magnetic hysteresis is due to the martensitic phase transition whereas the low temperature hysteresis occurs around the magnetic anomaly signifying the transition from a paramagnetic-like state to the ferromagnetic ground state within the martensite. Clear thermal hysteresis along with the sign of the curvatures of Arrott plot curves confirm the first-order nature of both the transitions. In addition, the studied alloy is found to be functionally rich with the observation of large magnetoresistance (-45% and -4% at 80 kOe) and magnetocaloric effect (+16.7 J kg-1 K-1 and -2.25 J kg-1 K-1 at 50 kOe) around these two hysteresis regions (300 K and 195 K respectively).

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

    PubMed

    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

    2015-01-01

    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 m(2)/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. PMID:26100970

  19. 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.

  20. 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.

  1. Enhanced room temperature ferromagnetism in antiferromagnetic NiO nanoparticles

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    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 μB/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 (TC) 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 TC and moderate magnetic moment at room temperature with cubic structure would be useful to expedite for spintronic devices.

  2. 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.

  3. 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

  4. Imprinting bulk amorphous alloy at room temperature

    DOE PAGES

    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 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

  5. Bioinduced Room-Temperature Methanol Reforming.

    PubMed

    Heim, Leo E; Thiel, Daniel; Gedig, Christian; Deska, Jan; Prechtl, Martin H G

    2015-08-24

    Imitating nature's approach in nucleophile-activated formaldehyde dehydrogenation, air-stable ruthenium complexes proved to be exquisite catalysts for the dehydrogenation of formaldehyde hydrate as well as for the transfer hydrogenation to unsaturated organic substrates at loadings as low as 0.5 mol %. Concatenation of the chemical hydrogen-fixation route with an oxidase-mediated activation of methanol gives an artificial methylotrophic in vitro metabolism providing methanol-derived reduction equivalents for synthetic hydrogenation purposes. Moreover, for the first time methanol reforming at room temperature was achieved on the basis of this bioinduced dehydrogenation path delivering hydrogen gas from aqueous methanol.

  6. Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites

    PubMed Central

    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.

    2014-01-01

    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. PMID:24732685

  7. 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.

  8. Room temperature exchange bias in SmFeO3 single crystal

    NASA Astrophysics Data System (ADS)

    Wang (王晓雄), Xiaoxiong; Cheng (程相义), Xiangyi; Gao (高尚), Shang; Song (宋俊达), Junda; Ruan (阮可青), Keqing; Li (李晓光), Xiaoguang

    2016-02-01

    Exchange bias phenomenon is generally ascribed to the unidirectional magnetic shift along the field axes at interface of two magnetic materials. Room temperature exchange bias is found in SmFeO3 single crystal. The behavior after different cooling procedure is regular, and the training behavior is attributed to the athermal training and its pinning origin is attributed to the antiferromagnetic clusters. Its being single phase and occurring at room temperature make it an appropriate candidate for application.

  9. 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).

  10. Proposal of a general scheme to obtain room-temperature spin polarization in asymmetric antiferromagnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Li, Xingxing; Wu, Xiaojun; Li, Zhenyu; Yang, Jinlong

    2015-09-01

    Exploring magnetic semiconductors is one of the most important questions for spintronic applications. Although various solutions, such as dilute magnetic semiconductors, have been proposed, a practical spintronic device working at room temperature has not been realized. The key to address this issue is to find magnetic materials with both room-temperature magnetic ordering and large spin polarization around the Fermi energy level. Here, we predict a new concept of asymmetric antiferromagnetic (AFM) semiconductors (AAFMSs) with both features. The high temperature magnetic ordering originates from the AFM coupling between different transition metal ions with strong super-exchange interaction, whereas the large spin polarization around the Fermi energy level owes to d orbital mismatch among these ions. Through first-principles calculations, a family of double perovskites A2Cr M O6 (A =Ca ,Sr ,Ba , and M =Ru ,Os ) are predicted to be AAFMSs. This paper provides a way for developing spintronic devices working at room temperature.

  11. 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.

  12. 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.

  13. 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).

  14. Green synthesis of the Cu/Fe3O4 nanoparticles using Morinda morindoides leaf aqueous extract: A highly efficient magnetically separable catalyst for the reduction of organic dyes in aqueous medium at room temperature

    NASA Astrophysics Data System (ADS)

    Nasrollahzadeh, Mahmoud; Atarod, Monireh; Sajadi, S. Mohammad

    2016-02-01

    This paper reports the green and in-situ preparation of the Cu/Fe3O4 magnetic nanocatalyst synthesized using Morinda morindoides leaf extract without stabilizers or surfactants. The catalyst was characterized by XRD, SEM, EDS, UV-visible, TEM, VSM and TGA-DTA. The catalytic performance of the resulting nanocatalyst was examined for the reduction of 4-nitrophenol (4-NP), Congo red (CR) and Rhodamine B (RhB) in an environmental friendly medium at room temperature. The catalyst was recovered using an external magnet and reused several times without appreciable loss of its catalytic activity. In addition, the stability of the recycled catalyst has been proved by SEM and EDS techniques.

  15. 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

  16. Giant and reversible room-temperature elastocaloric effect in a single-crystalline Ni-Fe-Ga magnetic shape memory alloy.

    PubMed

    Li, Yang; Zhao, Dewei; Liu, Jian

    2016-01-01

    Good mechanical properties and large adiabatic temperature change render Heusler-type Ni2FeGa-based magnetic shape memory alloys as a promising candidate material for solid-state mechanical cooling application at ambient conditions. Superelastic behavior and associated elastocaloric effect strongly reply on deformation conditions (e.g. applied strain rate and strain level) of stress-induced martensitic transformations. With the aim of developing high-performance elastic cooling materials, in this work, we have carried out a systematic study on a Ni54Fe19Ga27 [420]-oriented single crystal by exploring the interaction between dynamic deformation parameters and thermal response. A giant and reversible adiabatic temperature change of ±7.5 K triggered by a low stress of 30 MPa was achieved. Such a high specific cooling performance thus offers the great advantage for the small scale solid-state mechanical cooling applications. Besides, a significant temporary residual strain effect has been observed at high strain rate, which is unfavorable for reversible elastocaloric effect but can be overcome by reducing stress hysteresis, and/or by elevating initial environmental temperature. The established criterion for the desirable reversible elastocaloric properties goes beyond the present system, and can be applicable for other shape memory alloys used for elastic cooling techniques. PMID:27138030

  17. Giant and reversible room-temperature elastocaloric effect in a single-crystalline Ni-Fe-Ga magnetic shape memory alloy

    PubMed Central

    Li, Yang; Zhao, Dewei; Liu, Jian

    2016-01-01

    Good mechanical properties and large adiabatic temperature change render Heusler-type Ni2FeGa-based magnetic shape memory alloys as a promising candidate material for solid-state mechanical cooling application at ambient conditions. Superelastic behavior and associated elastocaloric effect strongly reply on deformation conditions (e.g. applied strain rate and strain level) of stress-induced martensitic transformations. With the aim of developing high-performance elastic cooling materials, in this work, we have carried out a systematic study on a Ni54Fe19Ga27 [420]-oriented single crystal by exploring the interaction between dynamic deformation parameters and thermal response. A giant and reversible adiabatic temperature change of ±7.5 K triggered by a low stress of 30 MPa was achieved. Such a high specific cooling performance thus offers the great advantage for the small scale solid-state mechanical cooling applications. Besides, a significant temporary residual strain effect has been observed at high strain rate, which is unfavorable for reversible elastocaloric effect but can be overcome by reducing stress hysteresis, and/or by elevating initial environmental temperature. The established criterion for the desirable reversible elastocaloric properties goes beyond the present system, and can be applicable for other shape memory alloys used for elastic cooling techniques. PMID:27138030

  18. Giant and reversible room-temperature elastocaloric effect in a single-crystalline Ni-Fe-Ga magnetic shape memory alloy.

    PubMed

    Li, Yang; Zhao, Dewei; Liu, Jian

    2016-05-03

    Good mechanical properties and large adiabatic temperature change render Heusler-type Ni2FeGa-based magnetic shape memory alloys as a promising candidate material for solid-state mechanical cooling application at ambient conditions. Superelastic behavior and associated elastocaloric effect strongly reply on deformation conditions (e.g. applied strain rate and strain level) of stress-induced martensitic transformations. With the aim of developing high-performance elastic cooling materials, in this work, we have carried out a systematic study on a Ni54Fe19Ga27 [420]-oriented single crystal by exploring the interaction between dynamic deformation parameters and thermal response. A giant and reversible adiabatic temperature change of ±7.5 K triggered by a low stress of 30 MPa was achieved. Such a high specific cooling performance thus offers the great advantage for the small scale solid-state mechanical cooling applications. Besides, a significant temporary residual strain effect has been observed at high strain rate, which is unfavorable for reversible elastocaloric effect but can be overcome by reducing stress hysteresis, and/or by elevating initial environmental temperature. The established criterion for the desirable reversible elastocaloric properties goes beyond the present system, and can be applicable for other shape memory alloys used for elastic cooling techniques.

  19. Giant and reversible room-temperature elastocaloric effect in a single-crystalline Ni-Fe-Ga magnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Li, Yang; Zhao, Dewei; Liu, Jian

    2016-05-01

    Good mechanical properties and large adiabatic temperature change render Heusler-type Ni2FeGa-based magnetic shape memory alloys as a promising candidate material for solid-state mechanical cooling application at ambient conditions. Superelastic behavior and associated elastocaloric effect strongly reply on deformation conditions (e.g. applied strain rate and strain level) of stress-induced martensitic transformations. With the aim of developing high-performance elastic cooling materials, in this work, we have carried out a systematic study on a Ni54Fe19Ga27 [420]-oriented single crystal by exploring the interaction between dynamic deformation parameters and thermal response. A giant and reversible adiabatic temperature change of ±7.5 K triggered by a low stress of 30 MPa was achieved. Such a high specific cooling performance thus offers the great advantage for the small scale solid-state mechanical cooling applications. Besides, a significant temporary residual strain effect has been observed at high strain rate, which is unfavorable for reversible elastocaloric effect but can be overcome by reducing stress hysteresis, and/or by elevating initial environmental temperature. The established criterion for the desirable reversible elastocaloric properties goes beyond the present system, and can be applicable for other shape memory alloys used for elastic cooling techniques.

  20. Magnetic nanoparticle temperature estimation

    SciTech Connect

    Weaver, John B.; Rauwerdink, Adam M.; Hansen, Eric W.

    2009-05-15

    The authors present a method of measuring the temperature of magnetic nanoparticles that can be adapted to provide in vivo temperature maps. Many of the minimally invasive therapies that promise to reduce health care costs and improve patient outcomes heat tissue to very specific temperatures to be effective. Measurements are required because physiological cooling, primarily blood flow, makes the temperature difficult to predict a priori. The ratio of the fifth and third harmonics of the magnetization generated by magnetic nanoparticles in a sinusoidal field is used to generate a calibration curve and to subsequently estimate the temperature. The calibration curve is obtained by varying the amplitude of the sinusoidal field. The temperature can then be estimated from any subsequent measurement of the ratio. The accuracy was 0.3 deg. K between 20 and 50 deg. C using the current apparatus and half-second measurements. The method is independent of nanoparticle concentration and nanoparticle size distribution.

  1. High-temperature metal-organic magnets.

    PubMed

    Jain, Rajsapan; Kabir, Khayrul; Gilroy, Joe B; Mitchell, Keith A R; Wong, Kin-chung; Hicks, Robin G

    2007-01-18

    For over two decades there have been intense efforts aimed at the development of alternatives to conventional magnets, particularly materials comprised in part or wholly of molecular components. Such alternatives offer the prospect of realizing magnets fabricated through controlled, low-temperature, solution-based chemistry, as opposed to high-temperature metallurgical routes, and also the possibility of tuning magnetic properties through synthesis. However, examples of magnetically ordered molecular materials at or near room temperature are extremely rare, and the properties of these materials are often capricious and difficult to reproduce. Here we present a versatile solution-based route to a new class of metal-organic materials exhibiting magnetic order well above room temperature. Reactions of the metal (M) precursor complex bis(1,5-cyclooctadiene)nickel with three different organics A-TCNE (tetracyanoethylene), TCNQ (7,7,8,8-tetracyanoquinodimethane) or DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone)--proceed via electron transfer from nickel to A and lead to materials containing Ni(II) ions and reduced forms of A in a 2:1 Ni:A ratio--that is, opposite to that of conventional (low Curie temperature) MA(2)-type magnets. These materials also contain oxygen-based species within their architectures. Magnetic characterization of the three compounds reveals spontaneous field-dependent magnetization and hysteresis at room temperature, with ordering temperatures well above ambient. The unusual stoichiometry and striking magnetic properties highlight these three compounds as members of a class of stable magnets that are at the interface between conventional inorganic magnets and genuine molecule-based magnets.

  2. Room-temperature ferromagnetism in graphitic petal arrays.

    PubMed

    Rout, Chandra Sekhar; Kumar, Anurag; Kumar, Nitesh; Sundaresan, A; Fisher, Timothy S

    2011-03-01

    We report room-temperature ferromagnetism of graphitic petal arrays grown on Si substrates by microwave plasma chemical vapor deposition without catalyst. The samples have been characterized by Raman and X-ray photoelectron spectroscopy to confirm the absence of possible ferromagnetic impurities. The petals exhibit ferromagnetic hysteresis with saturation magnetization of ∼4.67 emu cm(-3) and coercivity of ∼105 Oe at 300 K, comparable to the reported behavior of few-layer graphene. Upon O2 annealing the saturation magnetization and coercivity decreased to 2.1 emu cm(-3) and ∼75 Oe respectively. The origin of ferromagnetism is believed to arise from the edge defects and vacancies in the petals. PMID:21264436

  3. Room-temperature ferromagnetism in graphitic petal arrays

    NASA Astrophysics Data System (ADS)

    Rout, Chandra Sekhar; Kumar, Anurag; Kumar, Nitesh; Sundaresan, A.; Fisher, Timothy S.

    2011-03-01

    We report room-temperature ferromagnetism of graphitic petal arrays grown on Si substrates by microwave plasma chemical vapor deposition without catalyst. The samples have been characterized by Raman and X-ray photoelectron spectroscopy to confirm the absence of possible ferromagnetic impurities. The petals exhibit ferromagnetic hysteresis with saturation magnetization of ~4.67 emu cm-3 and coercivity of ~105 Oe at 300 K, comparable to the reported behavior of few-layer graphene. Upon O2 annealing the saturation magnetization and coercivity decreased to 2.1 emu cm-3 and ~75 Oe respectively. The origin of ferromagnetism is believed to arise from the edge defects and vacancies in the petals.

  4. Observation of room-temperature skyrmion Hall effect

    NASA Astrophysics Data System (ADS)

    Jiang, W.; Zhang, X.; Upadhyaya, P.; Zhang, W.; Yu, G.; Jungfleisch, M.; Fradin, F.; Pearson, J.; Tserkovnyak, Y.; Wang, K.; Heinonen, O.; Zhou, Y.; Te Velthuis, Suzanne; Hoffmann, A.

    The realization of room-temperature magnetic skyrmions is key to enabling the implementation of skyrmion-based spintronics. In this work, we present the efficient conversion of chiral stripe domains into Néel skyrmions through a geometrical constriction patterned in a Ta/CoFeB/TaOx trilayer film at room temperature. This is enabled by an interfacial Dzyaloshinskii-Moriya interaction, and laterally divergent current-induced spin-orbit torques. We further show the generation of magnetic skyrmions solely by the divergent spin-orbit torques through a nonmagnetic point contact. By increasing the current density, we observe the skyrmion Hall effect - that is the accumulation of skyrmions at one side of the device. The related Hall angle for skyrmion motion is also revealed under an ac driving current. Financial support for the work at Argonne came from Department of Energy, Office of Science, Basic Energy Science, Materials Sciences and Engineering Division, work at UCLA was supported by TANMS.

  5. Digital magnetic temperature transducer.

    NASA Technical Reports Server (NTRS)

    Tchernev, D. I.; Collier, T. E.

    1971-01-01

    A new digital magnetic temperature transducer is reported. The device utilizes the discontinuous behavior of the initial permeability with temperature at the Curie temperature of some magnetic materials. Since the Curie temperature is determined by the chemical and crystallographic composition of the particular material only, the transducer requires no calibration and has extremely high stability and reproducibility with time. The output of the transducer is inherently digital and, therefore, is directly compatible with the digital information processing and control without A/D conversion. The temperature-sensing portion of the transducer consists only of magnetic cores and wire and, therefore, has extremely high reliability, is shock and radiation insensitive, small, and virtually indestructible.

  6. 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.

  7. 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.

  8. Room temperature molecular up conversion in solution.

    PubMed

    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

  9. 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.

  10. 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

  11. Near-room temperature relaxor multiferroic

    NASA Astrophysics Data System (ADS)

    Sanchez, Dilsom A.; Kumar, A.; Ortega, N.; Katiyar, R. S.; Scott, J. F.

    2010-11-01

    We report the fabrication and characterization of highly oriented Pb(Zr0.53Ti0.47)0.60(Fe0.5Ta0.5)0.40O3 thin films. Dielectric spectra showed a maximum (Tm) around 350 K for 1 kHz that shifted to higher temperatures (by ˜30 K) with an increase in frequency up to 1 MHz. High dielectric dispersion below and above Tm, low dielectric loss (2%-5%), high dielectric constant (˜1380@1 kHz), ferroelectric polarization, and weak magnetic moment are observed. Real and imaginary dielectric data were fitted with a nonlinear Vogel-Fulcher equation, implying a relaxor nature. The ac conductivity shows frequency-dependent conductivity, low loss, and frequency-dependent kinks near Tm.

  12. Room temperature ferroelectric and magnetic investigations and detailed phase analysis of Aurivillius phase Bi{sub 5}Ti{sub 3}Fe{sub 0.7}Co{sub 0.3}O{sub 15} thin films

    SciTech Connect

    Keeney, Lynette; Kulkarni, Santosh; Deepak, Nitin; Schmidt, Michael; Petkov, Nikolay; Zhang, Panfeng F.; Roy, Saibal; Pemble, Martyn E.; Whatmore, Roger W.; Cavill, Stuart

    2012-09-01

    Aurivillius phase Bi{sub 5}Ti{sub 3}Fe{sub 0.7}Co{sub 0.3}O{sub 15} (BTF7C3O) thin films on {alpha}-quartz substrates were fabricated by a chemical solution deposition method and the room temperature ferroelectric and magnetic properties of this candidate multiferroic were compared with those of thin films of Mn{sup 3+} substituted, Bi{sub 5}Ti{sub 3}Fe{sub 0.7}Mn{sub 0.3}O{sub 15} (BTF7M3O). Vertical and lateral piezoresponse force microscopy (PFM) measurements of the films conclusively demonstrate that BTF7C3O and BTF7M3O thin films are piezoelectric and ferroelectric at room temperature, with the major polarization vector in the lateral plane of the films. No net magnetization was observed for the in-plane superconducting quantum interference device (SQUID) magnetometry measurements of BTF7M3O thin films. In contrast, SQUID measurements of the BTF7C3O films clearly demonstrated ferromagnetic behavior, with a remanent magnetization, B{sub r}, of 6.37 emu/cm{sup 3} (or 804 memu/g), remanent moment = 4.99 Multiplication-Sign 10{sup -5} emu. The BTF7C3O films were scrutinized by x-ray diffraction, high resolution transmission electron microscopy, scanning transmission electron microscopy, and energy dispersive x-ray analysis mapping to assess the prospect of the observed multiferroic properties being intrinsic to the main phase. The results of extensive micro-structural phase analysis demonstrated that the BTF7C3O films comprised of a 3.95% Fe/Co-rich spinel phase, likely CoFe{sub 2-x}Ti{sub x}O{sub 4}, which would account for the observed magnetic moment in the films. Additionally, x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM) imaging confirmed that the majority of magnetic response arises from the Fe sites of Fe/Co-rich spinel phase inclusions. While the magnetic contribution from the main phase could not be determined by the XMCD-PEEM images, these data however imply that the Bi{sub 5}Ti{sub 3}Fe{sub 0.7}Co{sub 0.3}O{sub 15} thin

  13. Room-Temperature Multiferroic Hexagonal LuFeO3

    SciTech Connect

    Cheng, Xuemei; Balke, Nina; Chi, Miaofang; Gai, Zheng; Keavney, David; Lee, Ho Nyung; Shen, Jian; Snijders, Paul C; Wang, Wenbin; Ward, Thomas Z; Xu, Xiaoshan; Yi, Jieyu; Zhu, Leyi; Christen, Hans M; Zhao, Jun

    2013-01-01

    We observed the coexistence of ferroelectricity and weak ferromagnetism at room temperature in the hexagonal phase of LuFeO3 stabilized by epitaxial thin film growth. While the ferroelectricity in hexagonal LuFeO3 can be understood as arising from its polar structure, the observation of weak ferromagnetism at room temperature is remarkable considering the frustrated triangular spin structure. An explanation of the room temperature weak ferromagnetism is proposed in terms of a subtle lattice distortion revealed by the structural characterization. The combination of ferroelectricity and weak ferromagnetism in epitaxial films at room temperature offers great potential for the application of this novel multiferroic material in next generation devices.

  14. 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.

  15. 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.

  16. Water in Room Temperature Ionic Liquids

    NASA Astrophysics Data System (ADS)

    Fayer, Michael

    2014-03-01

    Room temperature ionic liquids (or RTILs, salts with a melting point below 25 °C) have become a subject of intense study over the last several decades. Currently, RTIL application research includes synthesis, batteries, solar cells, crystallization, drug delivery, and optics. RTILs are often composed of an inorganic anion paired with an asymmetric organic cation which contains one or more pendant alkyl chains. The asymmetry of the cation frustrates crystallization, causing the salt's melting point to drop significantly. In general, RTILs are very hygroscopic, and therefore, it is of interest to examine the influence of water on RTIL structure and dynamics. In addition, in contrast to normal aqueous salt solutions, which crystallize at low water concentration, in an RTIL it is possible to examine isolated water molecules interacting with ions but not with other water molecules. Here, optical heterodyne-detected optical Kerr effect (OHD-OKE) measurements of orientational relaxation on a series of 1-alkyl-3-methylimidazolium tetrafluoroborate RTILs as a function of chain length and water concentration are presented. The addition of water to the longer alkyl chain RTILs causes the emergence of a long time bi-exponential orientational anisotropy decay. Such decays have not been seen previously in OHD-OKE experiments on any type of liquid and are analyzed here using a wobbling-in-a-cone model. The orientational relaxation is not hydrodynamic, with the slowest relaxation component becoming slower as the viscosity decreases for the longest chain, highest water content samples. The dynamics of isolated D2O molecules in 1-butyl-3-methylimidazolium hexafluorophosphate (BmImPF6) were examined using two dimensional infrared (2D IR) vibrational echo spectroscopy. Spectral diffusion and incoherent and coherent transfer of excitation between the symmetric and antisymmetric modes are examined. The coherent transfer experiments are used to address the nature of inhomogeneous

  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. 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.

  19. Understanding the magnetic interaction between intrinsic defects and impurity ions in room-temperature ferromagnetic Mg1-xFexO thin films.

    PubMed

    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

    2016-04-20

    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-xFexO 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. PMID:26987741

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

    NASA Astrophysics Data System (ADS)

    Binek, Christian

    2011-03-01

    Voltage-controlled spintronics is of particular importance to continue progress in information technology through reduced power consumption, enhanced processing speed, integration density, and functionality in comparison with present day CMOS electronics. Almost all existing and prototypical solid-state spintronic devices rely on tailored interface magnetism, enabling spin-selective transmission or scattering of electrons. Controlling magnetism at thin-film interfaces, preferably by purely electrical means, is a key challenge to better spintronics. Currently, most attempts to electrically control magnetism focus on potentially large magnetoelectric effects of multiferroics. We report on our interest in magnetoelectric Cr 2 O3 (chromia). Robust isothermal electric control of exchange bias is achieved at room temperature in perpendicular anisotropic Cr 2 O3 (0001)/CoPd exchange bias heterostructures. This discovery promises significant implications for potential spintronics. From the perspective of basic science, our finding serves as macroscopic evidence for roughness-insensitive and electrically controllable equilibrium boundary magnetization in magnetoelectric antiferromagnets. The latter evolves at chromia (0001) surfaces and interfaces when chromia is in one of its two degenerate antiferromagnetic single domain states selected via magnetoelectric annealing. Theoretical insight into the boundary magnetization and its role in electrically controlled exchange bias is gained from first-principles calculations and general symmetry arguments. Measurements of spin-resolved ultraviolet photoemission, magnetometry at Cr 2 O3 (0001) surfaces, and detailed investigations of the unique exchange bias properties of Cr 2 O3 (0001)/CoPd including its electric controllability provide macroscopically averaged information about the boundary magnetization of chromia. Laterally resolved X-ray PEEM and temperature dependent MFM reveal detailed microscopic information of the chromia

  1. Realization of ground-state artificial skyrmion lattices at room temperature

    SciTech Connect

    Gilbert, Dustin A.; Maranville, Brian B.; Balk, Andrew L.; Kirby, Brian J.; Fischer, Peter; Pierce, Daniel T.; Unguris, John; Borchers, Julie A.; Liu, Kai

    2015-10-08

    We report that the topological nature of magnetic skyrmions leads to extraordinary properties that provide new insights into fundamental problems of magnetism and exciting potentials for novel magnetic technologies. Prerequisite are systems exhibiting skyrmion lattices at ambient conditions, which have been elusive so far. We demonstrate the realization of artificial Bloch skyrmion lattices over extended areas in their ground state at room temperature by patterning asymmetric magnetic nanodots with controlled circularity on an underlayer with perpendicular magnetic anisotropy (PMA). Polarity is controlled by a tailored magnetic field sequence and demonstrated in magnetometry measurements. The vortex structure is imprinted from the dots into the interfacial region of the underlayer via suppression of the PMA by a critical ion-irradiation step. In conclusion, the imprinted skyrmion lattices are identified directly with polarized neutron reflectometry and confirmed by magnetoresistance measurements. Our results demonstrate an exciting platform to explore room-temperature ground-state skyrmion lattices.

  2. Realization of ground-state artificial skyrmion lattices at room temperature

    DOE PAGES

    Gilbert, Dustin A.; Maranville, Brian B.; Balk, Andrew L.; Kirby, Brian J.; Fischer, Peter; Pierce, Daniel T.; Unguris, John; Borchers, Julie A.; Liu, Kai

    2015-10-08

    We report that the topological nature of magnetic skyrmions leads to extraordinary properties that provide new insights into fundamental problems of magnetism and exciting potentials for novel magnetic technologies. Prerequisite are systems exhibiting skyrmion lattices at ambient conditions, which have been elusive so far. We demonstrate the realization of artificial Bloch skyrmion lattices over extended areas in their ground state at room temperature by patterning asymmetric magnetic nanodots with controlled circularity on an underlayer with perpendicular magnetic anisotropy (PMA). Polarity is controlled by a tailored magnetic field sequence and demonstrated in magnetometry measurements. The vortex structure is imprinted from themore » dots into the interfacial region of the underlayer via suppression of the PMA by a critical ion-irradiation step. In conclusion, the imprinted skyrmion lattices are identified directly with polarized neutron reflectometry and confirmed by magnetoresistance measurements. Our results demonstrate an exciting platform to explore room-temperature ground-state skyrmion lattices.« less

  3. Realization of ground-state artificial skyrmion lattices at room temperature

    PubMed Central

    Gilbert, Dustin A.; Maranville, Brian B.; Balk, Andrew L.; Kirby, Brian J.; Fischer, Peter; Pierce, Daniel T.; Unguris, John; Borchers, Julie A.; Liu, Kai

    2015-01-01

    The topological nature of magnetic skyrmions leads to extraordinary properties that provide new insights into fundamental problems of magnetism and exciting potentials for novel magnetic technologies. Prerequisite are systems exhibiting skyrmion lattices at ambient conditions, which have been elusive so far. Here, we demonstrate the realization of artificial Bloch skyrmion lattices over extended areas in their ground state at room temperature by patterning asymmetric magnetic nanodots with controlled circularity on an underlayer with perpendicular magnetic anisotropy (PMA). Polarity is controlled by a tailored magnetic field sequence and demonstrated in magnetometry measurements. The vortex structure is imprinted from the dots into the interfacial region of the underlayer via suppression of the PMA by a critical ion-irradiation step. The imprinted skyrmion lattices are identified directly with polarized neutron reflectometry and confirmed by magnetoresistance measurements. Our results demonstrate an exciting platform to explore room-temperature ground-state skyrmion lattices. PMID:26446515

  4. 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).

  5. Giant dielectric and magnetoelectric responses in insulating nanogranular films at room temperature

    PubMed Central

    Kobayashi, Nobukiyo; Masumoto, Hiroshi; Takahashi, Saburo; Maekawa, Sadamichi

    2014-01-01

    The electric and magnetic properties of matter are of great interest for materials science and their use in electronic applications. Large dielectric and magnetoelectric responses of materials at room temperature are a great advantage for electromagnetic device applications. Here we present a study of FeCo-MgF nanogranular films exhibiting giant dielectric and magnetoelectric responses at room temperature; with dielectric constant ε′=490 and magnetoelectric response Δε′/ε′0=3%. In these films, Fe-Co alloy-based nanometer-sized magnetic granules are dispersed in a Mg-fluoride-based insulator matrix. Insulating nanogranular films are a new class of multifunctional materials. The giant responses are caused by spin-dependent charge oscillation between magnetic granules via quantum-mechanical tunnelling. A possible application of such insulating nanogranular materials with giant response is in the construction of a tunable device, in which impedance components such as capacitance and inductance are tunable at room temperature. PMID:25048805

  6. Room-Temperature Ferromagnetism in TiO2 Nanocrystals Synthesized by the Controlled Hydrolysis Procedure.

    PubMed

    Gu, Deen; Sun, Zhanhong; Zhou, Lv; Hu, Yongda; Jiang, Yadong

    2016-03-01

    TiO2 nanocrystals were prepared by a controlled hydrolysis procedure at room temperature. The effect of V-doping, N-doping and V/N codoping on the lattice parameters and magnetic properties of TiO2 nanocrystals was investigated by means of X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy and vibration sample magnetometry. Doping performed at room temperature causes the expansion of lattice parameters. Undoped and doped TiO2 nanocrystals show room-temperature ferromagnetism. A monotonic correlation between saturation magnetization and the ratio of the lattice parameter c to a (c/a) was observed. Saturation magnetization of TiO2 nanocrystals increases with the value of c/a.

  7. Designing room-temperature multiferroic materials in a single-phase solid-solution film

    NASA Astrophysics Data System (ADS)

    Mao, H. J.; Song, C.; Cui, B.; Peng, J. J.; Li, F.; Xiao, L. R.; Pan, F.

    2016-09-01

    The search for multiferroic materials with simultaneous ferroelectric and ferromagnetic properties in a single phase at room temperature continues to be fuelled from the perspective of developing multifunctional devices. Here we design a single-phase multiferroic La0.67Sr0.33MnO3-BaTiO3 film, which possesses epitaxial single-crystal and solid-solution structure, high magnetic Curie temperature (~640 K) as well as switchable ferroelectric polarization. Moreover, a notable strain-mediated magnetoelectric coupling at room temperature in the way of modulating the magnetism with an external applied voltage is also observed. The synthetic solid-solution multiferroic film may open an extraordinary avenue for exploring a series of room-temperature multiferroic materials.

  8. Entanglement and Bell's inequality violation above room temperature in metal carboxylates.

    SciTech Connect

    Souza, A M; Soares-Pinto, D O; Sarthour, R S; Oliveira, I S; Reis, Mario S; Brandao, Paula; Moreira Dos Santos, Antonio F

    2009-01-01

    In the present work we show that a particular family of materials, the metal carboxylates, may have entangled states up to very high temperatures. From magnetic-susceptibility measurements, we have estimated the critical temperature below which entanglement exists in the copper carboxylate {Cu-2(O2CH)(4)}{Cu(O2CH)(2)(2-methylpyridine)(2)}, and we have found this to be above room temperature (T-e similar to 630 K). Furthermore, the results show that the system remains maximally entangled until close to similar to 100 K and the Bell's inequality is violated up to nearly room temperature (similar to 290 K).

  9. Room-temperature ferromagnetism in zinc-blende and deformed CrAs thin films

    NASA Astrophysics Data System (ADS)

    Bi, J. F.; Zhao, J. H.; Deng, J. J.; Zheng, Y. H.; Li, S. S.; Wu, X. G.; Jia, Q. J.

    2006-04-01

    We try to clarify the controversy about the origin of room-temperature ferromagnetism in a CrAs compound. Two kinds of CrAs thin films were grown on GaAs by molecular-beam epitaxy. Structural analyses confirm that the as-grown CrAs film is a pure zinc-blende phase. Magnetic measurements suggest that room-temperature ferromagnetism exists in zinc-blende CrAs. In contrast, the CrAs film turns into a mixture of zinc-blende and deformed CrAs after annealing. A ferromagnetic signal measured at room temperature demonstrates that zinc-blende CrAs remains room-temperature ferromagnetism even when it is partly deformed into a non-zinc-blende phase.

  10. 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.

  11. 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%.

  12. 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.

  13. Realization of Ground State Artificial Skyrmion Lattices at Room Temperature

    NASA Astrophysics Data System (ADS)

    Gilbert, Dustin A.; Maranville, Brian B.; Balk, Andrew J.; Kirby, Brian J.; Pierce, Daniel T.; Unguris, John; Borchers, Julie A.; Fischer, Peter; Liu, Kai

    Artificial skyrmion lattices stable at ambient conditions offer a convenient and powerful platform to explore skyrmion physics and topological phenomena and motivates their inclusion in next-generation data and logic devices. In this work we present direct experimental evidence of artificial skyrmion lattices with a stable ground state at room temperature. Our approach is to pattern vortex-state Co nanodots (560 nm diameter) in hexagonal arrays on top of a Co/Pd multilayer with perpendicular magnetic anisotropy; the skyrmion state is prepared using a specific magnetic field sequence. Ion irradiation has been employed to suppress PMA in the underlayer and allow imprinting of the vortex structure from the nanodots to form skyrmion lattices, as revealed by polarized neutron reflectometry. Circularity control is realized through Co dot shape asymmetry, and confirmed by microscopy and FORC magnetometry. The vortex polarity is set during the field sequence and confirmed by magnetometry. Spin-transport studies further demonstrate a sensitivity to the skyrmion spin texture.Work supported by NSF (DMR-1008791, ECCS-1232275 and DMR-1543582)

  14. Giant single-molecule anisotropic magnetoresistance at room temperature.

    PubMed

    Li, Ji-Jun; Bai, Mei-Lin; Chen, Zhao-Bin; Zhou, Xiao-Shun; Shi, Zhan; Zhang, Meng; Ding, Song-Yuan; Hou, Shi-Min; Schwarzacher, Walther; Nichols, Richard J; Mao, Bing-Wei

    2015-05-13

    We report an electrochemically assisted jump-to-contact scanning tunneling microscopy (STM) break junction approach to create reproducible and well-defined single-molecule spintronic junctions. The STM break junction is equipped with an external magnetic field either parallel or perpendicular to the electron transport direction. The conductance of Fe-terephthalic acid (TPA)-Fe single-molecule junctions is measured and a giant single-molecule tunneling anisotropic magnetoresistance (T-AMR) up to 53% is observed at room temperature. Theoretical calculations based on first-principles quantum simulations show that the observed AMR of Fe-TPA-Fe junctions originates from electronic coupling at the TPA-Fe interfaces modified by the magnetic orientation of the Fe electrodes with respect to the direction of current flow. The present study highlights new opportunities for obtaining detailed understanding of mechanisms of charge and spin transport in molecular junctions and the role of interfaces in determining the MR of single-molecule junctions. PMID:25894840

  15. 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.

  16. Direct electrochemistry and electrocatalysis of heme proteins immobilised in carbon-coated nickel magnetic nanoparticle-chitosan-dimethylformamide composite films in room-temperature ionic liquids.

    PubMed

    Wang, Ting; Wang, Lu; Tu, Jiaojiao; Xiong, Huayu; Wang, Shengfu

    2013-12-01

    The direct electrochemistry and electrocatalysis of heme proteins entrapped in carbon-coated nickel magnetic nanoparticle-chitosan-dimethylformamide (CNN-CS-DMF) composite films were investigated in the hydrophilic ionic liquid [bmim][BF4]. The surface morphologies of a representative set of films were characterised via scanning electron microscopy. The proteins immobilised in the composite films were shown to retain their native secondary structure using UV-vis spectroscopy. The electrochemical performance of the heme proteins-CNN-CS-DMF films was evaluated via cyclic voltammetry and chronoamperometry. A pair of stable and well-defined redox peaks was observed for the heme protein films at formal potentials of -0.151 V (HRP), -0.167 V (Hb), -0.155 V (Mb) and -0.193 V (Cyt c) in [bmim][BF4]. Moreover, several electrochemical parameters of the heme proteins were calculated by nonlinear regression analysis of the square-wave voltammetry. The addition of CNN significantly enhanced not only the electron transfer of the heme proteins but also their electrocatalytic activity toward the reduction of H2O2. Low apparent Michaelis-Menten constants were obtained for the heme protein-CNN-CS-DMF films, demonstrating that the biosensors have a high affinity for H2O2. In addition, the resulting electrodes displayed a low detection limit and improved sensitivity for detecting H2O2, which indicates that the biocomposite film can serve as a platform for constructing new non-aqueous biosensors for real detection.

  17. 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.

  18. Magnetic force microscopy investigation of the magnetization reversal of permalloy particles at high temperatures

    NASA Astrophysics Data System (ADS)

    Nurgazizov, N. I.; Khanipov, T. F.; Bizyaev, D. A.; Bukharaev, A. A.; Chuklanov, A. P.

    2014-09-01

    The magnetization reversal of an array of permalloy particles formed by scanning probe lithography on the silicon dioxide surface has been investigated in the temperature range from room temperature to 800 K. Using scanning magnetic force microscopy and numerical calculations of the magnetic anisotropy field of a particle at different temperatures, it has been shown that an increase in the temperature leads to a decrease in the external magnetic field required to reverse the magnetization direction of the particle. From the obtained results, it has been concluded that the magnetization reversal of the studied particles is accompanied by the formation of an intermediate state with an inhomogeneous magnetization structure.

  19. Selective on/off switching at room temperature of a magnetic bistable {Fe2Co2} complex with single crystal-to-single crystal transformation via intramolecular electron transfer.

    PubMed

    Cao, Li; Tao, Jun; Gao, Qian; Liu, Tao; Xia, Zhengcai; Li, Dongfeng

    2014-02-18

    A cyano-bridged {Fe2Co2} complex shows reversible single crystal-to-single crystal transformation between diamagnetic and paramagnetic states switched specifically by losing and absorbing methanol at room temperature in the solid state. And the solvent loss form presents temperature- and pressure-induced intramolecular electron transfer behaviour.

  20. Thermal Effect in Opal Below Room Temperature

    PubMed Central

    Buerger, Martin J.; Shoemaker, Gerald L.

    1972-01-01

    Opal, once believed to be amorphous silica, was shown by Levin and Ott (1932, J. Amer. Chem. Soc. 54, 828-829) to give an x-ray powder pattern of the high-temperature form of cristobalite. The early explanation of this anomalous existence of a phase below its high-low transition temperature is now known to be untenable. One of us suggested that the tiny sizes of the component cristobalite crystals might explain the anomaly; if so, the transition might be expected below ambient temperatures. The record of a du Pont 900 Thermoanalyzer indeed revealed heat effects in opal below ambient temperatures, with an exotherm having a maximum at about -40° on cooling and an endotherm that began about -50° on heating. This was not a latent-heat effect due to the high-low transition of cristobalite, however, for the low-cristobalite pattern persisted to below -50°. Opal normally contains 4-9% water, which is tenaciously held; water loss is nearly linear with temperatures up to about 422°, when water loss is abruptly complete. Water-free opal does not display the thermal effect, but the same opal rehydrated does display it. Water is housed in minute voids, judged to be a few hundred Ångströms across, between minute particles of cristobalite. This water behaves differently from water in bulk, for its begins to melt at about -50°. PMID:16592025

  1. 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.

  2. 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.

  3. Temperature compensation for miniaturized magnetic sector

    NASA Technical Reports Server (NTRS)

    Sinha, Mahadeva P. (Inventor)

    2002-01-01

    Temperature compensation for a magnetic sector used in mass spectrometry. A high temperature dependant magnetic sector is used. This magnetic sector is compensated by a magnetic shunt that has opposite temperature characteristics to those of the magnet.

  4. Large Magnetoresistance at Room Temperature in Ferromagnet/Topological Insulator Contacts

    NASA Astrophysics Data System (ADS)

    Majumder, Sarmita; Guchhait, Samaresh; Dey, Rik; Register, Leonard Franklin; Banerjee, Sanjay K.

    2016-07-01

    We report magnetoresistance for current flow through iron/topological insulator (Fe/TI) and Fe/evaporated-oxide/TI contacts when a magnetic field is used to initially orient the magnetic alignment of the incorporated ferromagnetic Fe bar, at temperatures ranging from 100 K to room temperature. This magnetoresistance is associated with the relative orientation of the Fe bar magnetization and spin-polarization of electrons moving on the surface of the TI with helical spin-momentum locking. The magnitude of the observed magnetoresistance is relatively large compared to that observed in prior work.

  5. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    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.

  7. 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

  8. 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.

  9. Direct observation of a highly spin-polarized organic spinterface at room temperature

    PubMed Central

    Djeghloul, F.; Ibrahim, F.; Cantoni, M.; Bowen, M.; Joly, L.; Boukari, S.; Ohresser, P.; Bertran, F.; Le Fèvre, P.; Thakur, P.; Scheurer, F.; Miyamachi, T.; Mattana, R.; Seneor, P.; Jaafar, A.; Rinaldi, C.; Javaid, S.; Arabski, J.; Kappler, J. -P; Wulfhekel, W.; Brookes, N. B.; Bertacco, R.; Taleb-Ibrahimi, A.; Alouani, M.; Beaurepaire, E.; Weber, W.

    2013-01-01

    Organic semiconductors constitute promising candidates toward large-scale electronic circuits that are entirely spintronics-driven. Toward this goal, tunneling magnetoresistance values above 300% at low temperature suggested the presence of highly spin-polarized device interfaces. However, such spinterfaces have not been observed directly, let alone at room temperature. Thanks to experiments and theory on the model spinterface between phthalocyanine molecules and a Co single crystal surface, we clearly evidence a highly efficient spinterface. Spin-polarised direct and inverse photoemission experiments reveal a high degree of spin polarisation at room temperature at this interface. We measured a magnetic moment on the molecule's nitrogen π orbitals, which substantiates an ab-initio theoretical description of highly spin-polarised charge conduction across the interface due to differing spinterface formation mechanisms in each spin channel. We propose, through this example, a recipe to engineer simple organic-inorganic interfaces with remarkable spintronic properties that can endure well above room temperature. PMID:23412079

  10. Observation of a large spin-dependent transport length in organic spin valves at room temperature.

    PubMed

    Zhang, Xianmin; Mizukami, Shigemi; Kubota, Takahide; Ma, Qinli; Oogane, Mikihiko; Naganuma, Hiroshi; Ando, Yasuo; Miyazaki, Terunobu

    2013-01-01

    The integration of organic semiconductors and magnetism has been a fascinating topic for fundamental scientific research and future applications in electronics, because organic semiconductors are expected to possess a large spin-dependent transport length based on weak spin-orbit coupling and weak hyperfine interaction. However, to date, this length has typically been limited to several nanometres at room temperature, and a large length has only been observed at low temperatures. Here we report on a novel organic spin valve device using C(60) as the spacer layer. A magnetoresistance ratio of over 5% was observed at room temperature, which is one of the highest magnetoresistance ratios ever reported. Most importantly, a large spin-dependent transport length of approximately 110 nm was experimentally observed for the C(60) layer at room temperature. These results provide insights for further understanding spin transport in organic semiconductors and may strongly advance the development of spin-based organic devices. PMID:23340432

  11. 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. PMID:25042767

  12. Nanostructured Materials for Room-Temperature Gas Sensors.

    PubMed

    Zhang, Jun; Liu, Xianghong; Neri, Giovanni; Pinna, Nicola

    2016-02-01

    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.

  13. Ether-based nonflammable electrolyte for room temperature sodium battery

    NASA Astrophysics Data System (ADS)

    Feng, Jinkui; Zhang, Zhen; Li, Lifei; Yang, Jian; Xiong, Shenglin; Qian, Yitai

    2015-06-01

    Safety problem is one of the key points that hinder the development of room temperature sodium batteries. In this paper, four well-known nonflammable organic compounds, Trimethyl Phosphate (TMP), Tri(2,2,2-trifluoroethyl) phosphite (TFEP), Dimethyl Methylphosphonate (DMMP), Methyl nonafluorobuyl Ether (MFE), are investigated as nonflammable solvents in sodium batteries for the first time. Among them, MFE is stable towards sodium metal at room temperature. The electrochemical properties and electrode compatibility of MFE based electrolyte are investigated. Both Prussian blue cathode and carbon nanotube anode show good electrochemical performance retention in this electrolyte. The results suggest that MFE is a promising option as nonflammable electrolyte additive for sodium batteries.

  14. 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.

  15. Room-temperature in situ nuclear spin hyperpolarization from optically pumped nitrogen vacancy centres in diamond

    SciTech Connect

    King, Jonathan P.; Jeong, Keunhong; Vassiliou, Christophoros C.; Shin, Chang S.; Page, Ralph H.; Avalos, Claudia E.; Wang, Hai-Jing; Pines, Alexander

    2015-12-07

    Low detection sensitivity stemming from the weak polarization of nuclear spins is a primary limitation of magnetic resonance spectroscopy and imaging. Methods have been developed to enhance nuclear spin polarization but they typically require high magnetic fields, cryogenic temperatures or sample transfer between magnets. Here we report bulk, room-temperature hyperpolarization of 13C nuclear spins observed via high-field magnetic resonance. The technique harnesses the high optically induced spin polarization of diamond nitrogen vacancy centres at room temperature in combination with dynamic nuclear polarization. We observe bulk nuclear spin polarization of 6%, an enhancement of ~170,000 over thermal equilibrium. The signal of the hyperpolarized spins was detected in situ with a standard nuclear magnetic resonance probe without the need for sample shuttling or precise crystal orientation. In conclusion, hyperpolarization via optical pumping/dynamic nuclear polarization should function at arbitrary magnetic fields enabling orders of magnitude sensitivity enhancement for nuclear magnetic resonance of solids and liquids under ambient conditions.

  16. Room-temperature in situ nuclear spin hyperpolarization from optically pumped nitrogen vacancy centres in diamond

    DOE PAGES

    King, Jonathan P.; Jeong, Keunhong; Vassiliou, Christophoros C.; Shin, Chang S.; Page, Ralph H.; Avalos, Claudia E.; Wang, Hai-Jing; Pines, Alexander

    2015-12-07

    Low detection sensitivity stemming from the weak polarization of nuclear spins is a primary limitation of magnetic resonance spectroscopy and imaging. Methods have been developed to enhance nuclear spin polarization but they typically require high magnetic fields, cryogenic temperatures or sample transfer between magnets. Here we report bulk, room-temperature hyperpolarization of 13C nuclear spins observed via high-field magnetic resonance. The technique harnesses the high optically induced spin polarization of diamond nitrogen vacancy centres at room temperature in combination with dynamic nuclear polarization. We observe bulk nuclear spin polarization of 6%, an enhancement of ~170,000 over thermal equilibrium. The signal ofmore » the hyperpolarized spins was detected in situ with a standard nuclear magnetic resonance probe without the need for sample shuttling or precise crystal orientation. In conclusion, hyperpolarization via optical pumping/dynamic nuclear polarization should function at arbitrary magnetic fields enabling orders of magnitude sensitivity enhancement for nuclear magnetic resonance of solids and liquids under ambient conditions.« less

  17. A novel NO2 gas sensor based on Hall effect operating at room temperature

    NASA Astrophysics Data System (ADS)

    Lin, J. Y.; Xie, W. M.; He, X. L.; Wang, H. C.

    2016-09-01

    Tungsten trioxide nanoparticles were obtained by a simple thermal oxidation approach. The structural and morphological properties of these nanoparticles are investigated using XRD, SEM and TEM. A WO3 thick film was deposited on the four Au electrodes to be a WO3 Hall effect sensor. The sensor was tested between magnetic field in a plastic test chamber. Room-temperature nitrogen dioxide sensing characteristics of Hall effect sensor were studied for various concentration levels of nitrogen dioxide at dry air and humidity conditions. A typical room-temperature response of 3.27 was achieved at 40 ppm of NO2 with a response and recovery times of 36 and 45 s, respectively. NO2 gas sensing mechanism of Hall effect sensor was also studied. The room-temperature operation, with the low deposition cost of the sensor, suggests suitability for developing a low-power cost-effective nitrogen dioxide sensor.

  18. 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.

  19. Near room temperature magnetodielectric consequence in (Li, Ti) doped NiO ceramic

    NASA Astrophysics Data System (ADS)

    Mukherjee, S.; Chatterjee, S.; Rayaprol, S.; Kaushik, S. D.; Bhattacharya, S.; Jana, P. K.

    2016-04-01

    In the quest for high-k dielectrics with decent magnetodielectric (MD) response, ball-milled processed (Li, Ti) doped NiO ceramics have been evaluated by various experimental techniques. Magnetic properties in these ceramics manifest with a pronounced anomaly appearing at ˜260 K, suggesting ferrimagnetic phase (related to cluster magnetism) and co-existence with a glassy-like antiferromagnetic phase at ˜7 K. Room temperature neutron diffraction pattern shows the existence of short-range magnetic correlations. In the magnetically ordered state below 250 K, the magnetic structure is found to be phase coexistence of G-type antiferromagnet and ferrimagnet. Impedance spectroscopy measurements over a wide temperature range can be perfectly described with appropriate microstructural model (internal barrier layer capacitor), based on domain and domain boundary relaxations, justifying the enhancement of the dielectric response. The low-temperature (T < 100 K) dielectric relaxation is polaronic in nature, associated with the charge ordering of a mixed valence states of Ti ions (co-existence of Ti3+ and Ti4+). Finally, our investigations in external magnetic fields up to 15 T reveal the occurrence of negative MD effect near room temperature. This intriguing intrinsic feature has been understood by the mechanism of charge-hopping-mediated MD effects.

  20. Reversible room-temperature ferromagnetism in Nb-doped SrTiO3 single crystals

    NASA Astrophysics Data System (ADS)

    Liu, Z. Q.; Lü, W. M.; Lim, S. L.; Qiu, X. P.; Bao, N. N.; Motapothula, M.; Yi, J. B.; Yang, M.; Dhar, S.; Venkatesan, T.; Ariando

    2013-06-01

    The search for oxide-based room-temperature ferromagnetism has been one of the holy grails in condensed matter physics. Room-temperature ferromagnetism observed in Nb-doped SrTiO3 single crystals is reported in this Rapid Communication. The ferromagnetism can be eliminated by air annealing (making the samples predominantly diamagnetic) and can be recovered by subsequent vacuum annealing. The temperature dependence of magnetic moment resembles the temperature dependence of carrier density, indicating that the magnetism is closely related to the free carriers. Our results suggest that the ferromagnetism is induced by oxygen vacancies. In addition, hysteretic magnetoresistance was observed for magnetic field parallel to the current, indicating that the magnetic moments are in the plane of the samples. The x-ray photoemission spectroscopy, the static time-of-flight and the dynamic secondary ion mass spectroscopy and proton induced x-ray emission measurements were performed to examine the magnetic impurities, showing that the observed ferromagnetism is unlikely due to any magnetic contaminant.

  1. Magnetically suspended stepping motors for clean room and vacuum environments

    NASA Astrophysics Data System (ADS)

    Higuchi, Toshiro

    1994-05-01

    To answer the growing needs for super-clean or contact free actuators for uses in clean rooms, vacuum chambers, and space, innovative actuators which combine the functions of stepping motors and magnetic bearings in one body were developed. The rotor of the magnetically suspended stepping motor is suspended like a magnetic bearing and rotated and positioned like a stepping motor. The important trait of the motor is that it is not a simple mixture or combination of a stepping motor and conventional magnetic bearing, but an amalgam of a stepping motor and a magnetic bearing. Owing to optimal design and feed-back control, a toothed stator and rotor are all that are needed structurewise for stable suspension. More than ten types of motors such as linear type, high accuracy rotary type, two-dimensional type, and high vacuum type were built and tested. This paper describes the structure and design of these motors and their performance for such applications as precise positioning rotary table, linear conveyor system, and theta-zeta positioner for clean room and high vacuum use.

  2. Magnetically suspended stepping motors for clean room and vacuum environments

    NASA Technical Reports Server (NTRS)

    Higuchi, Toshiro

    1994-01-01

    To answer the growing needs for super-clean or contact free actuators for uses in clean rooms, vacuum chambers, and space, innovative actuators which combine the functions of stepping motors and magnetic bearings in one body were developed. The rotor of the magnetically suspended stepping motor is suspended like a magnetic bearing and rotated and positioned like a stepping motor. The important trait of the motor is that it is not a simple mixture or combination of a stepping motor and conventional magnetic bearing, but an amalgam of a stepping motor and a magnetic bearing. Owing to optimal design and feed-back control, a toothed stator and rotor are all that are needed structurewise for stable suspension. More than ten types of motors such as linear type, high accuracy rotary type, two-dimensional type, and high vacuum type were built and tested. This paper describes the structure and design of these motors and their performance for such applications as precise positioning rotary table, linear conveyor system, and theta-zeta positioner for clean room and high vacuum use.

  3. 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.

  4. Low-temperature magnetic refrigerator

    DOEpatents

    Barclay, J.A.

    1983-05-26

    The invention relates to magnetic refrigeration and more particularly to low temperature refrigeration between about 4 and about 20 K, with an apparatus and method utilizing a belt of magnetic material passed in and out of a magnetic field with heat exchangers within and outside the field operably disposed to accomplish refrigeration.

  5. Low-temperature magnetic refrigerator

    DOEpatents

    Barclay, John A.

    1985-01-01

    The disclosure is directed to a low temperature 4 to 20 K. refrigeration apparatus and method utilizing a ring of magnetic material moving through a magnetic field. Heat exchange is accomplished in and out of the magnetic field to appropriately utilize the device to execute Carnot and Stirling cycles.

  6. Variable Temperature Equipment for a Commercial Magnetic Susceptibility Balance

    ERIC Educational Resources Information Center

    Lotz, Albert

    2008-01-01

    Variable temperature equipment for the magnetic susceptibility balance MSB-MK1 of Sherwood Scientific, Ltd., is described. The sample temperature is controlled with streaming air heated by water in a heat exchanger. Whereas the balance as sold commercially can be used only for room temperature measurements, the setup we designed extends the…

  7. Protocols for dry DNA storage and shipment at room temperature

    PubMed Central

    Ivanova, Natalia V; Kuzmina, Masha L

    2013-01-01

    The globalization of DNA barcoding will require core analytical facilities to develop cost-effective, efficient protocols for the shipment and archival storage of DNA extracts and PCR products. We evaluated three dry-state DNA stabilization systems: commercial Biomatrica® DNAstable® plates, home-made trehalose and polyvinyl alcohol (PVA) plates on 96-well panels of insect DNA stored at 56 °C and at room temperature. Controls included unprotected samples that were stored dry at room temperature and at 56 °C, and diluted samples held at 4 °C and at −20 °C. PCR and selective sequencing were performed over a 4-year interval to test the condition of DNA extracts. Biomatrica® provided better protection of DNA at 56 °C and at room temperature than trehalose and PVA, especially for diluted samples. PVA was the second best protectant after Biomatrica® at room temperature, whereas trehalose was the second best protectant at 56 °C. In spite of lower PCR success, the DNA stored at −20 °C yielded longer sequence reads and stronger signal, indicating that temperature is a crucial factor for DNA quality which has to be considered especially for long-term storage. Although it is premature to advocate a transition to DNA storage at room temperature, dry storage provides an additional layer of security for frozen samples, protecting them from degradation in the event of freezer failure. All three forms of DNA preservation enable shipment of dry DNA and PCR products between barcoding facilities. PMID:23789643

  8. Room temperature table-like magnetocaloric effect in amorphous Gd50Co45Fe5 ribbon

    NASA Astrophysics Data System (ADS)

    Liu, G. L.; Zhao, D. Q.; Bai, H. Y.; Wang, W. H.; Pan, M. X.

    2016-02-01

    Gd50Co45Fe5 amorphous alloy ribbon with a table-like magnetocaloric effect (MCE) suitable for the ideal Ericsson cycle at room temperature has been developed. In addition to a high magnetic transition temperature of 289 K very close to that of Gd (294 K), a relatively large value of refrigerant capacity (~521 J kg-1) has been achieved under a field change of 5 T. This value of refrigerant capacity (RC) is about 27% and 70% larger than those of Gd (~410 J kg-1) and Gd5Si2Ge2 (~306 J kg-1). More importantly, the peak value of magnetic entropy change (-Δ S\\text{M}\\max ) approaches a nearly constant value of ~3.8 J  ṡ  kg-1  ṡ  K-1 under an applied field change of 0~5 T in a wide temperature span over 40 K around room temperature, which could be used as the candidate working material in the Ericsson-cycle magnetic regenerative refrigerator around room temperature.

  9. 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.

  10. Coherent population trapping in a crystalline solid at room temperature

    NASA Astrophysics Data System (ADS)

    Kolesov, Roman

    2005-11-01

    Observation of coherent population trapping (CPT) at ground-state Zeeman sublevels of Cr3+ 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.

  11. 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.

  12. A device to investigate the delamination strength in laminates at room and cryogenic temperature.

    PubMed

    Zhang, Xingyi; Liu, Wei; Zhou, Jun; Zhou, You-He

    2014-12-01

    We construct an instrument to study the behavior of delamination strength in laminates which can be defined as the critical transverse stress at which an actual delamination occurs. The device allows the anvil measurements at room temperature or the liquid nitrogen temperature. For the electro-magnetic laminated materials (e.g., a superconducting YaBa2Cu3O(7-x) coated conductor which has a typical laminated structure), the delamination strength was measured while the properties of transport current were also recorded. Moreover, the influences of external magnetic field on the delamination strength were presented. PMID:25554334

  13. 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.

  14. Room temperature dual ferroic behaviour of ball mill synthesized NdFeO3 orthoferrite

    NASA Astrophysics Data System (ADS)

    Aparnadevi, N.; Saravana Kumar, K.; Manikandan, M.; Paul Joseph, D.; Venkateswaran, C.

    2016-07-01

    Phase pure NdFeO3 has been achieved using high energy ball milling of oxide precursors with subsequent sintering. It is established that structural arrangement of NdFeO3 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 Fe3+ 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 Fe3+ 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/cm2 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 NdFeO3.

  15. Deterministic switching of ferromagnetism at room temperature using an electric field.

    PubMed

    Heron, J T; Bosse, J L; He, Q; Gao, Y; Trassin, M; Ye, L; Clarkson, J D; Wang, C; Liu, Jian; Salahuddin, S; Ralph, D C; Schlom, D G; Iñiguez, J; Huey, B D; Ramesh, R

    2014-12-18

    The technological appeal of multiferroics is the ability to control magnetism with electric field. For devices to be useful, such control must be achieved at room temperature. The only single-phase multiferroic material exhibiting unambiguous magnetoelectric coupling at room temperature is BiFeO3 (refs 4 and 5). Its weak ferromagnetism arises from the canting of the antiferromagnetically aligned spins by the Dzyaloshinskii-Moriya (DM) interaction. Prior theory considered the symmetry of the thermodynamic ground state and concluded that direct 180-degree switching of the DM vector by the ferroelectric polarization was forbidden. Instead, we examined the kinetics of the switching process, something not considered previously in theoretical work. Here we show a deterministic reversal of the DM vector and canted moment using an electric field at room temperature. First-principles calculations reveal that the switching kinetics favours a two-step switching process. In each step the DM vector and polarization are coupled and 180-degree deterministic switching of magnetization hence becomes possible, in agreement with experimental observation. We exploit this switching to demonstrate energy-efficient control of a spin-valve device at room temperature. The energy per unit area required is approximately an order of magnitude less than that needed for spin-transfer torque switching. Given that the DM interaction is fundamental to single-phase multiferroics and magnetoelectrics, our results suggest ways to engineer magnetoelectric switching and tailor technologically pertinent functionality for nanometre-scale, low-energy-consumption, non-volatile magnetoelectronics. PMID:25519134

  16. Atom inlays performed at room temperature using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Sugimoto, Yoshiaki; Abe, Masayuki; Hirayama, Shinji; Oyabu, Noriaki; Custance, Óscar; Morita, Seizo

    2005-02-01

    The ability to manipulate single atoms and molecules laterally for creating artificial structures on surfaces is driving us closer to the ultimate limit of two-dimensional nanoengineering. However, experiments involving this level of manipulation have been performed only at cryogenic temperatures. Scanning tunnelling microscopy has proved, so far, to be a unique tool with all the necessary capabilities for laterally pushing, pulling or sliding single atoms and molecules, and arranging them on a surface at will. Here we demonstrate, for the first time, that it is possible to perform well-controlled lateral manipulations of single atoms using near-contact atomic force microscopy even at room temperature. We report the creation of 'atom inlays', that is, artificial atomic patterns formed from a few embedded atoms in the plane of a surface. At room temperature, such atomic structures remain stable on the surface for relatively long periods of time.

  17. Room temperature manipulation of long lifetime spins in metallic-like carbon nanospheres

    NASA Astrophysics Data System (ADS)

    Náfrádi, Bálint; Choucair, Mohammad; Dinse, Klaus-Peter; Forró, László

    2016-07-01

    The time-window for processing electron spin information (spintronics) in solid-state quantum electronic devices is determined by the spin-lattice and spin-spin relaxation times of electrons. Minimizing the effects of spin-orbit coupling and the local magnetic contributions of neighbouring atoms on spin-lattice and spin-spin relaxation times at room temperature remain substantial challenges to practical spintronics. Here we report conduction electron spin-lattice and spin-spin relaxation times of 175 ns at 300 K in 37+/-7 nm carbon spheres, which is remarkably long for any conducting solid-state material of comparable size. Following the observation of spin polarization by electron spin resonance, we control the quantum state of the electron spin by applying short bursts of an oscillating magnetic field and observe coherent oscillations of the spin state. These results demonstrate the feasibility of operating electron spins in conducting carbon nanospheres as quantum bits at room temperature.

  18. Anion pairs in room temperature ionic liquids predicted by molecular dynamics simulation, verified by spectroscopic characterization

    SciTech Connect

    Schwenzer, Birgit; Kerisit, Sebastien N.; Vijayakumar, M.

    2014-01-01

    Molecular-level spectroscopic analyses of an aprotic and a protic room-temperature ionic liquid, BMIM OTf and BMIM HSO4, respectively, have been carried out with the aim of verifying molecular dynamics simulations that predict anion pair formation in these fluid structures. Fourier-transform infrared spectroscopy, Raman spectroscopy and nuclear magnetic resonance spectroscopy of various nuclei support the theoretically-determined average molecular arrangements.

  19. Effects of room temperature aging on two cryogenic temperature sensor models used in aerospace applications

    NASA Astrophysics Data System (ADS)

    Courts, S. Scott; Krause, John

    2012-06-01

    Cryogenic temperature sensors used in aerospace applications are typically procured far in advance of the mission launch date. Depending upon the program, the temperature sensors may be stored at room temperature for extended periods as installation and groundbased testing can take years before the actual flight. The effects of long term storage at room temperature are sometimes approximated by the use of accelerated aging at temperatures well above room temperature, but this practice can yield invalid results as the sensing material and/or electrical contacting method can be increasingly unstable with higher temperature exposure. To date, little data are available on the effects of extended room temperature aging on sensors commonly used in aerospace applications. This research examines two such temperature sensors models - the Lake Shore Cryotronics, Inc. model CernoxTM and DT-670-SD temperature sensors. Sample groups of each model type have been maintained for ten years or longer with room temperature storage between calibrations. Over an eighteen year period, the CernoxTM temperature sensors exhibited a stability of better than ±20 mK for T<30 K and better than ±0.1% of temperature for T>30 K. Over a ten year period the model DT-670-SD sensors exhibited a stability of better than ±140 mK for T<25 K and better than ±75 mK for T>25 K.

  20. 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.

  1. 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.

  2. Room-temperature reactions for self-cleaning molecular nanosensors.

    PubMed

    Warnick, Keith H; Wang, Bin; Cliffel, David E; Wright, David W; Haglund, Richard F; Pantelides, Sokrates T

    2013-02-13

    New sensing techniques for detecting molecules, especially self-cleaning sensors, are in demand. Here we describe a room-temperature process in which a nanostructured substrate catalyzes the reaction of a target molecule with atmospheric oxygen and the reaction energy is absorbed by the substrate, where it can in principle be detected. Specifically, we report first-principles calculations describing a reaction between 2,4-dinitrotoluene (DNT) and atmospheric O(2) catalyzed by Fe-porphyrin at room temperature, incorporating an oxygen into the methyl group of DNT and releasing 1.9 eV per reaction. The atomic oxygen left on the Fe site can be removed by reacting with another DNT molecule, restoring the Fe catalyst.

  3. Room temperature hyperpolarization of nuclear spins in bulk

    PubMed Central

    Tateishi, Kenichiro; Negoro, Makoto; Nishida, Shinsuke; Kagawa, Akinori; Morita, Yasushi; Kitagawa, Masahiro

    2014-01-01

    Dynamic nuclear polarization (DNP), a means of transferring spin polarization from electrons to nuclei, can enhance the nuclear spin polarization (hence the NMR sensitivity) in bulk materials at most 660 times for 1H spins, using electron spins in thermal equilibrium as polarizing agents. By using electron spins in photo-excited triplet states instead, DNP can overcome the above limit. We demonstrate a 1H spin polarization of 34%, which gives an enhancement factor of 250,000 in 0.40 T, while maintaining a bulk sample (∼0.6 mg, ∼0.7 × 0.7 × 1 mm3) containing >1019 1H spins at room temperature. Room temperature hyperpolarization achieved with DNP using photo-excited triplet electrons has potentials to be applied to a wide range of fields, including NMR spectroscopy and MRI as well as fundamental physics. PMID:24821773

  4. 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.

  5. 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.

  6. Stability of blood gases in ice and at room temperature.

    PubMed

    Liss, H P; Payne, C P

    1993-04-01

    Arterial blood samples from 75 patients were analyzed for PO2, PCO2, and pH at 0, 15, and 30 min. After the baseline analysis, 60 samples were kept in ice while 59 samples were left at room temperature. There was a statistically significant increase in the PO2 at 15 min and again at 30 min in both groups. There was a statistically significant decrease in the PCO2 at 15 min in both groups. There were no further changes in the PCO2 at 30 min in either group. There was a statistically significant decrease in the pH at 15 min in both groups. There was a further statistically significant decrease in the pH at 30 min in the group of blood samples left at room temperature but not in those in ice. There is no reason to keep arterial blood in ice if blood gas analysis is done within 30 min. PMID:8131450

  7. 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.

  8. Aggregation-based growth of silver nanowires at room temperature

    NASA Astrophysics Data System (ADS)

    Sun, Lanlan; Wang, Li; Song, Yonghai; Guo, Cunlan; Sun, Yujing; Peng, Chongyang; Liu, Zhelin; Li, Zhuang

    2008-02-01

    We describe an aggregation-based growth mechanism for formation of silver nanowires at room temperature. It is found that the pH of solution and the concentration of L-cysteine capping molecules have an important effect on the formation and growth of nanowires. Characterization by atomic force microscopy (AFM) and UV-vis spectroscopy recorded as time clearly shows that the silver nanowires are grown at the expense of nanoparticles.

  9. Room Temperature, Metal-Free Arylation of Aliphatic Alcohols

    PubMed Central

    Ghosh, Raju; Lindstedt, Erik; Jalalian, Nazli; Olofsson, Berit

    2014-01-01

    Diaryliodonium salts are demonstrated as efficient arylating agents of aliphatic alcohols under metal-free conditions. The reaction proceeds at room temperature within 90 min to give alkyl aryl ethers in good to excellent yields. Aryl groups with electron-withdrawing substituents are transferred most efficiently, and unsymmetric iodonium salts give chemoselective arylations. The methodology has been applied to the formal synthesis of butoxycaine. PMID:24808991

  10. 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.

  11. 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.

  12. 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.

  13. A Na(+) Superionic Conductor for Room-Temperature Sodium Batteries.

    PubMed

    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.

  14. 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.

  15. 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

  16. 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

  17. A Na(+) Superionic Conductor for Room-Temperature Sodium Batteries.

    PubMed

    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

  18. 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.

  19. Room temperature magnetocaloric effect of La-deficient bulk perovskite manganite La 0.7MnO 3- δ

    NASA Astrophysics Data System (ADS)

    Wang, Zhiming; Xu, Qingyu; Sun, Jingzhi; Pan, Jian; Zhang, He

    2011-04-01

    Room temperature magnetocaloric effect in La-deficient bulk perovskite manganite La 0.7MnO 3- δ prepared by conventional solid-state reaction has been reported. The maximum value of the magnetic entropy change (about-1.32 J/kg K) and the refrigerant capacity (approximately close to 37 J/kg) had been obtained at 290 K corresponding to a magnetic field variation of 1 T for La 0.7MnO 3- δ. It is the strong Jahn-Teller coupling that changes Mn-O bond length and Mn-O-Mn bond angles and then the canted spin arrangement and induces the strong double-exchange coupling to a comparatively high magnetic transition temperature. This Curie temperature near room temperature with easy fabrication and higher chemical stability makes La 0.7MnO 3- δ a potential candidate as a working substance in magnetic refrigeration technology.

  20. 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.

  1. 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

  2. Room-temperature spin thermoelectrics in metallic films

    NASA Astrophysics Data System (ADS)

    Tölle, Sebastian; Gorini, Cosimo; Eckern, Ulrich

    2014-12-01

    Considering metallic films at room temperature, we present the first theoretical study of the spin Nernst and thermal Edelstein effects that takes into account dynamical spin-orbit coupling, i.e., direct spin-orbit coupling with the vibrating lattice (phonons) and impurities. This gives rise to a novel process, namely, a dynamical side-jump mechanism, and to dynamical Elliott-Yafet spin relaxation, never before considered in this context. Both are the high-temperature counterparts of the well-known T =0 side-jump and Elliott-Yafet, central to the current understanding of the spin Hall, spin Nernst and Edelstein (current-induced spin polarization) effects at low T . We consider the experimentally relevant regime T >TD , with TD the Debye temperature, as the latter is lower than room temperature in transition metals such as Pt, Au and Ta typically employed in spin injection/extraction experiments. We show that the interplay between intrinsic (Bychkov-Rashba type) and extrinsic (dynamical) spin-orbit coupling yields a nonlinear T dependence of the spin Nernst and spin Hall conductivities.

  3. Investigation of room temperature ferromagnetic nanoparticles of Gd5Si4

    DOE PAGES

    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 highmore » temperature of 275K decreases with the increase in the milling time.« less

  4. Ultralow field NMR spectrometer with an atomic magnetometer near room temperature.

    PubMed

    Liu, Guobin; Li, Xiaofeng; Sun, Xianping; Feng, Jiwen; Ye, Chaohui; Zhou, Xin

    2013-12-01

    We present a Cs atomic magnetometer with a sensitivity of 150fT/Hz(1/2) operating near room temperature. The nuclear magnetic resonance (NMR) signal of 125μL tap water was detected at an ultralow magnetic field down to 47nT, with the signal-to-noise ratio (SNR) of the NMR signal approaching 50 after eight averages. Relaxivity experiments with a Gd(DTPA) contrast agent in zero field were performed, in order to show the magnetometer's ability to measure spin-lattice relaxation time with high accuracy. This demonstrates the feasibility of an ultralow field NMR spectrometer based on a Cs atomic magnetometer, which has a low working temperature, short data acquisition time and high sensitivity. This kind of NMR spectrometer has great potential in applications such as chemical analysis and magnetic relaxometry detection in ultralow or zero fields.

  5. 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

    2016-01-01

    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. PMID:27652564

  6. 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.

  7. Room temperature positive magnetoresistance via charge trapping in polyaniline-iron oxide nanoparticle composites

    NASA Astrophysics Data System (ADS)

    Lin, Aigu L.; Wu, Tom; Chen, Wei; Wee, Andrew T. S.

    2013-07-01

    We demonstrate a polyaniline-iron oxide nanoparticle (PANI-NP) organic hybrid composite device with room temperature positive magnetoresistance of 85.7%. Temperature dependent resistivity measurements attribute this observation to the decrease in localization length of the charge carriers in the presence of an external magnetic field which result in them being trapped within the device between the insulating PANI layer, hence allowing the device to maintain its resistive state even when the power is switched off, thus exhibiting a memory effect.

  8. Tiny Ni-NiO nanocrystals with exchange bias induced room temperature ferromagnetism

    NASA Astrophysics Data System (ADS)

    Chaghouri, Hanan Al; Tuna, F.; Santhosh, P. N.; Thomas, P. John

    2016-03-01

    Ni nanocrystals coated with a thin layer of NiO with a diameter of 5.0 nm show exchange bias induced ferromagnetism at room temperature. These particulates are freely dispersible in water and were obtained by annealing Ni nanoparticles coated with a thin amorphous layer of NiO. Particulates with diameters between 5.0 and 16.8 nm are studied. Detailed magnetic measurements reveal signs consistent with strong exchange bias including elevated blocking temperatures and tangible loop shifts. The structure of the particulates are characterized by high resolution transmission electron microscopy, energy dispersive x-ray analysis and x-ray diffraction.

  9. Noninvasive liver-iron measurements with a room-temperature susceptometer.

    PubMed

    Avrin, William F; Kumar, Sankaran

    2007-04-01

    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 microg 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.

  10. 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.

  11. 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.

  12. Room temperature GaAsSb single nanowire infrared photodetectors.

    PubMed

    Li, Ziyuan; Yuan, Xiaoming; Fu, Lan; Peng, Kun; Wang, Fan; Fu, Xiao; Caroff, Philippe; White, Thomas P; Hoe Tan, Hark; Jagadish, Chennupati

    2015-11-01

    Antimonide-based ternary III-V nanowires (NWs) allow for a tunable bandgap over a wide range, which is highly interesting for optoelectronics applications, and in particular for infrared photodetection. Here we demonstrate room temperature operation of GaAs0.56Sb0.44 NW infrared photodetectors grown by metal organic vapor phase epitaxy. These GaAs0.56Sb0.44 NWs have uniform axial composition and show p-type conductivity with a peak field-effect mobility of ∼12 cm(2) V(-1) s(-1)). Under light illumination, single GaAs0.56Sb0.44 NW photodetectors exhibited typical photoconductor behavior with an increased photocurrent observed with the increase of temperature owing to thermal activation of carrier trap states. A broadband infrared photoresponse with a long wavelength cutoff at ∼1.66 μm was obtained at room temperature. At a low operating bias voltage of 0.15 V a responsivity of 2.37 (1.44) A/W with corresponding detectivity of 1.08 × 10(9) (6.55 × 10(8)) cm√Hz/W were achieved at the wavelength of 1.3 (1.55) μm, indicating that ternary GaAs0.56Sb0.44 NWs are promising photodetector candidates for small footprint integrated optical telecommunication systems. PMID:26451616

  13. Room temperature luminescence and ferromagnetism of AlN:Fe

    NASA Astrophysics Data System (ADS)

    Li, H.; Cai, G. M.; Wang, W. J.

    2016-06-01

    AlN:Fe polycrystalline powders were synthesized by a modified solid state reaction (MSSR) method. Powder X-ray diffraction and transmission electron microscopy results reveal the single phase nature of the doped samples. In the doped AlN samples, Fe is in Fe2+ state. Room temperature ferromagnetic behavior is observed in AlN:Fe samples. Two photoluminescence peaks located at about 592 nm (2.09 eV) and 598 nm (2.07 eV) are observed in AlN:Fe samples. Our results suggest that AlN:Fe is a potential material for applications in spintronics and high power laser devices.

  14. Icelike water monolayer adsorbed on mica at room temperature

    SciTech Connect

    Miranda, P.B.; Xu, L.; Shen, Y.R.; Salmeron, M.

    1998-10-01

    The structure of a water film formed on mica at room temperature, in equilibrium with water vapor at various relative humidities (RH), was studied using sum-frequency-generation (SFG) vibrational spectroscopy and scanning polarization force microscopy (SPFM). Analysis of the O-D stretch modes in the SFG spectra of D{sub 2}O on mica indicates that as RH increases, the submonolayer water structure evolves into a more ordered hydrogen-bonding network. At full monolayer coverage ({approximately} 90% RH), the SFG spectrum suggests an icelike film with no dangling O-D groups, in agreement with a recent molecular dynamics simulation.

  15. Experimental evidence for ferromagnetism at room temperature in MgO thin films.

    PubMed

    Kapilashrami, Mukes; Xu, Jun; Rao, K V; Belova, Lyuba; Carlegrim, Elin; Fahlman, Mats

    2010-09-01

    Ferromagnetic ordering at room temperature (RTFM) in MgO thin films deposited by RF magnetron sputtering under various atmospheric conditions and temperatures is reported. A saturation magnetization (M(S)) value as high as 1.58 emu g(-1) is (0.046 μB/unit cell) observed for a 170 nm film deposited at RT under an oxygen pressure of 1.3 × 10(-4) mbar. In contrast, films deposited at elevated temperature (under an identical oxygen pressure), or at higher oxygen pressures, as well as under a nitrogen atmosphere at RT show significantly suppressed magnetization. The ferromagnetic order in the MgO matrix is believed to be defect induced.

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

    PubMed

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

    2015-12-01

    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.

  17. A Room Temperature Ultrasensitive Magnetoelectric Susceptometer for Quantitative Tissue Iron Detection

    PubMed Central

    Xi, Hao; Qian, Xiaoshi; Lu, Meng-Chien; Mei, Lei; Rupprecht, Sebastian; Yang, Qing X.; Zhang, Q. M.

    2016-01-01

    Iron is a trace mineral that plays a vital role in the human body. However, absorbing and accumulating excessive iron in body organs (iron overload) can damage or even destroy an organ. Even after many decades of research, progress on the development of noninvasive and low-cost tissue iron detection methods is very limited. Here we report a recent advance in a room-temperature ultrasensitive biomagnetic susceptometer for quantitative tissue iron detection. The biomagnetic susceptometer exploits recent advances in the magnetoelectric (ME) composite sensors that exhibit an ultrahigh AC magnetic sensitivity under the presence of a strong DC magnetic field. The first order gradiometer based on piezoelectric and magnetostrictive laminate (ME composite) structure shows an equivalent magnetic noise of 0.99 nT/rt Hz at 1 Hz in the presence of a DC magnetic field of 0.1 Tesla and a great common mode noise rejection ability. A prototype magnetoelectric liver susceptometry has been demonstrated with liver phantoms. The results indicate its output signals to be linearly responsive to iron concentrations from normal iron dose (0.05 mg Fe/g liver phantom) to 5 mg Fe/g liver phantom iron overload (100X overdose). The results here open up many innovative possibilities for compact-size, portable, cost-affordable, and room-temperature operated medical systems for quantitative determinations of tissue iron. PMID:27465206

  18. Giant room-temperature magnetodielectric coupling in spark plasma sintered brownmillerite ceramics

    SciTech Connect

    Wu, J. W.; Wang, J.; Liu, G.; Wu, Y. J.; Liu, X. Q. Chen, X. M.

    2014-12-01

    The dielectric, magnetic, and magnetodielectric properties of Ca{sub 2}FeAO{sub 5+δ} (A = Al, Ga) ceramics were investigated together with their crystal structures. Rietveld refinement of the X-ray diffraction data indicated that the space group of the Ca{sub 2}FeAlO{sub 5+δ} ceramic was Ibm2, whereas that of the Ca{sub 2}FeGaO{sub 5+δ} ceramic was Pcmn. Dielectric relaxation above room temperature, originating from the Maxwell–Wagner effect and polaronic hole hopping between Fe{sup 3+} and Fe{sup 4+} ions, was observed in both ceramics. Weak ferrimagnetic behavior was identified from the magnetic-field-dependent magnetization in these ceramics, which was attributed to the non-cancelled spins of the antiferromagnetic-ordered Fe{sup 3+} and Fe{sup 4+} ions. An intrinsic, giant, room-temperature magnetodielectric coefficient of up to −23.3% was achieved in the Ca{sub 2}FeAlO{sub 5+δ} ceramic at 50 MHz, which was attributed to the suppression of charge fluctuations of Fe{sup 3+} and Fe{sup 4+} ions in the magnetic field.

  19. A Room Temperature Ultrasensitive Magnetoelectric Susceptometer for Quantitative Tissue Iron Detection.

    PubMed

    Xi, Hao; Qian, Xiaoshi; Lu, Meng-Chien; Mei, Lei; Rupprecht, Sebastian; Yang, Qing X; Zhang, Q M

    2016-01-01

    Iron is a trace mineral that plays a vital role in the human body. However, absorbing and accumulating excessive iron in body organs (iron overload) can damage or even destroy an organ. Even after many decades of research, progress on the development of noninvasive and low-cost tissue iron detection methods is very limited. Here we report a recent advance in a room-temperature ultrasensitive biomagnetic susceptometer for quantitative tissue iron detection. The biomagnetic susceptometer exploits recent advances in the magnetoelectric (ME) composite sensors that exhibit an ultrahigh AC magnetic sensitivity under the presence of a strong DC magnetic field. The first order gradiometer based on piezoelectric and magnetostrictive laminate (ME composite) structure shows an equivalent magnetic noise of 0.99 nT/rt Hz at 1 Hz in the presence of a DC magnetic field of 0.1 Tesla and a great common mode noise rejection ability. A prototype magnetoelectric liver susceptometry has been demonstrated with liver phantoms. The results indicate its output signals to be linearly responsive to iron concentrations from normal iron dose (0.05 mg Fe/g liver phantom) to 5 mg Fe/g liver phantom iron overload (100X overdose). The results here open up many innovative possibilities for compact-size, portable, cost-affordable, and room-temperature operated medical systems for quantitative determinations of tissue iron. PMID:27465206

  20. A Room Temperature Ultrasensitive Magnetoelectric Susceptometer for Quantitative Tissue Iron Detection

    NASA Astrophysics Data System (ADS)

    Xi, Hao; Qian, Xiaoshi; Lu, Meng-Chien; Mei, Lei; Rupprecht, Sebastian; Yang, Qing X.; Zhang, Q. M.

    2016-07-01

    Iron is a trace mineral that plays a vital role in the human body. However, absorbing and accumulating excessive iron in body organs (iron overload) can damage or even destroy an organ. Even after many decades of research, progress on the development of noninvasive and low-cost tissue iron detection methods is very limited. Here we report a recent advance in a room-temperature ultrasensitive biomagnetic susceptometer for quantitative tissue iron detection. The biomagnetic susceptometer exploits recent advances in the magnetoelectric (ME) composite sensors that exhibit an ultrahigh AC magnetic sensitivity under the presence of a strong DC magnetic field. The first order gradiometer based on piezoelectric and magnetostrictive laminate (ME composite) structure shows an equivalent magnetic noise of 0.99 nT/rt Hz at 1 Hz in the presence of a DC magnetic field of 0.1 Tesla and a great common mode noise rejection ability. A prototype magnetoelectric liver susceptometry has been demonstrated with liver phantoms. The results indicate its output signals to be linearly responsive to iron concentrations from normal iron dose (0.05 mg Fe/g liver phantom) to 5 mg Fe/g liver phantom iron overload (100X overdose). The results here open up many innovative possibilities for compact-size, portable, cost-affordable, and room-temperature operated medical systems for quantitative determinations of tissue iron.

  1. Prediction of Near-Room-Temperature Quantum Anomalous Hall Effect on Honeycomb Materials

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    Recently, this long-sought quantum anomalous Hall effect was realized in the magnetic topological insulator. However, the requirement of an extremely low temperature (~ 30 mK) hinders realistic applications. Based on honeycomb lattices comprised of Sn and Ge, which are found to be 2D topological insulators, we propose a quantum anomalous Hall platform with large energy gap of 0.34 and 0.06 eV, respectively. The ferromagnetic 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 ferromagnetic insulator with 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. We thank the helpful discussions with C. Felser, S. Kanugo, C.-X. Liu, Z. Wang, Y. Xu, K. Wu, and Y. Zhou.

  2. Room-Temperature Electron Spin Relaxation of Triarylmethyl Radicals at X- and Q-bands

    PubMed Central

    Krumkacheva, Olesya A.; Strizhakov, Rodion K.; Rogozhnikova, Olga Yu.; Troitskaya, Tatiana I.

    2016-01-01

    Triarylmethyl radicals (trityls, TAMs) represent a relatively new class of spin labels. The long relaxation of trityls at room temperature in liquid solutions makes them a promising alternative for traditional nitroxides. In this work we have synthesized a series of TAMs including perdeuterated Finland trityl (D36 form) , mono-, di-, and tri-ester derivatives of Finland-D36 trityl, deuterated form of OX63, dodeca-n-butyl homologue of Finland trityl, and triamide derivatives of Finland trityl with primary and secondary amines attached. We have studied room-temperature relaxation properties of these TAMs in liquids using pulsed Electron Paramagnetic Resonance (EPR) at two microwave frequency bands. We have found the clear dependence of phase memory time (Tm~T2) on magnetic field: room-temperature Tm values are ~1.5-2.5 times smaller at Q-band (34 GHz, 1.2 T) compared to X-band (9 GHz, 0.3 T). This trend is ascribed to the contribution from g-anisotropy that is negligible at lower magnetic fields but comes into play at Q-band. In agreement with this, while T1~Tm at X-band, we observe T1>Tm at Q-band due to increased contributions from incomplete motional averaging of g-anisotropy. In addition, the viscosity dependence shows that (1/Tm-1/T1) is proportional to the tumbling correlation time of trityls. Based on the analysis of previous data and results of the present work, we conclude that in general situation where spin label is at least partly mobile, X-band is most suitable for application of trityls for room-temperature pulsed EPR distance measurements. PMID:26001103

  3. 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

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

    DOE PAGES

    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 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

  5. Giant volume magnetostriction in the Y2Fe17 single crystal at room temperature

    NASA Astrophysics Data System (ADS)

    Nikitin, S. A.; Pankratov, N. Yu.; Smarzhevskaya, A. I.; Politova, G. A.; Pastushenkov, Yu. G.; Skokov, K. P.; del Moral, A.

    2015-05-01

    An investigation of the Y2Fe17 compound belonging to the class of intermetallic alloys of rare-earth and 3d-transition metals is presented. The magnetization, magnetostriction, and thermal expansion of the Y2Fe17 single crystal were studied. The forced magnetostriction and magnetostriction constants were investigated in the temperature range of the magnetic ordering close to the room temperature. The giant field induced volume magnetostriction was discovered in the room temperature region in the magnetic field up to 1.2 T. The contributions of both anisotropic single-ion and isotropic pair exchange interactions to the volume magnetostriction and magnetostriction constants were determined. The experimental results were interpreted within the framework of the Standard Theory of Magnetostriction and the Landau thermodynamic theory. It was found out that the giant values of the volume magnetostriction were caused by the strong dependence of the 3d-electron Coulomb charge repulsion on the deformations and width of the 3d-electron energy band.

  6. Strong Facet-Induced and Light-Controlled Room-Temperature Ferromagnetism in Semiconducting β-FeSi2 Nanocubes.

    PubMed

    He, Zhiqiang; Xiong, Shijie; Wu, Shuyi; Zhu, Xiaobin; Meng, Ming; Wu, Xinglong

    2015-09-01

    Crystalline β-FeSi2 nanocubes with two {100} facets and four {011} lateral facets synthesized by spontaneous one-step chemical vapor deposition exhibit strong room-temperature ferromagnetism with saturation magnetization of 15 emu/g. The room-temperature ferromagnetism is observed from the β-FeSi2 nanocubes larger than 150 nm with both the {100} and {011} facets. The ferromagnetism is tentatively explained with a simplified model including both the itinerant electrons in surface states and the local moments on Fe atoms near the surfaces. The work demonstrates the transformation from a nonmagnetic semiconductor to a magnetic one by exposing specific facets and the room-temperature ferromagnetism can be manipulated under light irradiation. The semiconducting β-FeSi2 nanocubes may have large potential in silicon-based spintronic applications. PMID:26302086

  7. 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.

  8. CuInP₂S₆ Room Temperature Layered Ferroelectric.

    PubMed

    Belianinov, A; He, Q; Dziaugys, A; Maksymovych, P; Eliseev, E; Borisevich, A; Morozovska, A; Banys, J; Vysochanskii, Y; Kalinin, S V

    2015-06-10

    We explore ferroelectric properties of cleaved 2-D flakes of copper indium thiophosphate, CuInP2S6 (CITP), and probe size effects along with limits of ferroelectric phase stability, by ambient and ultra high vacuum scanning probe microscopy. CITP belongs to the only material family known to display ferroelectric polarization in a van der Waals, layered crystal at room temperature and above. Our measurements directly reveal stable, ferroelectric polarization as evidenced by domain structures, switchable polarization, and hysteresis loops. We found that at room temperature the domain structure of flakes thicker than 100 nm is similar to the cleaved bulk surfaces, whereas below 50 nm polarization disappears. We ascribe this behavior to a well-known instability of polarization due to depolarization field. Furthermore, polarization switching at high bias is also associated with ionic mobility, as evidenced both by macroscopic measurements and by formation of surface damage under the tip at a bias of 4 V-likely due to copper reduction. Mobile Cu ions may therefore also contribute to internal screening mechanisms. The existence of stable polarization in a van-der-Waals crystal naturally points toward new strategies for ultimate scaling of polar materials, quasi-2D, and single-layer materials with advanced and nonlinear dielectric properties that are presently not found in any members of the growing "graphene family".

  9. 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

    2016-01-01

    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

  10. Wetting behavior of dialkylimidazolium chloroaluminate, a room temperature molten salt

    SciTech Connect

    Eberhart, J.

    1985-08-01

    Eberhart (1979) has found that the wetting behavior of a battery electrolyte can have a dramatic effect on the internal resistance of the battery as well as its cycle life. Good wetting of battery separators by electrolyte is essential for the easy passage of ions through the separator pores, while porous, gas diffusion electrodes require a lesser degree of wetting. For several years, a room temperature molten salt system has been under study. This system is composed of 1-methyl-3-ethylimidazolium chloride (C6N2H11Cl or MeEtImCl) plus aluminum chloride. The application of this novel liquid solution as a battery electrolyte appears to be promising. Available data suggest that likely candidates include cells with a chlorine positive electrode reactant and a magnesium, aluminum, or zinc negative electrode material. The present investigation is concerned with an assessment of the wetting behavior in the considered system, taking into account a study of the contact angles of various room temperature molten salts on candidate battery separator and porous electrode materials. 10 references.

  11. 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

  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. Simple room temperature bonding of thermoplastics and poly(dimethylsiloxane).

    PubMed

    Sunkara, Vijaya; Park, Dong-Kyu; Hwang, Hyundoo; Chantiwas, Rattikan; Soper, Steven A; Cho, Yoon-Kyoung

    2011-03-01

    We describe a simple and versatile method for bonding thermoplastics to elastomeric polydimethylsiloxane (PDMS) at room temperature. The bonding of various thermoplastics including polycarbonate (PC), cyclic olefin copolymer (COC), polymethylmethacrylate (PMMA), and polystyrene (PS), to PDMS has been demonstrated at room temperature. An irreversible bonding was formed instantaneously when the thermoplastics, activated by oxygen plasma followed by aminopropyltriethoxysilane modification, were brought into contact with the plasma treated PDMS. The surface modified thermoplastics were characterized by water contact angle measurements and X-ray photoelectron spectroscopy. The tensile strength of the bonded hybrid devices fabricated with PC, COC, PMMA, and PS was found to be 430, 432, 385, and 388 kPa, respectively. The assembled devices showed high burst resistance at a maximum channel pressure achievable by an in-house built syringe pump, 528 kPa. Furthermore, they displayed very high hydrolytic stability; no significant change was observed even after the storage in water at 37 °C over a period of three weeks. In addition, this thermoplastic-to-PDMS bonding technique has been successfully employed to fabricate a relatively large sized device. For example, a lab-on-a-disc with a diameter of 12 cm showed no leakage when it spins for centrifugal fluidic pumping at a very high rotating speed of 6000 rpm. PMID:21152492

  14. Simple room temperature bonding of thermoplastics and poly(dimethylsiloxane).

    PubMed

    Sunkara, Vijaya; Park, Dong-Kyu; Hwang, Hyundoo; Chantiwas, Rattikan; Soper, Steven A; Cho, Yoon-Kyoung

    2011-03-01

    We describe a simple and versatile method for bonding thermoplastics to elastomeric polydimethylsiloxane (PDMS) at room temperature. The bonding of various thermoplastics including polycarbonate (PC), cyclic olefin copolymer (COC), polymethylmethacrylate (PMMA), and polystyrene (PS), to PDMS has been demonstrated at room temperature. An irreversible bonding was formed instantaneously when the thermoplastics, activated by oxygen plasma followed by aminopropyltriethoxysilane modification, were brought into contact with the plasma treated PDMS. The surface modified thermoplastics were characterized by water contact angle measurements and X-ray photoelectron spectroscopy. The tensile strength of the bonded hybrid devices fabricated with PC, COC, PMMA, and PS was found to be 430, 432, 385, and 388 kPa, respectively. The assembled devices showed high burst resistance at a maximum channel pressure achievable by an in-house built syringe pump, 528 kPa. Furthermore, they displayed very high hydrolytic stability; no significant change was observed even after the storage in water at 37 °C over a period of three weeks. In addition, this thermoplastic-to-PDMS bonding technique has been successfully employed to fabricate a relatively large sized device. For example, a lab-on-a-disc with a diameter of 12 cm showed no leakage when it spins for centrifugal fluidic pumping at a very high rotating speed of 6000 rpm.

  15. 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.

  16. 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.

  17. Synthesis of manganese spinel nanoparticles at room temperature by coprecipitation

    SciTech Connect

    Giovannelli, F.; Autret-Lambert, C.; Mathieu, C.; Chartier, T.; Delorme, F.; Seron, A

    2012-08-15

    This paper is focused on a new route to synthesize Mn{sub 3}O{sub 4} nanoparticles by alkalisation by sodium hydroxide on a manganeous solution at room temperature. The precipitates obtained at different pH values have been characterized by XRD and TEM. Since the first addition of sodium hydroxide, a white Mn(OH){sub 2} precipitate appears. At pH=7, {gamma}-MnOOH phase is predominant with needle like shaped particles. At pH=10, hausmanite nanoparticles, which exhibits well defined cubic shape in the range 50-120 nm are obtained. This new precipitation route is a fast and easy environmentally friendly process to obtain well crystallized hausmanite nanoparticles. - Graphical abstract: TEM image showing Mn{sub 3}O{sub 4} particles after a precipitation at pH=10. Highlights: Black-Right-Pointing-Pointer A new route to synthesize Mn{sub 3}O{sub 4} nanoparticles has been demonstrated. Black-Right-Pointing-Pointer Synthesis has been performed by precipitation at room temperature. Black-Right-Pointing-Pointer The size of the Mn{sub 3}O{sub 4} nanoparticles is between 50 and 120 nm.

  18. Directional molecular sliding at room temperature on a silicon runway

    NASA Astrophysics Data System (ADS)

    Bouju, Xavier; Chérioux, Frédéric; Coget, Sébastien; Rapenne, Gwénaël; Palmino, Frank

    2013-07-01

    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.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. Electronic supplementary information (ESI) available: Computational details, additional STM images and movies showing DETB molecules sliding on the SmSi(111)-(7 × 1) reconstruction obtained from semi-empirical calculations. See DOI: 10.1039/c3nr01685d

  19. 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.

  20. Enabling NIR imaging at room temperature using quantum dots

    NASA Astrophysics Data System (ADS)

    Le Calvez, S.; Bourvon, H.; Kanaan, H.; Meunier-Della Gatta, S.; Philippot, C.; Reiss, P.

    2011-10-01

    Imaging in visible light at room temperature is now a well-mastered technology, whereas imaging in the near infrared (NIR) remains a challenge. NIR imaging has many applications like sensing, night vision and biological diagnostics. Unfortunately, silicon detectors are inefficient above 1000 nm, and other IR technologies still need low working temperatures and are thus expensive. Colloidal quantum dots can overcome these limitations thanks to their absorption wavelength tunability depending on their chemical composition and size. After a brief review of this research field, we will present the preparation of hybrid photodetectors using NIR absorbing PbS quantum dots in combination with poly(3-hexylthiopene) and PCBM. We discuss different solution based deposition processes for device fabrication (spincoating, dip-coating, doctor blading, inkjet printing). Preliminary device tests result in a detectivity of 4.7.109 Jones at 1300 nm.

  1. 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.

  2. Synthesis and characterization of nano crystalline nickel zinc ferrite for chlorine gas sensor at room temperature

    SciTech Connect

    Pawar, C. S.; Gujar, M. P.; Mathe, V. L.

    2015-06-24

    Nano crystalline Nickel Zinc ferrite (Ni{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4}) thin films were synthesized by Sol Gel method for gas response. The phase and microstructure of the obtained Ni{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). The nanostructured Ni{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} thin film shows single spinel phase. Magnetic study was obtained with the help of VSM. The effects of working temperature on the gas response were studied. The results reveal that the Ni{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} thin film gas sensor shows good selectivity to chlorine gas at room temperature. The sensor shows highest sensitivity (∼50%) at room temperature, indicating its application in detecting chlorine gas at room temperature in the future.

  3. Temperature-Dependent Giant Magnetoimpedance Effect in Amorphous Soft Magnets

    NASA Astrophysics Data System (ADS)

    Kurniawan, M.; Roy, R. K.; Panda, A. K.; Greve, D. W.; Ohodnicki, P.; McHenry, M. E.

    2014-12-01

    Giant magnetoimpedance (GMI)-based devices offer potential as next-generation low-cost, flexible, ultrasensitive sensors. They can be used in applications that include current sensors, field sensors, stress sensors, and others. Challenging applications involve operation at high temperatures, and therefore studies of GMI temperature dependence and performance of soft magnetic materials are needed. We present a high-temperature GMI study on an amorphous soft magnetic microwire from room temperature to 560°C. The GMI ratio was observed to be nearly constant at ˜86% at low temperatures and to decrease rapidly at ˜290°C, finally reaching a near-zero value at 500°C. The rapid drop in GMI ratio at 290°C is associated with a reduction in the long-range ferromagnetic order as measured by the spontaneous magnetization ( M) at the Curie temperature ( T c). We also correlated the impedance with the magnetic properties of the material. From room temperature to 290°C, the impedance was found to be proportional to the square root of the magnetization to magnetic anisotropy ratio. Lastly, M( T) has been fit using a Handrich-Kobe model, which describes the system with a modified Brillouin function and an asymmetrical distribution of exchange interactions. We infer that the structural fluctuations of the amorphous phase result in a relatively small asymmetry in the fluctuation parameters.

  4. [Studies on the health standard for room temperature in cold regions].

    PubMed

    Meng, Z L

    1990-03-01

    The microclimate of 205 rooms of single storey houses in four new rural residential districts in coastal and inland Shandong was monitored and studied the blood circulation of the finger, skin temperature, sweating function and other physiological indexes among 2,401 peasants. We interrogated their personal sensation to cold and warmth. The count was done by the application of thermal equilibrium index (TEI), predicted 4-hour Sweat Rate (P4SR) and the uncomfortable index. The standard room temperature is recommended as follows. In rural area in winter the appropriate room temperature is 14-16 degrees C, the comfortable room temperature is 16-20 degrees C, the lowest room temperature must not be below 14 degrees C. In summer the appropriate room temperature is 25-28 degrees C, the comfortable room temperature is 26-27 degrees C, the highest temperature must not be above 28 degrees C. PMID:2364801

  5. Room temperature d 0 ferromagnetism in hole doped Y2O3: widening the choice of host to tailor DMS

    NASA Astrophysics Data System (ADS)

    Chakraborty, Brahmananda; Ramaniah, Lavanya M.

    2016-08-01

    Transition metal-free-ferromagnetism in diluted magnetic semiconductors (DMS) is of much current interest in view of the search for more efficient DMS materials for spintronics applications. Our DFT results predict for the first time, that impurities from group1A (Li+, Na+, K+) doped on Y2O3 can induce a magnetic signature with a magnetic moment around 2.0 μ B per defect at hole concentrations around 1.63  ×  1021 cm‑3, which is one order less than the critical hole density of ZnO with ferromagnetic coupling large enough to promote room temperature ferromagnetism. The induction of room temperature ferromagnetism by hole doping with an impurity atom from group 1A, which injects two holes per defect in the system, implies that the recommendation of three holes per defect given in the literature, which puts a restriction on the choice of host material and the impurity, is not a necessary criterion for hole induced room temperature ferromagnetism. DFT simulations with the generalized gradient approximation (GGA), confirmed by the more sophisticated hybrid functional, Heyd–Scuseria–Ernzerhof (HSE06), predict that the magnetic moment is mostly contributed by O atoms surrounding the impurity atom and the magnetic moment scale up with impurity concentration which is a positive indicator for practical applications. We quantitatively and extensively demonstrate through the analysis of the density of states and ferromagnetic coupling that the Stoner criterion is satisfied by pushing the Fermi level inside the valence band to activate room temperature ferromagnetism. The stability of the structure and the persistence of ferromagnetism at room temperature were demonstrated by ab initio MD simulations and computation of Curie temperature through the mean field approximation. This study widens the choice of host oxides to tailor DMS for spintronics applications.

  6. Room temperature d 0 ferromagnetism in hole doped Y2O3: widening the choice of host to tailor DMS

    NASA Astrophysics Data System (ADS)

    Chakraborty, Brahmananda; Ramaniah, Lavanya M.

    2016-08-01

    Transition metal-free-ferromagnetism in diluted magnetic semiconductors (DMS) is of much current interest in view of the search for more efficient DMS materials for spintronics applications. Our DFT results predict for the first time, that impurities from group1A (Li+, Na+, K+) doped on Y2O3 can induce a magnetic signature with a magnetic moment around 2.0 μ B per defect at hole concentrations around 1.63  ×  1021 cm-3, which is one order less than the critical hole density of ZnO with ferromagnetic coupling large enough to promote room temperature ferromagnetism. The induction of room temperature ferromagnetism by hole doping with an impurity atom from group 1A, which injects two holes per defect in the system, implies that the recommendation of three holes per defect given in the literature, which puts a restriction on the choice of host material and the impurity, is not a necessary criterion for hole induced room temperature ferromagnetism. DFT simulations with the generalized gradient approximation (GGA), confirmed by the more sophisticated hybrid functional, Heyd-Scuseria-Ernzerhof (HSE06), predict that the magnetic moment is mostly contributed by O atoms surrounding the impurity atom and the magnetic moment scale up with impurity concentration which is a positive indicator for practical applications. We quantitatively and extensively demonstrate through the analysis of the density of states and ferromagnetic coupling that the Stoner criterion is satisfied by pushing the Fermi level inside the valence band to activate room temperature ferromagnetism. The stability of the structure and the persistence of ferromagnetism at room temperature were demonstrated by ab initio MD simulations and computation of Curie temperature through the mean field approximation. This study widens the choice of host oxides to tailor DMS for spintronics applications.

  7. Room temperature d (0) ferromagnetism in hole doped Y2O3: widening the choice of host to tailor DMS.

    PubMed

    Chakraborty, Brahmananda; Ramaniah, Lavanya M

    2016-08-24

    Transition metal-free-ferromagnetism in diluted magnetic semiconductors (DMS) is of much current interest in view of the search for more efficient DMS materials for spintronics applications. Our DFT results predict for the first time, that impurities from group1A (Li(+), Na(+), K(+)) doped on Y2O3 can induce a magnetic signature with a magnetic moment around 2.0 μ B per defect at hole concentrations around 1.63  ×  10(21) cm(-3), which is one order less than the critical hole density of ZnO with ferromagnetic coupling large enough to promote room temperature ferromagnetism. The induction of room temperature ferromagnetism by hole doping with an impurity atom from group 1A, which injects two holes per defect in the system, implies that the recommendation of three holes per defect given in the literature, which puts a restriction on the choice of host material and the impurity, is not a necessary criterion for hole induced room temperature ferromagnetism. DFT simulations with the generalized gradient approximation (GGA), confirmed by the more sophisticated hybrid functional, Heyd-Scuseria-Ernzerhof (HSE06), predict that the magnetic moment is mostly contributed by O atoms surrounding the impurity atom and the magnetic moment scale up with impurity concentration which is a positive indicator for practical applications. We quantitatively and extensively demonstrate through the analysis of the density of states and ferromagnetic coupling that the Stoner criterion is satisfied by pushing the Fermi level inside the valence band to activate room temperature ferromagnetism. The stability of the structure and the persistence of ferromagnetism at room temperature were demonstrated by ab initio MD simulations and computation of Curie temperature through the mean field approximation. This study widens the choice of host oxides to tailor DMS for spintronics applications. PMID:27351301

  8. Room-temperature ultrasensitive mass spectrometer via dynamical decoupling

    NASA Astrophysics Data System (ADS)

    Zhao, Nan; Yin, Zhang-qi

    2014-10-01

    We propose an ultrasensitive mass spectrometer based on a coupled quantum-bit-oscillator system. Under dynamical decoupling control of the quantum bit (qubit), the qubit coherence exhibits a comb structure in the time domain. The time-comb structure enables high-precision measurements of oscillator frequency, which can be used as an ultrasensitive mass spectrometer. We show that, in the ideal case, the sensitivity η of the proposed mass spectrometer has better performance at higher temperature and scales with the temperature T as η ˜T-1 /2 . While taking into account qubit and oscillator decay, the optimal sensitivity reaches a universal value independent of environmental temperature T . The measurement sensitivity η also shows an improved dependence on the control-pulse number N as η ˜N-3 /2 , in comparison with the N-1 /2 scaling in previous magnetometry studies. With the present technology on solid-state spin qubit and high-quality optomechanical system, our proposal is feasible to realize an ultrasensitive room-temperature mass spectrometer.

  9. 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.

  10. Contracting cardiomyocytes in hydrophobic room-temperature ionic liquid

    SciTech Connect

    Hoshino, Takayuki; Fujita, Kyoko; Higashi, Ayako; Sakiyama, Keiko; Ohno, Hiroyuki; Morishima, Keisuke

    2012-10-19

    Highlights: Black-Right-Pointing-Pointer Biocompatible room-temperature ionic liquid was applied on beating cardiomyocyte. Black-Right-Pointing-Pointer The lifetime of beating cardiomyocytes was depended on anion functional group. Black-Right-Pointing-Pointer A longer lifetime was recorded for no functional group on alkyl chain on their anion. Black-Right-Pointing-Pointer Amino group on alkyl chain and fluorine in anion induced fatal condition changes. Black-Right-Pointing-Pointer We reported liquid electrolyte interface to stimulate cardiomyocytes. -- Abstract: Room-temperature ionic liquids (RTILs) are drawing attention as a new class of nonaqueous solvents to replace organic and aqueous solvents for chemical processes in the liquid phase at room temperature. The RTILs are notable for their characteristics of nonvolatility, extremely low vapor pressure, electric conductivity, and incombustibility. These distinguished properties of RTILs have brought attention to them in applications with biological cells and tissue in vacuum environment for scanning electron microscopy, and in microfluidic devices for micro-total analysis system (micro-TAS). Habitable RTILs could increase capability of nonaqueous micro-TAS for living cells. Some RTILs seemed to have the capability to replace water in biological applications. However, these RTILs had been applied to just supplemental additives for biocompatible test, to fixed cells as a substitute for an aqueous solution, and to simple molecules. None of RTILs in which directly soaks a living cell culture. Therefore, we demonstrated the design of RTILs for a living cell culture and a liquid electrolyte to stimulate contracting cardiomyocytes using the RTILs. We assessed the effect of RTILs on the cardiomyocytes using the beating lifetime to compare the applicability of RTILs for biological applications. Frequent spontaneous contractions of cardiomyocytes were confirmed in amino acid anion RTILs [P{sub 8,8,8,8}][Leu] and [P{sub 8

  11. 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.

  12. 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

  13. Mobile Néel skyrmions at room temperature: status and future

    NASA Astrophysics Data System (ADS)

    Jiang, Wanjun; Zhang, Wei; Yu, Guoqiang; Jungfleisch, M. Benjamin; Upadhyaya, Pramey; Somaily, Hamoud; Pearson, John E.; Tserkovnyak, Yaroslav; Wang, Kang L.; Heinonen, Olle; te Velthuis, Suzanne G. E.; Hoffmann, Axel

    2016-05-01

    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. Towards the nanoscale Néel skyrmions, we further discuss the challenges from both material optimization and imaging characterization perspectives.

  14. Outcome of impact disruption of iron meteorites at room temperature

    NASA Astrophysics Data System (ADS)

    Katsura, T.; Nakamura, A.; Takabe, A.; Okamoto, T.; Sangen, K.; Hasegawa, S.; Liu, X.; Mashimo, T.

    2014-07-01

    The iron meteorites and some M-class asteroids are generally understood to originate in the cores of differentiated planetesimals or in the local melt pools of primitive bodies. On these primitive bodies and planetesimals, a wide range of collisional events at different mass scales, temperatures, and impact velocities would have occurred. Iron materials have a brittle-ductile transition at a certain temperature, which depends on metallurgical factors such as grain size and purity, and on conditions such as strain-rate and confining pressure [1]. An evolutional scenario of iron meteorite parent bodies was proposed in which they formed in the terrestrial planet region, after which they were scattered into the main belt by collisions, Yarkovsky thermal forces, and resonances [2]. In this case, they may have experienced collisional evolution in the vicinity of the Earth before they were scattered into the main belt. The size distribution of iron bodies in the main belt may therefore have depended on the disruption threshold of iron bodies at temperature above the brittle-ductile transition. This paper presents the results of impact-disruption experiments of iron meteorite and steel specimens mm-cm in size as projectiles or targets conducted at room temperature using three light-gas guns and one powder gun. Our iron specimens were almost all smaller in size than their counterparts (as targets or projectiles, respectively). The fragment size distribution of iron material was different from that of rocks. In iron fragmentation, a higher percentage of the mass is concentrated in larger fragments, i.e., the mass fraction of fine fragments is much less than that of rocks shown in the Figure (left). This is probably due to the ductile nature of the iron materials at room temperature. Furthermore, the Figure (right) shows that the largest fragment mass fraction f is dependent not only on the energy density but also on the size of the specimens. In order to obtain a generalized

  15. Thermoelectricity in atom-sized junctions at room temperatures.

    PubMed

    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 2e(2)/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

  16. Creep of Mg-PSZ at room temperature

    SciTech Connect

    Finlayson, T.R. . Dept. of Physics); Gross, A.K. . Dept. of Materials Engineering); Griffiths, J.R. . Div. of Manufacturing Technology); Kisi, E.H. . Faculty of Science and Technology)

    1994-03-01

    Transient [beta], or Andrade, creep occurs when magnesia-partially-stabilized zirconia is loaded in tension at room temperature. The equation relating the longitudinal or tensile creep strain [var epsilon][sub l][sup c] to the tensile stress, [sigma], and to the time, t, has been determined to be [var epsilon][sub l][sup c] = A[sigma][sup m]t[sup n] in which the constants A, m, and n depend on the phase content of the zirconia. Observations are reported of the tetragonal-to-monoclinic and tetragonal-to-orthorhombic phase transformations which occur during creep: there is also a progressive development of microcracking. It is shown that a combination of these phenomena can account for the observed creep behavior.

  17. Room temperature water splitting at the surface of magnetite.

    PubMed

    Parkinson, Gareth S; Novotný, Zbyněk; Jacobson, Peter; Schmid, Michael; Diebold, Ulrike

    2011-08-17

    An array of surface science measurements has revealed novel water adsorption behavior at the Fe(3)O(4)(001) surface. Following room temperature exposure to water, a low coverage of hydrogen atoms is observed, with no associated water hydroxyl group. Mild annealing of the hydrogenated surface leads to desorption of water via abstraction of surface oxygen atoms, leading to a reduction of the surface. These results point to an irreversible splitting of the water molecule. The observed phenomena are discussed in the context of recent DFT calculations (Mulakaluri, N.; Pentcheva, R.; Scheffler, M. J. Phys. Chem. C 2010, 114, 11148), which show that the Jahn-Teller distorted surface isolates adsorbed H in a geometry that could kinetically hinder recombinative desorption. In contrast, the adsorption geometry facilitates interaction between water hydroxyl species, which are concluded to leave the surface following a reactive desorption process, possibly via the creation of O(2).

  18. Gas sensing properties of nanocrystalline diamond at room temperature

    PubMed Central

    Kulha, Pavel; Laposa, Alexandr; Hruska, Karel; Demo, Pavel; Kromka, Alexander

    2014-01-01

    Summary This study describes an integrated NH3 sensor based on a hydrogenated nanocrystalline diamond (NCD)-sensitive layer coated on an interdigitated electrode structure. The gas sensing properties of the sensor structure were examined using a reducing gas (NH3) at room temperature and were found to be dependent on the electrode arrangement. A pronounced response of the sensor, which was comprised of dense electrode arrays (of 50 µm separation distance), was observed. The sensor functionality was explained by the surface transfer doping effect. Moreover, the three-dimensional model of the current density distribution of the hydrogenated NCD describes the transient flow of electrons between interdigitated electrodes and the hydrogenated NCD surface, that is, the formation of a closed current loop. PMID:25551062

  19. Extraordinary room-temperature photoluminescence in triangular WS2 monolayers.

    PubMed

    Gutiérrez, Humberto R; Perea-López, Nestor; Elías, Ana Laura; Berkdemir, Ayse; Wang, Bei; Lv, Ruitao; López-Urías, Florentino; Crespi, Vincent H; Terrones, Humberto; Terrones, Mauricio

    2013-08-14

    Individual monolayers of metal dichalcogenides are atomically thin two-dimensional crystals with attractive physical properties different from those of their bulk counterparts. Here we describe the direct synthesis of WS2 monolayers with triangular morphologies and strong room-temperature photoluminescence (PL). The Raman response as well as the luminescence as a function of the number of S-W-S layers is also reported. The PL weakens with increasing number of layers due to a transition from direct band gap in a monolayer to indirect gap in multilayers. The edges of WS2 monolayers exhibit PL signals with extraordinary intensity, around 25 times stronger than that at the platelet's center. The structure and chemical composition of the platelet edges appear to be critical for PL enhancement.

  20. 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.

  1. 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.

  2. Electrically Injected Photon-Pair Source at Room Temperature

    NASA Astrophysics Data System (ADS)

    Boitier, Fabien; Orieux, Adeline; Autebert, Claire; Lemaître, Aristide; Galopin, Elisabeth; Manquest, Christophe; Sirtori, Carlo; Favero, Ivan; Leo, Giuseppe; Ducci, Sara

    2014-05-01

    One of the main challenges for future quantum information technologies is the miniaturization and integration of high performance components in a single chip. In this context, electrically driven sources of nonclassical states of light have a clear advantage over optically driven ones. Here we demonstrate the first electrically driven semiconductor source of photon pairs working at room temperature and telecom wavelengths. The device is based on type-II intracavity spontaneous parametric down-conversion in an AlGaAs laser diode and generates pairs at 1.57 μm. Time-correlation measurements of the emitted pairs give an internal generation efficiency of 7×10-11 pairs/injected electron. The capability of our platform to support the generation, manipulation, and detection of photons opens the way to the demonstration of massively parallel systems for complex quantum operations.

  3. Icelike Water Monolayer Adsorbed on Mica at Room Temperature

    SciTech Connect

    Miranda, P.B.; Xu, L.; Shen, Y.R.; Salmeron, M.

    1998-12-01

    The structure of a water film formed on mica at room temperature, in equilibrium with water vapor at various relative humidities (RH), was studied using sum-frequency-generation (SFG) vibrational spectroscopy and scanning polarization force microscopy (SPFM). Analysis of the O-D stretch modes in the SFG spectra of D{sub 2}O on mica indicates that as RH increases, the submonolayer water structure evolves into a more ordered hydrogen-bonding network. At full monolayer coverage ({approximately} 90{percent} RH) , the SFG spectrum suggests an icelike film with no dangling O-D groups, in agreement with a recent molecular dynamics simulation. {copyright} {ital 1998} {ital The American Physical Society}

  4. Calculation of the room-temperature shapes of unsymmetric laminates

    NASA Technical Reports Server (NTRS)

    Hyer, M. W.

    1981-01-01

    A theory explaining the characteristics of the cured shapes of unsymmetric laminates is presented. The theory is based on an extension of classical lamination theory which accounts for geometric nonlinearities. A Rayleigh-Ritz approach to minimizing the total potential energy is used to obtain quantitative information regarding the room temperature shapes of square T300/5208 (0(2)/90(2))T and (0(4)/90(4))T graphite-epoxy laminates. It is shown that, depending on the thickness of the laminate and the length of the side the square, the saddle shape configuration is actually unstable. For values of length and thickness that render the saddle shape unstable, it is shown that two stable cylindrical shapes exist. The predictions of the theory are compared with existing experimental data.

  5. Emergence of room-temperature ferroelectricity at reduced dimensions.

    PubMed

    Lee, D; Lu, H; Gu, Y; Choi, S-Y; Li, S-D; Ryu, S; Paudel, T R; Song, K; Mikheev, E; Lee, S; Stemmer, S; Tenne, D A; Oh, S H; Tsymbal, E Y; Wu, X; Chen, L-Q; Gruverman, A; Eom, C B

    2015-09-18

    The enhancement of the functional properties of materials at reduced dimensions is crucial for continuous advancements in nanoelectronic applications. Here, we report that the scale reduction leads to the emergence of an important functional property, ferroelectricity, challenging the long-standing notion that ferroelectricity is inevitably suppressed at the scale of a few nanometers. A combination of theoretical calculations, electrical measurements, and structural analyses provides evidence of room-temperature ferroelectricity in strain-free epitaxial nanometer-thick films of otherwise nonferroelectric strontium titanate (SrTiO3). We show that electrically induced alignment of naturally existing polar nanoregions is responsible for the appearance of a stable net ferroelectric polarization in these films. This finding can be useful for the development of low-dimensional material systems with enhanced functional properties relevant to emerging nanoelectronic devices. PMID:26383947

  6. Radiation stability of some room temperature ionic liquids

    NASA Astrophysics Data System (ADS)

    Jagadeeswara Rao, Ch.; Venkatesan, K. A.; Tata, B. V. R.; Nagarajan, K.; Srinivasan, T. G.; Vasudeva Rao, P. R.

    2011-05-01

    Radiation stability of some room temperature ionic liquids (RTILs) that find useful electrochemical applications in nuclear fuel cycle has been evaluated. The ionic liquids such as protonated betaine bis(trifluoromethylsulfonyl)imide (HbetNTf 2), aliquat 336 (tri-n-octlymethylammonium chloride), 1-butyl-3-methylimidazolium chloride (bmimCl), 1-hexyl-3-methylimidazolium chloride (hmimCl), N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPyNTf 2) and N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide (MPPiNTf 2) have been irradiated to various absorbed dose levels, up to 700 kGy. The effect of gamma radiation on these ionic liquids has been evaluated by determining the variations in the physical properties such as color, density, viscosity, refractive index and electrochemical window. The changes in density, viscosity and refractive index of these ionic liquids upon irradiation were insignificant; however, the color and electrochemical window varied significantly with increase of absorbed dose.

  7. Complete S matrix in a microwave cavity at room temperature.

    PubMed

    Barthélemy, Jérôme; Legrand, Olivier; Mortessagne, Fabrice

    2005-01-01

    We experimentally study the widths of resonances in a two-dimensional microwave cavity at room temperature. By developing a model for the coupling antennas, we are able to discriminate their contribution from those of Ohmic losses to the broadening of resonances. Concerning Ohmic losses, we experimentally put to evidence two mechanisms: damping along propagation and absorption at the contour, the latter being responsible for variations of widths from mode to mode due to its dependence on the spatial distribution of the field at the contour. A theory, based on an S -matrix formalism, is given for these variations. It is successfully validated through measurements of several hundreds of resonances in a rectangular cavity.

  8. Room-Temperature, Low-Barrier Boron Doping of Graphene

    NASA Astrophysics Data System (ADS)

    Du, Shixuan

    Doping graphene with boron has been difficult because of high reaction barriers. Here, we describe a low-energy reaction route derived from first-principles calculations and validated by experiments. We find that a boron atom on graphene on a ruthenium(0001) substrate can replace a carbon by pushing it through, with substrate attraction helping to reduce the barrier to only 0.1 eV, implying that the doping can take place at room temperature. High-quality graphene is grown on a Ru(0001) surface and exposed to B2H6. Scanning tunneling microscopy/spectroscopy and X-ray photoelectron spectroscopy confirmed that boron is indeed incorporated substitutionally without disturbing the graphene lattice. (L.D. Pan et al., Nano Lett. 2015, 15, 6464. In collaboration with Lida Pan, Yande Que, Hui Chen, Dongfei Wang, Jun Li, Chengmin Shen, Wende Xiao, Hongjun Gao in CAS, and S. Pantellides in Vanderbilt University.)

  9. Room-Temperature, Low-Barrier Boron Doping of Graphene.

    PubMed

    Pan, Lida; Que, Yande; Chen, Hui; Wang, Dongfei; Li, Jun; Shen, Chengmin; Xiao, Wende; Du, Shixuan; Gao, Hongjun; Pantelides, Sokrates T

    2015-10-14

    Doping graphene with boron has been difficult because of high reaction barriers. Here, we describe a low-energy reaction route derived from first-principles calculations and validated by experiments. We find that a boron atom on graphene on a ruthenium(0001) substrate can replace a carbon by pushing it through, with substrate attraction helping to reduce the barrier to only 0.1 eV, implying that the doping can take place at room temperature. High-quality graphene is grown on a Ru(0001) surface and exposed to B2H6. Scanning tunneling microscopy/spectroscopy and X-ray photoelectron spectroscopy confirmed that boron is indeed incorporated substitutionally without disturbing the graphene lattice.

  10. 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.

  11. Mechanical and Thermal Characteristics of Insulation Materials for the KSTAR Magnet System at Cryogenic Temperature

    NASA Astrophysics Data System (ADS)

    Chung, Wooho; Lim, Bungsu; Kim, Myungkyu; Park, Hyunki; Kim, Keeman; Chu, Yong; Lee, Sangil

    2004-06-01

    The KSTAR(Korea Superconducting Tokamak Advanced Research) superconducting magnet is electrically insulated by the composite material of epoxy resin and glass fiber (2.5 kV/mm) and Kapton (8 kV/mm). The insulation composite material of epoxy resin and glass fiber is prepared using a VPI (Vacuum Pressure Impregnation) process. The superconducting magnet is under mechanical stress caused by the large temperature difference between the operation temperature of the magnet and room temperature. The large electro-magnetic force during the operation of the magnet is also exerted on the magnet. Therefore, the characteristics of the insulation material at cryogenic temperatures are very important and the tensile stress and thermal expansion coefficient for the insulation materials of the KSTAR superconducting magnet are measured. This paper presents results on mechanical properties of the insulation material for KSTAR magnets, such as density, ultimate tensile stress and thermal contraction between room temperature and cryogenic temperatures.

  12. Reduced graphene oxide for room-temperature gas sensors

    NASA Astrophysics Data System (ADS)

    Lu, Ganhua; Ocola, Leonidas E.; Chen, Junhong

    2009-11-01

    We demonstrated high-performance gas sensors based on graphene oxide (GO) sheets partially reduced via low-temperature thermal treatments. Hydrophilic graphene oxide sheets uniformly suspended in water were first dispersed onto gold interdigitated electrodes. The partial reduction of the GO sheets was then achieved through low-temperature, multi-step annealing (100, 200, and 300 °C) or one-step heating (200 °C) of the device in argon flow at atmospheric pressure. The electrical conductance of GO was measured after each heating cycle to interpret the level of reduction. The thermally-reduced GO showed p-type semiconducting behavior in ambient conditions and was responsive to low-concentration NO2 and NH3 gases diluted in air at room temperature. The sensitivity can be attributed mainly to the electron transfer between the reduced GO and adsorbed gaseous molecules (NO2/NH3). Additionally, the contact between GO and the Au electrode is likely to contribute to the overall sensing response because of the adsorbates-induced Schottky barrier variation. A simplified model is used to explain the experimental observations.

  13. 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.

  14. Pronounced multiferroicity in oleic acid stabilized BiFeO3 nanocrystals at room temperature.

    PubMed

    Mahesh, Dabbugalla; Mandal, Swapan K; Mahato, Bipul K; Rana, Bivas; Barman, Anjan

    2013-06-01

    We report on the experimental observation of pronounced multiferroicity in BiFeO3 nanocrystals (size approximately 40 nm) at room temperature. Large scale BiFeO3 nanocrystals are synthesized using a low temperature chemical route and further stabilized with oleic acid. The nanocrystals exhibit a significant distortion in lattice parameter c compared to the bulk. Oleic acid plays an important role in reducing oxygen vacancies and Fe2+ ions at the nanocrystal surface giving rise to a high resistivity (approximately 10(10) omega-cm at 300 K) of the sample. The direct band gap of nanocrystals is measured to be approximately 4.2 eV (about 1.5 times the bulk value) suggesting a strong quantum confinement effect. The nanocrystals show a remarkably high spontaneous saturation magnetization approximately 4.39 emu/g along with a prominent ferroelectric hysteresis loop at room temperature. Particle size effect leading to the appearance of large number of uncompensated spins and suppression of modulated spin structure have resulted a strong spontaneous magnetization in such nanoscale multiferroic materials. PMID:23862453

  15. Low Temperature Crystal Structure and Magnetic Properties of RAl2

    SciTech Connect

    Pathak, Arjun K.; Paudyal, Durga; Gschneidner, Karl A.; Pecharsky, Vitalij K.

    2014-01-08

    Low temperature crystal structure and magnetic properties of RAl2 (R = Pr and Nd) have been studied using temperature dependent powder x-ray diffraction, magnetization, and heat capacity measurements. Unlike PrAl2, NdAl2 retains cubic MgCu2-type structure from room temperature down to 5 K, which is also confirmed from first principles electronic structure calculations. The magnetization measurements show both PrAl2 and NdAl2 order ferromagnetically at TC = 32 K and 77 K, respectively. However, the magnetization measurements show the former is a hard ferromagnet compared to the latter which is a soft ferromagnetic material. The magnetic entropy change obtained from heat capacity measurements at ΔH = 30 kOe for PrAl2 and NdAl2 are 3.15 J mol-1 K-1 and 1.18 J mol-1 K-1, respectively.

  16. Room-temperature local ferromagnetism and its nanoscale expansion in the ferromagnetic semiconductor Ge1–xFex

    PubMed Central

    Wakabayashi, Yuki K.; Sakamoto, Shoya; Takeda, Yuki-haru; Ishigami, Keisuke; Takahashi, Yukio; Saitoh, Yuji; Yamagami, Hiroshi; Fujimori, Atsushi; Tanaka, Masaaki; Ohya, Shinobu

    2016-01-01

    We investigate the local electronic structure and magnetic properties of the group-IV-based ferromagnetic semiconductor, Ge1−xFex (GeFe), using soft X-ray magnetic circular dichroism. Our results show that the doped Fe 3d electrons are strongly hybridized with the Ge 4p states, and have a large orbital magnetic moment relative to the spin magnetic moment; i.e., morb/mspin ≈ 0.1. We find that nanoscale local ferromagnetic regions, which are formed through ferromagnetic exchange interactions in the high-Fe-content regions of the GeFe films, exist even at room temperature, well above the Curie temperature of 20–100 K. We observe the intriguing nanoscale expansion of the local ferromagnetic regions with decreasing temperature, followed by a transition of the entire film into a ferromagnetic state at the Curie temperature. PMID:26996202

  17. Room Temperature Giant and Linear Magnetoresistance in Topological Insulator Bi2Te3 Nanosheets

    NASA Astrophysics Data System (ADS)

    Wang, Xiaolin; Du, Yi; Dou, Shixue; Zhang, Chao

    2012-06-01

    Topological insulators, a new class of condensed matter having bulk insulating states and gapless metallic surface states, have demonstrated fascinating quantum effects. However, the potential practical applications of the topological insulators are still under exploration worldwide. We demonstrate that nanosheets of a Bi2Te3 topological insulator several quintuple layers thick display giant and linear magnetoresistance. The giant and linear magnetoresistance achieved is as high as over 600% at room temperature, with a trend towards further increase at higher temperatures, as well as being weakly temperature-dependent and linear with the field, without any sign of saturation at measured fields up to 13 T. Furthermore, we observed a magnetic field induced gap below 10 K. The observation of giant and linear magnetoresistance paves the way for 3D topological insulators to be useful for practical applications in magnetoelectronic sensors such as disk reading heads, mechatronics, and other multifunctional electromagnetic applications.

  18. Room-temperature ferromagnetism in n-type Cu-doped ZnO thin films

    SciTech Connect

    Hou, D. L.; Ye, X. J.; Zhao, X. Y.; Meng, H. J.; Zhou, H. J.; Li, X. L.; Zhen, C. M.

    2007-08-01

    A series of n-type Cu-doped ZnO thin films was prepared by magnetron sputtering. Such films have shown ferromagnetic properties at room temperature. The Cu ion is in a univalent state as identified by x-ray photoelectron spectroscopy. The moment per Cu ion decreases as the Cu concentration increases. The largest moment about 0.52 {mu}{sub B}/Cu was observed for Zn{sub 0.95}Cu{sub 0.05}O thin film. The Curie temperature about 360 K was observed for Zn{sub 0.95}Cu{sub 0.05}O:N film. To explore the relationship between ferromagnetism and carrier density, nitrogen was introduced into the samples which resulted magnetization and the transition temperature decreasing. These results indicate that the electron density plays an important role in ferromagnetism.

  19. Tetragonal phase of epitaxial room-temperature antiferromagnet CuMnAs.

    PubMed

    Wadley, P; Novák, V; Campion, R P; Rinaldi, C; Martí, X; Reichlová, H; Zelezný, J; Gazquez, J; Roldan, M A; Varela, M; Khalyavin, D; Langridge, S; Kriegner, D; Máca, F; Mašek, J; Bertacco, R; Holý, V; Rushforth, A W; Edmonds, K W; Gallagher, B L; Foxon, C T; Wunderlich, J; Jungwirth, T

    2013-01-01

    Recent studies have demonstrated the potential of antiferromagnets as the active component in spintronic devices. This is in contrast to their current passive role as pinning layers in hard disk read heads and magnetic memories. Here we report the epitaxial growth of a new high-temperature antiferromagnetic material, tetragonal CuMnAs, which exhibits excellent crystal quality, chemical order and compatibility with existing semiconductor technologies. We demonstrate its growth on the III-V semiconductors GaAs and GaP, and show that the structure is also lattice matched to Si. Neutron diffraction shows collinear antiferromagnetic order with a high Néel temperature. Combined with our demonstration of room-temperature-exchange coupling in a CuMnAs/Fe bilayer, we conclude that tetragonal CuMnAs films are suitable candidate materials for antiferromagnetic spintronics.

  20. Room temperature ferromagnetism in Mn- and Fe-doped indium tin oxide thin films

    NASA Astrophysics Data System (ADS)

    Venkatesan, M.; Gunning, R. D.; Stamenov, P.; Coey, J. M. D.

    2008-04-01

    Undoped and transition-metal doped indium tin oxide films have been grown by pulsed laser deposition technique, on single crystalline c-plane (0001) and r-plane (1102) sapphire substrates maintained at 500-850°C. Magnetization measurements of films deposited at different temperatures indicate that ferromagnetism appears for deposition temperatures, Tdep>600°C, with the highest moment for films deposited around 750°C. Qualitative different ferromagnetic behavior has been observed at room temperature in Fe- and Mn-doped thin films. The stable, hysteretic ferromagnetism of the Fe-doped films is due to the presence of magnetite, as seen in transmission Mössbauer spectra. The Mn-doped films show anhysteretic ferromagnetism which decays over time. It is somehow intrinsic, but not due to the Mn ions, which remains paramagnetic down to 4K. No anomalous Hall effect is observed.

  1. Evidence for room temperature electric polarization in RMn(2)O(5) multiferroics.

    PubMed

    Balédent, V; Chattopadhyay, S; Fertey, P; Lepetit, M B; Greenblatt, M; Wanklyn, B; Saouma, F O; Jang, J I; Foury-Leylekian, P

    2015-03-20

    It is established that the multiferroics RMn(2)O(5) crystallize in the centrosymmetric Pbam space group and that the magnetically induced electric polarization appearing at low temperature is accompanied by a symmetry breaking. However, both our present x-ray study-performed on compounds with R=Pr,Nd,Gd,Tb, and Dy-and first-principles calculations unambiguously rule out this picture. Based on structural refinements, geometry optimization, and physical arguments, we demonstrate in this Letter that the actual space group is likely to be Pm. This turns out to be of crucial importance for RMn(2)O(5) multiferroics since Pm is not centrosymmetric. Ferroelectricity is thus already present at room temperature, and its enhancement at low temperature is a spin-enhanced process. This result is also supported by direct observation of optical second harmonic generation. This fundamental result calls into question the actual theoretical approaches that describe the magnetoelectric coupling in this multiferroic family.

  2. Tetragonal phase of epitaxial room-temperature antiferromagnet CuMnAs.

    PubMed

    Wadley, P; Novák, V; Campion, R P; Rinaldi, C; Martí, X; Reichlová, H; Zelezný, J; Gazquez, J; Roldan, M A; Varela, M; Khalyavin, D; Langridge, S; Kriegner, D; Máca, F; Mašek, J; Bertacco, R; Holý, V; Rushforth, A W; Edmonds, K W; Gallagher, B L; Foxon, C T; Wunderlich, J; Jungwirth, T

    2013-01-01

    Recent studies have demonstrated the potential of antiferromagnets as the active component in spintronic devices. This is in contrast to their current passive role as pinning layers in hard disk read heads and magnetic memories. Here we report the epitaxial growth of a new high-temperature antiferromagnetic material, tetragonal CuMnAs, which exhibits excellent crystal quality, chemical order and compatibility with existing semiconductor technologies. We demonstrate its growth on the III-V semiconductors GaAs and GaP, and show that the structure is also lattice matched to Si. Neutron diffraction shows collinear antiferromagnetic order with a high Néel temperature. Combined with our demonstration of room-temperature-exchange coupling in a CuMnAs/Fe bilayer, we conclude that tetragonal CuMnAs films are suitable candidate materials for antiferromagnetic spintronics. PMID:23959149

  3. Room temperature giant and linear magnetoresistance in topological insulator Bi2Te3 nanosheets.

    PubMed

    Wang, Xiaolin; Du, Yi; Dou, Shixue; Zhang, Chao

    2012-06-29

    Topological insulators, a new class of condensed matter having bulk insulating states and gapless metallic surface states, have demonstrated fascinating quantum effects. However, the potential practical applications of the topological insulators are still under exploration worldwide. We demonstrate that nanosheets of a Bi(2)Te(3) topological insulator several quintuple layers thick display giant and linear magnetoresistance. The giant and linear magnetoresistance achieved is as high as over 600% at room temperature, with a trend towards further increase at higher temperatures, as well as being weakly temperature-dependent and linear with the field, without any sign of saturation at measured fields up to 13 T. Furthermore, we observed a magnetic field induced gap below 10 K. The observation of giant and linear magnetoresistance paves the way for 3D topological insulators to be useful for practical applications in magnetoelectronic sensors such as disk reading heads, mechatronics, and other multifunctional electromagnetic applications.

  4. Electrodrift purification of materials for room temperature radiation detectors

    DOEpatents

    James, Ralph B.; Van Scyoc, III, John M.; Schlesinger, Tuviah E.

    1997-06-24

    A method of purifying nonmetallic, crystalline semiconducting materials useful for room temperature radiation detecting devices by applying an electric field across the material. The present invention discloses a simple technology for producing purified ionic semiconducting materials, in particular PbI.sub.2 and preferably HgI.sub.2, which produces high yields of purified product, requires minimal handling of the material thereby reducing the possibility of introducing or reintroducing impurities into the material, is easy to control, is highly selective for impurities, retains the stoichiometry of the material and employs neither high temperatures nor hazardous materials such as solvents or liquid metals. An electric field is applied to a bulk sample of the material causing impurities present in the sample to drift in a preferred direction. After all of the impurities have been transported to the ends of the sample the current flowing through the sample, a measure of the rate of transport of mobile impurities, falls to a low, steady state value, at which time the end sections of the sample where the impurities have concentrated are removed leaving a bulk sample of higher purity material. Because the method disclosed here only acts on the electrically active impurities, the stoichiometry of the host material remains substantially unaffected.

  5. Electrodrift purification of materials for room temperature radiation detectors

    DOEpatents

    James, R.B.; Van Scyoc, J.M. III; Schlesinger, T.E.

    1997-06-24

    A method of purifying nonmetallic, crystalline semiconducting materials useful for room temperature radiation detecting devices by applying an electric field across the material is disclosed. The present invention discloses a simple technology for producing purified ionic semiconducting materials, in particular PbI{sub 2} and preferably HgI{sub 2}, which produces high yields of purified product, requires minimal handling of the material thereby reducing the possibility of introducing or reintroducing impurities into the material, is easy to control, is highly selective for impurities, retains the stoichiometry of the material and employs neither high temperatures nor hazardous materials such as solvents or liquid metals. An electric field is applied to a bulk sample of the material causing impurities present in the sample to drift in a preferred direction. After all of the impurities have been transported to the ends of the sample the current flowing through the sample, a measure of the rate of transport of mobile impurities, falls to a low, steady state value, at which time the end sections of the sample where the impurities have concentrated are removed leaving a bulk sample of higher purity material. Because the method disclosed here only acts on the electrically active impurities, the stoichiometry of the host material remains substantially unaffected. 4 figs.

  6. Engineering Room-temperature Superconductors Via ab-initio Calculations

    NASA Astrophysics Data System (ADS)

    Gulian, Mamikon; Melkonyan, Gurgen; Gulian, Armen

    The BCS, or bosonic model of superconductivity, as Little and Ginzburg have first argued, can bring in superconductivity at room temperatures in the case of high-enough frequency of bosonic mode. It was further elucidated by Kirzhnitset al., that the condition for existence of high-temperature superconductivity is closely related to negative values of the real part of the dielectric function at finite values of the reciprocal lattice vectors. In view of these findings, the task is to calculate the dielectric function for real materials. Then the poles of this function will indicate the existence of bosonic excitations which can serve as a "glue" for Cooper pairing, and if the frequency is high enough, and the dielectric matrix is simultaneously negative, this material is a good candidate for very high-Tc superconductivity. Thus, our approach is to elaborate a methodology of ab-initio calculation of the dielectric function of various materials, and then point out appropriate candidates. We used the powerful codes (TDDF with the DP package in conjunction with ABINIT) for computing dielectric responses at finite values of the wave vectors in the reciprocal lattice space. Though our report is concerned with the particular problem of superconductivity, the application range of the data processing methodology is much wider. The ability to compute the dielectric function of existing and still non-existing (though being predicted!) materials will have many more repercussions not only in fundamental sciences but also in technology and industry.

  7. A computed room temperature line list for phosphine

    NASA Astrophysics Data System (ADS)

    Sousa-Silva, Clara; Yurchenko, Sergei N.; Tennyson, Jonathan

    2013-06-01

    An accurate and comprehensive room temperature rotation-vibration transition line list for phosphine (31PH3) is computed using a newly refined potential energy surface and a previously constructed ab initio electric dipole moment surface. Energy levels, Einstein A coefficients and transition intensities are computed using these surfaces and a variational approach to the nuclear motion problem as implemented in the program TROVE. A ro-vibrational spectrum is computed, covering the wavenumber range 0-8000 cm-1. The resulting line list, which is appropriate for temperatures up to 300 K, consists of a total of 137 million transitions between 5.6 million energy levels. Several of the band centres are shifted to better match experimental transition frequencies. The line list is compared to the most recent HITRAN database and other laboratorial sources. Transition wavelengths and intensities are generally found to be in good agreement with the existing experimental data, with particularly close agreement for the rotational spectrum. An analysis of the comparison between the theoretical data created and the existing experimental data is performed, and suggestions for future improvements and assignments to the HITRAN database are made.

  8. New Flexible Channels for Room Temperature Tunneling Field Effect Transistors

    DOE PAGES

    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 variousmore » 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.« less

  9. Silicene field-effect transistors operating at room temperature

    NASA Astrophysics Data System (ADS)

    Tao, Li; Cinquanta, Eugenio; Chiappe, Daniele; Grazianetti, Carlo; Fanciulli, Marco; Dubey, Madan; Molle, Alessandro; Akinwande, Deji

    2015-03-01

    Free-standing silicene, a silicon analogue of graphene, has a buckled honeycomb lattice and, because of its Dirac bandstructure combined with its sensitive surface, offers the potential for a widely tunable two-dimensional monolayer, where external fields and interface interactions can be exploited to influence fundamental properties such as bandgap and band character for future nanoelectronic devices. The quantum spin Hall effect, chiral superconductivity, giant magnetoresistance and various exotic field-dependent states have been predicted in monolayer silicene. Despite recent progress regarding the epitaxial synthesis of silicene and investigation of its electronic properties, to date there has been no report of experimental silicene devices because of its air stability issue. Here, we report a silicene field-effect transistor, corroborating theoretical expectations regarding its ambipolar Dirac charge transport, with a measured room-temperature mobility of ˜100 cm2 V-1 s-1 attributed to acoustic phonon-limited transport and grain boundary scattering. These results are enabled by a growth-transfer-fabrication process that we have devised—silicene encapsulated delamination with native electrodes. This approach addresses a major challenge for material preservation of silicene during transfer and device fabrication and is applicable to other air-sensitive two-dimensional materials such as germanene and phosphorene. Silicene's allotropic affinity with bulk silicon and its low-temperature synthesis compared with graphene or alternative two-dimensional semiconductors suggest a more direct integration with ubiquitous semiconductor technology.

  10. New Flexible Channels for Room Temperature Tunneling Field Effect Transistors

    PubMed Central

    Hao, Boyi; Asthana, Anjana; Hazaveh, Paniz Khanmohammadi; Bergstrom, Paul L.; Banyai, Douglas; Savaikar, Madhusudan A.; Jaszczak, John A.; Yap, Yoke Khin

    2016-01-01

    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. PMID:26846587

  11. Room temperature triplet state spectroscopy of organic semiconductors.

    PubMed

    Reineke, Sebastian; Baldo, Marc A

    2014-01-01

    Organic light-emitting devices and solar cells are devices that create, manipulate, and convert excited states in organic semiconductors. It is crucial to characterize these excited states, or excitons, to optimize device performance in applications like displays and solar energy harvesting. This is complicated if the excited state is a triplet because the electronic transition is 'dark' with a vanishing oscillator strength. As a consequence, triplet state spectroscopy must usually be performed at cryogenic temperatures to reduce competition from non-radiative rates. Here, we control non-radiative rates by engineering a solid-state host matrix containing the target molecule, allowing the observation of phosphorescence at room temperature and alleviating constraints of cryogenic experiments. We test these techniques on a wide range of materials with functionalities spanning multi-exciton generation (singlet exciton fission), organic light emitting device host materials, and thermally activated delayed fluorescence type emitters. Control of non-radiative modes in the matrix surrounding a target molecule may also have broader applications in light-emitting and photovoltaic devices. PMID:24445870

  12. Room temperature triplet state spectroscopy of organic semiconductors

    PubMed Central

    Reineke, Sebastian; Baldo, Marc A.

    2014-01-01

    Organic light-emitting devices and solar cells are devices that create, manipulate, and convert excited states in organic semiconductors. It is crucial to characterize these excited states, or excitons, to optimize device performance in applications like displays and solar energy harvesting. This is complicated if the excited state is a triplet because the electronic transition is ‘dark’ with a vanishing oscillator strength. As a consequence, triplet state spectroscopy must usually be performed at cryogenic temperatures to reduce competition from non-radiative rates. Here, we control non-radiative rates by engineering a solid-state host matrix containing the target molecule, allowing the observation of phosphorescence at room temperature and alleviating constraints of cryogenic experiments. We test these techniques on a wide range of materials with functionalities spanning multi-exciton generation (singlet exciton fission), organic light emitting device host materials, and thermally activated delayed fluorescence type emitters. Control of non-radiative modes in the matrix surrounding a target molecule may also have broader applications in light-emitting and photovoltaic devices. PMID:24445870

  13. Silicene field-effect transistors operating at room temperature.

    PubMed

    Tao, Li; Cinquanta, Eugenio; Chiappe, Daniele; Grazianetti, Carlo; Fanciulli, Marco; Dubey, Madan; Molle, Alessandro; Akinwande, Deji

    2015-03-01

    Free-standing silicene, a silicon analogue of graphene, has a buckled honeycomb lattice and, because of its Dirac bandstructure combined with its sensitive surface, offers the potential for a widely tunable two-dimensional monolayer, where external fields and interface interactions can be exploited to influence fundamental properties such as bandgap and band character for future nanoelectronic devices. The quantum spin Hall effect, chiral superconductivity, giant magnetoresistance and various exotic field-dependent states have been predicted in monolayer silicene. Despite recent progress regarding the epitaxial synthesis of silicene and investigation of its electronic properties, to date there has been no report of experimental silicene devices because of its air stability issue. Here, we report a silicene field-effect transistor, corroborating theoretical expectations regarding its ambipolar Dirac charge transport, with a measured room-temperature mobility of ∼100 cm(2) V(-1) s(-1) attributed to acoustic phonon-limited transport and grain boundary scattering. These results are enabled by a growth-transfer-fabrication process that we have devised--silicene encapsulated delamination with native electrodes. This approach addresses a major challenge for material preservation of silicene during transfer and device fabrication and is applicable to other air-sensitive two-dimensional materials such as germanene and phosphorene. Silicene's allotropic affinity with bulk silicon and its low-temperature synthesis compared with graphene or alternative two-dimensional semiconductors suggest a more direct integration with ubiquitous semiconductor technology.

  14. High Temperature, Permanent Magnet Biased, Fault Tolerant, Homopolar Magnetic Bearing Development

    NASA Technical Reports Server (NTRS)

    Palazzolo, Alan; Tucker, Randall; Kenny, Andrew; Kang, Kyung-Dae; Ghandi, Varun; Liu, Jinfang; Choi, Heeju; Provenza, Andrew

    2008-01-01

    This paper summarizes the development of a magnetic bearing designed to operate at 1,000 F. A novel feature of this high temperature magnetic bearing is its homopolar construction which incorporates state of the art high temperature, 1,000 F, permanent magnets. A second feature is its fault tolerance capability which provides the desired control forces with over one-half of the coils failed. The construction and design methodology of the bearing is outlined and test results are shown. The agreement between a 3D finite element, magnetic field based prediction for force is shown to be in good agreement with predictions at room and high temperature. A 5 axis test rig will be complete soon to provide a means to test the magnetic bearings at high temperature and speed.

  15. 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.

  16. Demonstration of charge breeding in a compact room temperature electron beam ion trap

    SciTech Connect

    Vorobjev, G.; Sokolov, A.; Herfurth, F.; Kester, O.; Quint, W.; Stoehlker, Th.; Thorn, A.; Zschornack, G.

    2012-05-15

    For the first time, a small room-temperature electron beam ion trap (EBIT), operated with permanent magnets, was successfully used for charge breeding experiments. The relatively low magnetic field of this EBIT does not contribute to the capture of the ions; single-charged ions are only caught by the space charge potential of the electron beam. An over-barrier injection method was used to fill the EBIT's electrostatic trap with externally produced, single-charged potassium ions. Charge states as high as K{sup 19+} were reached after about a 3 s breeding time. The capture and breeding efficiencies up to 0.016(4)% for K{sup 17+} have been measured.

  17. Room-temperature amorphous alloy field-effect transistor exhibiting particle and wave electronic transport

    SciTech Connect

    Fukuhara, M.; Kawarada, H.

    2015-02-28

    The realization of room-temperature macroscopic field effect transistors (FETs) will lead to new epoch-making possibilities for electronic applications. The I{sub d}-V{sub g} characteristics of the millimeter-sized aluminum-oxide amorphous alloy (Ni{sub 0.36}Nb{sub 0.24}Zr{sub 0.40}){sub 90}H{sub 10} FETs were measured at a gate-drain bias voltage of 0–60 μV in nonmagnetic conditions and under a magnetic fields at room temperature. Application of dc voltages to the gate electrode resulted in the transistor exhibiting one-electron Coulomb oscillation with a period of 0.28 mV, Fabry-Perot interference with a period of 2.35 μV under nonmagnetic conditions, and a Fano effect with a period of 0.26 mV for Vg and 0.2 T under a magnetic field. The realization of a low-energy controllable device made from millimeter-sized Ni-Nb-Zr-H amorphous alloy throws new light on cluster electronics.

  18. Room temperature manipulation of long lifetime spins in metallic-like carbon nanospheres.

    PubMed

    Náfrádi, Bálint; Choucair, Mohammad; Dinse, Klaus-Peter; Forró, László

    2016-01-01

    The time-window for processing electron spin information (spintronics) in solid-state quantum electronic devices is determined by the spin-lattice and spin-spin relaxation times of electrons. Minimizing the effects of spin-orbit coupling and the local magnetic contributions of neighbouring atoms on spin-lattice and spin-spin relaxation times at room temperature remain substantial challenges to practical spintronics. Here we report conduction electron spin-lattice and spin-spin relaxation times of 175 ns at 300 K in 37±7 nm carbon spheres, which is remarkably long for any conducting solid-state material of comparable size. Following the observation of spin polarization by electron spin resonance, we control the quantum state of the electron spin by applying short bursts of an oscillating magnetic field and observe coherent oscillations of the spin state. These results demonstrate the feasibility of operating electron spins in conducting carbon nanospheres as quantum bits at room temperature. PMID:27426851

  19. Room-temperature amorphous alloy field-effect transistor exhibiting particle and wave electronic transport

    NASA Astrophysics Data System (ADS)

    Fukuhara, M.; Kawarada, H.

    2015-02-01

    The realization of room-temperature macroscopic field effect transistors (FETs) will lead to new epoch-making possibilities for electronic applications. The Id-Vg characteristics of the millimeter-sized aluminum-oxide amorphous alloy (Ni0.36Nb0.24Zr0.40)90H10 FETs were measured at a gate-drain bias voltage of 0-60 μV in nonmagnetic conditions and under a magnetic fields at room temperature. Application of dc voltages to the gate electrode resulted in the transistor exhibiting one-electron Coulomb oscillation with a period of 0.28 mV, Fabry-Perot interference with a period of 2.35 μV under nonmagnetic conditions, and a Fano effect with a period of 0.26 mV for Vg and 0.2 T under a magnetic field. The realization of a low-energy controllable device made from millimeter-sized Ni-Nb-Zr-H amorphous alloy throws new light on cluster electronics.

  20. Room temperature manipulation of long lifetime spins in metallic-like carbon nanospheres

    PubMed Central

    Náfrádi, Bálint; Choucair, Mohammad; Dinse, Klaus-Peter; Forró, László

    2016-01-01

    The time-window for processing electron spin information (spintronics) in solid-state quantum electronic devices is determined by the spin–lattice and spin–spin relaxation times of electrons. Minimizing the effects of spin–orbit coupling and the local magnetic contributions of neighbouring atoms on spin–lattice and spin–spin relaxation times at room temperature remain substantial challenges to practical spintronics. Here we report conduction electron spin–lattice and spin–spin relaxation times of 175 ns at 300 K in 37±7 nm carbon spheres, which is remarkably long for any conducting solid-state material of comparable size. Following the observation of spin polarization by electron spin resonance, we control the quantum state of the electron spin by applying short bursts of an oscillating magnetic field and observe coherent oscillations of the spin state. These results demonstrate the feasibility of operating electron spins in conducting carbon nanospheres as quantum bits at room temperature. PMID:27426851

  1. 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. PMID:26675052

  2. Improved x-ray spectroscopy with room temperature CZT detectors.

    PubMed

    Fritz, Shannon G; Shikhaliev, Polad M; Matthews, Kenneth L

    2011-09-01

    Compact, room temperature x-ray spectroscopy detectors are of interest in many areas including diagnostic x-ray imaging, radiation protection and dosimetry. Room temperature cadmium zinc telluride (CZT) semiconductor detectors are promising candidates for these applications. One of the major problems for CZT detectors is low-energy tailing of the energy spectrum due to hole trapping. Spectral post-correction methods to correct the tailing effect do not work well for a number of reasons; thus it is advisable to eliminate the hole trapping effect in CZT using physical methods rather than correcting an already deteriorated energy spectrum. One method is using a CZT detector with an electrode configuration which modifies the electric field in the CZT volume to decrease low-energy tailing. Another method is to irradiate the CZT surface at a tilted angle, which modifies depth of interaction to decrease low-energy tailing. Neither method alone, however, eliminates the tailing effect. In this work, we have investigated the combination of modified electric field and tilted angle irradiation in a single detector to further decrease spectral tailing. A planar CZT detector with 10 × 10 × 3 mm³ size and CZT detector with 5 × 5 × 5 mm³ size and cap-shaped electrode were used in this study. The cap-shaped electrode (referred to as CAPture technology) modifies the electric field distribution in the CZT volume and decreases the spectral tailing effect. The detectors were investigated at 90° (normal) and 30° (tilted angle) irradiation modes. Two isotope sources with 59.6 and 122 keV photon energies were used for gamma-ray spectroscopy experiments. X-ray spectroscopy was performed using collimated beams at 60, 80 and 120 kVp tube voltages, in both normal and tilted angle irradiation. Measured x-ray spectra were corrected for K x-ray escape fractions that were calculated using Monte Carlo methods. The x-ray spectra measured with tilted angle CAPture detector at 60, 80 and 120

  3. Room temperature nonlinear magnetoelectric effect in lead-free and Nb-doped AlFeO{sub 3} compositions

    SciTech Connect

    Cótica, Luiz F.; Santos, Guilherme M.; Santos, Ivair A.; Freitas, Valdirlei F.; Coelho, Adelino A.; Pal, Madhuparna; Guo, Ruyan; Bhalla, Amar S.; Garcia, Ducinei; Eiras, José A.

    2015-02-14

    It is still a challenging problem to obtain technologically useful materials displaying strong magnetoelectric coupling at room temperature. In the search for new effects and materials to achieve this kind of coupling, a nonlinear magnetoelectric effect was proposed in the magnetically disordered relaxor ferroelectric materials. In this context, the aluminum iron oxide (AlFeO{sub 3}), a room temperature ferroelectric relaxor and magnetic spin glass compound, emerges as an attractive lead-free magnetoelectric material along with nonlinear magnetoelectric effects. In this work, static, dynamic, and temperature dependent ferroic and magnetoelectric properties in lead-free AlFeO{sub 3} and 2 at. % Nb-doped AlFeO{sub 3} multiferroic magnetoelectric compositions are studied. Pyroelectric and magnetic measurements show changes in ferroelectric and magnetic states close to each other (∼200 K). The magnetoelectric coefficient behavior as a function of H{sub bias} suggests a room temperature nonlinear magnetoelectric coupling in both single-phase and Nb-doped AlFeO{sub 3}-based ceramic compositions.

  4. Critical phenomenon of the near room temperature skyrmion material FeGe

    PubMed Central

    Zhang, Lei; Han, Hui; Ge, Min; Du, Haifeng; Jin, Chiming; Wei, Wensen; Fan, Jiyu; Zhang, Changjin; Pi, Li; Zhang, Yuheng

    2016-01-01

    The cubic B20 compound FeGe, which exhibits a near room temperature skyrmion phase, is of great importance not only for fundamental physics such as nonlinear magnetic ordering and solitons but also for future application of skyrmion states in spintronics. In this work, the critical behavior of the cubic FeGe is investigated by means of bulk dc-magnetization. We obtain the critical exponents (β = 0.336 ± 0.004, γ = 1.352 ± 0.003 and β = 5.276 ± 0.001), where the self-consistency and reliability are verified by the Widom scaling law and scaling equations. The magnetic exchange distance is found to decay as r−4.9, which is close to the theoretical prediction of 3D-Heisenberg model (r−5). The critical behavior of FeGe indicates a short-range magnetic interaction. Meanwhile, the critical exponents also imply an anisotropic magnetic coupling in this system. PMID:26926007

  5. Critical phenomenon of the near room temperature skyrmion material FeGe.

    PubMed

    Zhang, Lei; Han, Hui; Ge, Min; Du, Haifeng; Jin, Chiming; Wei, Wensen; Fan, Jiyu; Zhang, Changjin; Pi, Li; Zhang, Yuheng

    2016-01-01

    The cubic B20 compound FeGe, which exhibits a near room temperature skyrmion phase, is of great importance not only for fundamental physics such as nonlinear magnetic ordering and solitons but also for future application of skyrmion states in spintronics. In this work, the critical behavior of the cubic FeGe is investigated by means of bulk dc-magnetization. We obtain the critical exponents (β = 0.336 ± 0.004, γ = 1.352 ± 0.003 and β = 5.276 ± 0.001), where the self-consistency and reliability are verified by the Widom scaling law and scaling equations. The magnetic exchange distance is found to decay as r(-4.9), which is close to the theoretical prediction of 3D-Heisenberg model (r(-5)). The critical behavior of FeGe indicates a short-range magnetic interaction. Meanwhile, the critical exponents also imply an anisotropic magnetic coupling in this system. PMID:26926007

  6. Critical phenomenon of the near room temperature skyrmion material FeGe

    NASA Astrophysics Data System (ADS)

    Zhang, Lei; Han, Hui; Ge, Min; Du, Haifeng; Jin, Chiming; Wei, Wensen; Fan, Jiyu; Zhang, Changjin; Pi, Li; Zhang, Yuheng

    2016-02-01

    The cubic B20 compound FeGe, which exhibits a near room temperature skyrmion phase, is of great importance not only for fundamental physics such as nonlinear magnetic ordering and solitons but also for future application of skyrmion states in spintronics. In this work, the critical behavior of the cubic FeGe is investigated by means of bulk dc-magnetization. We obtain the critical exponents (β = 0.336 ± 0.004, γ = 1.352 ± 0.003 and β = 5.276 ± 0.001), where the self-consistency and reliability are verified by the Widom scaling law and scaling equations. The magnetic exchange distance is found to decay as r-4.9, which is close to the theoretical prediction of 3D-Heisenberg model (r-5). The critical behavior of FeGe indicates a short-range magnetic interaction. Meanwhile, the critical exponents also imply an anisotropic magnetic coupling in this system.

  7. Spin-valve-like magnetoresistance in Mn2NiGa at room temperature.

    PubMed

    Singh, Sanjay; Rawat, R; Muthu, S Esakki; D'Souza, S W; Suard, E; Senyshyn, A; Banik, S; Rajput, P; Bhardwaj, S; Awasthi, A M; Ranjan, Rajeev; Arumugam, S; Schlagel, D L; Lograsso, T A; Chakrabarti, Aparna; Barman, S R

    2012-12-14

    Spin valves have revolutionized the field of magnetic recording and memory devices. Spin valves are generally realized in thin film heterostructures, where two ferromagnetic (FM) layers are separated by a nonmagnetic conducting layer. Here, we demonstrate spin-valve-like magnetoresistance at room temperature in a bulk ferrimagnetic material that exhibits a magnetic shape memory effect. The origin of this unexpected behavior in Mn(2)NiGa has been investigated by neutron diffraction, magnetization, and ab initio theoretical calculations. The refinement of the neutron diffraction pattern shows the presence of antisite disorder where about 13% of the Ga sites are occupied by Mn atoms. On the basis of the magnetic structure obtained from neutron diffraction and theoretical calculations, we establish that these antisite defects cause the formation of FM nanoclusters with parallel alignment of Mn spin moments in a Mn(2)NiGa bulk lattice that has antiparallel Mn spin moments. The direction of the Mn moments in the soft FM cluster reverses with the external magnetic field. This causes a rotation or tilt in the antiparallel Mn moments at the cluster-lattice interface resulting in the observed asymmetry in magnetoresistance. PMID:23368355

  8. Optical diode effect at spin-wave excitations in the room-temperature multiferroic BiFeO3.

    DOE PAGES

    Kezsmarki, I.; Nagel, U.; Bordacs, S.; Fishman, Randy Scott; Lee, Jun Hee; Yi, Hee Taek; Cheong, Sang-Wook; Room, T.

    2015-09-15

    The ability to read and write a magnetic state current-free by an electric voltage would provide a huge technological advantage. Dynamic or optical ME effects are equally interesting, because they give rise to unidirectional light propagation as recently observed in low-temperature multiferroics. This phenomenon, if realized at room temperature, would allow the development of optical diodes which transmit unpolarized light in one, but not in the opposite, direction. Here, we report strong unidirectional transmission in the room-temperature multiferroic BiFeO3 over the gigahertz-terahertz frequency range. The supporting theory attributes the observed unidirectional transmission to the spin-current-driven dynamic ME effect. Our findingsmore » are an important step toward the realization of optical diodes, supplemented by the ability to switch the transmission direction with a magnetic or electric field.« less

  9. Peculiarly strong room-temperature ferromagnetism from low Mn-doping in ZnO grown by molecular beam epitaxy

    SciTech Connect

    Zuo Zheng; Morshed, Muhammad; Liu Jianlin; Beyermann, W. P.; Zheng Jianguo; Xin Yan

    2013-03-15

    Strong room-temperature ferromagnetism is demonstrated in single crystalline Mn-doped ZnO thin films grown by molecular beam epitaxy. Very low Mn doping concentration is investigated, and the measured magnetic moment is much larger than what is expected for an isolated ion based on Hund's rules. The ferromagnetic behavior evolves with Mn concentration. Both magnetic anisotropy and anomalous Hall effect confirm the intrinsic nature of ferromagnetism. While the Mn dopant plays a crucial role, another entity in the system is needed to explain the observed large magnetic moments.

  10. Room temperature semiconductor detectors for hard x-ray astrophysics

    NASA Astrophysics Data System (ADS)

    Parsons, Ann M.; Stahle, Carl M.; Lisse, Casey M.; Babu, Sachi; Gehrels, Neil A.; Teegarden, Bonnard J.; Shu, Peter K.

    1994-09-01

    Room temperature cadmium zinc telluride (CdZnTe) and mercuric iodide (HgI2) semiconductor hard X-ray detectors are currently being evaluated at NASA Goddard Space Flight Center for use in future balloon and satellite applications. PoRTIA, a small engineering prototype hard X-ray (20 - 150 keV) balloon instrument will contain both a CdZnTe and a HgI2 detector, each 6.5 cm2 x .15 - .2 cm and sharing the same 5 degree(s) field-of-view. PoRTIA will be launched from Alice Springs, Australia in the Spring of 1995 as a piggyback instrument aboard the GRIS balloon payload. PoRTIA will provide valuable information about detector efficiency, durability and material dependent detector background components at balloon altitudes as it observes the Crab Nebula. In addition, a CdZnTe research and development program has been initiated to develop the capability to produce improved CdZnTe detectors for astrophysics applications. The work at Goddard continues in an effort to develop CdZnTe detectors with improvements in electronics, contacts and packaging methods.

  11. Gradient Limitations in Room Temperature and Superconducting Acceleration Structures

    SciTech Connect

    Solyak, N. A.

    2009-01-22

    Accelerating gradient is a key parameter of the accelerating structure in large linac facilities, like future Linear Collider. In room temperature accelerating structures the gradient is limited mostly by breakdown phenomena, caused by high surface electric fields or pulse surface heating. High power processing is a necessary procedure to clean surface and improve the gradient. In the best tested X-band structures the achieved gradient is exceed 100 MV/m in of {approx}200 ns pulses for breakdown rate of {approx}10{sup -7}. Gradient limit depends on number of factors and no one theory which can explain all sets of experimental results and predict gradient in new accelerating structure. In paper we briefly overview the recent experimental results of breakdown studies, progress in understanding of gradient limitations and scaling laws. Although superconducting rf technology has been adopted throughout the world for ILC, it has frequently been difficult to reach the predicted performance in these structures due to a number of factors: multipactoring, field emission, Q-slope, thermal breakdown. In paper we are discussing all these phenomena and the ways to increase accelerating gradient in SC cavity, which are a part of worldwide R and D program.

  12. Gradient limitations in room temperature and superconducting acceleration structures

    SciTech Connect

    Solyak, N.A.; /Fermilab

    2008-10-01

    Accelerating gradient is a key parameter of the accelerating structure in large linac facilities, like future Linear Collider. In room temperature accelerating structures the gradient is limited mostly by breakdown phenomena, caused by high surface electric fields or pulse surface heating. High power processing is a necessary procedure to clean surface and improve the gradient. In the best tested X-band structures the achieved gradient is exceed 100 MV/m in of {approx}200 ns pulses for breakdown rate of {approx} 10{sup -7}. Gradient limit depends on number of factors and no one theory which can explain all sets of experimental results and predict gradient in new accelerating structure. In paper we briefly overview the recent experimental results of breakdown studies, progress in understanding of gradient limitations and scaling laws. Although superconducting rf technology has been adopted throughout the world for ILC, it has frequently been difficult to reach the predicted performance in these structures due to a number of factors: multipactoring, field emission, Q-slope, thermal breakdown. In paper we are discussing all these phenomena and the ways to increase accelerating gradient in SC cavity, which are a part of worldwide R&D program.

  13. Proactive aquatic ecotoxicological assessment of room-temperature ionic liquids

    USGS Publications Warehouse

    Kulacki, K.J.; Chaloner, D.T.; Larson, J.H.; Costello, D.M.; Evans-White, M. A.; Docherty, K.M.; Bernot, R.J.; Brueseke, M.A.; Kulpa, C.F.; Lamberti, G.A.

    2011-01-01

    Aquatic environments are being contaminated with a myriad of anthropogenic chemicals, a problem likely to continue due to both unintentional and intentional releases. To protect valuable natural resources, novel chemicals should be shown to be environmentally safe prior to use and potential release into the environment. Such proactive assessment is currently being applied to room-temperature ionic liquids (ILs). Because most ILs are water-soluble, their effects are likely to manifest in aquatic ecosystems. Information on the impacts of ILs on numerous aquatic organisms, focused primarily on acute LC50 and EC50 endpoints, is now available, and trends in toxicity are emerging. Cation structure tends to influence IL toxicity more so than anion structure, and within a cation class, the length of alkyl chain substituents is positively correlated with toxicity. While the effects of ILs on several aquatic organisms have been studied, the challenge for aquatic toxicology is now to predict the effects of ILs in complex natural environments that often include diverse mixtures of organisms, abiotic conditions, and additional stressors. To make robust predictions about ILs will require coupling of ecologically realistic laboratory and field experiments with standard toxicity bioassays and models. Such assessments would likely discourage the development of especially toxic ILs while shifting focus to those that are more environmentally benign. Understanding the broader ecological effects of emerging chemicals, incorporating that information into predictive models, and conveying the conclusions to those who develop, regulate, and use those chemicals, should help avoid future environmental degradation. ?? 2011 Bentham Science Publishers Ltd.

  14. Mesophases in nearly 2D room-temperature ionic liquids.

    PubMed

    Manini, N; Cesaratto, M; Del Pópolo, M G; Ballone, P

    2009-11-26

    Computer simulations of (i) a [C(12)mim][Tf(2)N] film of nanometric thickness squeezed at kbar pressure by a piecewise parabolic confining potential reveal a mesoscopic in-plane density and composition modulation reminiscent of mesophases seen in 3D samples of the same room-temperature ionic liquid (RTIL). Near 2D confinement, enforced by a high normal load, as well as relatively long aliphatic chains are strictly required for the mesophase formation, as confirmed by computations for two related systems made of (ii) the same [C(12)mim][Tf(2)N] adsorbed at a neutral solid surface and (iii) a shorter-chain RTIL ([C(4)mim][Tf(2)N]) trapped in the potential well of part i. No in-plane modulation is seen for ii and iii. In case ii, the optimal arrangement of charge and neutral tails is achieved by layering parallel to the surface, while, in case iii, weaker dispersion and packing interactions are unable to bring aliphatic tails together into mesoscopic islands, against overwhelming entropy and Coulomb forces. The onset of in-plane mesophases could greatly affect the properties of long-chain RTILs used as lubricants. PMID:19886615

  15. High-power room-temperature-operated CO laser

    NASA Astrophysics Data System (ADS)

    Shimizu, Kouki; Taniwaki, Manabu; Sato, Shunichi; Kumagai, Mikio; Takashima, Yoich; Naito, Yasuhiro; Nagano, Hiroshi; Hasuike, Toru

    2000-04-01

    The objectives of this study are to achieve high-power, efficient operation of a room-temperature CO laser and to collect data for designing the CO laser system for nuclear reactor decommissioning. The influence of the H2O concentration in the laser gas on the output performance was investigated, and it was found that the H2O concentration should be kept as low as possible (less than 260 ppm) to obtain stable, high-power outputs. To improve output performance, the rf frequency was increased from 13.56 MHz to 27.12 MHz. The output power for the 27.12 MHz excitation was increased by 10 to 20% compared with that for the 13.56 MHz excitation. The laser output was scaled by extending the discharge tube inner diameter from 19 mm to 30 mm. By optimizing the air gap length and the curvature radius of the outer metallic electrode, the operating gas conditions, and the reflectivity of the output coupler, a maximum output of 830 W was obtained at a laser efficiency of 12.2% with adding neither Kr nor Xe. The addition of Kr was more effective for increasing the output than the addition of Xe. A maximum output of 910 W was obtained at a laser efficiency of 14.8% with Kr addition, and a maximum output of 810 W was obtained at a laser efficiency of 16.2% with Xe addition.

  16. Microstructure of room temperature ionic liquids at stepped graphite electrodes

    DOE PAGES

    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 ionmore » 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.« less

  17. Room-temperature luminescence from kaolin induced by organic amines

    NASA Technical Reports Server (NTRS)

    Coyne, L. M.; Kloepping, R.; Pollack, G.

    1984-01-01

    Several new, room-temperature luminescent phenomena, resulting from the interaction of kaolin and various amino compounds, have been observed. The emission of light from kaolin pastes (treated with quinoline, pyridine, hydrazine, monoethanolamine, n-butylamine, and piperidine) was shown to decay monotonically over a period of hours to days. More light was released by a given amino compound after it was dried and purified. Hydrazine, in addition to the monotonically decaying photon release, produces delayed pulses of light with peak emission wavelength of 365 nm which last between several hours and several days. These photon bursts are acutely sensitive to the initial dryness of the hydrazine, both in the number of bursts and the integrated photon output. The amount of light and the capacity of the kaolin to produce the delayed burst appeared to be strongly dependent on preliminary heating and on gamma-irradiation, analogous to the dehydration-induced light pulse previously reported from the Ames Research Center. A small, delayed burst of photons occurred when piperidine and n-butylamine were removed by evaporation into an H2SO4 reservoir.

  18. Controlled synthesis of pentagonal gold nanotubes at room temperature.

    PubMed

    Bi, Yingpu; Lu, Gongxuan

    2008-07-01

    Large quantities of pentagonal gold nanotubes have been synthesized by reducing chloroauric acid with silver nanowires in an aqueous solution of hexadecyltrimethylammonium bromide (CTAB) at room temperature. These gold nanotubes possess perfect structures, smooth surfaces, highly crystalline walls, and similar cross-sections to that of the silver template. In this process, the CTAB participation was found to be crucial for shape-controlled synthesis of pentagonal gold nanotubes. In the absence of CTAB, loose and hollow gold structures were routinely generated, while bundled gold nanotubes with rough surfaces were obtained by replacing the CTAB with poly(vinyl pyrrolidone) (PVP). The possible formation mechanism of pentagonal gold nanotubes has also been discussed on the basis of various growth stages studied by field-emission scanning electron microscopy (FE-SEM) images. In addition, the catalytic properties of these hollow nanostructures for hydrogen generation reaction from HCHO solution have also been investigated. They showed higher activity than that of spherical gold nanoparticles. PMID:21828702

  19. Water-driven structure transformation in nanoparticles at room temperature.

    PubMed

    Zhang, Hengzhong; Gilbert, Benjamin; Huang, Feng; Banfield, Jillian F

    2003-08-28

    The thermodynamic behaviour of small particles differs from that of the bulk material by the free energy term gammaA--the product of the surface (or interfacial) free energy and the surface (or interfacial) area. When the surfaces of polymorphs of the same material possess different interfacial free energies, a change in phase stability can occur with decreasing particle size. Here we describe a nanoparticle system that undergoes structural changes in response to changes in the surface environment rather than particle size. ZnS nanoparticles (average diameter 3 nm) were synthesized in methanol and found to exhibit a reversible structural transformation accompanying methanol desorption, indicating that the particles readily adopt minimum energy structural configurations. The binding of water to the as-formed particles at room temperature leads to a dramatic structural modification, significantly reducing distortions of the surface and interior to generate a structure close to that of sphalerite (tetrahedrally coordinated cubic ZnS). These findings suggest a route for post-synthesis control of nanoparticle structure and the potential use of the nanoparticle structural state as an environmental sensor. Furthermore, the results imply that the structure and reactivity of nanoparticles at planetary surfaces, in interplanetary dust and in the biosphere, will depend on both particle size and the nature of the surrounding molecules. PMID:12944961

  20. Room temperature molten salt as medium for lithium battery

    NASA Astrophysics Data System (ADS)

    Fung, Y. S.; Zhou, R. Q.

    Due to the wide electrochemical window and high ionic conductivity, the 1-methyl-3-ethylimidazolium chloride (MeEtImCl) room temperature molten salt (RTMS) was investigated as the medium for lithium battery in the present work. The addition of C 6H 5SO 2Cl to the RTMS was shown to improve its chemical stability and the reversibility of the lithium electrode because of the removal of Al 2Cl 7- from the melt. Electrochemical reaction which occurred at the LiCoO 2 was studied and the carbon current collector was found to interact with the melt. Out of the various carbon materials studied, graphite was found to be the best material. A LiAl/LiCoO 2 battery using RTMS as the electrolyte was assembled for battery test. Satisfactory results were obtained in preliminary cycling, showing a cell voltage of 3.45 V with better than 90% coulombic efficiency and a discharging capacity of 112 mA h/g LiCoO 2 at current density of 1 mA/cm 2.

  1. Instantaneous radioiodination of rose bengal at room temperature and a cold kit therefor

    DOEpatents

    O'Brien, Jr., Harold A.; Hupf, Homer B.; Wanek, Philip M.

    1981-01-01

    The disclosure relates to the radioiodination of rose bengal at room temperature and a cold-kit therefor. A purified rose bengal tablet is stirred into acidified ethanol at or near room temperature, until a suspension forms. Reductant-free .sup.125 I.sup.- is added and the resulting mixture stands until the exchange label reaction occurs at room temperature. A solution of sterile isotonic phosphate buffer and sodium hydroxide is added and the final resulting mixture is sterilized by filtration.

  2. 40 CFR Table B-4 to Subpart B of... - Line Voltage and Room Temperature Test Conditions

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 6 2013-07-01 2013-07-01 false Line Voltage and Room Temperature Test... B-4 Table B-4 to Subpart B of Part 53—Line Voltage and Room Temperature Test Conditions Test day... Temperatures shall be controlled to ± 1 °C....

  3. Room temperature single-photon detectors for high bit rate quantum key distribution

    SciTech Connect

    Comandar, L. C.; Patel, K. A.; Fröhlich, B. Lucamarini, M.; Sharpe, A. W.; Dynes, J. F.; Yuan, Z. L.; Shields, A. J.; Penty, R. V.

    2014-01-13

    We report room temperature operation of telecom wavelength single-photon detectors for high bit rate quantum key distribution (QKD). Room temperature operation is achieved using InGaAs avalanche photodiodes integrated with electronics based on the self-differencing technique that increases avalanche discrimination sensitivity. Despite using room temperature detectors, we demonstrate QKD with record secure bit rates over a range of fiber lengths (e.g., 1.26 Mbit/s over 50 km). Furthermore, our results indicate that operating the detectors at room temperature increases the secure bit rate for short distances.

  4. Room-temperature near-infrared silicon carbide nanocrystalline emitters based on optically aligned spin defects

    NASA Astrophysics Data System (ADS)

    Muzha, A.; Fuchs, F.; Tarakina, N. V.; Simin, D.; Trupke, M.; Soltamov, V. A.; Mokhov, E. N.; Baranov, P. G.; Dyakonov, V.; Krueger, A.; Astakhov, G. V.

    2014-12-01

    Bulk silicon carbide (SiC) is a very promising material system for bio-applications and quantum sensing. However, its optical activity lies beyond the near infrared spectral window for in-vivo imaging and fiber communications due to a large forbidden energy gap. Here, we report the fabrication of SiC nanocrystals and isolation of different nanocrystal fractions ranged from 600 nm down to 60 nm in size. The structural analysis reveals further fragmentation of the smallest nanocrystals into ca. 10-nm-size clusters of high crystalline quality, separated by amorphization areas. We use neutron irradiation to create silicon vacancies, demonstrating near infrared photoluminescence. Finally, we detect room-temperature spin resonances of these silicon vacancies hosted in SiC nanocrystals. This opens intriguing perspectives to use them not only as in-vivo luminescent markers but also as magnetic field and temperature sensors, allowing for monitoring various physical, chemical, and biological processes.

  5. Room-temperature near-infrared silicon carbide nanocrystalline emitters based on optically aligned spin defects

    SciTech Connect

    Muzha, A.; Fuchs, F.; Simin, D.; Astakhov, G. V.; Tarakina, N. V.; Trupke, M.; Soltamov, V. A.; Mokhov, E. N.; Baranov, P. G.; Dyakonov, V.; and others

    2014-12-15

    Bulk silicon carbide (SiC) is a very promising material system for bio-applications and quantum sensing. However, its optical activity lies beyond the near infrared spectral window for in-vivo imaging and fiber communications due to a large forbidden energy gap. Here, we report the fabrication of SiC nanocrystals and isolation of different nanocrystal fractions ranged from 600 nm down to 60 nm in size. The structural analysis reveals further fragmentation of the smallest nanocrystals into ca. 10-nm-size clusters of high crystalline quality, separated by amorphization areas. We use neutron irradiation to create silicon vacancies, demonstrating near infrared photoluminescence. Finally, we detect room-temperature spin resonances of these silicon vacancies hosted in SiC nanocrystals. This opens intriguing perspectives to use them not only as in-vivo luminescent markers but also as magnetic field and temperature sensors, allowing for monitoring various physical, chemical, and biological processes.

  6. Exchange bias up to room temperature in antiferromagnetic hexagonal Mn3Ge

    NASA Astrophysics Data System (ADS)

    Qian, J. F.; Nayak, A. K.; Kreiner, G.; Schnelle, W.; Felser, C.

    2014-07-01

    Mn3.04Ge0.96 has a hexagonal crystal structure, which can be stabilized by high-temperature annealing, and shows antiferromagnetic order with a small ferromagnetic component of less than 0.1μB and a coercivity of 0.45 T. In the ordered phase, magnetization curves M(H) exhibit an exchange bias of 62 mT at T = 2 K after field cooling, which is observable up to room temperature. The exchange anisotropy is suggested to originate from the exchange interaction between the host of triangular-antiferromagnetic Mn3Ge units and embedded ferrimagnetic-like clusters. Such clusters develop when excess Mn atoms occupy empty Ge sites in the original triangular-antiferromagnetic structure of Mn3Ge.

  7. Electric field dependence of junction magnetoresistance in magnetite/semiconductor heterostructure at room temperature

    NASA Astrophysics Data System (ADS)

    Aireddy, H.; Bhaumik, S.; Das, A. K.

    2015-12-01

    We have fabricated Fe3O4/p-Si heterojunction using pulsed laser deposition technique and explored its electro-magnetic transport properties. The heterojunction exhibits backward rectifying property at all temperatures, and appraisal of giant junction magnetoresistance (JMR) is observed at room temperature (RT). Conspicuously, the variation and sign change of JMR as a function of electric field is observed at RT. The backward rectifying behavior of the device is ascribed to the highly doped p-type (p++) semiconducting nature of Fe3O4, and the origin of electric field (voltage) dependence of magnetoresistance is explained proposing electronic band diagram of Fe3O4/SiO2/p-Si heterojunction. This interesting result may have importance to integrate Si-based magnetoresistance sources in multifunctional spintronic devices.

  8. Electric field dependence of junction magnetoresistance in magnetite/semiconductor heterostructure at room temperature

    SciTech Connect

    Aireddy, H.; Bhaumik, S.; Das, A. K.

    2015-12-07

    We have fabricated Fe{sub 3}O{sub 4}/p-Si heterojunction using pulsed laser deposition technique and explored its electro-magnetic transport properties. The heterojunction exhibits backward rectifying property at all temperatures, and appraisal of giant junction magnetoresistance (JMR) is observed at room temperature (RT). Conspicuously, the variation and sign change of JMR as a function of electric field is observed at RT. The backward rectifying behavior of the device is ascribed to the highly doped p-type (p{sup ++}) semiconducting nature of Fe{sub 3}O{sub 4}, and the origin of electric field (voltage) dependence of magnetoresistance is explained proposing electronic band diagram of Fe{sub 3}O{sub 4}/SiO{sub 2}/p-Si heterojunction. This interesting result may have importance to integrate Si-based magnetoresistance sources in multifunctional spintronic devices.

  9. Electrical control of antiferromagnetic domains in multiferroicBiFeO3 film at room temperature

    SciTech Connect

    Zhao, T.; Scholl, A.; Zavaliche, F.; Lee, K.; Barry, M.; Doran,A.; Cruz, M.P.; Chu, Y.H.; Ederer, C.; Spaldin, N.A.; Das, R.R.; Kim,D.M.; Baek, S.H.; Eom, C.B.; Ramesh, R.

    2006-09-11

    Multiferroic materials, which offer the possibility ofmanipulating the magnetic state by an electric field or vice versa, areof great current interest. In this work, we demonstrate the firstobservation of electrical control of antiferromagnetic domain structurein a single-phase multiferroic material at room temperature.High-resolution images of both antiferromagnetic and ferroelectric domainstructures of (001)-oriented multiferroic BiFeO3 filmsrevealed a cleardomain correlation, indicating a strong coupling between the two types oforder. The ferroelectric structure was measured using piezo forcemicroscopy, whereas X-ray photoemission electron microscopy as well asits temperature dependence was used to detect the antiferromagneticconfiguration. Antiferromagnetic domainswitching induced by ferroelectricpolarization switching was observed, in agreement with theoreticalpredictions.

  10. Producing >60,000-fold room-temperature 89Y NMR signal enhancement

    NASA Astrophysics Data System (ADS)

    Lumata, Lloyd; Jindal, Ashish; Merritt, Matthew; Malloy, Craig; Sherry, A. Dean; Kovacs, Zoltan

    2011-03-01

    89 Y in chelated form is potentially valuable in medical imaging because its chemical shift is sensitive to local factors in tumors such as pH. However, 89 Y has a low gyromagnetic ratio γn thus its NMR signal is hampered by low thermal polarization. Here we show that we can enhance the room-temperature NMR signal of 89 Y up to 65,000 times the thermal signal, which corresponds to 10 % nuclear polarization, via fast dissolution dynamic nuclear polarization (DNP). The relatively long spin-lattice relaxation time T1 (~ 500 s) of 89 Y translates to a long polarization lifetime. The 89 Y NMR enhancement is optimized by varying the glassing matrices and paramagnetic agents as well as doping the samples with a gadolinium relaxation agent. Co-polarization of 89 Y-DOTA with a 13 C sample shows that both nuclear spin species acquire the same spin temperature Ts , consistent with thermal mixing mechanism of DNP. The high room-temperature NMR signal enhancement places 89 Y, one of the most challenging nuclei to detect by NMR, in the list of viable magnetic resonance imaging (MRI) agents when hyperpolarized under optimized conditions. This work is supported in part by the National Institutes of Health grant numbers 1R21EB009147-01 and RR02584.

  11. Room-temperature macromolecular serial crystallography using synchrotron radiation

    PubMed Central

    Stellato, Francesco; Oberthür, Dominik; Liang, Mengning; Bean, Richard; Gati, Cornelius; Yefanov, Oleksandr; Barty, Anton; Burkhardt, Anja; Fischer, Pontus; Galli, Lorenzo; Kirian, Richard A.; Meyer, Jan; Panneerselvam, Saravanan; Yoon, Chun Hong; Chervinskii, Fedor; Speller, Emily; White, Thomas A.; Betzel, Christian; Meents, Alke; Chapman, Henry N.

    2014-01-01

    A new approach for collecting data from many hundreds of thousands of microcrystals using X-ray pulses from a free-electron laser has recently been developed. Referred to as serial crystallography, diffraction patterns are recorded at a constant rate as a suspension of protein crystals flows across the path of an X-ray beam. Events that by chance contain single-crystal diffraction patterns are retained, then indexed and merged to form a three-dimensional set of reflection intensities for structure determination. This approach relies upon several innovations: an intense X-ray beam; a fast detector system; a means to rapidly flow a suspension of crystals across the X-ray beam; and the computational infrastructure to process the large volume of data. Originally conceived for radiation-damage-free measurements with ultrafast X-ray pulses, the same methods can be employed with synchrotron radiation. As in powder diffraction, the averaging of thousands of observations per Bragg peak may improve the ratio of signal to noise of low-dose exposures. Here, it is shown that this paradigm can be implemented for room-temperature data collection using synchrotron radiation and exposure times of less than 3 ms. Using lysozyme microcrystals as a model system, over 40 000 single-crystal diffraction patterns were obtained and merged to produce a structural model that could be refined to 2.1 Å resolution. The resulting electron density is in excellent agreement with that obtained using standard X-ray data collection techniques. With further improvements the method is well suited for even shorter exposures at future and upgraded synchrotron radiation facilities that may deliver beams with 1000 times higher brightness than they currently produce. PMID:25075341

  12. Towards Room Temperature Silicon Memory Using Single Electron Effects.^*

    NASA Astrophysics Data System (ADS)

    Tiwari, Sandip

    1996-03-01

    In a semiconductor device, transport, where single electron effects prevail, is usually characterized by sub-μ A currents, large time-constants, and non-linearities that are not suitably harnessed by conventional methods of implementing logic. However, many of the attributes of single electron effects are quite appropriate for memories and we summarize one promising implementation involving low interface state density nano-crystals of silicon that are electrostatically coupled to a conducting channel whose conduction is modulated by a control gate.(S. Tiwari, et al., Digest of 52nd Annual Device Research Conference IVA-4 (1994))(S. Tiwari, et al., Digest of 53rd Annual Device Research Conference, 50 (1995))(S. Tiwari, et al., Digest of International Electron Devices Meeting (1995)) Single electron effects manifest themselves in the nano-crystals of silicon (5--7 nm in dimensions) where Coulombic energies of ≈ 60 meV are presently achieved, sufficient for 77 K demonstrations. Large threshold voltage shifts (> 0.2--0.25 V) are achieved by using large enough density of such nano-crystals where single/multiple electron storage occurs and appear as plateaus in threshold voltage - gate voltage characteristics. The charging of the nano-crystals occurs from an inversion layer and discharging occurs to a depletion region. Scaling of nano-crystals size is expected to shift this operational behavior to room temperature, and very low power behavior should be expected from scaled structures utilizing only a single nano-crystal. ^*Performed in collaboration with F. Rana, K. Chan, J. Welser, and H. Hanafi

  13. Room-temperature macromolecular serial crystallography using synchrotron radiation.

    PubMed

    Stellato, Francesco; Oberthür, Dominik; Liang, Mengning; Bean, Richard; Gati, Cornelius; Yefanov, Oleksandr; Barty, Anton; Burkhardt, Anja; Fischer, Pontus; Galli, Lorenzo; Kirian, Richard A; Meyer, Jan; Panneerselvam, Saravanan; Yoon, Chun Hong; Chervinskii, Fedor; Speller, Emily; White, Thomas A; Betzel, Christian; Meents, Alke; Chapman, Henry N

    2014-07-01

    A new approach for collecting data from many hundreds of thousands of microcrystals using X-ray pulses from a free-electron laser has recently been developed. Referred to as serial crystallography, diffraction patterns are recorded at a constant rate as a suspension of protein crystals flows across the path of an X-ray beam. Events that by chance contain single-crystal diffraction patterns are retained, then indexed and merged to form a three-dimensional set of reflection intensities for structure determination. This approach relies upon several innovations: an intense X-ray beam; a fast detector system; a means to rapidly flow a suspension of crystals across the X-ray beam; and the computational infrastructure to process the large volume of data. Originally conceived for radiation-damage-free measurements with ultrafast X-ray pulses, the same methods can be employed with synchrotron radiation. As in powder diffraction, the averaging of thousands of observations per Bragg peak may improve the ratio of signal to noise of low-dose exposures. Here, it is shown that this paradigm can be implemented for room-temperature data collection using synchrotron radiation and exposure times of less than 3 ms. Using lysozyme microcrystals as a model system, over 40 000 single-crystal diffraction patterns were obtained and merged to produce a structural model that could be refined to 2.1 Å resolution. The resulting electron density is in excellent agreement with that obtained using standard X-ray data collection techniques. With further improvements the method is well suited for even shorter exposures at future and upgraded synchrotron radiation facilities that may deliver beams with 1000 times higher brightness than they currently produce.

  14. Room-temperature macromolecular serial crystallography using synchrotron radiation.

    PubMed

    Stellato, Francesco; Oberthür, Dominik; Liang, Mengning; Bean, Richard; Gati, Cornelius; Yefanov, Oleksandr; Barty, Anton; Burkhardt, Anja; Fischer, Pontus; Galli, Lorenzo; Kirian, Richard A; Meyer, Jan; Panneerselvam, Saravanan; Yoon, Chun Hong; Chervinskii, Fedor; Speller, Emily; White, Thomas A; Betzel, Christian; Meents, Alke; Chapman, Henry N

    2014-07-01

    A new approach for collecting data from many hundreds of thousands of microcrystals using X-ray pulses from a free-electron laser has recently been developed. Referred to as serial crystallography, diffraction patterns are recorded at a constant rate as a suspension of protein crystals flows across the path of an X-ray beam. Events that by chance contain single-crystal diffraction patterns are retained, then indexed and merged to form a three-dimensional set of reflection intensities for structure determination. This approach relies upon several innovations: an intense X-ray beam; a fast detector system; a means to rapidly flow a suspension of crystals across the X-ray beam; and the computational infrastructure to process the large volume of data. Originally conceived for radiation-damage-free measurements with ultrafast X-ray pulses, the same methods can be employed with synchrotron radiation. As in powder diffraction, the averaging of thousands of observations per Bragg peak may improve the ratio of signal to noise of low-dose exposures. Here, it is shown that this paradigm can be implemented for room-temperature data collection using synchrotron radiation and exposure times of less than 3 ms. Using lysozyme microcrystals as a model system, over 40 000 single-crystal diffraction patterns were obtained and merged to produce a structural model that could be refined to 2.1 Å resolution. The resulting electron density is in excellent agreement with that obtained using standard X-ray data collection techniques. With further improvements the method is well suited for even shorter exposures at future and upgraded synchrotron radiation facilities that may deliver beams with 1000 times higher brightness than they currently produce. PMID:25075341

  15. Room temperature in-plane 〈100〉 magnetic easy axis for Fe{sub 3}O{sub 4}/SrTiO{sub 3}(001):Nb grown by infrared pulsed laser deposition

    SciTech Connect

    Monti, Matteo; Sanz, Mikel; Oujja, Mohamed; Rebollar, Esther; Castillejo, Marta; Marco, José F.; Figuera, Juan de la; Pedrosa, Francisco J.; Bollero, Alberto; Camarero, Julio; Cuñado, Jose Luis F.; Nemes, Norbert M.; Mompean, Federico J.; Garcia-Hernández, Mar; Nie, Shu; McCarty, Kevin F.; N'Diaye, Alpha T.; Chen, Gong; Schmid, Andreas K.

    2013-12-14

    We examine the magnetic easy-axis directions of stoichiometric magnetite films grown on SrTiO{sub 3}:Nb by infrared pulsed-laser deposition. Spin-polarized low-energy electron microscopy reveals that the individual magnetic domains are magnetized along the in-plane 〈100〉 film directions. Magneto-optical Kerr effect measurements show that the maxima of the remanence and coercivity are also along in-plane 〈100〉 film directions. This easy-axis orientation differs from bulk magnetite and films prepared by other techniques, establishing that the magnetic anisotropy can be tuned by film growth.

  16. 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.

  17. Highly Efficient Room Temperature Spin Injection Using Spin Filtering in MgO

    NASA Astrophysics Data System (ADS)

    Jiang, Xin

    2007-03-01

    Efficient electrical spin injection into GaAs/AlGaAs quantum well structures was demonstrated using CoFe/MgO tunnel spin injectors at room temperature. The spin polarization of the injected electron current was inferred from the circular polarization of electroluminescence from the quantum well. Polarization values as high as 57% at 100 K and 47% at 290 K were obtained in a perpendicular magnetic field of 5 Tesla. The interface between the tunnel spin injector and the GaAs interface remained stable even after thermal annealing at 400 ^oC. The temperature dependence of the electron-hole recombination time and the electron spin relaxation time in the quantum well was measured using time-resolved optical techniques. By taking into account of these properties of the quantum well, the intrinsic spin injection efficiency can be deduced. We conclude that the efficiency of spin injection from a CoFe/MgO spin injector is nearly independent of temperature and, moreover, is highly efficient with an efficiency of ˜ 70% for the temperature range studied (10 K to room temperature). Tunnel spin injectors are thus highly promising components of future semiconductor spintronic devices. Collaborators: Roger Wang^1, 3, Gian Salis^2, Robert Shelby^1, Roger Macfarlane^1, Seth Bank^3, Glenn Solomon^3, James Harris^3, Stuart S. P. Parkin^1 ^1 IBM Almaden Research Center, San Jose, CA 95120 ^2 IBM Zurich Research Laboratory, S"aumerstrasse 4, 8803 R"uschlikon, Switzerland ^3 Solid States and Photonics Laboratory, Stanford University, Stanford, CA 94305

  18. Symmetries and multiferroic properties of novel room-temperature magnetoelectrics: Lead iron tantalate – lead zirconate titanate (PFT/PZT)

    DOE PAGES

    Sanchez, Dilsom A.; Ortega, N.; Kumar, Ashok; Roque-Malherbe, R.; Polanco, R.; Scott, J. F.; Katiyar, Ram S.

    2011-12-01

    Mixing 60-70% lead zirconate titanate with 40-30% lead iron tantalate produces a single-phase, low-loss, room-temperature multiferroic with magnetoelectric coupling: (PbZr₀.₅₃Ti₀.₄₇O₃) (1-x)- (PbFe₀.₅Ta₀.₅O₃)x. The present study combines x-ray scattering, magnetic and polarization hysteresis in both phases, plus a second-order dielectric divergence (to epsilon = 6000 at 475 K for 0.4 PFT; to 4000 at 520 K for 0.3 PFT) for an unambiguous assignment as a C2v-C4v (Pmm2-P4mm) transition. The material exhibits square saturated magnetic hysteresis loops with 0.1 emu/g at 295 K and saturation polarization Pr = 25 μC/cm², which actually increases (to 40 μC/cm²) in the high-T tetragonal phase, representingmore » an exciting new room temperature oxide multiferroic to compete with BiFeO₃. Additional transitions at high temperatures (cubic at T>1300 K) and low temperatures (rhombohedral or monoclinic at T<250 K) are found. These are the lowest-loss room-temperature multiferroics known, which is a great advantage for magnetoelectric devices.« less

  19. N2-broadening coefficients of methyl chloride at room temperature

    NASA Astrophysics Data System (ADS)

    Bray, C.; Jacquemart, D.; Buldyreva, J.; Lacome, N.; Perrin, A.

    2012-07-01

    Methyl chloride is of interest for atmospheric applications, since this molecule is directly involved in the catalytic destruction of ozone in the lower stratosphere. In a previous work [Bray et al. JQSRT 2011;112:2446], lines positions and intensities of self-perturbed 12CH335Cl and 12CH337Cl have been studied into details for the 3.4 μm spectral region. The present work is focused on measurement and calculation of N2-broadening coefficients of the 12CH335Cl and 12CH337Cl isotopologues. High-resolution Fourier Transform spectra of CH3Cl-N2 mixtures at room-temperature have been recorded between 2800 and 3200 cm-1 at LADIR (using a classical source) and between 47 and 59 cm-1 at SOLEIL (using the synchrotron source on the AILES beamline). 612 mid-infrared transitions of the ν1 band and 86 far-infrared transitions of the pure rotational band have been analyzed using a multispectrum fitting procedure. Average accuracy on the deduced N2-broadening coefficients has been estimated to 5% and 10% in the mid- and far-infrared spectral regions, respectively. The J- and K-rotational dependences of these coefficients have been observed in the mid-infrared region and then a simulation has been performed using an empirical model for 0≤J≤50, K≤9. The 12CH335Cl-N2 line widths for 0≤J≤50 and K≤10 of the ν1 band and for 55≤J≤67 and K≤15 of the pure rotational band have been computed using a semi-classical approach involving exact trajectories and a real symmetric-top geometry of the active molecule. Finally, a global comparison with the experimental and theoretical data existing in the literature has been performed. Similar J- and K-rotational dependences have been appeared while no clear evidence for any vibrational or isotopic dependences have been pointed out.

  20. High energy sodium based room temperature flow batteries

    NASA Astrophysics Data System (ADS)

    Shamie, Jack

    As novel energy sources such as solar, wind and tidal energies are explored it becomes necessary to build energy storage facilities to load level the intermittent nature of these energy sources. Energy storage is achieved by converting electrical energy into another form of energy. Batteries have many properties that are attractive for energy storage including high energy and power. Among many different types of batteries, redox flow batteries (RFBs) offer many advantages. Unlike conventional batteries, RFBs store energy in a liquid medium rather than solid active materials. This method of storage allows for the separation of energy and power unlike conventional batteries. Additionally flow batteries may have long lifetimes because there is no expansion or contraction of electrodes. A major disadvantage of RFB's is its lower energy density when compared to traditional batteries. In this Thesis, a novel hybrid Na-based redox flow battery (HNFB) is explored, which utilizes a room temperature molten sodium based anode, a sodium ion conducting solid electrolyte and liquid catholytes. The sodium electrode leads to high voltages and energy and allows for the possibility of multi-electron transfer per molecule. Vanadium acetylacetonate (acac) and TEMPO have been investigated for their use as catholytes. In the vanadium system, 2 electrons transfers per vanadium atom were found leading to a doubling of capacity. In addition, degradation of the charged state was found to be reversible within the voltage range of the cell. Contamination by water leads to the formation of vanadyl acetylacetonate. Although it is believed that vanadyl complex need to be taken to low voltages to be reduced back to vanadium acac, a new mechanism is shown that begins at higher voltages (2.1V). Vanadyl complexes react with excess ligand and protons to reform the vanadium complex. During this reaction, water is reformed leading to the continuous cycle in which vanadyl is formed and then reduced back

  1. Tomographic reconstruction of indoor spatial temperature distributions using room impulse responses

    NASA Astrophysics Data System (ADS)

    Bleisteiner, M.; Barth, M.; Raabe, A.

    2016-03-01

    Temperature can be estimated by acoustic travel time measurements along known sound paths. By using a multitude of known sound paths in combination with a tomographic reconstruction technique a spatial and temporal resolution of the temperature field can be achieved. Based on it, this article focuses on an experimental method in order to determine the spatially differentiated development of room temperature with only one loudspeaker and one microphone. The theory of geometrical room acoustics is being used to identify sound paths under consideration of reflections. The travel time along a specific sound path is derived from the room impulse response. Temporal variances in room impulse response can be attributed primarily to a change in air temperature and airflow. It is shown that in the absence of airflow a 3D acoustic monitoring of the room temperature can be realized with a fairly limited use of hardware.

  2. Room-temperature ferromagneticlike behavior in Mn-implanted and postannealed InAs layers deposited by molecular beam epitaxy

    SciTech Connect

    Gonzalez-Arrabal, R.; Gonzalez, Y.; Gonzalez, L.; Martin-Gonzalez, M. S.; Munnik, F.

    2009-04-01

    We report on the magnetic and structural properties of Ar- and Mn-implanted InAs epitaxial films grown on GaAs (100) by molecular beam epitaxy and the effect of rapid thermal annealing (RTA) for 30 s at 750 deg. C. Channeling particle induced x-ray emission (PIXE) experiments reveal that after Mn implantation almost all Mn atoms are substitutional in the In site of the InAs lattice, like in a diluted magnetic semiconductor. All of these samples show diamagnetic behavior. However, after RTA treatment the Mn-InAs films exhibit room-temperature magnetism. According to PIXE measurements the Mn atoms are no longer substitutional. When the same set of experiments was performed with Ar as implantation ion, all of the layers present diamagnetism without exception. This indicates that the appearance of room-temperature ferromagneticlike behavior in the Mn-InAs-RTA layer is not related to lattice disorder produced during implantation but to a Mn reaction produced after a short thermal treatment. X-ray diffraction patterns and Rutherford backscattering measurements evidence the segregation of an oxygen-deficient MnO{sub 2} phase (nominally MnO{sub 1.94}) in the Mn-InAs-RTA epitaxial layers which might be the origin of the room-temperature ferromagneticlike response observed.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    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(dc nm)]5 multilayers with dc = 3 nm and dc = 6 nm. Only remnant circular dichroism (CD) was observed from the dc = 3 nm sample but not when dc = 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.

  4. Giant Spin-Driven Ferroelectric Polarization in BiFeO3 at Room Temperature

    DOE PAGES

    Lee, Jun Hee; Fishman, Randy S.

    2015-11-11

    Although BiFeO3 is the most extensively investigated multiferroic material, its magnetoelectic couplings are barely understood. Here we report a thorough study of the magentoelectric (ME) couplings in spin-cycloidal buk BiFeO3 using first-principles calculations and microscopic spin-wave models compared with neutron-scattering measurements. We find that huge exchange-striction (ES) polarizations, i.e. the electric response of the magnetic exchange through ferroelectric and antiferrodistortive distortions, is giant enough to dominate over all other ME couplings. We show that BiFeO3 has a hidden record-high spin-driven polarization ( 3 C/cm2) at room-temperature. The huge ES polarizations can be tuned by coupling to the antiferrodistortive rotations.

  5. 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.

  6. Room Temperature Ferromagnetism in Cu Doped ZnO Thin Films

    SciTech Connect

    Khan, Zaheer Ahmed; Ghosh, Subhasis

    2011-07-15

    We report on the growth of Cu doped ZnO thin films for different Cu concentration from 0.1%, to10% by RF magnetron sputtering. The X-ray diffraction study has shown single phase wurtzite type ZnO thin films with no evidence of copper/copper oxide or any other secondary phases. Room temperature ferromagnetism was observed in RF sputtered Cu doped ZnO films with magnetic moment per Cu atom first increasing and then decreasing with an increasing Cu content. Decrease of band gap with Cu doping, indicating strong p-d mixing of O and Cu is clear by the absorption spectroscopy study. The surface morphology by AFM of pure and Cu doped ZnO thin films show average grain size of 110nm and RMS surface roughness of 2.15 nm.

  7. Three-dimensional spin mapping of antiferromagnetic nanopyramids having spatially alternating surface anisotropy at room temperature.

    PubMed

    Wang, Kangkang; Smith, Arthur R

    2012-11-14

    Antiferromagnets play a key role in modern spintronic devices owing to their ability to modify the switching behavior of adjacent ferromagnets via the exchange bias effect. Consequently, detailed measurements of the spin structure at antiferromagnetic interfaces and surfaces are highly desirable, not only for advancing technologies but also for enabling new insights into the underlying physics. Here using spin-polarized scanning tunneling microscopy at room-temperature, we reveal in three-dimensions an orthogonal spin structure on antiferromagnetic compound nanopyramids. Contrary to expected uniaxial anisotropy based on bulk properties, the atomic terraces are found to have alternating in-plane and out-of-plane magnetic anisotropies. The observed layer-wise alternation in anisotropy could have strong influences on future nanoscale spintronic applications.

  8. Multiferroicity in polar phase LiNbO3 at room temperature

    NASA Astrophysics Data System (ADS)

    Manikandan, M.; Saravana Kumar, K.; Aparnadevi, N.; Praveen Shanker, N.; Venkateswaran, C.

    2015-10-01

    LiNbO3, prepared by ball milling assisted ceramic method, exhibits weak ferromagnetism and ferroelectricity at room temperature. X-ray diffraction pattern reveals the rhombohedral phase of LiNbO3 with hexagonal unit cell symmetry. The weak ferromagnetic behavior, obtained using VSM, has been explained using Dzyaloshinskii-Moriya interaction caused by the ferroelectric distortion in its magnetic order. The P-E loop measurement shows lossy natured ferroelectric loop. Electrical and dielectric properties analyzed using impedance spectroscopy show two thermally activated conduction processes, derived from the Arrhenius plot. A gradual increase in the dielectric constant below 493 K and a rapid increase above 493 K reveals the contribution of polarization components and Lithium ion hopping.

  9. 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.

  10. Magnetic insulation at finite temperatures

    SciTech Connect

    Goedecke, G. H.; Davis, Brian T.; Chen, Chiping

    2006-08-15

    A finite-temperature non-neutral plasma (FTNNP) theory of magnetically insulated (MI) electron flows in crossed-field vacuum devices is developed and applied in planar geometry. It is shown that, in contrast to the single type of MI flow predicted by traditional cold-plasma treatments, the nonlinear FTNNP equations admit five types of steady flow, of which three types are MI flows, including flows in which the electric field and/or the tangential velocity at the cathode may be zero or nonzero. It is also shown that finite-temperature Vlasov-Poisson treatments yield solutions for electron number densities and electrostatic potentials that are a subset of the FTNNP solutions. The algorithms that are used to solve the FTNNP equations numerically are discussed, and the numerical results are presented for several examples of the three types of MI flow. Results include prediction of the existence, boundaries, number density profiles, and other properties of sheaths of electrons in the anode-cathode gap.

  11. Electrically-Induced Polarization and the Spin Hall Effect in Semiconductors at Room Temperature

    NASA Astrophysics Data System (ADS)

    Stern, Nathaniel

    2007-03-01

    The capability to generate and manipulate spin polarization through the spin-orbit interaction inspires growing interest in all-electrical techniques to exploit electron spins for applications in semiconductor spintronics. Experiments show spin polarization can be electrically generated by current- induced spin polarization from internal magnetic fields in the bulk of a conducting channel, or accumulation of spin polarization near sample edges due to transverse spin currents generated by the spin Hall. These spin currents can drive spin accumulation over micron length scales in semiconductor arms transverse to a conducting channel. More recently, we investigate electrical generation of spin polarization in n-ZnSe epilayers using Kerr rotation spectroscopy The internal magnetic field is studied and found to only be measurable in strained layers, likely due to the weak spin-orbit interaction in ZnSe. Despite this, unstrained n-ZnSe layers exhibit both in-plane bulk current-induced spin polarization and an out-of-plane spin accumulation of opposite sign on opposite edges of a conducting channel indicative of the spin Hall effect. The spin Hall conductivity is estimated according to a spin accumulation model and is found to be consistent with the extrinsic spin- dependent scattering mechanism. Both the current-induced spin polarization and the spin Hall effect are robust to room temperature in ZnSe. These results suggest the potential for practical utilization of electrically generated spin polarization in room temperature semiconductor devices. V. Sih, W. H. Lau, R. C. Myers, V. R. Horowitz, A. C. Gossard and D. D. Awschalom, Phys. Rev. Lett. 97, 096605 (2006). N.P. Stern, S. Ghosh, G. Xiang, M. Zhu, N. Samarth, and D. D. Awschalom, Phys. Rev. Lett. 97, 126603 (2006).

  12. Ballistic spin filtering across ferromagnet/semiconductor interfaces at room temperature

    NASA Astrophysics Data System (ADS)

    Hirohata, A.; Steinmueller, S. J.; Cho, W. S.; Xu, Y. B.; Guertler, C. M.; Wastlbauer, G.; Bland, J. A.; Holmes, S. N.

    2002-07-01

    Circularly polarized light was used to generate spin-polarized electrons at room temperature in ferromagnet/GaAs Schottky diode structures (with spin polarization perpendicular to the film plane). The Schottky barrier dependence of the helicity-dependent photocurrent was observed using various ferromagnetic materials (NiFe, Co, and Fe) and GaAs doping densities. A change in the helicity-dependent photocurrent was obtained in all cases in reverse bias when the ferromagnetic layer magnetization was realigned from perpendicular to parallel to the photon helicity. This effect is attributed to spin filtering of photoexcited electrons generated in the GaAs due to the spin split density of states at the Fermi level in the ferromagnet which occurs when the magnetization is aligned with the photon helicity. NiFe shows significant spin filtering, Fe shows either strong or weak spin filtering according to the Schottky barrier strength, while Co shows almost none. Antiferromagnetic Cr/GaAs shows no spin-dependent effects as expected. These spin transport effects in all cases vanish for very high doping due to the collapse of the Schottky barrier. As the photon energy approaches the energy gap of the GaAs, the effects associated with the optically induced spin polarization in the GaAs become larger, confirming that polarized electrons are first excited in the semiconductor and then filtered by the ferromagnetic layer. The spin filtering effects in all cases increase with increasing ferromagnetic layer thickness, and are much larger than the estimated magnetocircular dichroism in permalloy. These results unambiguously indicate that highly efficient spin transport from the semiconductor to the ferromagnet occurs at room temperature and that strong spin filtering occurs in reverse bias.

  13. Ordered iron aluminide alloys having an improved room-temperature ductility and method thereof

    DOEpatents

    Sikka, Vinod K.

    1992-01-01

    A process is disclosed for improving the room temperature ductility and strength of iron aluminide intermetallic alloys. The process involves thermomechanically working an iron aluminide alloy by means which produce an elongated grain structure. The worked alloy is then heated at a temperature in the range of about 650.degree. C. to about 800.degree. C. to produce a B2-type crystal structure. The alloy is rapidly cooled in a moisture free atmosphere to retain the B2-type crystal structure at room temperature, thus providing an alloy having improved room temperature ductility and strength.

  14. Novel spintronics devices for memory and logic: prospects and challenges for room temperature all spin computing

    NASA Astrophysics Data System (ADS)

    Wang, Jian-Ping

    An energy efficient memory and logic device for the post-CMOS era has been the goal of a variety of research fields. The limits of scaling, which we expect to reach by the year 2025, demand that future advances in computational power will not be realized from ever-shrinking device sizes, but rather by innovative designs and new materials and physics. Magnetoresistive based devices have been a promising candidate for future integrated magnetic computation because of its unique non-volatility and functionalities. The application of perpendicular magnetic anisotropy for potential STT-RAM application was demonstrated and later has been intensively investigated by both academia and industry groups, but there is no clear path way how scaling will eventually work for both memory and logic applications. One of main reasons is that there is no demonstrated material stack candidate that could lead to a scaling scheme down to sub 10 nm. Another challenge for the usage of magnetoresistive based devices for logic application is its available switching speed and writing energy. Although a good progress has been made to demonstrate the fast switching of a thermally stable magnetic tunnel junction (MTJ) down to 165 ps, it is still several times slower than its CMOS counterpart. In this talk, I will review the recent progress by my research group and my C-SPIN colleagues, then discuss the opportunities, challenges and some potential path ways for magnetoresitive based devices for memory and logic applications and their integration for room temperature all spin computing system.

  15. Room-temperature tetragonal non-collinear Heusler antiferromagnet Pt2MnGa.

    PubMed

    Singh, Sanjay; D'Souza, S W; Nayak, J; Suard, E; Chapon, L; Senyshyn, A; Petricek, V; Skourski, Y; Nicklas, M; Felser, C; Chadov, S

    2016-01-01

    Antiferromagnetic spintronics is a rapidly growing field, which actively introduces new principles of magnetic storage. Despite that, most applications have been suggested for collinear antiferromagnets. In this study, we consider an alternative mechanism based on long-range helical order, which allows for direct manipulation of the helicity vector. As the helicity of long-range homogeneous spirals is typically fixed by the Dzyaloshinskii-Moriya interactions, bi-stable spirals (left- and right-handed) are rare. Here, we report a non-collinear room-temperature antiferromagnet in the tetragonal Heusler group. Neutron diffraction reveals a long-period helix propagating along its tetragonal axis. Ab-initio analysis suggests its pure exchange origin and explains its helical character resulting from a large basal plane magnetocrystalline anisotropy. The actual energy barrier between the left- and right-handed spirals is relatively small and might be easily overcome by magnetic pulse, suggesting Pt2MnGa as a potential candidate for non-volatile magnetic memory.

  16. 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.

  17. Room-temperature tetragonal non-collinear Heusler antiferromagnet Pt2MnGa

    PubMed Central

    Singh, Sanjay; D'Souza, S. W.; Nayak, J.; Suard, E.; Chapon, L.; Senyshyn, A.; Petricek, V.; Skourski, Y.; Nicklas, M.; Felser, C.; Chadov, S.

    2016-01-01

    Antiferromagnetic spintronics is a rapidly growing field, which actively introduces new principles of magnetic storage. Despite that, most applications have been suggested for collinear antiferromagnets. In this study, we consider an alternative mechanism based on long-range helical order, which allows for direct manipulation of the helicity vector. As the helicity of long-range homogeneous spirals is typically fixed by the Dzyaloshinskii–Moriya interactions, bi-stable spirals (left- and right-handed) are rare. Here, we report a non-collinear room-temperature antiferromagnet in the tetragonal Heusler group. Neutron diffraction reveals a long-period helix propagating along its tetragonal axis. Ab-initio analysis suggests its pure exchange origin and explains its helical character resulting from a large basal plane magnetocrystalline anisotropy. The actual energy barrier between the left- and right-handed spirals is relatively small and might be easily overcome by magnetic pulse, suggesting Pt2MnGa as a potential candidate for non-volatile magnetic memory. PMID:27561795

  18. Room-temperature tetragonal non-collinear Heusler antiferromagnet Pt2MnGa

    NASA Astrophysics Data System (ADS)

    Singh, Sanjay; D'Souza, S. W.; Nayak, J.; Suard, E.; Chapon, L.; Senyshyn, A.; Petricek, V.; Skourski, Y.; Nicklas, M.; Felser, C.; Chadov, S.

    2016-08-01

    Antiferromagnetic spintronics is a rapidly growing field, which actively introduces new principles of magnetic storage. Despite that, most applications have been suggested for collinear antiferromagnets. In this study, we consider an alternative mechanism based on long-range helical order, which allows for direct manipulation of the helicity vector. As the helicity of long-range homogeneous spirals is typically fixed by the Dzyaloshinskii-Moriya interactions, bi-stable spirals (left- and right-handed) are rare. Here, we report a non-collinear room-temperature antiferromagnet in the tetragonal Heusler group. Neutron diffraction reveals a long-period helix propagating along its tetragonal axis. Ab-initio analysis suggests its pure exchange origin and explains its helical character resulting from a large basal plane magnetocrystalline anisotropy. The actual energy barrier between the left- and right-handed spirals is relatively small and might be easily overcome by magnetic pulse, suggesting Pt2MnGa as a potential candidate for non-volatile magnetic memory.

  19. Singular robust room-temperature spin response from topological Dirac fermions.

    PubMed

    Zhao, Lukas; Deng, Haiming; Korzhovska, Inna; Chen, Zhiyi; Konczykowski, Marcin; Hruban, Andrzej; Oganesyan, Vadim; Krusin-Elbaum, Lia

    2014-06-01

    Topological insulators are a class of solids in which the non-trivial inverted bulk band structure gives rise to metallic surface states that are robust against impurity scattering. In three-dimensional (3D) topological insulators, however, the surface Dirac fermions intermix with the conducting bulk, thereby complicating access to the low-energy (Dirac point) charge transport or magnetic response. Here we use differential magnetometry to probe spin rotation in the 3D topological material family (Bi2Se3, Bi2Te3 and Sb2Te3). We report a paramagnetic singularity in the magnetic susceptibility at low magnetic fields that persists up to room temperature, and which we demonstrate to arise from the surfaces of the samples. The singularity is universal to the entire family, largely independent of the bulk carrier density, and consistent with the existence of electronic states near the spin-degenerate Dirac point of the 2D helical metal. The exceptional thermal stability of the signal points to an intrinsic surface cooling process, probably of thermoelectric origin, and establishes a sustainable platform for the singular field-tunable Dirac spin response.

  20. Room-temperature tetragonal non-collinear Heusler antiferromagnet Pt2MnGa.

    PubMed

    Singh, Sanjay; D'Souza, S W; Nayak, J; Suard, E; Chapon, L; Senyshyn, A; Petricek, V; Skourski, Y; Nicklas, M; Felser, C; Chadov, S

    2016-01-01

    Antiferromagnetic spintronics is a rapidly growing field, which actively introduces new principles of magnetic storage. Despite that, most applications have been suggested for collinear antiferromagnets. In this study, we consider an alternative mechanism based on long-range helical order, which allows for direct manipulation of the helicity vector. As the helicity of long-range homogeneous spirals is typically fixed by the Dzyaloshinskii-Moriya interactions, bi-stable spirals (left- and right-handed) are rare. Here, we report a non-collinear room-temperature antiferromagnet in the tetragonal Heusler group. Neutron diffraction reveals a long-period helix propagating along its tetragonal axis. Ab-initio analysis suggests its pure exchange origin and explains its helical character resulting from a large basal plane magnetocrystalline anisotropy. The actual energy barrier between the left- and right-handed spirals is relatively small and might be easily overcome by magnetic pulse, suggesting Pt2MnGa as a potential candidate for non-volatile magnetic memory. PMID:27561795

  1. Spin coherence and echo modulation of the silicon vacancy in 4 H -SiC at room temperature

    NASA Astrophysics Data System (ADS)

    Carter, S. G.; Soykal, Ã.-. O.; Dev, Pratibha; Economou, Sophia E.; Glaser, E. R.

    2015-10-01

    The silicon vacancy in silicon carbide is a strong emergent candidate for applications in quantum information processing and sensing. We perform room temperature optically detected magnetic resonance and spin echo measurements on an ensemble of vacancies and find the spin echo properties depend strongly on magnetic field. The spin echo decay time varies from less than 10 μ s at low fields to 80 μ s at 68 mT, and a strong field-dependent spin echo modulation is also observed. The modulation is attributed to the interaction with nuclear spins and is well described by a theoretical model.

  2. Room temperature scanning Hall probe microscopy using GaAs/AlGaAs and Bi micro-hall probes.

    PubMed

    Sandhu, A; Masuda, H; Oral, A; Bending, S J; Yamada, A; Konagai, M

    2002-05-01

    A room temperature scanning Hall probe microscope system utilizing GaAs/AlGaAs and bismuth micro-Hall probes was used for magnetic imaging of ferromagnetic domain structures on the surfaces of crystalline thin film garnets and permanent magnets. The Bi micro-Hall probes had dimensions ranging between 0.25 and 2.8 microm2 and were fabricated using a combination of optical lithography and focused ion beam milling. The use of bismuth was found to overcome surface depletion effects associated with semiconducting micro-Hall probes. Our experiments demonstrated that Bi is a practical choice of material for fabricating sub-micron sized Hall sensors.

  3. Oxygen Vacancy Induced Room-Temperature Metal-Insulator Transition in Nickelate Films and Its Potential Application in Photovoltaics.

    PubMed

    Wang, Le; Dash, Sibashisa; Chang, Lei; You, Lu; Feng, Yaqing; He, Xu; Jin, Kui-juan; Zhou, Yang; Ong, Hock Guan; Ren, Peng; Wang, Shiwei; Chen, Lang; Wang, Junling

    2016-04-20

    Oxygen vacancy is intrinsically coupled with magnetic, electronic, and transport properties of transition-metal oxide materials and directly determines their multifunctionality. Here, we demonstrate reversible control of oxygen content by postannealing at temperature lower than 300 °C and realize the reversible metal-insulator transition in epitaxial NdNiO₃ films. Importantly, over 6 orders of magnitude in the resistance modulation and a large change in optical bandgap are demonstrated at room temperature without destroying the parent framework and changing the p-type conductive mechanism. Further study revealed that oxygen vacancies stabilized the insulating phase at room temperature is universal for perovskite nickelate films. Acting as electron donors, oxygen vacancies not only stabilize the insulating phase at room temperature, but also induce a large magnetization of ∼50 emu/cm³ due to the formation of strongly correlated Ni²⁺ t(2g)⁶e(g)² states. The bandgap opening is an order of magnitude larger than that of the thermally driven metal-insulator transition and continuously tunable. Potential application of the newly found insulating phase in photovoltaics has been demonstrated in the nickelate-based heterojunctions. Our discovery opens up new possibilities for strongly correlated perovskite nickelates.

  4. Room-temperature electric polarization induced by phase separation in multiferroic GdMn2O5

    NASA Astrophysics Data System (ADS)

    Khannanov, B. Kh.; Sanina, V. A.; Golovenchits, E. I.; Scheglov, M. P.

    2016-02-01

    It was generally accepted until recently that multiferroics RMn2O5 crystallized in the centrosymmetric space group Pbam and ferroelectricity in them could exist only at low temperatures due to the magnetic exchange striction. Recent comprehensive structural studies [V. Baledent et al., Phys. Rev. Lett. 114, 117601 (2015)] have shown that the actual symmetry of RMn2O5 at room temperature is a noncentrosymmetric monoclinic space group Pm, which allows room temperature ferroelectricity to exist. However, such a polarization has not yet been found. Our electric polarization loop studies of GdMn2O5 have revealed that a polarization does exist up to room temperature. This polarization occurs mainly in restricted polar domains that arise in the initial GdMn2O5 matrix due to phase separation and charge carrier self-organization. These domains are selfconsistent with the matrix, which leads to the noncentrosymmetricity of the entire crystal. The polarization is controlled by a magnetic field, thereby demonstrating the presence of magnetoelectric coupling. The lowtemperature ferroelectricity enhances the restricted polar domain polarization along the b axis.

  5. Bose-Einstein condensation of spin wave quanta at room temperature.

    PubMed

    Dzyapko, O; Demidov, V E; Melkov, G A; Demokritov, S O

    2011-09-28

    Spin waves are delocalized excitations of magnetic media that mainly determine their magnetic dynamics and thermodynamics at temperatures far below the critical one. The quantum-mechanical counterparts of spin waves are magnons, which can be considered as a gas of weakly interacting bosonic quasi-particles. Here, we discuss the room-temperature kinetics and thermodynamics of the magnon gas in yttrium iron garnet films driven by parametric microwave pumping. We show that for high enough pumping powers, the thermalization of the driven gas results in a quasi-equilibrium state described by Bose-Einstein statistics with a non-zero chemical potential. Further increases of the pumping power cause a Bose-Einstein condensation documented by an observation of the magnon accumulation at the lowest energy level. Using the sensitivity of the Brillouin light scattering spectroscopy to the degree of coherence of the scattering magnons, we confirm the spontaneous emergence of coherence of the magnons accumulated at the bottom of the spectrum, occurring if their density exceeds a critical value.

  6. Room-temperature synthesis, hydrothermal recrystallization, and properties of metastable stoichiometric FeSe.

    PubMed

    Nitsche, F; Goltz, T; Klauss, H-H; Isaeva, A; Müller, U; Schnelle, W; Simon, P; Doert, Th; Ruck, M

    2012-07-01

    Room-temperature precipitation from aqueous solutions yields the hitherto unknown metastable stoichiometric iron selenide (ms-FeSe) with tetragonal anti-PbO type structure. Samples with improved crystallinity are obtained by diffusion-controlled precipitation or hydrothermal recrystallization. The relations of ms-FeSe to superconducting β-FeSe(1-x) and other neighbor phases of the iron-selenium system are established by high-temperature X-ray diffraction, DSC/TG/MS (differential scanning calorimetry/thermogravimetry/mass spectroscopy), (57)Fe Mössbauer spectroscopy, magnetization measurements, and transmission electron microscopy. Above 300 °C, ms-FeSe decomposes irreversibly to β-FeSe(1-x) and Fe(7)Se(8). The structural parameters of ms-FeSe (P4/nmm, a = 377.90(1) pm, c = 551.11(3) pm, Z = 2), obtained by Rietveld refinement, differ significantly from literature data for β-FeSe(1-x). The Mössbauer spectrum rules out interstitial iron atoms or additional phases. Magnetization data suggest canted antiferromagnetism below T(N) = 50 K. Stoichiometric non-superconducting ms-FeSe can be regarded as the true "parent" compound for the "11" iron-chalcogenide superconductors and may serve as starting point for new chemical modifications.

  7. 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.

  8. Observation of direct magneto-dielectric behaviour in Lu3Fe5O12-δ above room-temperature.

    PubMed

    Manimuthu, P; Vidya, R; Ravindran, P; Fjellvåg, H; Venkateswaran, C

    2015-07-21

    The coupling of dielectric and magnetic order is highly nontrivial and seldom observed in rare-earth iron garnets. Careful investigations on polycrystalline Lu3Fe5O12-δ, prepared by the solid state route, establish a direct correlation between the magnetic and dielectric order parameters. A dielectric anomaly at the magnetic ordering temperature supports this correlation. The dielectric permittivity at various magnetic fields is measured using an indigenously developed connector setup. Lu3Fe5O12-δ exhibits a magneto-dielectric coupling of ∼6% at room temperature, which is significant in the case of a single-phase magneto-dielectric material at low fields. Rietveld refinement of the X-ray diffraction pattern, bond valence sum method, Mössbauer spectroscopy, and X-ray photoelectron spectroscopy indicate two different oxidation states of Fe. Complete structural optimizations performed using the density functional theory establish a ferrimagnetic ground state and provide structural parameters in agreement with experimental values. Electronic structure analysis shows that Lu3Fe5O12 exhibits insulating behavior both in ferromagnetic and ferrimagnetic configurations. The capability of Lu3Fe5O12-δ to exhibit room temperature magneto-dielectric response is a key factor in designing and fabricating various electronic devices and sensors.

  9. Optical Diode Effect at Spin-Wave Excitations of the Room-Temperature Multiferroic BiFeO_{3}.

    PubMed

    Kézsmárki, I; Nagel, U; Bordács, S; Fishman, R S; Lee, J H; Yi, Hee Taek; Cheong, S-W; Rõõm, T

    2015-09-18

    Multiferroics permit the magnetic control of the electric polarization and the electric control of the magnetization. These static magnetoelectric (ME) effects are of enormous interest: The ability to read and write a magnetic state current-free by an electric voltage would provide a huge technological advantage. Dynamic or optical ME effects are equally interesting, because they give rise to unidirectional light propagation as recently observed in low-temperature multiferroics. This phenomenon, if realized at room temperature, would allow the development of optical diodes which transmit unpolarized light in one, but not in the opposite, direction. Here, we report strong unidirectional transmission in the room-temperature multiferroic BiFeO_{3} over the gigahertz-terahertz frequency range. The supporting theory attributes the observed unidirectional transmission to the spin-current-driven dynamic ME effect. These findings are an important step toward the realization of optical diodes, supplemented by the ability to switch the transmission direction with a magnetic or electric field.

  10. Optical Diode Effect at Spin-Wave Excitations of the Room-Temperature Multiferroic BiFeO3

    NASA Astrophysics Data System (ADS)

    Kézsmárki, I.; Nagel, U.; Bordács, S.; Fishman, R. S.; Lee, J. H.; Yi, Hee Taek; Cheong, S.-W.; Rõõm, T.

    2015-09-01

    Multiferroics permit the magnetic control of the electric polarization and the electric control of the magnetization. These static magnetoelectric (ME) effects are of enormous interest: The ability to read and write a magnetic state current-free by an electric voltage would provide a huge technological advantage. Dynamic or optical ME effects are equally interesting, because they give rise to unidirectional light propagation as recently observed in low-temperature multiferroics. This phenomenon, if realized at room temperature, would allow the development of optical diodes which transmit unpolarized light in one, but not in the opposite, direction. Here, we report strong unidirectional transmission in the room-temperature multiferroic BiFeO3 over the gigahertz-terahertz frequency range. The supporting theory attributes the observed unidirectional transmission to the spin-current-driven dynamic ME effect. These findings are an important step toward the realization of optical diodes, supplemented by the ability to switch the transmission direction with a magnetic or electric field.

  11. Two phase multiferroics for voltage-induced entropy change with application in near-room-temperature refrigeration

    NASA Astrophysics Data System (ADS)

    Giri, Prakash; Kumar, Dhananjay; Binek, Christian

    The demand for environmental friendly, cost-effective and energy efficient cooling drives the emerging technology of magnetic refrigeration at room temperature. We fabricate a two phase mutiferroic La0.7Sr0.3MnO3/Pb(Mg1/3Nb2/3) O3-PbTiO3(001) via pulsed laser deposition for application in advanced near room-temperature refrigeration and miniature cooling devices. The key innovation rests on utilizing the magnetocaloric effect in zero applied magnetic fields. The magnetocaloric effect of the composite is activated purely by electric field. We utilize strain originating from stress which is voltage-induced via the inverse piezoelectric effect of PMN-PT. The strain is carried over into the adjacent LSMO thin film thus changing its magnetic order. The voltage-induced variation in magnetization leads to change in isothermal entropy when the experiment is carried out in contact with a thermostat and gives correspondingly rise to an adiabatic temperature change when heat exchange is suppressed. This project is supported by NSF through Nebraska MRSEC DMR-1420645.

  12. Nano-structured TiO2 film fabricated at room temperature and its acoustic properties

    PubMed Central

    Zhu, Jie; Cao, Wenwu; Jiang, Bei; Zhang, D S; Zheng, H; Zhou, Q; Shung, K K

    2009-01-01

    Nano-structured TiO2 thin film has been successfully fabricated at room temperature. Using a quarter wavelength characterization method, we have measured the acoustic impedance of this porous film, which can be adjusted from 5.3 to 7.19 Mrayl by curing it at different temperatures. The uniform microstructure and easy fabrication at room temperature make this material an excellent candidate for matching layers of ultra-high frequency ultrasonic imaging transducers. PMID:19672322

  13. Substrate Temperature Effects on Room Temperature Sensing Properties of Nanostructured ZnO Thin Films.

    PubMed

    Reddy, Jonnala Rakesh; Mani, Ganesh Kumar; Shankar, Prabakaran; Rayappan, John Bosco Balaguru

    2016-01-01

    Zinc oxide (ZnO) thin films were deposited on glass substrates using chemical spray pyrolysis technique at different substrate temperatures such as 523, 623 and 723 K. X-ray diffraction (XRD) patterns confirmed the formation of polycrystalline films with hexagonal wurtzite crystal structure and revealed the change in preferential orientation of the crystal planes. Scanning electron micrographs showed the formation of uniformly distributed spherical shaped grains at low deposition temperature and pebbles like structure at the higher temperature. Transmittance of 85% was observed for the film deposited at 723 K. The band gap of the films was found to be increased from 3.15 to 3.23 eV with a rise in deposition temperature. The electrical conductivity of the films was found to be improved with an increase in substrate temperature. Surface of ZnO thin films deposited at 523 K, 623 K and 723 K were found to be hydrophobic with the contact angles of 92°, 105° and 128° respectively. The room temperature gas sensing characteristics of all the films were studied and found that the film deposited at 623 K showed a better response towards ammonia vapour. PMID:27398478

  14. Deformation and fracture characteristics of Inconel X-750 at room temperature and elevated temperatures

    SciTech Connect

    Mills, W.J.

    1980-06-01

    Electron fractographic and thin foil electron metallographic techniques were used to evaluate the deformation and fracture characteristics of Inconel X-750 at temperatures ranging from 24 to 816/sup 0/C. Operative dislocation mechanisms and fracture surface morphologies were related to the overall tensile response of this nickel-base superalloy. At room temperature, failure occurred primarily by an intergranular dimple rupture mechanism associated with microvoid coalescence along grain boundary denuded regions. A fairly high density of dislocations throughout the matrix resulted in relatively high ductility levels even though failure occurred by an intergranular mechanism. Under intermediate temperature conditions (316 to 427/sup 0/C), increased transgranular fracture coupled with extensive dislocation activity within the Inconel X-750 matrix caused a slight increase in ductility. At progressively higher temperatures, 538 to 704/sup 0/C, all dislocation activity was channeled through narrow slip bands which subsequently initiated localized separation and resulted in a very faceted fracture surface appearance. The absence of a homogeneous dislocation substructure in this temperature regime resulted in a severe degradation in ductility levels. At the highest test temperature (816/sup 0/C), a uniform dislocation network throughout the Inconel X-750 matrix coupled with intense dislocation activity in the grain boundary denuded zone resulted in a marked improvement in ductility. Furthermore, the extensive dislocation activity along grain boundary regions ultimately resulted in an intergranular fracture morphology.

  15. 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.

  16. Local magnetoresistance in Fe/MgO/Si lateral spin valve at room temperature

    SciTech Connect

    Sasaki, Tomoyuki Koike, Hayato; Oikawa, Tohru; Suzuki, Toshio; Ando, Yuichiro; Suzuki, Yoshishige; Shiraishi, Masashi

    2014-02-03

    Room temperature local magnetoresistance in two-terminal scheme is reported. By employing 1.6 nm-thick MgO tunnel barrier, spin injection efficiency is increased, resulting in large non-local magnetoresistance. The magnitude of the non-local magnetoresistance is estimated to be 0.0057 Ω at room temperature. As a result, a clear rectangle signal is observed in local magnetoresistance measurement even at room temperature. We also investigate the origin of local magnetoresistance by measuring the spin accumulation voltage of each contact separately.

  17. Pentacene on Ni(111): room-temperature molecular packing and temperature-activated conversion to graphene.

    PubMed

    Dinca, L E; De Marchi, F; MacLeod, J M; Lipton-Duffin, J; Gatti, R; Ma, D; Perepichka, D F; Rosei, F

    2015-02-21

    We investigate, using scanning tunnelling microscopy, the adsorption of pentacene on Ni(111) at room temperature and the behaviour of these monolayer films with annealing up to 700 °C. We observe the conversion of pentacene into graphene, which begins from as low as 220 °C with the coalescence of pentacene molecules into large planar aggregates. Then, by annealing at 350 °C for 20 minutes, these aggregates expand into irregular domains of graphene tens of nanometers in size. On surfaces where graphene and nickel carbide coexist, pentacene shows preferential adsorption on the nickel carbide phase. The same pentacene to graphene transformation was also achieved on Cu(111), but at a higher activation temperature, producing large graphene domains that exhibit a range of moiré superlattice periodicities.

  18. Does apartment's distance to an in-built transformer room predict magnetic field exposure levels?

    PubMed

    Huss, Anke; Goris, Kelly; Vermeulen, Roel; Kromhout, Hans

    2013-01-01

    It has been shown that magnetic field exposure in apartments located directly on top or adjacent to transformer rooms is higher compared with exposure in apartments located further away from the transformer rooms. It is unclear whether this also translates into exposure contrast among individuals living in these apartments. We performed spot measurements of magnetic fields in 35 apartments in 14 apartment buildings with an in-built transformer and additionally performed 24-h personal measurements in a subsample of 24 individuals. Apartments placed directly on top of or adjacent to a transformer room had on average exposures of 0.42 μT, apartments on the second floor on top of a transformer room, or sharing a corner or edge with the transformer room had 0.11 μT, and apartments located further away from the transformer room had levels of 0.06 μT. Personal exposure levels were approximately a factor 2 lower compared with apartment averages, but still showed exposure contrasts, but only for those individuals who live in the apartments directly on top or adjacent to a transformer room compared with those living further away, with 0.23 versus 0.06 μT for personal exposure when indoors, respectively. A classification of individuals into 'high' and 'low' exposed based on the location of their apartment within a building with an in-built transformer is possible and could be applied in future epidemiological studies.

  19. Rapid and controllable covalent functionalization of single-walled carbon nanotubes at room temperature.

    PubMed

    Martínez-Rubí, Yadienka; Guan, Jingwen; Lin, Shuqiong; Scriver, Christine; Sturgeon, Ralph E; Simard, Benoit

    2007-12-28

    We report a rapid and efficient procedure to functionalize SWNT where free radicals generated at room temperature by a redox reaction between reduced SWNT and diacyl peroxide derivatives were covalently attached to the SWNT wall. PMID:18060123

  20. Evaluation of DNA/RNAshells for room temperature nucleic acids storage.

    PubMed

    Liu, Xiaopan; Li, Qiyuan; Wang, Xian; Zhou, Xiaolin; He, Xuheng; Liao, Qiuyan; Zhu, Fengqin; Cheng, Le; Zhang, Yong

    2015-02-01

    Traditional nucleic acids preservation methods rely on maintaining samples in cold environments, which are costly to operate and time sensitive. Recent work validated that using room temperature for the storage of nucleic acids is possible if the samples are completely protected from water and oxygen. Here, we conducted accelerated aging and real-time degradation studies to evaluate the new technology DNAshell and RNAshell, which preserves DNA and RNA at room temperature, including the DNA and RNA yield, purity, and integrity. DNA and RNA solutions are dried in the presence of stabilizers in stainless steel minicapsules, then redissolved after different time points of heating and storing at room temperature. Results show that DNAshell and RNAshell ensure the safe storage of nucleic acids at room temperature for long periods of time, and that the quality of these nucleic acids is suitable for common downstream analysis.

  1. Robust room temperature valley polarization in monolayer and bilayer WS2.

    PubMed

    Nayak, Pramoda K; Lin, Fan-Cheng; Yeh, Chao-Hui; Huang, Jer-Shing; Chiu, Po-Wen

    2016-03-21

    We report robust room temperature valley polarization in chemical-vapor-deposition (CVD) grown monolayer and bilayer WS2via polarization-resolved photoluminescence measurements using excitation below the bandgap. We show that excitation with energy slightly below the bandgap of the multi-valleyed transition metal chalcogenides can effectively suppress the random redistribution of excited electrons and, thereby, greatly enhance the efficiency of valley polarization at room temperature. Compared to mechanically exfoliated WS2, our CVD grown WS2 films also show enhancement in the coupling of spin, layer and valley degree of freedom and, therefore, provide improved valley polarization. At room temperature, using below-bandgap excitation and CVD grown monolayer and bilayer WS2, we have reached a record-high valley polarization of 35% and 80%, respectively, exceeding the previously reported values of 10% and 65% for mechanically exfoliated WS2 layers using resonant excitation. This observation provides a new direction to enhance valley control at room temperature.

  2. ROOM TEMPERATURE BULK AND TEMPLATE-FREE SYNTHESIS OF LEUCOEMARLDINE POLYANILINE NANOFIBERS

    EPA Science Inventory

    Herein, we describe a simple strategy for the bulk and template-free synthesis of reduced leucoemarldine polyaniline nanofibers size ranging from as low as 10 nm to 50 nm without the use of any reducing agents at room temperature.

  3. Saccharides as Prospective Immobilizers of Nucleic Acids for Room-Temperature Structural EPR Studies.

    PubMed

    Kuzhelev, Andrey A; Shevelev, Georgiy Yu; Krumkacheva, Olesya A; Tormyshev, Victor M; Pyshnyi, Dmitrii V; Fedin, Matvey V; Bagryanskaya, Elena G

    2016-07-01

    Pulsed dipolar electron paramagnetic resonance (EPR) spectroscopy is a powerful tool for structural studies of biomolecules and their complexes. This method, whose applicability has been recently extended to room temperatures, requires immobilization of the studied biosystem to prevent averaging of dipolar couplings; at the same time, the modification of native conformations by immobilization must be avoided. In this work, we provide first demonstration of room-temperature EPR distance measurements in nucleic acids using saccharides trehalose, sucrose, and glucose as immobilizing media. We propose an approach that keeps structural conformation and unity of immobilized double-stranded DNA. Remarkably, room-temperature electron spin dephasing time of triarylmethyl-labeled DNA in trehalose is noticeably longer compared to previously used immobilizers, thus providing a broader range of available distances. Therefore, saccharides, and especially trehalose, can be efficiently used as immobilizers of nucleic acids, mimicking native conditions and allowing wide range of structural EPR studies at room temperatures. PMID:27320083

  4. Red photoluminescence of living systems at the room temperature : measurements and results

    NASA Astrophysics Data System (ADS)

    Kudryashova, I. S.; Rud, V. Yu; Shpunt, V. Ch; Rud, Yu V.; Glinushkin, A. P.

    2016-08-01

    Presents results of a study of the red luminescence of living plants at room temperature. The analysis of obtained results allows to conclude that the photoluminescence spectra for green leaves in all cases represent the two closely spaced bands.

  5. A room-temperature adenosine-based molecular beacon for highly sensitive detection of nucleic acids.

    PubMed

    Lin, Yen-Hsiu; Tseng, Wei-Lung

    2012-06-25

    This study developed a simple, sensitive, and selective molecular beacon for detecting nucleic acids at room temperature based on coralyne induced conformational change of a MB through A(2)-coralyne-A(2) coordination.

  6. Improvement of magnetic hardness at finite temperatures: Ab initio disordered local-moment approach for YCo5

    NASA Astrophysics Data System (ADS)

    Matsumoto, Munehisa; Banerjee, Rudra; Staunton, Julie B.

    2014-08-01

    Temperature dependence of the magnetocrystalline anisotropy energy and magnetization of the prototypical rare-earth magnet YCo5 is calculated from first principles, utilizing the relativistic disordered local-moment approach. We discuss a strategy to enhance the finite-temperature anisotropy field by hole doping, paving the way for an improvement of the coercivity near room temperature or higher.

  7. Room-temperature susceptometry predicts biopsy-determined hepatic iron in patients with elevated serum ferritin

    PubMed Central

    Maliken, Bryan D.; Avrin, William F.; Nelson, James E.; Mooney, Jody; Kumar, Sankaran; Kowdley, Kris V.

    2012-01-01

    Background There is an ongoing clinical need for novel methods to measure hepatic iron content (HIC) noninvasively. Both magnetic resonance imaging (MRI) and superconducting quantum interference device (SQUID) methods have previously shown promise for estimation of HIC, but these methods can be expensive and are not widely available. Room-temperature susceptometry (RTS) represents an inexpensive alternative and was previously found to be strongly correlated with HIC estimated by SQUID measurements among patients with transfusional iron overload related to thalassemia. Aim The goal of the current study was to examine the relationship between RTS and biochemical HIC measured in liver biopsy specimens in a more varied patient cohort. Methods Susceptometry was performed in a diverse group of patients with hyperferritinemia due to hereditary hemochromatosis (HHC) (n=2), secondary iron overload (n=3), nonalcoholic fatty liver disease (NAFLD) (n=2), and chronic viral hepatitis (n=3) within one month of liver biopsy in the absence of iron depletion therapy. Results The correlation coefficient between HIC estimated by susceptometry and by biochemical iron measurement in liver tissue was 0.71 (p=0.022). Variance between liver iron measurement and susceptometry measurement was primarily related to reliance on the patient’s body-mass index (BMI) to estimate the magnetic susceptibility of tissue overlying the liver. Conclusions In conclusion, we believe RTS holds promise for noninvasive measurement of HIC. Improved measurement techniques, including more accurate overlayer correction, may further improve the accuracy of liver susceptometry in patients with liver disease. PMID:22166564

  8. Moessbauer study at room temperature of zinc ferrite as sorbent for hot coal gas desulphurization

    SciTech Connect

    Ahmed, M.A.

    2009-07-01

    Abstract: The method of using Moessbauer spectroscopy at room temperature was applied to assign the iron sites in one fresh zinc ferrite sample ZF with (1:1) concentration of their component oxides and calcined at 900C as well as its sulfurization derivatives at 750C in different coal gas of composition 0.5% H{sub 2}S + 0.5% H{sub 2}; 0.5% H{sub 2}S + 10% H{sub 2}; 0.5% H{sub 2}S + 25% H{sub 2}, and 0.5% H{sub 2}S + 10% H{sub 2}O (v). The most important iron phase obtained in the sulfurized samples, was pyrrhotite, Fe1-xS that exhibit three well different ional sextets. From the peak area and the associated magnetic hyperfine fields, the average magnetic field was calculated and indicates lowering in the number of iron vacancies whereas x is close to 0.

  9. High temperature thermoplastic elastomers synthesized by living anionic polymerization in hydrocarbon solvent at room temperature

    DOE PAGES

    Schlegel, Ralf; Williams, Katherine; Voyloy, Dimitry; Steren, Carlos A.; Goodwin, Andrew; Coughlin, E. Bryan; Gido, Samuel; Beiner, Mario; Hong, Kunlun; Kang, Nam -Goo; et al

    2016-03-30

    We present the synthesis and characterization of a new class of high temperature thermoplastic elastomers composed of polybenzofulvene–polyisoprene–polybenzofulvene (FIF) triblock copolymers. All copolymers were prepared by living anionic polymerization in benzene at room temperature. Homopolymerization and effects of additives on the glass transition temperature (Tg) of polybenzofulvene (PBF) were also investigated. Among all triblock copolymers studied, FIF with 14 vol % of PBF exhibited a maximum stress of 14.3 ± 1.3 MPa and strain at break of 1390 ± 66% from tensile tests. The stress–strain curves of FIF-10 and 14 were analyzed by a statistical molecular approach using a nonaffinemore » tube model to estimate the thermoplastic elastomer behavior. Dynamic mechanical analysis showed that the softening temperature of PBF in FIF was 145 °C, much higher than that of thermoplastic elastomers with polystyrene hard blocks. Microphase separation of FIF triblock copolymers was observed by small-angle X-ray scattering, even though long-range order was not achieved under the annealing conditions employed. Additionally, the microphase separation of the resulting triblock copolymers was examined by atomic force microscopy.« less

  10. Copper-Catalyzed N-Arylation of 2-Pyridones Employing Diaryliodonium Salts at Room Temperature.

    PubMed

    Jung, Seo-Hee; Sung, Dan-Bi; Park, Cho-Hee; Kim, Won-Suk

    2016-09-01

    A new and mild synthetic approach for the N-arylation of 2-pyridones with diaryliodonium salts has been developed. Most reactions proceed readily at room temperature in the presence of 10 mol % of copper chloride. As a result, a wide range of N-arylpyridine-2-ones were synthesized in yields of 23% to 99%. With this method, an antifibrotic drug, Pirfenidone, was successfully synthesized in 99% yield within 30 min at room temperature. PMID:27484240

  11. Ultra-Low-Cost Room Temperature SiC Thin Films

    NASA Technical Reports Server (NTRS)

    Faur, Maria

    1997-01-01

    The research group at CSU has conducted theoretical and experimental research on 'Ultra-Low-Cost Room Temperature SiC Thin Films. The effectiveness of a ultra-low-cost room temperature thin film SiC growth technique on Silicon and Germanium substrates and structures with applications to space solar sells, ThermoPhotoVoltaic (TPV) cells and microelectronic and optoelectronic devices was investigated and the main result of this effort are summarized.

  12. Room-temperature single-photon sources based on nanocrystal fluorescence in photonic/plasmonic nanostructures

    NASA Astrophysics Data System (ADS)

    Lukishova, S. G.; Winkler, J. M.; Bissell, L. J.; Mihaylova, D.; Liapis, Andreas C.; Shi, Z.; Goldberg, D.; Menon, V. M.; Boyd, R. W.; Chen, G.; Prasad, P.

    2014-10-01

    Results are presented here towards robust room-temperature SPSs based on fluorescence in nanocrystals: colloidal quantum dots, color-center diamonds and doped with trivalent rare-earth ions (TR3+). We used cholesteric chiral photonic bandgap and Bragg-reflector microcavities for single emitter fluorescence enhancement. We also developed plasmonic bowtie nanoantennas and 2D-Si-photonic bandgap microcavities. The paper also provides short outlines of other technologies for room-temperature single-photon sources.

  13. Giant volume magnetostriction in the Y{sub 2}Fe{sub 17} single crystal at room temperature

    SciTech Connect

    Nikitin, S. A. Pankratov, N. Yu.; Smarzhevskaya, A. I.; Politova, G. A.; Pastushenkov, Yu. G. Skokov, K. P.; Moral, A. del

    2015-05-21

    An investigation of the Y{sub 2}Fe{sub 17} compound belonging to the class of intermetallic alloys of rare-earth and 3d-transition metals is presented. The magnetization, magnetostriction, and thermal expansion of the Y{sub 2}Fe{sub 17} single crystal were studied. The forced magnetostriction and magnetostriction constants were investigated in the temperature range of the magnetic ordering close to the room temperature. The giant field induced volume magnetostriction was discovered in the room temperature region in the magnetic field up to 1.2 T. The contributions of both anisotropic single-ion and isotropic pair exchange interactions to the volume magnetostriction and magnetostriction constants were determined. The experimental results were interpreted within the framework of the Standard Theory of Magnetostriction and the Landau thermodynamic theory. It was found out that the giant values of the volume magnetostriction were caused by the strong dependence of the 3d-electron Coulomb charge repulsion on the deformations and width of the 3d-electron energy band.

  14. Room-Temperature Creation and Spin-Orbit Torque Manipulation of Skyrmions in Thin Films with Engineered Asymmetry.

    PubMed

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

    2016-03-01

    Magnetic skyrmions, which are topologically protected spin textures, are promising candidates for ultralow-energy and ultrahigh-density magnetic data storage and computing applications. To date, most experiments on skyrmions have been carried out at low temperatures. The choice of available materials is limited, and there is a lack of electrical means to control skyrmions in devices. In this work, we demonstrate a new method for creating a stable skyrmion bubble phase in the CoFeB-MgO material system at room temperature, by engineering the interfacial perpendicular magnetic anisotropy of the ferromagnetic layer. Importantly, we also demonstrate that artificially engineered symmetry breaking gives rise to a force acting on the skyrmions, in addition to the current-induced spin-orbit torque, which can be used to drive their motion. This room-temperature creation and manipulation of skyrmions offers new possibilities to engineer skyrmionic devices. The results bring skyrmionic memory and logic concepts closer to realization in industrially relevant and manufacturable thin film material systems.

  15. Observation of temperature-gradient-induced magnetization

    PubMed Central

    Hou, Dazhi; Qiu, Zhiyong; Iguchi, R.; Sato, K.; Vehstedt, E. K.; Uchida, K.; Bauer, G. E. W.; Saitoh, E.

    2016-01-01

    Applying magnetic fields has been the method of choice to magnetize non-magnetic materials, but they are difficult to focus. The magneto-electric effect and voltage-induced magnetization generate magnetization by applied electric fields, but only in special compounds or heterostructures. Here we demonstrate that a simple metal such as gold can be magnetized by a temperature gradient or magnetic resonance when in contact with a magnetic insulator by observing an anomalous Hall-like effect, which directly proves the breakdown of time-reversal symmetry. Such Hall measurements give experimental access to the spectral spin Hall conductance of the host metal, which is closely related to other spin caloritronics phenomena such as the spin Nernst effect and serves as a reference for theoretical calculation. PMID:27457185

  16. Observation of temperature-gradient-induced magnetization

    NASA Astrophysics Data System (ADS)

    Hou, Dazhi; Qiu, Zhiyong; Iguchi, R.; Sato, K.; Vehstedt, E. K.; Uchida, K.; Bauer, G. E. W.; Saitoh, E.

    2016-07-01

    Applying magnetic fields has been the method of choice to magnetize non-magnetic materials, but they are difficult to focus. The magneto-electric effect and voltage-induced magnetization generate magnetization by applied electric fields, but only in special compounds or heterostructures. Here we demonstrate that a simple metal such as gold can be magnetized by a temperature gradient or magnetic resonance when in contact with a magnetic insulator by observing an anomalous Hall-like effect, which directly proves the breakdown of time-reversal symmetry. Such Hall measurements give experimental access to the spectral spin Hall conductance of the host metal, which is closely related to other spin caloritronics phenomena such as the spin Nernst effect and serves as a reference for theoretical calculation.

  17. Graphene-based room-temperature implementation of a modified Deutsch-Jozsa quantum algorithm.

    PubMed

    Dragoman, Daniela; Dragoman, Mircea

    2015-12-01

    We present an implementation of a one-qubit and two-qubit modified Deutsch-Jozsa quantum algorithm based on graphene ballistic devices working at room temperature. The modified Deutsch-Jozsa algorithm decides whether a function, equivalent to the effect of an energy potential distribution on the wave function of ballistic charge carriers, is constant or not, without measuring the output wave function. The function need not be Boolean. Simulations confirm that the algorithm works properly, opening the way toward quantum computing at room temperature based on the same clean-room technologies as those used for fabrication of very-large-scale integrated circuits. PMID:26541203

  18. Graphene-based room-temperature implementation of a modified Deutsch-Jozsa quantum algorithm

    NASA Astrophysics Data System (ADS)

    Dragoman, Daniela; Dragoman, Mircea

    2015-12-01

    We present an implementation of a one-qubit and two-qubit modified Deutsch-Jozsa quantum algorithm based on graphene ballistic devices working at room temperature. The modified Deutsch-Jozsa algorithm decides whether a function, equivalent to the effect of an energy potential distribution on the wave function of ballistic charge carriers, is constant or not, without measuring the output wave function. The function need not be Boolean. Simulations confirm that the algorithm works properly, opening the way toward quantum computing at room temperature based on the same clean-room technologies as those used for fabrication of very-large-scale integrated circuits.

  19. Room-temperature calorimeter for x-ray free-electron lasers

    SciTech Connect

    Tanaka, T. Kato, M.; Saito, N.; Tono, K.; Yabashi, M.; Ishikawa, T.

    2015-09-15

    We have developed a room-temperature calorimeter for absolute radiant power measurements of x-ray free-electron lasers. This room-temperature calorimeter is an electrical substitution device based on the equivalence of electrical and radiant heating. Consequently, the measured radiant powers are traceable to electrical standards, i.e., the International System Units (SI). We demonstrated the performance of the room-temperature calorimeter by electrical power measurements (offline tests). In the offline tests, the room-temperature calorimeter was proven to be able to measure external powers up to at least 6.9 mW, which exceeds the upper limit (∼4 mW) of a cryogenic radiometer (the primary standard detector in Japan). In addition, measurement uncertainties of the room-temperature calorimeter were evaluated to be less than 1.0%, which is adequate for the radiant power measurements of x-ray free-electron lasers. An indirect comparison with the cryogenic radiometer was performed using a synchrotron radiation source to confirm the validity of the absolute radiant powers measured with the room-temperature calorimeter. The absolute radiant powers measured by the calorimeter agreed with those measured by the cryogenic radiometer within 0.6%, which is less than the relative standard uncertainty of the comparison (1.0%)

  20. Evolution of Dust Structures from Room to Cryogenic Temperatures

    SciTech Connect

    Antipov, S. N.; Asinovskii, E. I.; Kirillin, A. V.; Markovets, V. V.; Petrov, O. F.; Fortov, V. E.

    2008-09-07

    In this work dusty plasma of dc glow discharge at the temperatures in the range of 4.2-300 K was experimentally and numerically investigated. As it was shown in the experiments, the deep cooling of discharge tube walls leads to dramatic change of dusty plasma properties. In particular, sufficient increase of dust particle kinetic temperature (by about an order) and dust density (by several orders) was observed at low (cryogenic) temperatures. At 4.2 K, this can lead to the forming of a super dense dust structures with novel properties. Numerical simulations of charging process, dust charge fluctuation and screening of dust particle charge in plasma were made in dependence with the neutral gas temperature and dust density. The main attention was given to proper ion-atom collision analysis that allows us to investigate mechanisms of dust structure transformation observed in the cryogenic experiments.

  1. Controlling temperature in magnetic hyperthermia with low Curie temperature particles

    NASA Astrophysics Data System (ADS)

    Astefanoaei, Iordana; Dumitru, Ioan; Chiriac, Horia; Stancu, Alexandru

    2014-05-01

    Hyperthermia induced by the heating of magnetic particles (MPs) in alternating magnetic field receives a considerable attention in cancer therapy. An interesting development in the studies dedicated to magnetically based hyperthermia is the possibility to control the temperature using MPs with selective magnetic absorption properties. This paper analyzes the temperature field determined by the heating of MPs having low Curie temperature (a FeCrNbB particulate system) injected within a malignant tissue, subjected to an ac magnetic field. The temperature evolution within healthy and tumor tissues was analyzed by finite element method simulations in a thermo-fluid model. The cooling effect produced by blood flowing in blood vessels was considered. This effect is intensified at the increase of blood velocity. The FeCrNbB particles, having the Curie temperature close to the therapeutic range, transfer the heat more homogeneous in the tumor keeping the temperature within the therapeutic range in whole tumor volume. Having the possibility to automatically control the temperature within a tumor, these particle type opens new research horizons in the magnetic hyperthermia.

  2. Tuning structural instability toward enhanced magnetocaloric effect around room temperature in MnCo(1-x)Zn(x)Ge.

    PubMed

    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 MnCo(1-x)Zn(x)Ge 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

  3. 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

  4. 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.

  5. Gamma-ray irradiation on microsized Nd-Fe-B and Sr-ferrite magnets at low temperature.

    PubMed

    Han, Young Chul; Cha, Hyun Gil; Kim, Chang Woo; Kim, Young Hwan; Ji, Eun Sun; Kang, Young Soo

    2009-07-01

    The gamma-ray irradiation on microsized Nd-Fe-B and Sr-Fe permanent magnet at low temperature and room temperature was investigated. The change of shape and magnetic properties of two kinds of magnet powder before and after irradiation at low temperature was measured. The crystal structure of each permanent magnet powders was analyzed using X-ray powder diffraction (XRD) and the size and shape were characterized by scanning electron microscope (SEM). The changed magnetic properties of magnet such as saturation magnetization (M(s)) and coercivity (H(c)) were measured by VSM.

  6. 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.

  7. Large magneto-conductance and magneto-electroluminescence in exciplex-based organic light-emitting diodes at room temperature

    NASA Astrophysics Data System (ADS)

    Ling, Yongzhou; Lei, Yanlian; Zhang, Qiaoming; Chen, Lixiang; Song, Qunliang; Xiong, Zuhong

    2015-11-01

    In this work, we report on large magneto-conductance (MC) over 60% and magneto-electroluminescence (MEL) as high as 112% at room temperature in an exciplex-based organic light-emitting diode (OLED) with efficient reverse intersystem crossing (ISC). The large MC and MEL are individually confirmed by the current density-voltage characteristics and the electroluminescence spectra under various magnetic fields. We proposed that this type of magnetic field effect (MFE) is governed by the field-modulated reverse ISC between the singlet and triplet exciplex. The temperature-dependent MFEs reveal that the small activation energy of reverse ISC accounts for the large MFEs in the present exciplex-based OLEDs.

  8. Synthesis of Room-Temperature Ferromagnetic Cr-doped TiO₂(110) Rutile Single Crystals using Ion Implantation

    SciTech Connect

    Shutthanandan, V.; Thevuthasan, Suntharampillai; Droubay, Timothy C.; Heald, Steve M.; Engelhard, Mark H.; McCready, David E.; Chambers, Scott A.; Nachimuthu, Ponnusamy; Mun, B. S.

    2006-01-01

    Ferromagnetic Cr-doped rutile TiO₂ single crystals were synthesized by high-temperature ion implantation. The associated structural, compositional and magnetic properties were studied by x-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, proton induced x-ray emission, x-ray diffraction, Cr K- and L-shell near-edge x-ray absorption spectroscopy, and vibrating sample magnetometry. Cr was distributed uniformly to the depth of about 300 nm with an average concentration of ~1 at. %. The samples are semiconducting and ferromagnetic as implanted, with a saturation magnetization of 0.29 B/Cr atom at room temperature. Cr is in a formal oxidation state of +3 throughout the implanted region, and no CrO₂ is detected.

  9. Spin-Induced Polarizations and Nonreciprocal Directional Dichroism of the Room-Temperature Multiferroic BiFeO3

    DOE PAGES

    Fishman, Randy Scott; Lee, Jun Hee; Bordacs, Sandor; Kezsmarki, Istvan; Nagel, Urmas; Room, Toomas

    2015-09-14

    A microscopic model for the room-temperature multiferroic BiFeO3 that includes two Dzyaloshinskii-Moriya interactions and single-ion anisotropy along the ferroelectric polarization predicts both the zero-field spectroscopic modes as well as their splitting and evolution in a magnetic field. Due to simultaneously broken time-reversal and spatial-inversion symmetries, the absorption of light changes as the magnetic field or the direction of light propagation is reversed. We discuss three physical mechanisms that may contribute to this absorption asymmetry known as directional dichroism: the spin current, magnetostriction, and single-ion anisotropy. We conclude that the directional dichroism in BiFeO3 is dominated by the spin-current polarization andmore » is insensitive to the magnetostriction and easy-axis anisotropy. With three independent spin-current parameters, our model accurately describes the directional dichroism observed for magnetic field along [1, -1, 0]. Since some modes are almost transparent to light traveling in one direction but opaque for light traveling in the opposite direction, BiFeO3 can be used as a room-temperature optical diode at certain frequencies in the GHz to THz range. This work demonstrates that an analysis of the directional dichroism spectra based on an effective spin model supplemented by first-principles calculations can produce a quantitative microscopic theory of the magnetoelectric couplings in multiferroic materials.« less

  10. Room temperature weak ferromagnetism in Sn1-xMnxSe2 2D films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Dong, Sining; Liu, Xinyu; Li, Xiang; Kanzyuba, Vasily; Yoo, Taehee; Rouvimov, Sergei; Vishwanath, Suresh; Xing, Huili G.; Jena, Debdeep; Dobrowolska, Margaret; Furdyna, Jacek K.

    2016-03-01

    We discuss growth and magnetic properties of high-quality two dimensional (2D) Sn1-xMnxSe2 films. Thin films of this 2D ternary alloy with a wide range of Mn concentrations were successfully grown by molecular beam epitaxy. Mn concentrations up to x ≈ 0.60 were achieved without destroying the crystal structure of the parent SnSe2 2D system. Most important, the specimens show clear weak ferromagnetic behavior above room temperature, which should be of interest for 2D spintronic applications.

  11. Magneto-Optic Effect in Amorphous Bi3Fe5O12 Waveguides Sputtered at Room Temperature

    NASA Astrophysics Data System (ADS)

    Taura, Hiroshi; Shishido, Yohei; Tanushi, Yuichiro; Tokunaga, Tomohiro; Onimaru, Takahiro; Yokoyama, Shin

    2008-04-01

    We have fabricated optical waveguides using amorphous Bi3Fe5O12 (BIG) film deposited by RF magnetron sputtering at room temperature and evaluated the Faraday effect. The fabricated waveguide consists of Si waveguides and a short BIG waveguide. Light propagation loss of the BIG waveguide is 100 dB/cm. The optical modulation of 9% was obtained on the basis of the Faraday effect using the BIG waveguide/polarizer system at an external magnetic field of 2000 Oe. The figure of merit of 10 deg/dB, which is 1/4 that of an epitaxial BIG film, was obtained.

  12. Coexistence of electric field controlled ferromagnetism and resistive switching for TiO{sub 2} film at room temperature

    SciTech Connect

    Ren, Shaoqing; Qin, Hongwei; Bu, Jianpei; Zhu, Gengchang; Xie, Jihao; Hu, Jifan E-mail: hu-jf@vip.163.com

    2015-08-10

    The Ag/TiO{sub 2}/Nb:SrTiO{sub 3}/Ag device exhibits the coexistence of electric field controlled ferromagnetism and resistive switching at room temperature. The bipolar resistive switching in Ag/TiO{sub 2}/Nb:SrTiO{sub 3}/Ag device may be dominated by the modulation of Schottky-like barrier with the electron injection-trapped/detrapped process at the interface of TiO{sub 2}/Nb:SrTiO{sub 3}. We suggest that the electric field-induced magnetization modulation originates mainly from the creation/annihilation of lots of oxygen vacancies in TiO{sub 2}.

  13. Room Temperature Ferrimagnetism and Ferroelectricity in Strained, Thin Films of BiFe0.5Mn0.5O3

    PubMed Central

    Choi, Eun-Mi; Fix, Thomas; Kursumovic, Ahmed; Kinane, Christy J; Arena, Darío; Sahonta, Suman-Lata; Bi, Zhenxing; Xiong, Jie; Yan, Li; Lee, Jun-Sik; Wang, Haiyan; Langridge, Sean; Kim, Young-Min; Borisevich, Albina Y; MacLaren, Ian; Ramasse, Quentin M; Blamire, Mark G; Jia, Quanxi; MacManus-Driscoll, Judith L

    2014-01-01

    Highly strained films of BiFe0.5Mn0.5O3 (BFMO) grown at very low rates by pulsed laser deposition were demonstrated to exhibit both ferrimagnetism and ferroelectricity at room temperature and above. Magnetisation measurements demonstrated ferrimagnetism (TC ∼ 600K), with a room temperature saturation moment (MS) of up to 90 emu/cc (∼ 0.58 μB/f.u) on high quality (001) SrTiO3. X-ray magnetic circular dichroism showed that the ferrimagnetism arose from antiferromagnetically coupled Fe3+ and Mn3+. While scanning transmission electron microscope studies showed there was no long range ordering of Fe and Mn, the magnetic properties were found to be strongly dependent on the strain state in the films. The magnetism is explained to arise from one of three possible mechanisms with Bi polarization playing a key role. A signature of room temperature ferroelectricity in the films was measured by piezoresponse force microscopy and was confirmed using angular dark field scanning transmission electron microscopy. The demonstration of strain induced, high temperature multiferroism is a promising development for future spintronic and memory applications at room temperature and above. PMID:26213531

  14. Room temperature ferrimagnetism and ferroelectricity in strained, thin films of BiFe 0.5 Mn 0.5 O 3

    DOE PAGES

    Choi, Eun -Mi; Fix, Thomas; Kursumovic, Ahmed; Kinane, Christy J.; Arena, Darío; Sahonta, Suman -Lata; Bi, Zhenxing; Xiong, Jie; Yan, Li; Lee, Jun -Sik; et al

    2014-10-14

    Highly strained films of BiFe0.5Mn0.5O₃ (BFMO) grown at very low rates by pulsed laser deposition were demonstrated to exhibit both ferrimagnetism and ferroelectricity at room temperature and above. Magnetisation measurements demonstrated ferrimagnetism (TC ~ 600K), with a room temperature saturation moment (MS) of up to 90 emu/cc (~ 0.58 μB/f.u) on high quality (001) SrTiO₃. X-ray magnetic circular dichroism showed that the ferrimagnetism arose from antiferromagnetically coupled Fe³⁺ and Mn³⁺. While scanning transmission electron microscope studies showed there was no long range ordering of Fe and Mn, the magnetic properties were found to be strongly dependent on the strain statemore » in the films. The magnetism is explained to arise from one of three possible mechanisms with Bi polarization playing a key role. A signature of room temperature ferroelectricity in the films was measured by piezoresponse force microscopy and was confirmed using angular dark field scanning transmission electron microscopy. The demonstration of strain induced, high temperature multiferroism is a promising development for future spintronic and memory applications at room temperature and above.« less

  15. Room temperature ferrimagnetism and ferroelectricity in strained, thin films of BiFe 0.5 Mn 0.5 O 3

    SciTech Connect

    Choi, Eun -Mi; Fix, Thomas; Kursumovic, Ahmed; Kinane, Christy J.; Arena, Darío; Sahonta, Suman -Lata; Bi, Zhenxing; Xiong, Jie; Yan, Li; Lee, Jun -Sik; Wang, Haiyan; Langridge, Sean; Kim, Young -Min; Borisevich, Albina Y.; MacLaren, Ian; Ramasse, Quentin M.; Blamire, Mark G.; Jia, Quanxi; MacManus-Driscoll, Judith L.

    2014-10-14

    Highly strained films of BiFe0.5Mn0.5O₃ (BFMO) grown at very low rates by pulsed laser deposition were demonstrated to exhibit both ferrimagnetism and ferroelectricity at room temperature and above. Magnetisation measurements demonstrated ferrimagnetism (TC ~ 600K), with a room temperature saturation moment (MS) of up to 90 emu/cc (~ 0.58 μB/f.u) on high quality (001) SrTiO₃. X-ray magnetic circular dichroism showed that the ferrimagnetism arose from antiferromagnetically coupled Fe³⁺ and Mn³⁺. While scanning transmission electron microscope studies showed there was no long range ordering of Fe and Mn, the magnetic properties were found to be strongly dependent on the strain state in the films. The magnetism is explained to arise from one of three possible mechanisms with Bi polarization playing a key role. A signature of room temperature ferroelectricity in the films was measured by piezoresponse force microscopy and was confirmed using angular dark field scanning transmission electron microscopy. The demonstration of strain induced, high temperature multiferroism is a promising development for future spintronic and memory applications at room temperature and above.

  16. Room-temperature observations of the weak localization in low-mobility graphene films

    SciTech Connect

    Han, Junhao; Wang, Shanyue; Qian, Di; Song, Fengqi E-mail: bgwang@nju.edu.cn; Wang, Baigeng E-mail: bgwang@nju.edu.cn; Han, Min; Zhou, Jianfeng; Wang, Xinran; Wang, Xuefeng

    2013-12-07

    We report room-temperature observations of the quantum conductance corrections caused by the weak localization in graphene films synthesized using solid-state-source chemical vapor deposition. Both Raman spectroscopy and Hall measurements showed strong disorder in the samples with a low mobility of ∼430 cm{sup 2}/V s. The emergence of weak localization at room temperature arises from the competition between the valley-dependent scattering and the thermal dephasing in such low-quality samples, although quantum effects normally appear in the samples that have an ideal structure at cryogenic temperatures. The large disorder in our low-mobility samples unexpectedly preserved the quantum mechanical weak localization.

  17. Room-temperature ferroelectricity of SrTiO{sub 3} films modulated by cation concentration

    SciTech Connect

    Yang, Fang; Zhang, Qinghua; Yang, Zhenzhong; Gu, Junxing; Liang, Yan; Li, Wentao; Wang, Weihua; Jin, Kuijuan; Gu, Lin; Guo, Jiandong

    2015-08-24

    The room-temperature ferroelectricity of SrTiO{sub 3} is promising for oxide electronic devices controlled by multiple fields. An effective way to control the ferroelectricity is highly demanded. Here, we show that the off-centered antisite-like defects in SrTiO{sub 3} films epitaxially grown on Si (001) play the determinative role in the emergence of room-temperature ferroelectricity. The density of these defects changes with the film cation concentration sensitively, resulting in a varied coercive field of the ferroelectric behavior. Consequently, the room-temperature ferroelectricity of SrTiO{sub 3} films can be effectively modulated by tuning the temperature of metal sources during the molecular beam epitaxy growth. Such an easy and reliable modulation of the ferroelectricity enables the flexible engineering of multifunctional oxide electronic devices.

  18. Fundamental Properties of TBAF Clathrate for Usage as a Latent Heat Storage at a Room Temperature

    NASA Astrophysics Data System (ADS)

    Mizushima, Takanari; Kawamura, Hiroshi; Takao, Shingo; Yabe, Akira

    For promotion of further energy conservation, development of a coolant with a higher heat capacity regulated around a room temperature is strongly required. As a candidate of such a new coolant, we employ the clathrate hydrate, i.e., a mixture of Tetra n-butyl ammonium fluoride (TBAF) and water. This clathrate hydrate is composed of the micro crystals with an order of 100 μm in dimension. It retains fluidity and melting point at a room temperature of about 25 °C. Moreover, the melting point is able to be controlled between 25 °C and 0 °C by changing the concentration of TBAF. The temperature can be regulated by its latent heat at the melting point. Characteristics such as the latent heat and the crystal structure of the clathrate have been experimentally obtained to confirm the feasibility for its usage as the latent heat storage around a room temperature.

  19. 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.

  20. 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.

  1. Subtle variation in ambient room temperature influences the expression of social cognition.

    PubMed

    Vigil, Jacob M; Swartz, Tyler J; Rowell, Lauren N

    2013-10-01

    Social signaling models predict that subtle variation in climatic temperature induces systematic changes in expressed cognition. An experiment showed that perceived room temperature was associated with variability in self-descriptions, social reactions of others, and desiring differing types of social networks. The findings reflect the tendency to inflate capacity demonstrations in warmer climates as a result of the social networking opportunities they enable.

  2. Room temperature magneto-structural transition in Al for Sn substituted Ni-Mn-Sn melt spun ribbons

    NASA Astrophysics Data System (ADS)

    Maziarz, W.; Czaja, P.; Szczerba, M. J.; Przewoźnik, J.; Kapusta, C.; Żywczak, A.; Stobiecki, T.; Cesari, E.; Dutkiewicz, J.

    2013-12-01

    Martensitic and magnetic transformations in Ni48Mn39.5Sn12.5-xAlx (x=0, 1, 2, 3) Heusler alloy ribbons were investigated. It is demonstrated that both magnetic and structural transformations occur in all of the studied samples. It is also shown that substitution of Sn with Al causes the martensitic transformation (MT) and the reverse martensitic transformation (RMT) temperatures to increase to room temperature (ΔTMT=49 K; ΔTRMT=43 K), whereas the Curie temperature of martensite TCM decreases (ΔT=36 K) and the Curie temperature of austenite TCA remains practically insensitive to Al introduction. This then allows to tune TCA and the MT temperature leading to their coincidence at ambient temperature. The austenite phase with the L21 type structure has been identified to exist in all the samples regardless of composition. On the other hand the structure of martensite has been shown to be sensitive to composition. It has been determined as the 10 M martensite with (32¯) stacking sequence in Al free samples and the 4O martensite with the stacking periodicity (31¯) in Al containing samples. In addition, the splitting of the field cooling (FC) and the field heating (FH) thermo-magnetic curves at low (50 Oe) magnetic field and below the TCM has been attributed to intermartensitic transition. The application of large magnetic field (50 kOe) has shown the existence of two distinct ferromagnetic states with a considerable hysteresis loop. The properties of these materials make them promising for magnetocaloric applications.

  3. Room Temperature Aging Study of Butyl O-rings

    SciTech Connect

    Mark Wilson

    2009-08-07

    During testing under the Enhanced Surveillance Campaign in 2001, preliminary data detected a previously unknown and potentially serious concern with recently procured butyl o-rings. All butyl o-rings molded from a proprietary formulation throughout the period circa 1999 through 2001 had less than a full cure. Tests showed that sealing force values for these suspect o-rings were much lower than expected and their physical properties were very sensitive to further post curing at elevated temperatures. Further testing confirmed that these o-rings were approximately 50% cured versus the typical industry standard of > 90% cured. Despite this condition, all suspect o-rings fully conformed to their QC acceptance requirements, including their individual product drawing requirements.

  4. Continuous wave room temperature external ring cavity quantum cascade laser

    SciTech Connect

    Revin, D. G. Hemingway, M.; Vaitiekus, D.; Cockburn, J. W.; Hempler, N.; Maker, G. T.; Malcolm, G. P. A.

    2015-06-29

    An external ring cavity quantum cascade laser operating at ∼5.2 μm wavelength in a continuous-wave regime at the temperature of 15 °C is demonstrated. Out-coupled continuous-wave optical powers of up to 23 mW are observed for light of one propagation direction with an estimated total intra-cavity optical power flux in excess of 340 mW. The uni-directional regime characterized by the intensity ratio of more than 60 for the light propagating in the opposite directions was achieved. A single emission peak wavelength tuning range of 90 cm{sup −1} is realized by the incorporation of a diffraction grating into the cavity.

  5. Geopolymer - room-temperature ceramic matrix for composites

    SciTech Connect

    Davidovits, J.; Davidovics, M.

    1988-08-01

    The semiamorphous three-dimensional networks of polymeric Na, K, Li, and Mg aluminosilicates of both poly(sialate) and poly(sialate-siloxo) type, collectively known as geopolymers, harden at 20-120 C and are similar to thermoset resins, but are stable at up to 1200-1400 C without shrinkage. A wide variety of alkaline-resistant inorganic reinforcements, notably SiC fibers, have been combined with geopolymer matrices to yield nonburning, nonsmoking high-temperature composites. An SiC fiber-reinforced K-poly(sialate-siloxo) matrix, shaped and hardened at 70 C for 1.5 hr, develops flexural mean strengths of the order of 380 MPa that are retained after firing at up to 900 C. 16 references.

  6. Effects of reduced nocturnal temperature on pig performance and energy consumption in swine nursery rooms.

    PubMed

    Johnston, L J; Brumm, M C; Moeller, S J; Pohl, S; Shannon, M C; Thaler, R C

    2013-07-01

    The objective of this investigation was to determine the effect of a reduced nocturnal temperature (RNT) regimen on performance of weaned pigs and energy consumption during the nursery phase of production. The age of weaned pigs assigned to experiments ranged from 16 to 22 d. In Exp. 1, 3 stations conducted 2 trials under a common protocol that provided data from 6 control rooms (CON; 820 pigs) and 6 RNT rooms (818 pigs). Two mirror-image nursery rooms were used at each station. Temperature in the CON room was set to 30°C for the first 7 d, then reduced by 2°C per week through the remainder of the experiment. Room temperature settings were held constant throughout the day and night. The temperature setting in the RNT room was the same as CON during the first 7 d, but beginning on the night of d 7, the room temperature setting was reduced 6°C from the daytime temperature from 1900 to 0700 h. The use of heating fuel and electricity were measured weekly in each room. Overall, ADG (0.43 kg), ADFI (0.62 kg), and G:F (0.69) were identical for CON and RNT rooms. Consumption of heating fuel [9,658 vs. 7,958 British thermal units (Btu)·pig(-1)·d(-1)] and electricity (0.138 vs. 0.125 kilowatt-hour (kWh)·pig(-1)·d(-1)] were not statistically different for CON and RNT rooms, respectively. In Exp. 2, 4 stations conducted at least 2 trials that provided data from 9 CON rooms (2,122 pigs) and 10 RNT rooms (2,176 pigs). Experimental treatments and protocols were the same as Exp. 1, except that the RNT regimen was imposed on the night of d 5 and the targeted nighttime temperature reduction was 8.3°C. Neither final pig BW (21.8 vs. 21.5 kg; SE = 0.64), ADG (0.45 vs. 0.44 kg; SE = 0.016), ADFI (0.61 vs. 0.60 kg; SE = 0.019), nor G:F (0.75 vs. 0.75; SE = 0.012) were different for pigs housed in CON or RNT rooms, respectively. Consumption of heating fuel and electricity was consistently reduced in RNT rooms for all 4 stations. Consumption of heating fuel (10,019 vs. 7,061 Btu

  7. Room temperature strong light-matter coupling in 3D THz meta-atoms (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Paulillo, Bruno; Manceau, Jean-Michel; Li, Lianhe; Linfield, Edmund; Colombelli, Raffaele

    2016-04-01

    We demonstrate strong light-matter coupling at room temperature in the terahertz (THz) spectral region using 3D meta-atoms with extremely sub-wavelength volumes. Using an air-bridge fabrication scheme, we have implemented sub-wavelength 3D THz micro-resonators that rely on suspended loop antennas connected to semiconductor-filled patch cavities. We have experimentally shown that they possess the functionalities of lumped LC resonators: their frequency response can be adjusted by independently tuning the inductance associated the antenna element or the capacitance provided by the metal-semiconductor-metal cavity. Moreover, the radiation coupling and efficiency can be engineered acting on the design of the loop antenna, similarly to conventional RF antennas. Here we take advantage of this rich playground in the context of cavity electrodynamics/intersubband polaritonics. In the strong light-matter coupling regime, a cavity and a two-level system exchange energy coherently at a characteristic rate called the vacuum Rabi frequency ΩR which is dominant with respect to all other loss mechanisms involved. The signature, in the frequency domain, is the appearance of a splitting between the bare cavity and material system resonances: the new states are called upper and a lower polariton branches. So far, most experimental demonstrations of strong light-matter interaction between an intersubband transition and a deeply sub-wavelength mode in the THz or mid-infrared ranges rely on wavelength-scale or larger resonators such as photonic crystals, diffractive gratings, dielectric micro-cavities or patch cavities. Lately, planar metamaterials have been used to enhance the light-matter interaction and strongly reduce the interaction volume by engineering the electric and magnetic resonances of the individual subwavelength constituents. In this contribution we provide evidence of strong coupling between a THz intersubband transition and an extremely sub-wavelength mode (≈λ/10

  8. A moment model for phonon transport at room temperature

    NASA Astrophysics Data System (ADS)

    Mohammadzadeh, Alireza; Struchtrup, Henning

    2016-08-01

    Heat transfer in solids is modeled by deriving the macroscopic equations for phonon transport from the phonon-Boltzmann equation. In these equations, the Callaway model with frequency-dependent relaxation time is considered to describe the Resistive and Normal processes in the phonon interactions. Also, the Brillouin zone is considered to be a sphere, and its diameter depends on the temperature of the system. A simple model to describe phonon interaction with crystal boundary is employed to obtain macroscopic boundary conditions, where the reflection kernel is the superposition of diffusive reflection, specular reflection and isotropic scattering. Macroscopic moments are defined using a polynomial of the frequency and wave vector of phonons. As an example, a system of moment equations, consisting of three directional and seven frequency moments, i.e., 63 moments in total, is used to study one-dimensional heat transfer, as well as Poiseuille flow of phonons. Our results show the importance of frequency dependency in relaxation times and macroscopic moments to predict rarefaction effects. Good agreement with data reported in the literature is obtained.

  9. Ultrabright continuously tunable terahertz-wave generation at room temperature

    NASA Astrophysics Data System (ADS)

    Hayashi, Shin'ichiro; Nawata, Kouji; Taira, Takunori; Shikata, Jun-Ichi; Kawase, Kodo; Minamide, Hiroaki

    2014-06-01

    The hottest frequency region in terms of research currently lies in the `frequency gap' region between microwaves and infrared: terahertz waves. Although new methods for generating terahertz radiation have been developed, most sources cannot generate high-brightness terahertz beams. Here we demonstrate the generation of ultrabright terahertz waves (brightness ~0.2 GW/sr.cm2, brightness temperature of ~1018 K, peak power of >50 kW) using parametric wavelength conversion in a nonlinear crystal; this is brighter than many specialized sources such as far-infrared free-electron lasers (~1016 K, ~2 kW). We revealed novel parametric wavelength conversion using stimulated Raman scattering in LiNbO3 without stimulated Brillouin scattering using recently-developed microchip laser. Furthermore, nonlinear up-conversion techniques allow the intense terahertz waves to be visualized and their frequency determined. These results are very promising for extending applied research into the terahertz region, and we expect that this source will open up new research fields such as nonlinear optics in the terahertz region.

  10. Room temperature aluminum antimonide radiation detector and methods thereof

    DOEpatents

    Lordi, Vincenzo; Wu, Kuang Jen J.; Aberg, Daniel; Erhart, Paul; Coombs, III, Arthur W; Sturm, Benjamin W

    2015-03-03

    In one embodiment, a method for producing a high-purity single crystal of aluminum antimonide (AlSb) includes providing a growing environment with which to grow a crystal, growing a single crystal of AlSb in the growing environment which comprises hydrogen (H.sub.2) gas to reduce oxide formation and subsequent incorporation of oxygen impurities in the crystal, and adding a controlled amount of at least one impurity to the growing environment to effectively incorporate at least one dopant into the crystal. In another embodiment, a high energy radiation detector includes a single high-purity crystal of AlSb, a supporting structure for the crystal, and logic for interpreting signals obtained from the crystal which is operable as a radiation detector at a temperature of about 25.degree. C. In one embodiment, a high-purity single crystal of AlSb includes AlSb and at least one dopant selected from a group consisting of selenium (Se), tellurium (Te), and tin (Sn).

  11. Ultrabright continuously tunable terahertz-wave generation at room temperature

    PubMed Central

    Hayashi, Shin'ichiro; Nawata, Kouji; Taira, Takunori; Shikata, Jun-ichi; Kawase, Kodo; Minamide, Hiroaki

    2014-01-01

    The hottest frequency region in terms of research currently lies in the ‘frequency gap' region between microwaves and infrared: terahertz waves. Although new methods for generating terahertz radiation have been developed, most sources cannot generate high-brightness terahertz beams. Here we demonstrate the generation of ultrabright terahertz waves (brightness ~0.2 GW/sr·cm2, brightness temperature of ~1018 K, peak power of >50 kW) using parametric wavelength conversion in a nonlinear crystal; this is brighter than many specialized sources such as far-infrared free-electron lasers (~1016 K, ~2 kW). We revealed novel parametric wavelength conversion using stimulated Raman scattering in LiNbO3 without stimulated Brillouin scattering using recently-developed microchip laser. Furthermore, nonlinear up-conversion techniques allow the intense terahertz waves to be visualized and their frequency determined. These results are very promising for extending applied research into the terahertz region, and we expect that this source will open up new research fields such as nonlinear optics in the terahertz region. PMID:24898269

  12. 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.

  13. Pyridine-2,6-diyl dinitroxides as room-temperature triplet ligands

    NASA Astrophysics Data System (ADS)

    Kawakami, Hinako; Tonegawa, Asato; Ishida, Takayuki

    2016-02-01

    We have proposed tert-butyl 2-pyridyl nitroxide radicals as a promising paramagnetic chelating ligand, where the direct radical-metal bond leads to strong magnetic interaction. We successfully synthesized and isolated PyBN derivatives (pyridine-2,6-diyl bis(tert-butyl nitroxides)). The molecular and crystal structures of the target biradicals, MesPyBN, AntPyBN and tBuOPyBN were determined from the X-ray crystal structure analysis, which possess mesityl, 9-anthryl and tert-butoxy groups at the 5-position of the pyridine ring, respectively. The ground triplet state was characterized by means of SQUID susceptometry for each compound. On heating, the χmT values of all the PyBN derivatives increased and reached a plateau at ca. 1.0 cm3 K mol-1 at 300 K. It implies that biradicals behaved as triplet molecules even at room temperature, or 2J/kB >> 300 K. From the decay monitored in solution electron-spin resonance spectroscopy, MesPyBN was the most persistent, while tBuOPyBN was the most reactive, of the three.

  14. Instant synthesis of gold nanoparticles at room temperature and SERS applications

    NASA Astrophysics Data System (ADS)

    Britto Hurtado, R.; Cortez-Valadez, M.; Ramírez-Rodríguez, L. P.; Larios-Rodriguez, Eduardo; Alvarez, Ramón A. B.; Rocha-Rocha, O.; Delgado-Beleño, Y.; Martinez-Nuñez, C. E.; Arizpe-Chávez, H.; Hernández-Martínez, A. R.; Flores-Acosta, M.

    2016-08-01

    Nowadays, gold nanoparticles (AuNps) can be used in a variety of applications, thus efficient methods to produce them are necessary. Several methods have been proposed in this area, but NPs production time is one limitation of these approaches. In this study, we propose a high competitive method to synthesize gold colloidal nanoparticles, instantaneously, using no-toxic reducing agents. These substances allow the instantaneous synthesis at room temperature, even without magnetic stirrers, ovens or ultrasonic baths. Optic analysis showed two absorption bands, associated with surface Plasmon as function of HAuCl4 concentration. The nanoparticles synthesized have a 10-20 nm size, seen by the transmission electron microscopy (TEM). Therefore, it was possible to obtain several geometric patterns of AuNps, and the synthesis was performed reducing significantly processing time. Additionally, Mie and Fuchs theories were used to predict the location of the absorption bands linked to the plasmon surface in gold nanoparticles. The Surface Enhanced Raman Spectroscopy (SERS) effect was analyzed considering natural zeolite (Chabazite) as analyte, in order to determinate its possible application in soil analysis.

  15. 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.

  16. High temperature structural and magnetic properties of cobalt nanorods

    SciTech Connect

    Ait Atmane, Kahina; Zighem, Fatih; Soumare, Yaghoub; Ibrahim, Mona; Boubekri, Rym; Maurer, Thomas; Margueritat, Jeremie; Piquemal, Jean-Yves; Ott, Frederic; Chaboussant, Gregory; Schoenstein, Frederic; Jouini, Noureddine; Viau, Guillaume

    2013-01-15

    We present in this paper the structural and magnetic properties of high aspect ratio Co nanoparticles ({approx}10) at high temperatures (up to 623 K) using in-situ X ray diffraction (XRD) and SQUID characterizations. We show that the anisotropic shapes, the structural and texture properties are preserved up to 500 K. The coercivity can be modelled by {mu}{sub 0}H{sub C}=2(K{sub MC}+K{sub shape})/M{sub S} with K{sub MC} the magnetocrystalline anisotropy constant, K{sub shape} the shape anisotropy constant and M{sub S} the saturation magnetization. H{sub C} decreases linearly when the temperature is increased due to the loss of the Co magnetocrystalline anisotropy contribution. At 500 K, 50% of the room temperature coercivity is preserved corresponding to the shape anisotropy contribution only. We show that the coercivity drop is reversible in the range 300-500 K in good agreement with the absence of particle alteration. Above 525 K, the magnetic properties are irreversibly altered either by sintering or by oxidation. - Graphical abstract: We present in this paper the structural and magnetic properties of high aspect ratio Co nanorods ({approx}10) at high temperatures (up to 623 K) using in-situ X-ray diffraction and SQUID characterizations. We show that the anisotropic shapes, the structural and texture properties are preserved up to 500 K. Above 525 K, the magnetic properties are irreversibly altered either by sintering or by oxidation. Highlights: Black-Right-Pointing-Pointer Ferromagnetic Co nanorods are prepared using the polyol process. Black-Right-Pointing-Pointer The structural and texture properties of the Co nanorods are preserved up to 500 K. Black-Right-Pointing-Pointer The magnetic properties of the Co nanorods are irreversibly altered above 525 K.

  17. Performance evaluation of ZnO–CuO hetero junction solid state room temperature ethanol sensor

    SciTech Connect

    Yu, Ming-Ru; Suyambrakasam, Gobalakrishnan; Wu, Ren-Jang; Chavali, Murthy

    2012-07-15

    Graphical abstract: Sensor response (resistance) curves of time were changed from 150 ppm to 250 ppm alcohol concentration of ZnO–CuO 1:1. The response and recovery times were measured to be 62 and 83 s, respectively. The sensing material ZnO–CuO is a high potential alcohol sensor which provides a simple, rapid and highly sensitive alcohol gas sensor operating at room temperature. Highlights: ► The main advantages of the ethanol sensor are as followings. ► Novel materials ZnO–CuO ethanol sensor. ► The optimized ZnO–CuO hetero contact system. ► A good sensor response and room working temperature (save energy). -- Abstract: A semiconductor ethanol sensor was developed using ZnO–CuO and its performance was evaluated at room temperature. Hetero-junction sensor was made of ZnO–CuO nanoparticles for sensing alcohol at room temperature. Nanoparticles were prepared by hydrothermal method and optimized with different weight ratios. Sensor characteristics were linear for the concentration range of 150–250 ppm. Composite materials of ZnO–CuO were characterized using X-ray diffraction (XRD), temperature-programmed reduction (TPR) and high-resolution transmission electron microscopy (HR-TEM). ZnO–CuO (1:1) material showed maximum sensor response (S = R{sub air}/R{sub alcohol}) of 3.32 ± 0.1 toward 200 ppm of alcohol vapor at room temperature. The response and recovery times were measured to be 62 and 83 s, respectively. The linearity R{sup 2} of the sensor response was 0.9026. The sensing materials ZnO–CuO (1:1) provide a simple, rapid and highly sensitive alcohol gas sensor operating at room temperature.

  18. Point defects in silicon carbide as a promising basis for spectroscopy of single defects with controllable quantum states at room temperature

    NASA Astrophysics Data System (ADS)

    Soltamov, V. A.; Tolmachev, D. O.; Il'in, I. V.; Astakhov, G. V.; Dyakonov, V. V.; Soltamova, A. A.; Baranov, P. G.

    2015-05-01

    The spin and optical properties of silicon vacancy defects in silicon carbide of the hexagonal 6 H polytype have been investigated using photoluminescence, electron paramagnetic resonance, and X-band optically detected magnetic resonance. It has been shown that different configurations of these defects can be used to create an optical alignment of their spin sublevels as in the case of low temperatures and at temperatures close to room temperature ( T = 293 K). The main specific feature of silicon vacancy centers in silicon carbide is that the zero-magnetic-field-splitting parameter of some centers remains constant with variations in the temperature, which indicates prospects for the use of these centers for quantum magnetometry. It has also been shown that a number of centers, on the contrary, are characterized by a strong dependence of the zero-magnetic-field-splitting parameter on the temperature, which indicates prospects for the use of these centers as temperature sensors.

  19. Therapeutic Magnets Do Not Affect Tissue Temperatures.

    PubMed

    Sweeney, Kathleen B.; Merrick, Mark A.; Ingersoll, Christopher D.; Swez, John A.

    2001-03-01

    OBJECTIVE: Manufacturers of commercially available "therapeutic" magnets claim that these magnets cause physiologic thermal effects that promote tissue healing. We conducted this study to determine if skin or intramuscular temperatures differed among magnet, sham, and control treatments during 60 minutes of application to the quadriceps muscle. DESIGN AND SETTING: A 3 x 3 mixed-model, factorial design with repeated measures on both independent variables was used. The first independent variable, application duration, had 3 random levels (20, 40, and 60 minutes). The second independent variable, treatment, had 3 fixed levels (magnet, sham, and control). The dependent variable was tissue temperature ( degrees C). Measurement depth served as a control variable, with 2 levels: skin and 1 cm below the fat layer. Data were collected in a thermoneutral laboratory setting and analyzed using a repeated-measures analysis of variance. SUBJECTS: The study included 13 healthy student volunteers (8 men, 5 women; age, 20.5 +/- 0.9 years; height, 176.8 +/- 10.4 cm; weight, 73.8 +/- 11.8 kg; anterior thigh skinfold thickness, 16.9 +/- 6.5 mm). MEASUREMENTS: Temperatures were measured at 30-second intervals using surface and implantable thermocouples. Temperature data at 20, 40, and 60 minutes were used for analysis. Each subject received all 3 treatments on different days. RESULTS: Neither skin nor intramuscular temperatures were different across the 3 treatments at any time. For both skin and intramuscular temperatures, a statistically significant but not clinically meaningful temperature increase (less than 1 degrees C), was observed over time within treatments, but this increase was similar in all treatment groups. CONCLUSIONS: No meaningful thermal effect was observed with any treatment over time, and treatments did not differ from each other. We conclude that flexible therapeutic magnets were not effective for increasing skin or deep temperatures, contradicting one of the

  20. Therapeutic Magnets Do Not Affect Tissue Temperatures

    PubMed Central

    Sweeney, Kathleen B.; Ingersoll, Christopher D.; Swez, John A.

    2001-01-01

    Objective: Manufacturers of commercially available “therapeutic” magnets claim that these magnets cause physiologic thermal effects that promote tissue healing. We conducted this study to determine if skin or intramuscular temperatures differed among magnet, sham, and control treatments during 60 minutes of application to the quadriceps muscle. Design and Setting: A 3 × 3 mixed-model, factorial design with repeated measures on both independent variables was used. The first independent variable, application duration, had 3 random levels (20, 40, and 60 minutes). The second independent variable, treatment, had 3 fixed levels (magnet, sham, and control). The dependent variable was tissue temperature (°C). Measurement depth served as a control variable, with 2 levels: skin and 1 cm below the fat layer. Data were collected in a thermoneutral laboratory setting and analyzed using a repeated-measures analysis of variance. Subjects: The study included 13 healthy student volunteers (8 men, 5 women; age, 20.5 ± 0.9 years; height, 176.8 ± 10.4 cm; weight, 73.8 ± 11.8 kg; anterior thigh skinfold thickness, 16.9 ± 6.5 mm). Measurements: Temperatures were measured at 30-second intervals using surface and implantable thermocouples. Temperature data at 20, 40, and 60 minutes were used for analysis. Each subject received all 3 treatments on different days. Results: Neither skin nor intramuscular temperatures were different across the 3 treatments at any time. For both skin and intramuscular temperatures, a statistically significant but not clinically meaningful temperature increase (less than 1°C), was observed over time within treatments, but this increase was similar in all treatment groups. Conclusions: No meaningful thermal effect was observed with any treatment over time, and treatments did not differ from each other. We conclude that flexible therapeutic magnets were not effective for increasing skin or deep temperatures, contradicting one of the fundamental claims