Showing papers on "Magnetoresistance published in 2011"
Patent•
14 Feb 2011TL;DR: A magnetoresistive element according to an embodiment includes: a first ferromagnetic layer having an axis of easy magnetization in a direction perpendicular to a film plane; a second nonmagnetic layer placed between the first and the second magnetoresists; and a second interfacial magnetic layer between the second and the nonmagians as mentioned in this paper.
Abstract: A magnetoresistive element according to an embodiment includes: a first ferromagnetic layer having an axis of easy magnetization in a direction perpendicular to a film plane; a second ferromagnetic layer having an axis of easy magnetization in a direction perpendicular to a film plane; a nonmagnetic layer placed between the first ferromagnetic layer and the second ferromagnetic layer; a first interfacial magnetic layer placed between the first ferromagnetic layer and the nonmagnetic layer; and a second interfacial magnetic layer placed between the second ferromagnetic layer and the nonmagnetic layer The first interfacial magnetic layer includes a first interfacial magnetic film, a second interfacial magnetic film placed between the first interfacial magnetic film and the nonmagnetic layer and having a different composition from that of the first interfacial magnetic film, and a first nonmagnetic film placed between the first interfacial magnetic film and the second interfacial magnetic film
600 citations
TL;DR: It is shown, using angle-resolved photoemission spectroscopy, that there is a highly metallic universal 2DEG at the vacuum-cleaved surface of SrTiO3 (including the non-doped insulating material) independently of bulk carrier densities over more than seven decades.
Abstract: As silicon is the basis of conventional electronics, so strontium titanate (SrTiO(3)) is the foundation of the emerging field of oxide electronics. SrTiO(3) is the preferred template for the creation of exotic, two-dimensional (2D) phases of electron matter at oxide interfaces that have metal-insulator transitions, superconductivity or large negative magnetoresistance. However, the physical nature of the electronic structure underlying these 2D electron gases (2DEGs), which is crucial to understanding their remarkable properties, remains elusive. Here we show, using angle-resolved photoemission spectroscopy, that there is a highly metallic universal 2DEG at the vacuum-cleaved surface of SrTiO(3) (including the non-doped insulating material) independently of bulk carrier densities over more than seven decades. This 2DEG is confined within a region of about five unit cells and has a sheet carrier density of ∼0.33 electrons per square lattice parameter. The electronic structure consists of multiple subbands of heavy and light electrons. The similarity of this 2DEG to those reported in SrTiO(3)-based heterostructures and field-effect transistors suggests that different forms of electron confinement at the surface of SrTiO(3) lead to essentially the same 2DEG. Our discovery provides a model system for the study of the electronic structure of 2DEGs in SrTiO(3)-based devices and a novel means of generating 2DEGs at the surfaces of transition-metal oxides.
594 citations
TL;DR: An original spin-valve device is presented in which a non-magnetic molecular quantum dot is laterally coupled through supramolecular interactions to TbPc(2) single-molecule magnets (Pc=phthalocyanine), resulting in magnetoresistance ratios up to 300% at temperatures less than 1 K.
Abstract: Magnetic molecules are potential building blocks for the design of spintronic devices. Moreover, molecular materials enable the combination of bottom-up processing techniques, for example with conventional top-down nanofabrication. The development of solid-state spintronic devices based on the giant magnetoresistance, tunnel magnetoresistance and spin-valve effects has revolutionized magnetic memory applications. Recently, a significant improvement of the spin-relaxation time has been observed in organic semiconductor tunnel junctions, single non-magnetic molecules coupled to magnetic electrodes have shown giant magnetoresistance and hybrid devices exploiting the quantum tunnelling properties of single-molecule magnets have been proposed. Herein, we present an original spin-valve device in which a non-magnetic molecular quantum dot, made of a single-walled carbon nanotube contacted with non-magnetic electrodes, is laterally coupled through supramolecular interactions to TbPc(2) single-molecule magnets (Pc=phthalocyanine). Their localized magnetic moments lead to a magnetic field dependence of the electrical transport through the single-walled carbon nanotube, resulting in magnetoresistance ratios up to 300% at temperatures less than 1 K. We thus demonstrate the functionality of a supramolecular spin valve without magnetic leads. Our results open up prospects of new spintronic devices with quantum properties.
567 citations
TL;DR: This work demonstrates a spintronic element whose transport characteristics are governed by an antiferromagnet and demonstrates that sensitivity to low magnetic fields can be combined with large, spin-orbit-coupling-induced magnetotransport anisotropy using a single magnetic electrode.
Abstract: Spin-valve structures used in modern hard-drive read heads and magnetic random access memories comprise two ferromagnetic electrodes. It is now shown that antiferromagnets can be used as electrodes in spin valves. The results open a wide range of new possibilities for the choice of materials for spintronics devices.
476 citations
TL;DR: It is shown that conduction through double-stranded DNA oligomers is spin selective, demonstrating a true organic spin filter, and may reflect on the importance of spin in determining electron transfer rates through biological systems.
Abstract: Spin-based properties, applications, and devices are commonly related to magnetic effects and to magnetic materials. Most of the development in spintronics is currently based on inorganic materials. Despite the fact that the magnetoresistance effect has been observed in organic materials, until now spin selectivity of organic based spintronics devices originated from an inorganic ferromagnetic electrode and was not determined by the organic molecules themselves. Here we show that conduction through double-stranded DNA oligomers is spin selective, demonstrating a true organic spin filter. The selectivity exceeds that of any known system at room temperature. The spin dependent resistivity indicates that the effect cannot result solely from the atomic spin-orbit coupling and must relate to a special property resulting from the chirality symmetry. The results may reflect on the importance of spin in determining electron transfer rates through biological systems.
303 citations
TL;DR: Theoretical analysis identifies spin-dependent hybridization of molecular and electrode orbitals as the cause of the large magnetoresistance across a single, non-magnetic hydrogen phthalocyanine molecule contacted by the ferromagnetic tip of a scanning tunnelling microscope.
Abstract: A single magnetic molecule between ferromagnetic contacts exhibits a 60% magnetoresistance effect and nearly metallic conduction at the same time.
297 citations
Book•
23 Jun 2011
TL;DR: In this article, the authors present a survey of Magnetic Measurements and Diagnostics and their application in the field of Magnetic Diagnostics, including a discussion of magnetic sensors and their applications.
Abstract: Introduction to Magnetic Measurements Fundamentals of Magnetic Measurements Historical Background Main Terms The Magnetization Process of Ferromagnetic Materials Anisotropy and Texture Electromagnetic Loss Influence of the Magnetic Field on Physical Properties of a Material Magnetic Resonance Superconductivity Used in Magnetic Measurements Main Rules of Magnetics The Physical Principles of Magnetism The Magnetic Hysteresis Sources of a Magnetic Field The Samples and Circuits of the Material under Test Magnetic Shielding Magnetic Materials Soft Magnetic Materials: General Information Silicon Iron Electrical Steel Nickel- and Cobalt-Based Alloys Amorphous and Nanocrystalline Alloys Soft Ferrites Hard Magnetic Materials Special Magnetic Materials Magnetic Sensors General Remarks Induction Sensors Fluxgate Sensors Magnetoresistive and Magnetoimpedance Sensors Hall-Effect Sensors Resonance Sensors SQUID Sensors Resonance Sensors and Magnetometers Other Magnetic Sensors Testing of Magnetic Materials AC Testing of Soft Magnetic Materials DC Testing of Soft Magnetic Materials Testing of Hard Magnetic Materials Special Methods of Testing of Magnetic Materials Magnetic Field Measurements and Their Applications Environment Magnetic Fields Applications of Magnetic Field Measurements Magnetic Diagnostics Index References appear at the end of each chapter.
276 citations
TL;DR: In this paper, the authors consider single crystal thin films of Bi{}_{2}$Se${}_{3}, grown by molecular beam epitaxy, both with and without Pb doping, and demonstrate that an excellent account of quantum corrections to conductivity is achieved when both disorder and interaction are taken into account.
Abstract: We consider in our work single crystal thin films of Bi${}_{2}$Se${}_{3}$, grown by molecular beam epitaxy, both with and without Pb doping. Angle-resolved photoemission data demonstrate topological surface states with a Fermi level lying inside the bulk band gap in the Pb-doped films. Transport data show weak localization behavior, as expected for a thin film in the two-dimensional limit (when the thickness is smaller than the inelastic mean free path), but a detailed analysis within the standard theoretical framework of diffusive transport shows that the temperature and magnetic field dependences of resistance cannot be reconciled in a theory that neglects inter-electron interactions. We demonstrate that an excellent account of quantum corrections to conductivity is achieved when both disorder and interaction are taken into account. These results clearly demonstrate that it is crucial to include electron-electron interaction for a comprehensive understanding of diffusive transport in topological insulators. While both the ordinary bulk and the topological surface states presumably participate in transport, our analysis does not allow a clear separation of the two contributions.
264 citations
TL;DR: The magneto-Seebeck effect as mentioned in this paper is observed when a magnetic configuration changes the charge-based Seebeck coefficient, which can be measured as a voltage change directly without conversion of a spin current.
Abstract: Creating temperature gradients in magnetic nanostructures has resulted in a new research direction, that is, the combination of magneto- and thermoelectric effects. Here, we demonstrate the observation of one important effect of this class: the magneto-Seebeck effect. It is observed when a magnetic configuration changes the charge-based Seebeck coefficient. In particular, the Seebeck coefficient changes during the transition from a parallel to an antiparallel magnetic configuration in a tunnel junction. In this respect, it is the analogue to the tunnelling magnetoresistance. The Seebeck coefficients in parallel and antiparallel configurations are of the order of the voltages known from the charge-Seebeck effect. The size and sign of the effect can be controlled by the composition of the electrodes' atomic layers adjacent to the barrier and the temperature. The geometric centre of the electronic density of states relative to the Fermi level determines the size of the Seebeck effect. Experimentally, we realized 8.8% magneto-Seebeck effect, which results from a voltage change of about -8.7 μV K⁻¹ from the antiparallel to the parallel direction close to the predicted value of -12.1 μV K⁻¹. In contrast to the spin-Seebeck effect, it can be measured as a voltage change directly without conversion of a spin current.
259 citations
TL;DR: In the intermediate regime, quantum corrections to the Drude low-temperature conductivity are observed and negative magnetoresistance in this regime is isotropic, which points to magnetic scattering associated with the proximity of the system to either a spin-glass state or the charge ordered antiferromagnetic state observed in other rare earth nickelates.
Abstract: Transport in ultrathin films of LaNiO(3) evolves from a metallic to a strongly localized character as the film's thickness is reduced and the sheet resistance reaches a value close to h/e(2), the quantum of resistance in two dimensions. In the intermediate regime, quantum corrections to the Drude low-temperature conductivity are observed; they are accurately described by weak localization theory. Remarkably, the negative magnetoresistance in this regime is isotropic, which points to magnetic scattering associated with the proximity of the system to either a spin-glass state or the charge ordered antiferromagnetic state observed in other rare earth nickelates.
255 citations
TL;DR: This work uses patterned ferromagnetic thin film to demonstrate the profound effect of a substrate on the spin-dependent thermal transport and determined the intrinsic spin- dependent thermal transport with characteristics and field sensitivity similar to those of the anisotropic magnetoresistance effect.
Abstract: Most studies of spin caloritronic effects to date, including spin-Seebeck effect, utilize thin films on substrates. We use patterned ferromagnetic thin film to demonstrate the profound effect of a substrate on the spin-dependent thermal transport. With different sample patterns and on varying the direction of temperature gradient, both longitudinal and transverse thermal voltages exhibit asymmetric instead of symmetric spin dependence. This unexpected behavior is due to an out-of-plane temperature gradient imposed by the thermal conduction through the substrate and the mixture of anomalous Nernst effects. Only with substrate-free samples have we determined the intrinsic spin-dependent thermal transport with characteristics and field sensitivity similar to those of the anisotropic magnetoresistance effect.
TL;DR: In this article, the spin precession in inhomogeneous magnetic fields is shown to reduce the spin accumulation up to tenfold, and causes it to be inhomogene and noncollinear with the injector magnetization.
Abstract: Although the creation of spin polarization in various nonmagnetic media via electrical spin injection from a ferromagnetic tunnel contact has been demonstrated, much of the basic behavior is heavily debated. It is reported here that, for semiconductor/Al(2)O(3)/ferromagnet tunnel structures based on Si or GaAs, local magnetostatic fields arising from interface roughness dramatically alter and even dominate the accumulation and dynamics of spins in the semiconductor. Spin precession in inhomogeneous magnetic fields is shown to reduce the spin accumulation up to tenfold, and causes it to be inhomogeneous and noncollinear with the injector magnetization. The inverted Hanle effect serves as the experimental signature. This interaction needs to be taken into account in the analysis of experimental data, particularly in extracting the spin lifetime tau(s) and its variation with different parameters (temperature, doping concentration). It produces a broadening of the standard Hanle curve and thereby an apparent reduction of tau(s). For heavily doped n-type Si at room temperature it is shown that tau(s) is larger than previously determined, and a new lower bound of 0.29 ns is obtained. The results are expected to be general and to occur for spins near a magnetic interface not only in semiconductors but also in metals and organic and carbon-based materials including graphene, and in various spintronic device structures.
TL;DR: In this article, in-plane CoFeB-MgO magnetic tunnel junctions with perpendicular magnetic anisotropy in the free layer to reduce the spin transfer induced switching current were presented.
Abstract: We present in-plane CoFeB–MgO magnetic tunnel junctions with perpendicular magnetic anisotropy in the free layer to reduce the spin transfer induced switching current. The tunneling magnetoresistance ratio, resistance-area product, and switching current densities are compared in magnetic tunnel junctions with different CoFeB compositions. The effects of CoFeB free layer thickness on its magnetic anisotropy and current-induced switching characteristics are studied by vibrating sample magnetometry and electrical transport measurements on patterned elliptical nanopillar devices. Switching current densities ∼4 MA/cm2 are obtained at 10 ns write times.
TL;DR: It is shown, by first principles calculations, that β-Ag2Te with distorted antifluorite structure is in fact a topological insulator with gapless Dirac-type surface states.
Abstract: To explain the unusual nonsaturating linear magnetoresistance observed in silver chalcogenides, the quantum scenario has been proposed based on the assumption of gapless linear energy spectrum. Here we show, by first principles calculations, that beta-Ag2Te with distorted antifluorite structure is in fact a topological insulator with gapless Dirac-type surface states. The characteristic feature of this new binary topological insulator is the highly anisotropic Dirac cone, in contrast with known examples, such as Bi2Te3 and Bi2Se3. The Fermi velocity varies an order of magnitude by rotating the crystal axis.
TL;DR: A hydrodynamic description of the resistivity and magnetoresistance of an electron liquid in a smooth disorder potential that is valid when the electron-electron scattering length is sufficiently short is developed.
Abstract: We develop a hydrodynamic description of the resistivity and magnetoresistance of an electron liquid in a smooth disorder potential. This approach is valid when the electron-electron scattering length is sufficiently short. In a broad range of temperatures, the dissipation is dominated by heat fluxes in the electron fluid, and the resistivity is inversely proportional to the thermal conductivity, $\ensuremath{\kappa}$. This is in striking contrast to the Stokes flow, in which the resistance is independent of $\ensuremath{\kappa}$ and proportional to the fluid viscosity. We also identify a new hydrodynamic mechanism of spin magnetoresistance.
TL;DR: In this paper, a tunable and enhanced low-field magnetoresistance (LFMR) was observed in epitaxial (La 0.7Sr 0.3MnO3)0.5 self-assembled vertically aligned nanocomposite (VAN) thin films, which have been grown on SrTiO3 (001) substrates by pulsed laser deposition (PLD).
Abstract: Tunable and enhanced low-field magnetoresistance (LFMR) is observed in epitaxial (La0.7Sr0.3MnO3)0.5:(ZnO)0.5 (LSMO:ZnO) self-assembled vertically aligned nanocomposite (VAN) thin films, which have been grown on SrTiO3 (001) substrates by pulsed laser deposition (PLD). The enhanced LFMR properties of the VAN films reach values as high as 17.5% at 40 K and 30% at 154 K. They can be attributed to the spin-polarized tunneling across the artificial vertical grain boundaries (GBs) introduced by the secondary ZnO nanocolumns and the enhancement of spin fluctuation depression at the spin-disordered phase boundary regions. More interestingly, the vertical residual strain and the LFMR peak position of the VAN films can be systematically tuned by changing the deposition frequency. The tunability of the physical properties is associated with the vertical phase boundaries that change as a function of the deposition frequency. The results suggest that the tunable artificial vertical GB and spin-disordered phase boundary in the unique VAN system with vertical ferromagnetic-insulating-ferromagnetic (FM-I-FM) structure provides a viable route to manipulate the low-field magnetotransport properties in VAN films with favorable epitaxial quality.
TL;DR: Thermally induced spin transport in magnetized zigzag graphene nanoribbons (M-ZGNRs) is explored using first-principles calculations and indicates the possibility of developing graphene-based spin caloritronic devices.
Abstract: Thermally induced spin transport in magnetized zigzag graphene nanoribbons (M-ZGNRs) is explored using first-principles calculations. By applying temperature difference between the source and the drain of a M-ZGNR device, spin-up and spin-down currents flowing in opposite directions can be induced. This spin Seebeck effect in M-ZGNRs can be attributed to the asymmetric electron−hole transmission spectra of spin-up and spin-down electrons. Furthermore, these spin currents can be modulated and completely polarized by tuning the back gate voltage. Finally, thermal magnetoresistance of ZGNRs between ground states and magnetized states can reach 104% without an external bias. Our results indicate the possibility of developing graphene-based spin caloritronic devices.
TL;DR: In this article, the first experimental demonstration of electrical spin injection, transport, and detection in bulk germanium (Ge) was reported and the nonlocal magnetoresistance (MR) in n-type Ge was observable up to 225 K.
Abstract: We report the first experimental demonstration of electrical spin injection, transport, and detection in bulk germanium (Ge). The nonlocal magnetoresistance (MR) in n-type Ge is observable up to 225 K. Our results indicate that the spin relaxation rate in the n-type Ge is closely related to the momentum scattering rate, which is consistent with the predicted Elliot-Yafet spin relaxation mechanism for Ge. The bias dependence of the nonlocal MR and the spin lifetime in n-type Ge is also investigated.
TL;DR: In this article, dilute fluorinated graphene was created using a clean, controlled, and reversible approach, and the zero-field resistance was reduced by a factor of 40 at the highest field of 9 T and shows no sign of saturation.
Abstract: Adatoms offer an effective route to modify and engineer the properties of graphene. In this work, we create dilute fluorinated graphene using a clean, controlled, and reversible approach. At low carrier densities, the system is strongly localized and exhibits an unexpected, colossal negative magnetoresistance. The zero-field resistance is reduced by a factor of 40 at the highest field of 9 T and shows no sign of saturation. Unusual staircaselike field dependence is observed below 5 K. The magnetoresistance is highly anisotropic. These observations cannot be explained by existing theories, but likely require adatom-induced magnetism and/or a metal-insulator transition driven by quantum interference.
25 Aug 2011
TL;DR: In this paper, the authors present an overview of the history of spin transport and magnetoresistance in magnetic tunneling and spin relaxation in Semiconductors, as well as the application of spin relaxation and spin dynamics in the field of spintronics.
Abstract: Introduction Historical Overview: From Electron Transport in Magnetic Materials to Spintronics Albert Fert Spin Transport and Magnetism in Magnetic Metallic Multilayers Basics of Nano-Thin Film Magnetism Bretislav Heinrich Micromagnetism as a Prototype for Complexity. Anthony S. Arrott Giant Magnetoresistance: Experiment Jack Bass Giant Magnetoresistance: Theory Evgeny Y. Tsymbal, D.G. Pettifor, and Sadamichi Maekawa Spin Injection, Accumulation, and Relaxation in Metals Mark Johnson Spin Torque Effects: Experiment Maxim Tsoi Spin Torque in Magnetic Systems: Theory A. Manchon and Shufeng Zhang Hot Carrier Spin Transport Ron Jansen Spin Transport and Magnetism in Magnetic Tunnel Junctions Tunneling Magnetoresistance: Experiment (Non-MgO) Patrick R. LeClair and Jagadeesh S. Moodera Tunnel Magnetoresistance in MgO-Based Magnetic Tunnel JunctionsExperiment Shinji Yuasa Tunneling Magnetoresistance: Theory Kirill D. Belashchenko and Evgeny Y. Tsymbal Spin-Filter Tunneling Tiffany S. Santos and Jagadeesh S. Moodera Spin Torques in Magnetic Tunnel Junctions. Yoshishige Suzuki and Hitoshi Kubota Multiferroic Tunnel Junctions Manuel Bibes and Agnes Barthelemy Spin Transport and Magnetism in Semiconductors Spin Relaxation and Spin Dynamics in Semiconductors Jaroslav Fabian and M.W. Wu Electrical Spin Injection and Transport in Semiconductors Berend T. Jonker Spin-Polarized Ballistic Hot-Electron Injection and Detection in Hybrid Metal Semiconductor Devices Ian Appelbaum Magnetic Semiconductors: IIIV Semiconductors Carsten Timm Magnetism of Dilute Oxides J.M.D. Coey Tunneling Magnetoresistance and Spin Transfer with (Ga,Mn)As H. Jaffres and Jean Marie George Spin Transport in Organic Semiconductors Valentin Dediu, Luis E. Hueso, and Ilaria Bergenti Spin Transport in Ferromagnet/IIIV Semiconductor Heterostructures Paul A. Crowell and Scott A. Crooker Spin Polarization by Current Sergey D. Ganichev, Maxim Trushin, and John Schliemann Anomalous and Spin-Injection Hall Effects Jairo Sinova, Jorg Wunderlich, and Tomas Jungwirth Spin Transport and Magnetism at the Nanoscale Spin-Polarized Scanning Tunneling Microscopy Matthias Bode Point Contact Andreev Ref lection Spectroscopy Boris E. Nadgorny Ballistic Spin Transport. Bernard Doudin and N.T. Kemp Graphene Spintronics Csaba Jozsa and Bart J. van Wees Magnetism and Transport in Diluted Magnetic Semiconductor Quantum Dots Joaquin Fernandez Rossier and R. Aguado Spin Transport in Hybrid Nanostructures Saburo Takahashi and Sadamichi Maekawa Nonlocal Spin Valves in Metallic Nanostructures Yoshichika Otani and Takashi Kimura Molecular Spintronics Stefano Sanvito Applications Magnetoresistive Sensors Based on Magnetic Tunneling Junctions Gang Xiao Magnetoresistive Random Access Memory. Johan Akerman Emerging Spintronics Memories. Stuart Parkin, Masamitsu Hayashi, Luc Thomas, Xin Jiang, Rai Moriya, and William Gallagher GMR Spin-Valve Biosensors Drew A. Hall, Richard S. Gaster, and Shan X. Wang Semiconductor Spin-Lasers Rafal Oszwaldowski, Christian Gothgen, Jeongsu Lee, and Igor Zutic Spin Logic Devices Hanan Dery
TL;DR: In this paper, the superconducting proximity effect in nanoribbons of a candidate topological insulator (Bi{}_{2}$Se${}_{3}$) was observed.
Abstract: We report the observation of the superconducting proximity effect in nanoribbons of a candidate topological insulator (Bi${}_{2}$Se${}_{3}$), which is interfaced with superconducting (tungsten) contacts. We observe a supercurrent and multiple Andreev reflections for channel lengths that are much longer than the inelastic and diffusive thermal lengths deduced from normal-state transport. This suggests that the proximity effect couples preferentially to a ballistic surface transport channel, even in the presence of a coexisting diffusive bulk channel. When a magnetic field is applied perpendicular to the plane of the nanoribbon, we observe magnetoresistance oscillations that are periodic in magnetic field. Quantitative comparison with a model of vortex blockade relates the occurrence of these oscillations to the formation of Pearl vortices in the region of proximity-induced superconductivity.
TL;DR: A review of experimental and theoretical works concerning the investigation of magnetic and structural phase transitions and of the magnetocaloric effect in Ni-Mn-X (X = Ga, In, Sn, Sb) Heusler alloys is given in this article.
Abstract: A review is given of experimental and theoretical works concerning the investigation of magnetic and structural phase transitions and of the magnetocaloric effect in Ni-Mn-X (X = Ga, In, Sn, Sb) Heusler alloys possessing unique properties, such as the existence of coupled magnetostructural and metamagneto-structural phase transitions, giant magnetocaloric effect, shape-memory effect in the ferromagnetic state, giant magnetodeformation and magnetoresistance, exchange anisotropy. A conclusion is made that the Heusler alloys, because of their unique properties, are promising for the application in various engineering devices, including technology of magnetic refrigeration.
Journal Article•
TL;DR: In this paper, the authors derive diffusion equations that describe spin-charge coupled transport on the helical metal surface of a three-dimensional topological insulator and demonstrate tunability of this effect by applying a gate voltage, which makes it possible to operate the proposed device as a transistor.
Abstract: We derive diffusion equations, which describe spin-charge coupled transport on the helical metal surface of a three-dimensional topological insulator. The main feature of these equations is a large magnitude of the spin-charge coupling, which leads to interesting and observable effects. In particular, we predict a new magnetoresistance effect, which manifests in a non-Ohmic correction to a voltage drop between a ferromagnetic spin-polarized electrode and a nonmagnetic electrode, placed on top of the helical metal. This correction is proportional to the cross product of the spin polarization of the ferromagnetic electrode and the charge current between the two electrodes. We also demonstrate tunability of this effect by applying a gate voltage, which makes it possible to operate the proposed device as a transistor.
TL;DR: In this paper, the voltage-induced anisotropy change in an epitaxial magnetic tunnel junction (MTJ) with an ultrathin FeCo layer was investigated under various bias voltage applications for different FeCo thicknesses.
Abstract: We investigated the voltage-induced perpendicular magnetic anisotropy change in an epitaxial magnetic tunnel junction (MTJ) with an ultrathin FeCo layer. Tunneling magnetoresistance (TMR) curves were measured under various bias voltage applications for different FeCo thicknesses. Clear changes in the shape of TMR curves were observed depending on the voltage-controlled perpendicular magnetic anisotropy. By evaluating the relative angle of two ferromagnetic layers, we could estimate the anisotropy energy change quantitatively. The realization of voltage-induced anisotropy change in the MTJ structure makes it possible to control the magnetization dynamics, leading to a new area of electric-field-based spintronics devices.
TL;DR: Spin-dependent features in the conductivity of graphene, chemically modified by a random distribution of hydrogen adatoms, are explored theoretically and could serve as guidance for experimental observation of induced magnetism in graphene.
Abstract: Spin-dependent features in the conductivity of graphene, chemically modified by a random distribution of hydrogen adatoms, are explored theoretically. The spin effects are taken into account using a mean-field self-consistent Hubbard model derived from first-principles calculations. A Kubo transport methodology is used to compute the spin-dependent transport fingerprints of weakly hydrogenated graphene-based systems with realistic sizes. Conductivity responses are obtained for paramagnetic, antiferromagnetic, or ferromagnetic macroscopic states, constructed from the mean-field solutions obtained for small graphene supercells. Magnetoresistance signals up to similar to 7% are calculated for hydrogen densities around 0.25%. These theoretical results could serve as guidance for experimental observation of induced magnetism in graphene.
TL;DR: Using first-principles calculations, the possibility of functionalized graphene as a high-performance two-dimensional spintronics device is explored and a spin-valve device is constructed by introducing a magnetic field to stabilize its metallic ferromagnetic state.
Abstract: Using first-principles calculations, we explore the possibility of functionalized graphene as a high-performance two-dimensional spintronics device. Graphene functionalized with O on one side and H on the other side in the chair conformation is found to be a ferromagnetic metal with a spin-filter efficiency up to 54% at finite bias. The ground state of graphene semifunctionalized with F in the chair conformation is an antiferromagnetic semiconductor, and we construct a spin-valve device from it by introducing a magnetic field to stabilize its metallic ferromagnetic state. The resulting room-temperature magnetoresistance is up to 2200%, which is 1 order of magnitude larger than the available experimental values.
TL;DR: In this article, an energy-efficient technique for electrically modulating magnetoresistance was demonstrated in multiferroic anisotropic magnetorsistance (AMR) and GMR heterostructures using a giant electric field induced magnetic anisotropy caused by a strong magnetoelectric coupling.
Abstract: An energy-efficiency technique for electrically modulating magnetoresistance was demonstrated in multiferroic anisotropic magnetoresistance (AMR) and giant magnetoresistance (GMR) heterostructures. A giant electric field (E-field) induced magnetic anisotropy caused by a strong magnetoelectric coupling was utilized to control the orientation of magnetization and thus dynamically manipulate magnetoresistance in AMR and GMR devices. A multiband tunable AMR field sensor was designed and developed to dramatically enhance the measurement range by 15 times. In addition, two types of E-field determination of GMR in spin-valve structures are studied. The results indicate an energy efficiency approach to controlling magnetoresistance by E-field rather than magnetic field, which shows great potential for novel low power electronic and spintronic devices.
TL;DR: In this article, the transport properties of the semiconductor HgTe-based quantum well, recently shown to be a two-dimensional topological insulator, are studied experimentally in the diffusive regime.
Abstract: The transport properties of the ``inverted'' semiconductor HgTe-based quantum well, recently shown to be a two-dimensional topological insulator, are studied experimentally in the diffusive regime. Nonlocal transport measurements are performed in the absence of magnetic field, and a large signal due to the edge states is observed. This shows that the edge states can propagate over a long distance, $\ensuremath{\sim}$1 mm, and therefore, there is no difference between local and nonlocal electrical measurements in a topological insulator. In the presence of an in-plane magnetic field a strong decrease of the local resistance and complete suppression of the nonlocal resistance is observed. We attribute this behavior to an in-plane magnetic-field-induced transition from the topological insulator state to a conventional bulk metal state.
TL;DR: The results show that pairs of electron and hole Dirac cone states must be taken into account for an accurate interpretation in iron pnictides, which is in contrast with previous studies.
Abstract: Quantum transport of Dirac cone states in the iron pnictide Ba(FeAs)(2) with a d-multiband system is studied by using single crystal samples. Transverse magnetoresistance develops linearly against the magnetic field at low temperatures. The transport phenomena are interpreted in terms of the zeroth Landau level by applying the theory predicted by Abrikosov. The results of the semiclassical analyses of a two carrier system in a low magnetic field limit show that both the electron and hole reside as the high mobility states. Our results show that pairs of electron and hole Dirac cone states must be taken into account for an accurate interpretation in iron pnictides, which is in contrast with previous studies.
Patent•
05 May 2011TL;DR: In this paper, a low-resistance magnetoresistive element of a spin-injection write type is presented, where a crystallization promoting layer that promotes crystallization is formed in contact with an interfacial magnetic layer having an amorphous structure.
Abstract: The present invention provides a low-resistance magnetoresistive element of a spin-injection write type. A crystallization promoting layer that promotes crystallization is formed in contact with an interfacial magnetic layer having an amorphous structure, so that crystallization is promoted from the side of a tunnel barrier layer, and the interface between the tunnel barrier layer and the interfacial magnetic layer is adjusted. With this arrangement, it is possible to form a magnetoresistive element that has a low resistance so as to obtain a desired current value, and has a high TMR ratio.