共查询到20条相似文献,搜索用时 31 毫秒
1.
We predict an anomalous bias dependence of the spin transfer torque parallel to the interface, Tparallel, in magnetic tunnel junctions, which can be selectively tuned by the exchange splitting. It may exhibit a sign reversal without a corresponding sign reversal of the bias or even a quadratic bias dependence. We demonstrate that the underlying mechanism is the interplay of spin currents for the ferromagnetic (antiferromagnetic) configurations, which vary linearly (quadratically) with bias, respectively, due to the symmetric (asymmetric) nature of the barrier. The spin transfer torque perpendicular to interface exhibits a quadratic bias dependence. 相似文献
2.
Recent data on the bias dependence of the spin transfer effect in magnetic tunnel junctions have shown that torque remains intact at bias voltages for which the tunneling magnetoresistance has been strongly reduced. We show that the current induced excitations due to hot electrons, while reducing the magnetoresistance, enhance both the charge current and the spin transfer in magnetic tunnel junctions in such a manner that the ratio of the torque to the charge current does not significantly change. 相似文献
3.
Samir Garzon Richard A. Webb Shehzaad Kaka 《Journal of magnetism and magnetic materials》2009,321(19):3225-3230
In large magnetoresistance devices spin torque-induced changes in resistance can produce GHz current and voltage oscillations which can affect magnetization reversal. In addition, capacitive shunting in large resistance devices can further reduce the current, adversely affecting spin torque switching. Here, we simultaneously solve the Landau-Lifshitz-Gilbert equation with spin torque and the transmission line telegrapher's equations to study the effects of resistance feedback and capacitance on magnetization reversal of both spin valves and magnetic tunnel junctions. While for spin valves parallel (P) to anti-parallel (AP) switching is adversely affected by the resistance feedback due to saturation of the spin torque, in low resistance magnetic tunnel junctions P-AP switching is enhanced. We study the effect of resistance feedback on the switching time of magnetic tunnel junctions, and show that magnetization switching is only affected by capacitive shunting in the pF range. 相似文献
4.
Fuchs GD Katine JA Kiselev SI Mauri D Wooley KS Ralph DC Buhrman RA 《Physical review letters》2006,96(18):186603
We employ the spin-torque response of magnetic tunnel junctions with ultrathin MgO tunnel barrier layers to investigate the relationship between spin transfer and tunnel magnetoresistance (TMR) under finite bias, and find that the spin torque per unit current exerted on the free layer decreases by < 10% over a bias range where the TMR decreases by > 40%. This is inconsistent with free-electron-like spin-polarized tunneling and reduced-surface-magnetism models of the TMR bias dependence, but is consistent with magnetic-state-dependent decay lengths in the tunnel barrier. 相似文献
5.
Perpendicular magnetic tunnel junction and its application in magnetic random access memory
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Recent progresses in magnetic tunnel junctions with perpendicular magnetic anisotropy(PMA) are reviewed and summarized. At first, the concept and source of perpendicular magnetic anisotropy(PMA) are introduced. Next, a historical overview of PMA materials as magnetic electrodes, such as the RE–TM alloys TbFeCo and GdFeCo, novel tetragonal manganese alloys Mn–Ga, L10-ordered(Co, Fe)/Pt alloy, multilayer film [Co, Fe, CoFe/Pt, Pd, Ni, Au]N, and ultra-thin magnetic metal/oxidized barrier is offered. The other part of the article focuses on the optimization and fabrication of CoFeB/MgO/CoFeB p-MTJs, which is thought to have high potential to meet the main demands for non-volatile magnetic random access memory. 相似文献
6.
Chantis AN Belashchenko KD Smith DL Tsymbal EY van Schilfgaarde M Albers RC 《Physical review letters》2007,99(19):196603
A minority-spin resonant state at the Fe/GaAs(001) interface is predicted to reverse the spin polarization with the voltage bias of electrons transmitted across this interface. Using a Green's function approach within the local spin-density approximation, we calculate the spin-dependent current in a Fe/GaAs/Cu tunnel junction as a function of the applied bias voltage. We find a change in sign of the spin polarization of tunneling electrons with bias voltage due to the interface minority-spin resonance. This result explains recent experimental data on spin injection in Fe/GaAs contacts and on tunneling magnetoresistance in Fe/GaAs/Fe magnetic tunnel junctions. 相似文献
7.
We investigate bias and different barrier thicknesses effects on quantities related to spin and charge currents in MgO-based magnetic tunnel junctions. Using the non-Equilibrium Green's function formalism, we demonstrate that the in-plane and out-of-plane components of the spin-transfer torque have asymmetric and symmetric behaviors respectively. Magneto-resistance also decreases with increasing barrier thickness. The Landau–Lifshits–Gilbert equation describes the dynamics of the magnetization made by spin transfer torque. Increasing in spin current above its critical value or smaller the magnet reduces the switching time which is major result for making of new memory devices. 相似文献
8.
Petit S Baraduc C Thirion C Ebels U Liu Y Li M Wang P Dieny B 《Physical review letters》2007,98(7):077203
Voltage noise measurements were performed in the 3-7 GHz frequency range on magnetic tunnel junctions biased with a dc current. Magnetic noise associated with ferromagnetic resonance excitations is either amplified or reduced depending on the direction of the bias current. This effect is interpreted as the influence of spin transfer torque on the magnetization fluctuations and described using Gilbert dynamics equation including spin transfer torque and effective field terms. 相似文献
9.
Tunneling current in a ferromagnet/superconductor/ferromagnet double tunnel junction induces a nonequilibrium spin accumulation in the superconductor. We study theoretically the response of such a system to applied magnetic field. We show that the interplay between the magnetic field and the spin accumulation could lead to novel bias voltage dependence and magnetic field dependence of the superconducting gap function, and bring in anomalous asymmetry in the spin-dependent transport. Our study also indicates a possible application of the spin injection. 相似文献
10.
Wilczyński M 《J Phys Condens Matter》2011,23(45):456001
The thermopower, charge and thermal conductance, and figure of merit as well as the spin-transfer torque generated by the temperature gradient in the planar tunnel junction consisting of ferromagnetic layers and the nonmagnetic tunnel barrier are investigated in the free-electron-like spin-polarized one-band model. In particular, the influence of the parameters of the junction as well as the influence of the relative orientation of magnetic moments on the studied phenomena are investigated. The thermopower can be related to the voltage drop generated by the temperature difference between electrodes under the condition that the charge current vanishes. It depends on the magnetic configuration of the junction. In junctions with high barriers the thermopower is maximal in the antiparallel configuration and it can be enhanced in junctions with strong spin-splitting of the electron bands. The component of the torque studied in the present paper is oriented in the plane formed by magnetic moments and it appears in the absence of the bias voltage. Its magnitude is insensitive to the sign of the temperature difference in contrast to the bias-induced in-plane torque which strongly depends on the polarization of the bias. The studied torque is usually smaller than the torque generated by the bias: however, it can be significant in junctions with low barriers. 相似文献
11.
We theoretically explore the spin transport through nano-structures consisting of two serially coupled single-molecular magnets (SMM) sandwiched between two nonmagnetic electrodes. We find that the magnetization of SMM can be controlled by the spin transfer torque with respect to the bias voltage direction, and the electron current can be switched on/off in different magnetic structures. Such a manipulation is performed by full electrical manner, and needs neither external magnetic field nor ferromagnetic electrodes in the tunneling junction. The proposal device scheme can be realized with the use of the present technology [6] and has potential applications in molecular spintronics or quantum information processing. 相似文献
12.
An overview of recent experimental studies and new routes in the field of current-driven magnetization dynamics in nanostructured materials is given. The review introduces the basic concepts (Landau–Lifshitz phenomenology, critical current, spin currents in relation to spin accumulation, adiabatic/non-adiabatic spin-torque) and describes the main results of recent experiments on current-driven magnetization reversal within vertical pillar-like nanostructures and current-driven domain wall motion within laterally confined specimens. While for the pillar systems a discussion is provided of how the introduction of layers with perpendicular magnetic anisotropy, tunnel barriers and exchange bias and(or) oxide layers can be used to reduce the critical current densities for current-induced switching, the role of perpendicular anisotropy, use of spin valve structures, diluted magnetic semiconductors and epitaxial materials to increase the domain wall velocities are reviewed in the case of current-driven domain wall movement within lateral systems. 相似文献
13.
F. Romeo R. Citro 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(3):483-489
We study the spin polarized currents generation in a magnetic
(ferromagnetic/ferromagnetic) tunnel junction by means of
adiabatic quantum pumping. Using a scattering matrix approach, it
is shown that a pure spin current can be pumped from one
ferromagnetic lead into the adjacent one by adiabatic modulation
of the magnetization and the height of the barrier at the
interface in absence of external bias voltage. We numerically
study the characteristic features of the pure spin current and
discuss its behavior for realistic values of the parameters. We
show that the generated pure spin current is robust with respect
to the variation of the magnetization strength, a very important
feature for a realistic device, and that the proposed device can
operate close to the optimal pumping regime. An experimental
realization of a pure spin current injector is also discussed. 相似文献
14.
Lou X Adelmann C Furis M Crooker SA Palmstrøm CJ Crowell PA 《Physical review letters》2006,96(17):176603
We show that the accumulation of spin-polarized electrons at a forward-biased Schottky tunnel barrier between Fe and -GaAs can be detected electrically. The spin accumulation leads to an additional voltage drop across the barrier that is suppressed by a small transverse magnetic field, which depolarizes the spins in the semiconductor. The dependence of the electrical accumulation signal on magnetic field, bias current, and temperature is in good agreement with the predictions of a drift-diffusion model for spin-polarized transport. 相似文献
15.
Yu. A. Chesnokov A. G. Afonin V. T. Baranov G. I. Britvich P. N. Chirkov V. A. Maisheev D. A. Savin V. I. Terekhov 《Journal of Experimental and Theoretical Physics》2018,126(1):115-125
Dependences of the tunnel magnetoresistance and in-plane component of the spin transfer torque on the applied voltage in a magnetic tunnel junction have been calculated in the approximation of ballistic transport of conduction electrons through an insulating layer with embedded magnetic or nonmagnetic nanoparticles. A single-barrier magnetic tunnel junction with a nanoparticle embedded in an insulator forms a double-barrier magnetic tunnel junction. It has been shown that the in-plane component of the spin transfer torque in the double-barrier magnetic tunnel junction can be higher than that in the single-barrier one at the same thickness of the insulating layer. The calculations show that nanoparticles embedded in the tunnel junction increase the probability of tunneling of electrons, create resonance conditions, and ensure the quantization of the conductance in contrast to the tunnel junction without nanoparticles. The calculated dependences of the tunnel magnetoresistance correspond to experimental data demonstrating peak anomalies and suppression of the maximum magnetoresistances at low voltages. 相似文献
16.
17.
J. Xiao A. Zangwill M. D. Stiles 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(4):415-427
We present a numerical algorithm to solve the Boltzmann
equation for the electron distribution function in magnetic multilayer
heterostructures with non-collinear magnetizations. The solution is
based on a scattering matrix formalism for layers that are
translationally invariant in plane so that properties only vary
perpendicular to the planes. Physical quantities like spin density,
spin current, and spin-transfer torque are calculated directly from
the distribution function. We illustrate our solution method with a
systematic study of the spin-transfer torque in a spin valve as a
function of its geometry. The results agree with a
hybrid circuit theory developed by Slonczewski for geometries typical
of those measured experimentally. 相似文献
18.
利用Landau-Lifshitz-Gilbert-Slonczewski方程, 在理论上研究了由磁矩垂直于膜面的自由层和磁矩平行于膜面的极化层组成的自旋转矩振荡器的振荡特性. 数值结果表明面内的形状各向异性能, 可以使自旋转矩振荡器在无磁场情形下产生自激振荡. 此特性可以用能量平衡方程解释, 即面内形状各向异性能可以导致系统中自旋转矩提供的能量与阻尼过程所消耗的能量之间的平衡. 特别是, 面内的形状各向异性能越大, 自旋转矩振荡器的可操控电流范围越大, 并且产生微波信号的频率越大, 但其阈值电流几乎不变. 相似文献
19.
Dependence of switching process on the perpendicular magnetic anisotropy constant in P-MTJ
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We investigate the dependence of the switching process on the perpendicular magnetic anisotropy(PMA) constant in perpendicular spin transfer torque magnetic tunnel junctions(P-MTJs) using micromagnetic simulations. It is found that the final stable states of the magnetization distribution of the free layer after switching can be divided into three different states based on different PMA constants: vortex, uniform, and steady. Different magnetic states can be attributed to a trade-off among demagnetization, exchange, and PMA energies. The generation of the vortex state is also related to the non-uniform stray field from the polarizer, and the final stable magnetization is sensitive to the PMA constant. The vortex and uniform states have different switching processes, and the switching time of the vortex state is longer than that of the uniform state due to hindrance by the vortex. 相似文献
20.
Reyren N Bibes M Lesne E George JM Deranlot C Collin S Barthélémy A Jaffrès H 《Physical review letters》2012,108(18):186802
We report results of electrical spin injection at the high-mobility quasi-two-dimensional electron system (2-DES) that forms at the LaAlO3/SrTiO3 interface. In a nonlocal, three-terminal measurement geometry, we analyze the voltage variation associated with the precession of the injected spin accumulation driven by perpendicular or transverse magnetic fields (Hanle and inverted Hanle effect). The influence of bias and back-gate voltages reveals that the spin accumulation signal is amplified by resonant tunneling through localized states in the LaAlO3 strongly coupled to the 2-DES by tunneling transfer. 相似文献