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1.
在NM/FI/FI/NM型双自旋过滤隧道结(此处NM为非磁金属层,FI为铁磁绝缘体或半导体层)的基础上,我们提出一种NM/FI/NI/FI/NM新型双自旋过滤隧道结(此处NI表示非磁绝缘体或半导体层). 插入NI层的目的是为了避免原双自旋过滤隧道结中相邻FI层界面处磁的耦合作用所导致的对隧穿磁电阻的不利影响. 在自由电子近似的基础上,利用转移矩阵方法,对NM/FI/NI/FI/NM新型双自旋过滤隧道结的隧穿电导、隧穿磁电阻与FI层及NI层厚度的变化关系以及随偏压的变化关系进行了理论研究.计算结果表明,在NM/FI/NI/FI/NM新型双自旋过滤隧道结中仍可以得到很大的TMR值.
关键词:
双自旋过滤隧道结
隧穿磁电阻
非磁绝缘(半导)体间隔层 相似文献
2.
DONG Zheng-Chao 《理论物理通讯》2004,41(1):135-140
The tunneling conductance and tunneling magnetoresistance (TMR) are
investigated in ferromagnet/insulator/ferromagnet/insulator/d-wave
superconductor (FM/I/FM/I/d-wave SC) structures by applying an extended
Blonder-Tinkham-Klapwijk (BTK) approach. We study the effects of the
exchange splitting in the FM, the magnetic impurity scattering in the thin
insulator interface of FM/I/FM, and noncollinear magnetizations in adjacent
magnetic layers on the TMR. It is shown (1) that the tunneling conductance
and TMR exhibit amplitude-varying oscillating behavior with exchange
splitting, (2) that with the presence of spin-flip scattering in insulator
interface of FM/I/FM, the TMR can be dramatically enhanced, and (3)
that the TMR depends strongly on the angle between the magnetization of two
FMs. 相似文献
3.
K. Tamanoi M. Sato M. Oogane Y. Ando T. Tanaka Y. Uehara T. Uzumaki 《Journal of magnetism and magnetic materials》2008
We measured inelastic electron tunneling (IET) spectra and conductance for MgO tunneling magnetoresistance (TMR) films to obtain information on the ferromagnetic/barrier layer interface. The IET spectra showed the difference between amorphous and crystalline structures in the barrier. In the magnetic tunnel junction (MTJ) with a crystalline barrier the IET spectra indicated an Mg-O phonon peak at a low bias voltage by measurement with a parallel magnetization configuration. On the other hand, no peak was observed in the MTJ with an amorphous barrier. 相似文献
4.
5.
We investigate the spin-dependent tunneling transport in a heterostructure with two single molecular magnets (SMMs). The tunneling magnetoresistance (TMR) and negative differential conductance due to the strong resonant tunneling in the junction are demonstrated by the master equation approach. At low bias voltage, the device presents low/high resistant states with the initial states of the single molecular magnets parallel/antiparallel. Strong Coulomb repulsive interaction suppresses the current greatly in antiparallel situation. At high voltage, the middle system containing two SMMs tends to be non-polarized, and acts like ordinary quantum dots. 相似文献
6.
The variation of the tunnel spin-polarization (TSP) with energy is determined using a magnetic tunnel transistor, allowing quantification of the energy dependent TSP separately for both ferromagnet/insulator interfaces and direct correlation with the tunnel magnetoresistance (TMR) measured in the same device. The intrinsic TSP is reduced below the Fermi level, and more strongly so for tunneling into empty states above the Fermi level. For artificially doped barriers, the low bias TMR decreases due to defect-assisted tunneling. Yet, this mechanism becomes ineffective at large bias, where instead inelastic spin scattering causes a strong TMR decay. 相似文献
7.
The Keldysh nonequilibrium Green's function method is utilized to theoretically study spin-polarized transport through a graphene spin valve irradiated by a monochromatic laser field. It is found that the bias dependence of the differential conductance exhibits successive peaks corresponding to the resonant tunneling through the photon-assisted sidebands. The multi-photon processes originate from the combined effects of the radiation field and the graphene tunneling properties, and are shown to be substantially suppressed in a graphene spin valve which results in a decrease of the differential conductance for a high bias voltage. We also discuss the appearance of a dynamical gap around zero bias due to the radiation field. The gap width can be tuned by changing the radiation electric field strength and the frequency. This leads to a shift of the resonant peaks in the differential conductance. We also demonstrate numerically the dependences of the radiation and spin valve effects on the parameters of the external fields and those of the electrodes. We find that the combined effects of the radiation field, the graphene and the spin valve properties bring about an oscillatory behavior in the tunnel magnetoresistance, and this oscillatory amplitude can be changed by scanning the radiation field strength and/or the frequency. 相似文献
8.
A recent theoretical estimation indicated that the NM/FI/FI/NM double spin-filter junction (DSFJ, here the NM and FI represent the nonmagnetic electrode and the ferromagnetic insulator (semiconductor) spacer, respectively) could have very high tunneling magnetoresistance (TMR) at zero bias. To meet the requirement in research and application of the magnetoresistance devices, we have calculated the dependences of tunneling magnetoresistance of DSFJ on the bias (voltage), the thicknesses of ferromagnetic insulators (semiconductors) and the average barrier height. Our results show that except its very high value, the TMR of DSFJ does not decrease monotonously and rapidly with rising bias, but increase slowly at first and decrease then after having reached a maximum value. This feature is in distinct contrast to the ordinary magnetic tunnel junction FM/NI/FM (FM and NI denote the ferromagnetic electrode and the nonmagnetic insulator (semiconductor) spacer, respectively), and is of benefit to the use of DSFJ as a magnetoresistance device. 相似文献
9.
In a joint experimental and theoretical study, we investigate the bias-voltage dependence of the tunnel magnetoresistance (TMR) through a vacuum barrier. The TMR observed by spin-polarized scanning tunneling microscopy between an amorphous magnetic tip and a Co(0001) sample is almost independent of the bias voltage at large tip-sample separations. Whereas qualitative understanding is achieved by means of the electronic surface structure of Co, the experimental findings are compared quantitatively with bias-voltage dependent first-principles calculations for ballistic tunneling. At small tip-sample separations, a pronounced minimum in the experimental TMR was found at +200 mV bias. 相似文献
10.
11.
M. J. Ma M. B. A. Jalil S. G. Tan D. E. Koh 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,82(1):37-46
We theoretically study the spin-polarized transport
through double barrier magnetic tunnel junction (DBMTJ) consisting
of the quantum dot sandwiched by two ferromagnetic (FM) leads. The
tunneling current through the DBMTJ is evaluated based on the
Keldysh nonequilibrium Green’s function approach. The self-energy
and Green’s function of the dot are analytically obtained via the
equation of motion method, by systematically incorporating two
spin-flip phenomena, namely, intra-dot spin-flip, and spin-flip
coupling between the lead and the central dot region. The effects of
both spin-flip processes on the spectral functions, tunneling
current and tunnel magnetoresistance (TMR) are analyzed. The
spin-flip effects result in spin mixing, thus contributing to the
spectral function of the off-diagonal Green’s function components ( Gs[`(s)] r )\left( {G_{\sigma \bar \sigma }^r } \right). Interestingly, the spin-flip coupling
between the lead and dot enhances both the tunneling current and the
TMR for applied bias above the threshold voltage V
th
. On the
other hand, the intra-dot spin-flip results in an additional step in
the I-V characteristics near V
th
. Additionally, it
suppresses the tunneling current but enhances the TMR. The opposing
effects of the two types of spin-flip on the tunneling current means
that one spin-flip mechanism can be engineered to counteract the
other, so as to maintain the tunneling current without reducing the
TMR. Their additive effect on the TMR enables the DBMTJ to attain a
large tunneling current and high TMR for above threshold bias
values. 相似文献
12.
《中国物理 B》2015,(11)
Using the density functional theory and the nonequilibrium Green's function method, we studied the finite-bias quantum transport in a Cr/graphene/Cr magnetotunnel junction(MTJ) constructed by a single graphene layer sandwiched between two semi-infinite Cr(111) electrodes. We found that the tunneling magnetoresistance(TMR) ratio in this MTJ reached108%, which is close to that of a perfect spin filter. Under an external positive bias, we found that the TMR ratio remained constant at 65%, in contrast to Mg O-based MTJs, the TMR ratios of which decrease with increasing bias. These results indicate that the Cr/graphene/Cr MTJ is a promising candidate for spintronics applications. 相似文献
13.
LI Xiao-Wei 《理论物理通讯》2008,49(5):1345-1348
We have studied the quasiparticle transport in quantum-wire
/ferromagnetic-insulator/d wave superconductor Junction (q/FI/d) in the
framework of the Blonder-Tinkham-Klapwijk model. We calculate the tunneling conductance in q/FI/d as a function of the bias voltage at zero temperature and finite temperature based on Bogoliubov-de Gennes equations. Different from the case in normal-metal/insulator/d wave superconductor Junctions, the zero-bias conductance peaks vanish for the single-mode case. The tunneling conductance spectra depend on the magnitude of the exchange interaction at the ferromagnetic-insulator. 相似文献
14.
Based on the nearly-free-electron approximation, the bias dependencies of electron transport properties of ferromagnet/ferromagnetic insulator (semiconductor)/ferromagnet junctions have been studied. Resonances appear in electron transmission probability. These resonances cause oscillations in the zero-temperature tunnel current and the resonances occur in tunnel conductance. Tunnel magnetoresistance (TMR) is an oscillatory function of bias. The TMR can reach a value as high as 100%. The bins dependencies of electron transport properties relate to the magnetic configurations of the junctions. 相似文献
15.
Brun C Müller KH Hong IP Patthey F Flindt C Schneider WD 《Physical review letters》2012,108(12):126802
Electrical contacts between nanoengineered systems are expected to constitute the basic building blocks of future nanoscale electronics. However, the accurate characterization and understanding of electrical contacts at the nanoscale is an experimentally challenging task. Here, we employ low-temperature scanning tunneling spectroscopy to investigate the conductance of individual nanocontacts formed between flat Pb islands and their supporting substrates. We observe a suppression of the differential tunnel conductance at small bias voltages due to dynamical Coulomb blockade effects. The differential conductance spectra allow us to determine the capacitances and resistances of the electrical contacts which depend systematically on the island-substrate contact area. Calculations based on the theory of environmentally assisted tunneling agree well with the measurements. 相似文献
16.
Bo Chang 《Physics letters. A》2010,374(29):2985-2938
We report a theoretical analysis of electron transport through a quantum dot with an embedded biaxial single-molecule magnet (SMM) based on mapping of the many-body interaction-system onto a one-body problem by means of the non-equilibrium Green function technique. It is found that the conducting current exhibits a stepwise behavior and the nonlinear differential conductance displays additional peaks with variation of the sweeping speed and the magnitude of magnetic field. This observation can be interpreted by the interaction of electron-spin with the SMM and the quantum tunneling of magnetization. The inelastic conductance and the corresponding tunneling processes are investigated with normal as well as ferromagnetic electrodes. In the case of ferromagnetic configuration, the coupling to the SMM leads to an asymmetric tunneling magnetoresistance (TMR), which can be enhanced or suppressed greatly in certain regions. Moreover, a sudden TMR-switch with the variation of magnetic field is observed, which is seen to be caused by the inelastic tunneling. 相似文献
17.
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
18.
《Journal of magnetism and magnetic materials》2002,251(2):163-168
Taking into account the nonequilibrium spin accumulation, we apply a quantum-statistical approach to study the spin-polarized transport in a two-dimensional ferromagnet/semiconductor/ferromagnet (FM/SM/FM) double tunnel junction. It is found that the effective spin polarization is raised by increasing the barrier strength, resulting in an enhancement of the tunneling magnetoresistance (TMR). The nonequilibrium spin accumulation in SM may appear in both antiparallel and parallel alignments of magnetizations in two FMs, in particular for high bias voltages. The effects of spin accumulation and TMR on the bias voltage are discussed. 相似文献
19.
Oka H Tao K Wedekind S Rodary G Stepanyuk VS Sander D Kirschner J 《Physical review letters》2011,107(18):187201
We investigate the local tunnel magnetoresistance (TMR) effect within a single Co nanoisland using spin-polarized scanning tunneling microscopy. We observe a clear spatial modulation of the TMR ratio with an amplitude of ~20% and a spacing of ~1.3 nm between maxima and minima around the Fermi level. This result can be ascribed to a spatially modulated spin polarization within the Co island due to spin-dependent quantum interference. Our combined experimental and theoretical study reveals that spin-dependent electron confinement affects all transport properties such as differential conductance, conductance, and TMR. We demonstrate that the TMR within a nanostructured magnetic tunnel junction can be controlled on a length scale of 1 nm through spin-dependent quantum interference. 相似文献
20.
We study the electronic transport through a single-molecule transistor (SMT) by considering the phonon-associated tunneling rate. We find that the electron-phonon interaction (EPI) changes the constant conductivities of the leads into a multi-channel structure of single vibration frequency. This interference of the multi-channel tunneling process results in a bias-dependent tunneling rate and obscures the conductance peaks at large bias voltage. The bias-dependent tunneling rate further causes a remarkable conductivity gap between the chemical potential of the leads (n=0) and the first phonon sideband (n=1). These anomalies are consistent with the experimental observations in transport experiments. 相似文献