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1.
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
2.
L. F. Zhang C. Xu P. M. Hui Y. Q. Ma 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(3):305-309
The tunneling magnetoresistance (TMR) of a small magnetic dot
array with perpendicular anisotropy, is studied by using a
resistor network model. Because of the competition between dipolar
interaction and perpendicular anisotropy, the TMR ratio can be up
to a maximum value (~26%) as predicted by a theoretical
model. At moderate dipolar interaction strength, the perpendicular
TMR ratio exhibits abrupt jumps due to the switching of magnetic
moments in the array when the applied field (normal to the array
plane) decreases from a saturation field. This novel character
does not occur if the dipolar interaction between particles is
quite strong. Furthermore, the effect of the array size N on TMR
is also studied and the result shows that TMR ratio fluctuates
when N increases for a moderate dipolar interaction strength.
When the applied field he is parallel to the array plane, the
in-plane TMR curve seems insensitive to the dipolar interaction
strength, but the maximum TMR ratio (~26%) can also be
obtained at he=0. 相似文献
3.
J. Mathon 《Phase Transitions》2013,86(4-5):491-500
Rigorous theory of the tunneling magnetoresistance (TMR) based on the real-space Kubo formula and fully realistic tight-binding bands fitted to an ab initio band structure is described. It is first applied to calculate the TMR of two Co electrodes separated by a vacuum gap. The calculated TMR ratio reaches , 65% in the tunneling regime but can be as high as 280% in the metallic regime when the vacuum gap is of the order of the Co interatomic distance (abrupt domain wall). It is also shown that the spin polarization P of the tunneling current is negative in the metallic regime but becomes positive P , 35% in the tunneling regime. Calculation of the tunneling magnetoresistance of an epitaxial Fe/MgO/Fe(001) junction is also described. The calculated optimistic TMR ratio is in excess of 1000% for an MgO barrier of , 20 atomic planes and the spin polarization of the tunneling current is positive for all MgO thicknesses. It is also found that spin-dependent tunneling in an Fe/MgO/Fe(001) junction is not entirely determined by states at the o point ( k =0) even for MgO thicknesses as large as , 20 atomic planes. Finally, it is demonstrated that the TMR ratio calculated from the Kubo formula remains nonzero when one of the Co electrodes is covered with a copper layer. It is shown that non-zero TMR is due to quantum well states in the Cu layer which do not participate in transport. Since these only occur in the down-spin channel, their loss from transport creates a spin asymmetry of electrons tunneling from a Cu interlayer, i.e. non-zero TMR. Numerical modeling is used to show that diffuse scattering from a random distribution of impurities in the barrier may cause quantum well states to evolve into propagating states, in which case the spin asymmetry of the nonmagnetic layer is lost and with it the TMR. 相似文献
4.
Y.C. Tao X.F. Jiang J. Wang D.Y. Xing 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(4):463-469
An extended tunneling Hamiltonian method is proposed to study the temperature-dependent tunneling magnetoresistance (TMR)
in doped magnetic tunnel junctions. It is found that for nonmagnetic dopants (Si), impurity-assisted tunneling is mainly elastic,
giving rise to a weak spin polarization, thereby reduces the overall TMR, while for magnetic ions (Ni), the collective excitation
of local spins in δ-doped magnetic layer contributes to the severe drop of TMR and the behavior of the variation of TMR with
temperature different from that for Si-doping. The theoretical results can reproduce the main characteristic features of experiments.
Received 13 January 2002 / Received in final form 30 November 2002 Published online 6 March 2003
RID="a"
ID="a"e-mail: yctao12@163.com 相似文献
5.
J. H. Lee In-Woo Chang S. J. Byun K. Rhie Kyung-Ho Shin Kyung-Il Lee J. G. Ha B. C. Lee 《Journal of magnetism and magnetic materials》2002,240(1-3):149-151
The temperature dependence of the tunneling magnetoresistance (TMR) for magnetic tunneling junctions is investigated experimentally before and after the sample is annealed. As grown, the TMR is observed to increase with temperature from 80 to 160 K. A modified Julliere model in conjunction with a spin-dependent two-step tunneling is suggested to describe this temperature dependence. 相似文献
6.
Q.L. Ma J.F. Feng Gen Feng X.F. Han 《Journal of magnetism and magnetic materials》2010,322(1):108-111
MgO-based magnetic tunnel junctions were fabricated, with a thin pinned CoFeB layer in the unbalanced synthetic antiferromagnet part of the stack FeMn/CoFe/Ru/CoFeB. Inverted and normal tunneling magnetoresistance (TMR) values occur at low and high annealing temperatures (Ta), respectively. The TMR ratio remains inverted up to Ta=300 °C and it becomes normal around Ta=350 °C. The exchange bias of FeMn disappears at high Ta. The sign reversal of the TMR ratio is mainly attributed to the disappearance of the exchange bias due to manganese diffusion during the annealing process. 相似文献
7.
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
8.
The tunneling magnetoresistance (TMR) in GaMnAs/GaAs/GaMnAs magnetic tunnel junctions is studied under an extended coherent tunneling approach where both the contributions of the light holes and the heavy holes and their mutual competitions are investigated. It is shown that the TMR ratio can increase with decreasing the barrier strength, which is different from the results in the conventional magnetic tunnel junctions but a good news for the applications. It is also shown that the presence of the pinholes in the thin barrier layer gives a possible explanation of the peak in the barrier thickness dependence of the TMR ratio. 相似文献
9.
We have calculated the I–V curves, dynamical conductance, and tunneling magnetoresistance (TMR) of 1D magnetic tunneling junction through singleband tight binding model calculations based on the non-equilibrium Green's function approach. The difference in density of state of two ferromagnetic leads and the bias dependence of the propagator cause intrinsic asymmetries in TMR and dynamical conductance at finite bias. Besides, we have displayed that large TMR can be obtained even at high bias for half metallic leads. 相似文献
10.
11.
The observed tunneling magnetoresistance (TMR) effect in La0.9Ba0.1MnO3 (LBMO)/Nb-doped SrTiO3 (Nb-STO) p+-n junctions is investigated and a possible mechanism responsible for the TMR generation is proposed by taking into account the dynamic spin accumulation and paramagnetic magnetization in the Nb-STO layer. Because of carrier diffusion across the dynamic domain boundaries in the Nb-STO layer and spin disordering in the LBMO layer, the tunneling resistance through the junction is high at zero magnetic field. The spin disordering is suppressed upon applying a non-zero magnetic field, which results in the spin-polarized tunneling in this ferromagnetic/depletion layer/dynamic ferromagnetic sandwiched structure and thus the observed TMR effect. The dependence of the TMR effect on the domain size in the LBMO layer, the tunneling current and temperature as well is explained, qualitatively consistent with the experimental observation. 相似文献
12.
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
13.
《中国科学:物理学 力学 天文学(英文版)》2020,(1)
Magnetic tunnel junctions(MTJs) switched by spin-orbit torque(SOT) have attracted substantial interest owing to their advantages of ultrahigh speed and prolonged endurance. Both field-free magnetization switching and high tunneling magnetoresistance(TMR) are critical for the practical application of SOT magnetic random access memory(MRAM). In this work, we propose an MTJ structure based on an iridium(Ir) bottom layer. Ir metal is a desirable candidate for field-free SOT switching owing to its strong intrinsic spin Hall conductivity(SHC), which can be enhanced via doping. Herein, we study TMR in Ir-based MTJs with symmetric and asymmetric structures. Ir-based MTJs exhibit large TMR, which can be further enhanced by heavy metal symmetry owing to the resonant tunneling effect. Our comprehensive investigations illustrate that Ir-based MTJs are promising candidates for realizing SOT switching and high TMR. 相似文献
14.
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
15.
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
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.
A generalized approach to study quasiparticle transport across hybrid magnetic tunnel junctions (MTJs) is formulated using the non-equilibrium Green's function technique. This formalism allows for arbitrary thicknesses of the electrodes and the central scattering region comprising of materials with multiple electronic bands, and incorporates the many body interactions present in the electrode regions. While the method can be used to study the transport characteristics of various types of MTJs, we have used it to study the tunneling characteristics and magnetoresistance (MR) of MTJs in which s-f interaction is present at the electrode layers. It is also used to study the transport characteristics of MTJs with hybrid electrodes and double barrier. The magnetic correlation present in the electrodes is found to strongly influence the TMR. Eventhough the magnetic correlation in general suppress the TMR, the TMR is found to be enhanced strongly for certain band occupations of the electrodes. We observe a fall of TMR with increase in the number of layers in the insulating region. Band occupation of the metallic layer present at the middle of the insulating layers in the double barrier MTJ is found to be important in deciding its tunnel characteristics. Origin of the different types of behavior of TMR is analyzed in terms of the spin-dependent tunnel currents. 相似文献
19.
A. M. Bratkovsky 《JETP Letters》1997,65(5):452-457
The tunnel magnetoresistance (TMR) is analyzed for ferromagnet-insulator-ferromagnet junctions, including novel half-metallic
systems with 100% spin polarization. Direct tunneling is compared with the impurity-assisted and resonant TMR. Direct tunneling
in iron-group systems leads to about a 20% change in resistance, as observed experimentally. Impurity-assisted tunneling decreases
the TMR to 4% with Fe-based electrodes. A resonant tunnel diode structure would give a TMR of about 8%. The model applies
qualitatively to half-metallics, where the change in resistance in the absence of spin flips may be arbitrarily large and
even in the case of imperfect magnetic configurations the resistance change can be several thousand percent. Examples of half-metallic
ferromagnetic systems are CrO2/TiO2 and CrO2/RuO2. A discussion of their properties is presented.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 5, 430–435 (10 March 1997)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
20.
P. Sankowski P. Kacman J. Majewski T. Dietl 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):375
The Landauer–Büttiker formalism combined with the tight-binding transfer matrix method is used to describe the results of recent experiments: the high tunneling magnetoresistance (TMR) in (Ga,Mn)As-based trilayers and highly polarized spin injection in p-(Ga,Mn)As/n-GaAs Zener diode. For both TMR and Zener spin current polarization, the calculated values agree well with those observed experimentally. The role played in the spin dependent tunneling by carrier concentration and magnetic ion content is also studied. 相似文献