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使用两种不同的理论方法来计算磁性隧道结中的隧道磁电阻.结果显示,Slonczewski模型得出的隧道磁电阻比Julliere公式得到的要大得多.在Slonczewski模型中,当两边铁磁体的磁化方向相反时,为了确保平行于界面方向上的动量守恒,费米面上的电子只有一部分参与了隧穿过程;而在隧道哈密顿方法中,则假设费米面上所有的电子都参与了.还发现,在Slonczewski模型中,使用δ势垒与使用方势垒所求得的隧道磁电阻的差别是不大的
关键词:
隧道磁电阻
Slonczewski模型
隧道哈密顿方法
势垒 相似文献
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就如何在4英寸热氧化硅衬底上沉积高质量的磁性隧道结纳米多层薄膜材料和如何利用光刻方法微加工制备均匀性较好的磁性隧道结方面做了初步研究,并对磁性隧 道结的磁电性质及其工作特性进行了初步测量和讨论.利用现有的光刻设备和工艺条 件在4英寸热氧化硅衬底上直接制备出的磁性隧道结,其结电阻与面积的积 矢的绝对误差在10% 以内,隧穿磁电阻的绝对误差在7% 以内,样品的磁性隧道结性质具有较好的均匀性和一致性,可以满足研制磁随机存储器存储单元演示器件的基本要求.
关键词:
磁性隧道结
隧穿磁电阻
磁随机存储器
4英寸热氧化硅衬底 相似文献
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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
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利用磁控溅射方法沉积双势垒磁性隧道结多层膜, 其中Al-O势垒层由等离子体氧化1 nm厚的 金属铝膜方式制备,然后采用深紫外光曝光和Ar离子刻蚀技术、微加工制备出长短轴分别为 6和3 μm大小的椭圆形双势垒磁性隧道结(DBMTJ),并在室温和低温下对其自旋电子输运 特性进行了研究. DBMTJ的隧穿磁电阻(TMR)比值在室温和42 K分别达到27%和423%, 结电阻分别为136 kΩ·μm2和175 kΩ·μm2,并在实验中观 察到平行状 态下存在低电阻态及共振隧穿效应,反平行态下呈现高电阻态以及TMR随外加偏压或直流电 流的增加而发生振荡现象. 由此,设计了一种基于这种双势垒磁性隧道结隧穿特性的自旋晶 体管.
关键词:
双势垒磁性隧道结
隧穿磁电阻
共振隧穿效应
自旋晶体管 相似文献
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简要回顾了利用量子隧道效应测定铁磁金属传导电子自旋极化率的研究历史,综述了自旋极化电子隧穿产应导致的“铁磁金属/非磁绝缘体/铁磁金属”三层平面型隧道结中的巨磁电阻效应以及“铁磁金属/非磁绝缘体”颗粒膜系统中的隧穿类型巨磁电阻效应的研究进展。 相似文献
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Using the ion-beam-sputtering technique,we have fabricated Fe/Al2O3/Fe magnetic tunnelling junctions (MTJs).We have observed double-peaked shapes of curves,which have a level summit and a symmetrical feature,showing the magnetoresistance of the junction as a function of applied field.We have measured the tunnel conductance of MTJs which have insulating layers of different thicknesses.We have studied the dependence of the magnetoresistance of MTJs on tunnel conductance.The microstructures of hard-and soft-magnetic layers and interfaces of ferromagnets and insulators were probed.Analysing the influence of MJT microstructures,including those having clusters or/and granules in magnetic and non-magnetic films,a magnetization reversal mechanism(MRM) is proposed,which suggests that the MRM of tunnelling junctions may be explained by using a group-by-group reversal model of magnetic moments of the mesoscopical particles.We discuss the influence of MTJ microstructures,including those with clusters or/and granules in the ferromagnetic and non-magnetic films,on the MRM. 相似文献
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A suggestion to experimentally measure the electron tunnelling time by observing the tunnelling current cut-off as a function
of the magnetic field intensity in semiconductor pn tunnel junctions, when they are placed in a crossed electric and magnetic
field configuration, has been made in this paper. A simple and a rigorous quantum mechanical analysis to justify the above
proposition have been presented. An order of agreement between the tunnelling time values derived from the published experimental
data and our theoretical prediction has been noticed. 相似文献
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We have demonstrated that the bulk-like contribution to tunnelling magnetoresistance (TMR) exists in the magnetic tunnel junctions, and is determined by the tunnelling characteristic length of the ferromagnetic electrodes. In the experiment, a wedge-shaped CoFe layer is inserted at the interface between the insulating barrier and the reference electrode. It is found that TMR ratio increases from 18% without CoFe layer to a saturation value of 26.5% when the CoFe thickness is about 2.3 nm. The tunnelling characteristic length, l_{tc}, can be obtained to be about 0.8 nm for CoFe materials. 相似文献
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Negative tunnelling magnetoresistance in spin filtering magnetic junctions with spin-orbit coupling 下载免费PDF全文
We present theoretical calculations of spin transport in spin filtering magnetic tunnelling junctions based on the Landauer-Buttiker formalism and taking into account the spin-orbit coupling(SOC).It is shown that spin-flip scattering induced by SOC is stronger in parallel alignment of magnetization of the ferromegnet barrier(FB) and the ferromagnetic electrode than that in antiparallel case.The increase of negative tunnelling magnetoresistance with bias is in agreement with recent experimental observation. 相似文献
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At the interfaces between the metallic electrodes and barrier in magnetic tunnel junctions it is possible for localized states to form which are orthogonal to the itinerant states for the junction, as well as resonant states that can form at the interfaces. These states form highly conducting paths across the barrier when their orbitals point directly into the barrier; these paths are in addition to those formed by the itinerant states across the entire junction. Most calculations of transport in magnetic tunnel junctions are made with the assumptions that the transverse momentum of the tunnelling electrons is conserved, in which case the itinerant electron states remain orthogonal to localized states. In principle it is possible to include diffuse scattering in both the bulk of the electrodes and the barrier so that the transverse momentum is not conserved, as well as the processes that couple localized states at the electrode-barrier interface to the itinerant states in the bulk of the electrodes. However, including these effects leads to lengthy calculations. Therefore, to assess the conduction across the barrier through the localized states that exist in parallel to the itinerant states we propose an approximate scheme in which we calculate the conductance of only the barrier region. While we do not take explicit account of either of the effects mentioned above, we do calculate the tunnelling through all the states that exist at the electrode-barrier interfaces by placing reservoirs directly across the barriers. To calculate the current and magnetoresistance for magnetic tunnel junctions (the junction magnetoresistance (JMR)) we have used the lattice model developed by Caroli et al. The propagators, density of states and hopping integrals entering the expressions for the current are determined by using the spin polarized scalar-relativistic screened Korringa-Kohn-Rostoker method that has been adapted to layered structures. By using vacuum as the insulating barrier we have determined with no adjustable parameters the JMR in the linear response region of tunnel junctions with fcc Co(100), fccNi(100) and bcc Fe(100) as electrodes. The JMR ratios that we find for these metal/vacuum/metal junctions are comparable with those measured with alumina as the insulating barrier. For vacuum barriers we find that tunnelling currents have minority- spin polarization whereas the tunnelling currents for th se electrodes have been observed to be positively (majority) polarized for alumina barriers and minority polarized for SrTiO 3 barriers. In addition to determining the JMR ratios in linear response we have also determined how the magnetoresistance of magnetic tunnel junctions varies with a finite voltage bias applied across the junction. In particular we have found how the shape of the potential barrier is altered by the applied bias and how this affects the current. Comparisons with data as they become available will eventually determine whether our approximate scheme or the ballistic Landauer-Büttiker approach is better able to represent the features of the electronic structure that control tunnelling in magnetic tunnel junctions. 相似文献
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The effect of the ferromagnetic metal layer on tunnelling conductance and magnetoresistance in double magnetic planar junctions 下载免费PDF全文
Based on the free-electron approximation,we investigate the effect of the ferromagnetic metal layer on the tunnelling magnetoresistance(TMR) and tunnelling conductance(TC)in the double magnetic tunnel junctions(DMTJs) of the structure NM/FM/I(S)/NM/I(S)/FM/NM,where FM,NM and I(S) represent the ferromagnetic metal,nonmagetic metal and insulator(Semiconductor),respectively,The FM,I(S)and inner NM layers are of finite thickness,while the thickness of the outer NM layer is infinite.The calculated results show that,due to the spin-dependent interfacial potential barriers caused by electronic band mismatch between the various magnetic and nonmagnetic layers,the dependences of the TMR and TC on the thicknesses of the FM layers exhibit oscillations,and a much higher TMR can be obtained for suitable thicknesses of FM layers. 相似文献
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G. B. Arnold 《哲学杂志》2013,93(19):2811-2833
We calculate the Josephson critical current Ic across in-plane (001) tilt grain boundary junctions of high-temperature superconductors. We solve for the electronic states corresponding to the electron-doped cuprates, two slightly different hole-doped cuprates, and an extremely underdoped hole-doped cuprate in each half-space, and weakly connect the two half-spaces by either specular or random Josephson tunnelling. We treat symmetric, straight, and fully asymmetric junctions with s-, extended-s, or d x 2?y 2 -wave order parameters. For symmetric junctions with random grain boundary tunnelling, our results are generally in agreement with the Sigrist–Rice form for ideal junctions that has been used to interpret ‘phase-sensitive’ experiments consisting of such in-plane grain boundary junctions. For specular grain boundary tunnelling across symmetric junctions, our results depend upon the Fermi surface topology, but are usually rather consistent with the random facet model of Tsuei et al. Our results for asymmetric junctions of electron-doped cuprates are in agreement with the Sigrist–Rice form. However, our results for asymmetric junctions of hole-doped cuprates show that the details of the Fermi surface topology and of the tunnelling processes are both very important, so that the ‘phase-sensitive’ experiments based upon in-plane Josephson junctions are less definitive than has generally been thought. 相似文献
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The current-voltage characteristics for Bi-Sr-Ca-Cu-O bulk specimen incorporating manually carved constriction show both zero
voltage pair current and quasiparticle tunnelling current. The pair current amplitude modulates with applied d.c. magnetic
fields. Microwave-induced Shapiro steps are clearly seen in the I-V curves. The Josephson effects arise due to the presence
of arrays of grain boundary Josephson junctions. 相似文献
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Yiming Huai Mahendra PakalaZhitao Diao Dmytro ApalkovYunfei Ding Alex Panchula 《Journal of magnetism and magnetic materials》2006
Spin-transfer driven switching was observed in MgO based magnetic tunnelling junctions (MTJ) with tunnelling magnetoresistance ratio of up to 160% and the average intrinsic switching current density (Jc0) down to 2 MA/cm2, which are the best known results reported in spin-transfer switched MTJ nanostructures. Based on a comparison of results both from MgO and AlOx MTJs, further switching current decrease via MgO dual structures with two pinned layers is discussed. 相似文献