用外磁场控制电流感应磁化翻转效应中的临界电流方法

应用基于磁动力学方程的宏观唯象模型,研究了弱外磁场下纳米尺度赝自旋阀结构的电流感应磁化翻转效应.在统一考虑铁磁/非磁界面的自旋相关散射以及铁磁层中的自旋积累和弛豫过程后,给出了赝自旋阀结构在弱外磁场下的磁化翻转条件和临界电流.对该效应的数值计算解释了弱外磁场下赝自旋阀结构的电阻-电流回线的偏移,并给出了用外磁场控制电流感应磁化翻转效应中的临界电流方法. 关键词： 电流感应磁化翻转 外磁场 临界电流 赝自旋阀     

磁电子学讲座第三讲 磁性金属多层膜中的巨磁电阻效应

在许多磁性金属多层膜系统中都存在巨磁电阻效应，这些系统是由厚度为几个纳米的磁层与非磁层交替重叠而构成．出现巨磁电阻效应的必要条件是系统的磁化状态能被外加磁场所改变．该效应的物理原因是传导电子在界面处或磁层内的所谓自旋相关散射．层间耦合随隔离层厚度变化而振荡的现象，在隔离层为非磁过渡金属和贵金属的系统中普遍存在．自旋阀多层结构在信息存储技术中磁电阻“读出”头方面极具应用前景．     

垂直磁各向异性自旋阀结构中的铁磁共振

本文在理论上研究了垂直磁各向异性自旋阀结构中磁场激发和调节的铁磁共振. 通过线性展开包含自旋转移矩项的Landau-Lifshitz-Gilbert方程,获得了磁场激发和调节的铁磁共振谱. 给出了共振线宽、共振频率和共振磁场随直流电流密度大小和方向以及直流磁场的变化关系. 通过调节直流电流密度的大小和方向,系统的有效阻尼可以达到最小. 关键词： 自旋阀 自旋转移矩 垂直磁各向异性 铁磁共振     

材料化学分析的物理方法(Ⅱ)

原子核由一定数量的白旋为1／2的质子和中子组成．其总自旋视原子核的构成而各异自旋的原子核象个小磁体．无外加磁场时．原子核的自旋取向是随机分布的．加上一外磁场，则原子核的自旋取向受磁场的约束出现有规则的分布．以1H^1原子核为例．自旋，：1／2，在磁场下分为自旋为1／2和-1／2的两个分量．能量相差     

一维亚铁磁混合自旋链的磁特性的Monte Carlo模拟

基于一维自旋链模型，采用Monte Carlo方法对具有反铁磁相互作用的自旋一I和自旋-3／2交替混合的亚铁磁系统进行模拟计算，研究单离子各向异性对系统磁特性的影响．模拟结果发现：基态时系统的磁化强度在外加磁场作用下呈现出阶梯状，并获得了自旋-1和自旋-3／2交替混合的亚铁磁系统相图．最后，通过对系统能量和自旋组态的研究，解释了该系统中出现的阶梯效应和相图．     

磁场诱导制备Bi-Mn合金的结构和低温磁性研究

系统研究了在外加诱导磁场下制备的Bi-Mn 6%合金的结构和低温磁特性.结果表明,在外加诱导磁场下制备的Bi-Mn 6%合金呈现典型的双相结构和各向异性特征,MnBi相c轴沿外加诱导磁场方向定向排列.发现MnBi相的矫顽力随温度的升高而增大,而饱和磁化强度则随温度的升高而减小.MnBi相的自旋重定向温度TSR随测量磁场的增大逐渐向低温区移动,在高的外加测量磁场下这种自旋重定向特征消失,发现了TSR随外加诱导制备磁场的增大而逐渐向高温区移动.对磁场诱导制备织构化MnBi相和该类材料磁各向异性能的物理机制进行了分析和讨论.     

自旋场效应晶体管的原理和研究进展

基于电子具有自旋的特性,介绍了自旋场效应晶体管的基本原理和研究进展;通过研究发现自旋场效应晶体管具有良好的电导开关效应,外加磁场后则呈现出磁开关效应．     

Ⅱ-Ⅵ族稀磁半导体多层结构中的自旋极化隧穿

采用转移矩阵法和Airy函数,研究了ZnSe/ZnMnSe/ZnSe/ZnBeSe/ZnSe/ZnBeSe/ZnSe异质结构的自旋极化输运。在外加偏压和磁场对电子透射系数和自旋极化率的影响方面,所得到的结论显现出复杂而有趣的特性。磁场对自旋向上和向下电子隧穿的影响是不同的:对于自旋向上情况,出现双共振向单共振转换现象。     

磁性金属多层膜中的巨磁电阻效应

在许多磁性金属多层膜系统中都存在巨磁电阻效应，这些系统是由厚度为几个纳米的磁层与非磁层交替重叠构成，出现巨磁电阻效应的必要条件是系统的磁化状态能被外加磁场所改变。该效应的物理是传导电子在界面处或磁层内的所谓自旋相关散射，层间耦合随隔离层厚度变化而振荡的现象，在隔离层为非磁过渡金属和贵金属的系统中普遍存在，自旋阀多层结构在信息存储技术中磁电阻“读出”头方面极具应用前景。     

诱导磁场对Bi-Mn合金微观结构与磁性的影响

用x射线衍射和低温磁测量方法，系统研究了在外加诱导磁场下制备的Bi Mn合金的微观结构和磁性.结果表明，在外加诱导磁场下制备的Bi Mn wt6%合金呈现典型的双相结构和各向异性特征，MnBi相c轴沿外加诱导磁场方向取向排列.随外加诱导磁场的增大，剩余磁化强度Mr逐渐增大，这说明MnBi相的取向程度越来越好.发现MnBi相的自旋重取向温度TSR随外加诱导磁场的增大逐渐向高温区移动.对外加诱导磁场影响Bi Mn wt6%合金的微观结构和磁性以及该类材料磁各向异性能的物理机理进行了分析和讨论. 关键词： 磁场诱导 Bi Mn合金 MnBi相 定向排列     

Effective reduction of critical current for current-induced magnetization switching by a Ru layer insertion in an exchange-biased spin valve

Recently, it has been predicted that a spin-polarized electrical current perpendicular to plane directly flowing through a magnetic element can induce magnetization switching through spin-momentum transfer. In this Letter, the first observation of current-induced magnetization switching (CIMS) in exchange-biased spin valves (ESPVs) at room temperature is reported. The ESPVs show the CIMS behavior under a sweeping dc current with a very high critical current density. It is demonstrated that a thin ruthenium (Ru) layer inserted between a free layer and a top electrode effectively reduces the critical current densities for the CIMS. An "inverse" CIMS behavior is also observed when the thickness of the free layer increases.     

Instability of storage and temperature increment in nanopillars due to human body model electrostatic discharge

MRAM relevant to current induced magnetization switching (CIMS) is studied due to thermal increment caused by CIMS. In this paper, the instability of storage and the thermal increment caused by the transient current from the HBM ESD in nanopillars of MRAM are studied. We determine the voltage which can cause erroneous switching in MRAM by inducing CIMS. The finite element method is used to calculate the temperature increase caused by the discharge. Results indicate that this voltage is not sufficient to cause permanent physical or magnetic damage to MRAMs but only affects the reliability of the stored information.     

电流感应磁化翻转效应的改进的系综模型

运用宏观双通道扩散模型研究了赝自旋阀结构中的自旋相关输运过程,考虑到磁化强度矢量的横向分量的影响,建立了自由层磁化强度矢量的动力学方程,利用自旋流连续和化学势差连续作为边界条件.理论计算求解了电流感应磁化翻转效应中的临界电流,解释了铁磁层和非磁层电导率匹配问题和纵向场对电流感应磁化翻转效应中临界电流的影响. 关键词： 赝自旋阀 电导率匹配 自旋转移扭矩 电流感应磁化翻转效应     

Hard axis magnetic field dependence on current-induced magnetization switching in MgO-based magnetic tunnel junctions

We conducted a detailed study of hard axis magnetic field (H_hard) dependence on current-induced magnetization switching (CIMS) in MgO-based magnetic tunnel junctions (MTJs) with various junction sizes and various uniaxial anisotropy fields. The decreases in critical current density (J_c) and the intrinsic critical current density (J_c0) estimated from the pulse duration dependence on J_c in CIMS are observed when applying H_hard for all MTJs. The decrease in energy barrier of CIMS is also observed except for the largest sample. These results indicate that the reduction of J_c is attributable to both the increase of spin-transfer efficiency and the decrease in energy barrier in the case of applying H_hard. The J_c0 decreases with increase in the mutual angle between the direction of magnetization and the easy axis (θ_f), which is consistent with the theoretical prediction proposed by Slonczewski. The degree of the reduction of J_c0 for the same value of H_hard decreases with decreasing size of MTJs. This behavior is considered to be related to not only decrease in θ_f due to the increase in anisotropy field in MTJs, but also to the increase in the variance of the initial angle of magnetization due to the thermally activated magnon excitation. The stable switching endurance related to CIMS was observed in a wide range of MTJ sizes when applying H_hard. Moreover, we proposed a new architecture and a new switching method considering write disturbance. These results would be useful for application to spin memory and other spin-electronic devices.     

Suppression of coherent inelastic Mössbauer scattering of synchrotron radiation at grazing angles of incidence

Coherent inelastic Mössbauer scattering (CIMS) of synchrotron radiation (SR) by an isotopic interface (a flat interface between two regions of matter differing in the concentration of the Mössbauer isotope) at grazing angles of incidence of the SR beam is investigated theoretically. The qualitative features of CIMS as compared with conventional optics at small grazing angles of the SR beam are determined. Specifically, it is shown that for CIMS by an isotopic interface, instead of the phenomenon of total external (internal) reflection well known in optics, total suppression of reflection of the CIMS beam occurs at grazing angles of the SR beam less than a critical angle, and a maximum of the transmission and reflection at distinguished CIMS frequencies appears near the critical angle.     

Forward coherent inelastic Mössbauer scattering of synchrotron radiation

A theoretical analysis is presented of the possibilities of satisfying the conditions of phase matching (PM) in the coherent inelastic Mössbauer scattering (CIMS, which is scattering accompanied by the creation or annihilation of phonons) of synchrotron radiation (SR) and the conditions under which the maximum intensity of CIMS obtains are studied. Of the two types of CIMS — 1) participation of phonons in a scattering event only in the stage of absorption or only during re-emission of a photon, and 2) participation of phonons in both stages of scattering — PM is possible only in the first. The process in which phonons participate only at the photon absorption stage leads to efficient conversion of the SR from a wide spectral line into a narrow line, determined by the width of the Mössbauer transition. Photons of this type of CIMS effectively possess a higher penetrating power than the standard Mössbauer radiation, and their spectral distribution is shifted somewhat in the direction of low frequencies.     

Decrease in the Particle Size and Coercivity of Self‐Assembled CoNi Nanoparticles Synthesized Under a Repulsive Magnetic Field

Towards the challenge for synthesis of smaller‐sized heterostructures and hybrid composites for nanomagnets and magnetic fluid applications. Here, a novel method is reported to reduce the particle size of Cobalt–Nickel (CoNi) magnetic nanoparticles by placing them between a static, repulsive magnetic field (N–N/S–S) during synthesis in contrast to the conventional method of applying an attractive (N–S) magnetic field. The obtained smaller sized‐CoNi nanoparticles (≈40 nm) possess a uniform size, an excellent monodispersity, and outstanding magnetic properties. The results clearly demonstrate that the size and morphology change of CoNi nanoparticles have great influence on their magnetic properties. This study provides a footprint to design new heterostructured magnetic nanomaterials under the same‐poled magnetic field for potential applications in magnetic fluids, spintronics, and other related industries.     

The photoexcited spin-aligned state of high-density exciton magnetic polarons and the effect of magnetic field in semimagnetic semiconductor Cd(0.8)Mn(0.2)Te

In Cd(0.8)Mn(0.2)Te, nonlinear photoluminescence (PL) appears only when localized excitons are selectively excited to high-density states. Here, the effect of a magnetic field is compared between nonlinear PL and PL due to localized magnetic polarons. Nonlinear PL shows a shift towards lower energy under an applied magnetic field, whereas PL of a localized magnetic polaron band shows a slight shift towards higher energy. The experimental results support the hypothesis that the origin of the nonlinear PL is a spin-aligned state of high-density exciton magnetic polarons. In the spin-aligned state, most spins of electrons (holes) in many magnetic polarons point in the same direction. In this new high-density photoexcited state, the s, p-d exchange interaction between photoexcited electrons (holes) and magnetic ions plays an important role.     

HgMnTe磁性二维电子气自旋-轨道和交换相互作用研究

通过分析不同温度下HgMnTe磁性二维电子气Shubnikov-de Hass（SdH）振荡的拍频现象，研究了量子阱中电子自旋 轨道相互作用和spd交换相互作用.结果表明：（1）在零磁场下，电子的自旋 轨道相互作用导致电子发生零场自旋分裂；（2）在弱磁场下，电子的自旋-轨道相互作用占主导地位，并受Landau分裂和Zeeman分裂的影响，电子的自旋分裂随磁场增加而减小；（3）在高磁场下，电子的spd交换相互作用达到饱和，电子的自旋分裂主要表现为Zeeman分裂.实验证明了当电子的Zeeman分裂能量与零场 关键词： 磁性二维电子气 Zeeman分裂 Rashba自旋分裂