电子全息对磁隧道结势垒层的研究

利用电子全息显微学方法，从理论和实验两方面，系统研究了磁隧道结势垒层的内势分布，指出了一些在实验过程中应予以注意的实验现象，提出了可能的解决方法. 关键词： 电子全息 磁隧道结 平均内势     

具有不同交换偏置方向的外延FeGa/IrMn双层膜的磁各向异性与磁化翻转

采用磁控溅射方法在MgO(001)单晶衬底上制备了交换偏置分别沿着FeGa [100]和[110]方向的FeGa/IrMn外延交换偏置双层膜,研究了交换偏置取向对磁化翻转过程与磁化翻转场的影响.铁磁共振场的角度依赖关系的测量与拟合,表明样品存在不同取向的四重对称磁晶各向异性、单向交换磁各向异性和单轴磁各向异性的叠加.矢量磁光克尔效应测量表明交换偏置沿着[100]方向的样品在不同磁场方向下表现矩形、非对称和单边两步磁滞回线;交换偏置沿着[110]方向的样品在不同磁场方向下表现单边两步和双边两步磁滞回线.考虑不同交换偏置方向的畴壁形核和位移模型,能够很好地解释磁化翻转路径随磁场方向的变化规律和拟合磁化翻转场的角度依赖关系,表明交换偏置方向的改变使得畴壁形核能发生显著变化.     

具有纳米氧化层的磁性隧道结的热稳定性研究

研究发现在磁隧道结的反铁磁层和被钉扎铁磁层之间插入一层纳米氧化层，可以使磁隧道结的退火温度增加了40℃，即明显地提高了磁隧道结的温度稳定性.通过卢瑟福背散射实验直接观察到产生这一效应的原因是该纳米氧化层有效地抑制了Mn元素在退火过程中的扩散，从而使TMR值在较高的退火温度下得以保持. 关键词： 磁性隧道结 隧穿磁电阻 热稳定性 纳米氧化层     

磁随机存储器中垂直电流驱动的磁性隧道结自由层的磁化翻转

在基于磁性隧道结(Magnetic Tunneling Junction，MTJ)的磁随机存储器(Magnetoresistantive Random Access Memory，MRAM)中利用通过MTJ的垂直电流，实现信息写入的新方法，同时给出了基于此新方法的一种新的MRAM结构和驱动原理图，并分析了它的读和写操作的可行性具体过程. 关键词： 垂直电流 磁性隧道结 磁随机存储器     

金属-氧化物界面在磁隧道结中的作用

磁隧道结通常是指由两层磁性金属和它们所夹的一层氧化物绝缘层 (Ⅰ )所组成的三明治结构 .通过绝缘层势垒的隧穿电子是自旋极化的 ,这种自旋极化能够反映作为电极的铁磁金属费米能级处态密度 (ＤＯＳ)的变化 .起源于自旋极化的隧道磁阻(ＴＭＲ)效应已成为当代磁学的一个研究热点 .尽管目前在ＴＭＲ的研究和应用方面已有所发展 ,但在理解隧穿自旋极化方面还存在一定的分歧 ,争论的焦点是金属 -氧化物界面对自旋极化的影响 .对于Ｃｏ、Ｎｉ等铁磁金属 ,由于多数自旋电子所处的ｄ带位于费米能级之下 ,理论预期其自旋极化应该是负的 .然而Ｆ/Ａ…     

Co基磁性隧道结势垒结构的电子全息研究

利用高分辨电子显微术和电子全息方法研究了Co基磁性隧道结退火热处理前后的微观结构及相应势垒层结构的变化. 研究结果表明，退火处理可以明显地改善势垒层和顶电极、底电极之间的界面质量，改进势垒层本身的结构. 这与该磁性隧道结经过280℃退火处理后，隧道磁电阻值大大增加是一致的. 关键词： 磁性隧道结 隧道磁电阻 高分辨电子显微学 电子全息     

基于工艺偏差的电压调控磁各向异性磁隧道结电学模型及其在读写电路中的应用

电压调控磁各向异性磁隧道结(voltage controlled magnetic anisotropy magnetic tunnel junction, VCMA-MTJ)作为磁随机存储器(magnetic random access memory, MRAM)的核心器件,具有读写速度快、功耗低、与CMOS工艺相兼容等优点,现已得到国内外学者的广泛关注.然而随着VCMA-MTJ尺寸不断缩小、MRAM存储容量不断增大,工艺偏差对MTJ性能的影响变得越来越显著,甚至会引起VCMA-MTJ电路的读写错误.本文在充分考虑磁控溅射薄膜生长工艺中自由层厚度偏差(γ_tf)、氧化势垒层厚度偏差(γ_tox)以及离子束刻蚀工艺中由侧壁再沉积层引入的刻蚀工艺稳定因子(α)偏差影响的情况下,给出了基于工艺偏差的VCMA-MTJ电学模型,并将该模型应用到VCMA-MTJ读写电路中,研究了工艺偏差对上述电路读写错误率的影响.结果表明:当γ_tf≥13%, γ_tox≥11%时, VCMA-MTJ将无法实现磁化状态的有效切换;当...     

反铁磁耦合硬磁-软磁-硬磁三层膜体系的不可逆交换弹性反磁化过程

采用一维原子链模型研究了反铁磁耦合的硬磁/软磁/硬磁三层膜体系的反磁化过程. 研究结果表明,当考虑了软磁层的磁晶各向异性能后,软磁层厚度和界面交换耦合强度的改变都有可能导致软磁层的交换弹性反磁化过程由可逆过程转变为不可逆过程. 对软磁层很薄的体系,其反磁化过程是典型的可逆交换弹性反磁化过程. 然而,当软磁层厚度超过某一临界厚度t_c时,反磁化过程转变为不可逆的交换弹性反磁化过程. 软磁-硬磁界面交换耦合强度A_sh对反磁化行为也有很大的影响. 对于软磁层厚度小于临界厚度t_c的体系,也存在一个临界界面交换耦合强度A_sh^c. 当A_sh大于A_sh^c时,软磁层的反磁化过程是可逆的交换弹性反磁化过程;而当A_sh小于A_sh^c时,这一过程变为不可逆. 给出了体系的可逆与不可逆交换弹性反磁化过程随软磁层厚度和界面交换耦合强度变化的磁相图. 同时还研究了偏转场随软磁层厚度的变化关系. 关键词： 反铁磁耦合三层膜 交换弹性反磁化过程 反磁化机理 磁相图     

基于工艺偏差的自旋转移矩辅助压控磁各向异性磁隧道结电学模型及其应用研究

自旋转移矩辅助电压调控磁各向异性磁隧道结(STT辅助VCMA-MTJ)作为非易失性全加器(NV-FA)中的核心部件,具有切换速度快、功耗低,稳定性好等优点,将在物联网、人工智能等领域具有良好的发展前景.然而随着磁隧道结(MTJ)尺寸的不断缩小以及芯片集成度的不断提高,工艺偏差对MTJ及NV-FA电路性能的影响将变得越来越显著.本文基于STT辅助VCMA-MTJ磁化动力学,在充分考虑薄膜生长工艺偏差以及刻蚀工艺偏差影响的情况下,建立了更为精确的STT辅助VCMA-MTJ电学模型,研究了上述两种工艺偏差对MTJ及NV-FA电路性能的影响.结果表明,当自由层厚度偏差γ_tf≥6%或氧化层厚度偏差γ_tox≥0.7%时,MTJ将无法实现状态切换;当隧穿磁阻率偏差β增大到30%时,读取裕度SM将下降高达17.6%.对于NV-FA电路,通过增大电压V_b1以及写‘0’时增大电压V_b2或写‘1’时减小V_b2,可有效降低非易失性加数写入错误率;通过增大逻辑运算驱动电压V_dd,可...     

磁性多层膜磁特性的表面效应

利用Monte-Carlo方法和转移矩阵法研究了具有不同表面交换耦合J_s和薄膜厚度 磁性多层 膜的表面和尺寸对磁相变的影响.模拟结果表明，系统的相变温度随薄膜层数的变化取决于J_s/J(J为体内交换耦合)，当J_s/J大于某一临界值时，由于表面磁 有序先于体内磁有序 ，系统的相变温度随薄膜层数的增多而降低，反之，表面磁无序可与体内磁有序共存，系统 的相变温度随薄膜层数的增多而升高；当J_s/J较小时，随J_s增大 ，系统的居里温度缓慢 升高，趋近于体内相变温度，而当J_s/J较大时，随J_s增大，系统的 居里温度 呈线性升高.模拟结果与用转移矩阵法推导出的结果相当符合，且很好地解释了实验事实. 关键词： 磁星多层膜 交换耦合 Monte-Carlo模拟 转移矩阵法     

Thermally activated magnetization reversal in magnetic tunnel junctions

In this paper, the magnetization reversal of the ferromagnetic layers in the IrMn/CoFe/AlO_x/CoFe magnetic tunnel junction has been investigated using bulk magnetometry. The films exhibit very complex magnetization processes and reversal mechanism. Thermal activation phenomena such as the training effect, the asymmetry of reversal, the loop broadening and the decrease of exchange field while holding the film at negative saturation have been observed on the hysteresis loops of the pinned ferromagnetic layer while not on those of the free ferromagnetic layer. The thermal activation phenomena observed can be explained by the model of two energy barrier distributions with different time constants.     

磁性隧道结热稳定性的x射线光电子能谱研究

通过XPS等微观分析手段证实了磁性隧道结在高温退火后，反铁磁层中的Mn元素扩散到被钉 扎铁磁层及势垒层中，破坏了势垒层/铁磁层界面，从而导致了磁性隧道结高温退火后TMR的 下降.然而在反铁磁层和被钉扎铁磁层之间插入一层纳米氧化层后，Mn的扩散得到了抑制， 使磁性隧道结的热稳定性得以提高. 关键词： 磁性隧道结 纳米氧化层 x射线光电子能谱     

处理具有任意形状势垒的磁性隧道结中电子输运的一个简单方法

在Slonczewski自由电子模型的基础上,提出了一个可用于处理具有任意形状势垒的磁性隧道结中磁电子输运的简单方法,并以三种常见构形的势垒,即梯形势垒,计入了镜像势的梯形势垒和抛物线势垒为例,讨论了势垒形状对隧穿磁电阻及其随偏压变化的影响. 关键词： 磁性隧道结 隧穿磁电阻 任意形状势垒 非零偏压     

Structural and magnetic changes in MgO-based magnetic tunneling junctions during the early stages of annealing

We have studied the effects of the initial stages of the annealing on magnetic tunnel junctions with MgO barriers and CoFeB electrodes. We report changes in the resistance-voltage characteristics and tunneling magnetoresistance for patterned transport junctions, and correlate these with the observed changes in the structural and magnetic interface morphologies determined by soft X-ray resonant magnetic scattering from sheet films from the same wafer. An important feature of our experiment was that all measurements were carried out within the soft X-ray diffractometer on samples from the same wafer subjected to simultaneous annealing cycles, so that our magnetotransport and scattering data are directly comparable. The as-grown junction showed a tunneling magnetoresistance ratio of 5.5%, and a specific barrier resistance of . A anneal for 1 h resulted in a small rise in barrier resistance and magnetoresistance coupled with a smoothing of the magnetic interfaces, consistent with the healing of barrier defects and removal of tunneling hot-spots. A subsequent anneal for a further hour resulted in further smoothing, and a rise in the magnetoresistance ratio to 72%, and a much weaker dependence of the parallel state resistance upon voltage bias, indicating the development of crystallographic texture in the electrodes. Annealing to yielded a further decrease in magnetic interface width (the quadrature sum of roughness and intermixing length scales). The reduction in interface width for Co species occurred at higher temperatures than for Fe throughout the experiments.     

Perpendicular magnetic tunnel junction and its application in magnetic random access memory

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.     

Magnetoresistance in silicon based ferrite magnetic tunnel junction

We report magnetoresistance for silicon based magnetic tunnel junction. We used cobalt ferrite & cobalt nickel ferrite as free layer and pinned layer. The magnetoresistance measured at room temperature through silicon by fabricating FM/Si/FM magnetic tunnel junction. Magnetoresistance shows a loop type behavior with 3.7%. We have successfully demonstrated spin tunneling through silicon with ferrite junction that opens the door for potential candidate for spintronics devices. The spin-filtering effect for this double spin-filter junction is also discussed.     

Effect of Mo capping layers thickness on the perpendicular magnetic anisotropy in MgO/CoFeB based top magnetic tunnel junction structure

A detailed study of the magnetic characterizations of the top structure MgO/CoFeB/Mo is presented.The samples show strong perpendicular magnetic anisotropy(PMA) when the thickness of CoFeB is 0.9 nm and 1.1 nm.The saturation magnetic moment and interface anisotropy constant are 1566 emu/cm~3 and 3.75 erg/cm~2,respectively.The magnetic dead layer(MDL) is about 0.23 nm in this system.Furthermore,strong capping layer thickness dependence is also observed.The strong PMA of 1.1 nm CoFeB only exists in a Mo cap layer thickness window of 1.2-2 nm.To maintain PMA,the metal layer could not be too thin or thick in these multilayers.The oxidation and diffusion of the metal capping layer should be respectively responsibility for the degradation of PMA in these thin or thick metal capping layer samples.     

Hard layer demagnetization by soft layer cycling in a MgO-based perpendicular magnetic tunnel junction

We report here that in perpendicular tunnel junction the hard layer demagnetizes when the soft layer is cycled. This happens faster when the cycling field is closer to the reversal field of the hard layer. Magnetic force microscopy imaging done at different stages of the cycle after several loops show compact demagnetized areas surrounded by large saturated zones in the hard layer. A mechanism based on interlayer magnetostatic coupling induced by the stray field created by domain wall in the soft layer is presented.