Co2MnSi/L10-MnGa磁性双层膜的垂直磁各向异性及自旋极化度

MgO barrier based Co(Fe)/MgO structure exhibits high spin-injection efficiency. The half metallicity of ?1 band of magnetic layer, and well epitaxial relationship with MgO are the two key factors for this effect. Research on this kind of materials, which also have perpendicularly magnetic anisotropy and high spin polarization, like perpendicular magnetized Heusler alloys, is a hotspot in spintronics recently. These materials have important potential applications in scaling down the size of spintronic devices and lowering the critical current density of current-induced magnetization switching. Magnetic multilayer architecture is a more flexible way to design this kind of functional material. The traditional [Co/Pt、Pd、Ni]n multilayers and rare-earth/transition-metal alloy(noble-metal alloy)/CoFe bilayers still can not meet all the requirements for spintronic device with high performance. A novel bilayer structure is suggested in this proposal, which consists of perpendicularly magnetized L10-MnGa layer and high spin polarized Heusler alloy Co2MnSi. A reasonable fabrication process is proposed, in which migration enhanced molecular beam epitaxy is the key point. Furthermore, the important factors and mechanisms influencing the perpendicular magnetic anisotropy and spin polarization of this bilayer will be studied, which will demonstrate the way of designing a magnetic multilayer as a base of functional spintronic devices.

以MgO为势垒层的Co(Fe)/MgO结构具有极高的自旋注入效率，铁磁层?1能带的半金属性及与MgO完美的外延是出现这一效应的关键因素。探索具有这一特性并兼有垂直磁各向异性及高自旋极化度的半金属材料成为目前自旋电子学材料研究的焦点之一。这类材料在进一步缩小自旋电子学器件尺寸、减小电流诱导磁化翻转的临界电流密度等方面有重要应用。磁性多层膜的人工结构在开发这类功能材料上有更大的自由度。传统 [Co/Pt、Pd、Ni]n多层膜与稀土/过渡金属合金（贵金属合金）/CoFe双层膜结构在材料的制备和性能上还不能满足器件设计的全部要求。本项目拟研究具有高垂直磁各向异性的L10-MnGa与具有高自旋极化度的半金属Co2MnSi组成的磁性双层膜的迁移增强分子束外延生长、垂直磁化特性以及自旋极化度，弄清影响此磁性双层膜垂直磁各向异性及自旋极化度的关键因素及其物理机制，为开发多功能的自旋电子学器件材料提供基础。

基于自旋矩转移效应（spin torque transfer，STT）的MTJ结构通过电流直接在磁性层中写入信息，这可极大地提高集成密度和降低工艺难度，实现具有小尺寸、低功耗、高速度和非易失性特点的STT-MRAM，是当前随机存储器最有潜力的替代品之一，尤其是在航天、国防等特殊应用领域具有不可替代的优越性，现已成为国内外各大公司和政府研究机构角逐的焦点。本项目详细研究了MnGa/Co2MnSi以及MnGa/Co(Fe)两类双层膜结构的垂直易磁化特性，并在此基础上研制出垂直隧道结（p-MTJ）以及高场隧道结磁敏传感器。.第一，通过XMCD技术，首次直接观察到了MnGa/Co(Fe)垂直易磁化双层膜中超薄Co、Fe层与MnGa之间的铁磁和反铁磁两种不同的磁耦合情况，并通过理论和实验获得了磁耦合状态的调控条件；通过加和定则计算了Co、Fe的轨道及自旋磁矩，并以此推论出超薄Co插层不会增加双层膜的磁阻尼系数，这对降低垂直易磁化STT-MTJ的临界电流密度具有重要指导意义。第二，在MnGa/Co2MnSi中实现了高强度的反铁磁耦合，耦合强度达到-5erg/cm2，以此双层膜制备了MnGa/Co2MnSi/MgO/Co2MnSi/MnGa垂直易磁化MTJ，并在低温下实现了65%的隧穿磁电阻率，由此指明了通过超薄Heusler合金插层技术实现MnGa基垂直MTJ的方案，为后续STT-MTJ的研制奠定了基础。第三，分别以超薄Co、Co2MnSi为插层制备了MnGa/Co2MnSi(Co)/MgO/CoFe的垂直高场MTJ磁敏传感器，将传统MTJ的探测磁场范围提高到了±2T以上，室温TMR达30%。