Mn2Au反铁磁薄膜的电学操控机制与相关隧道结器件

Antiferromagnetic materials have fascinating features: they are robust against perturbation, produce no stray fields, and exhibit ultrafast dynamics. Replacing ferromagnets with antiferromagnets as a functional layer of the tunnel junction, the density, speed and stability of the magnetic storage will be enhanced dramatically. However, because of the zero net moment and insensitivity to the external magnetic field for antiferromagnets, there are great difficulties to detect and manipulate the antiferromagnetic moments. Mn2Au is known as one of the two antiferromagnets whose magnetic moment switching can be driven by electric current, therefore, it is of great value to write and read information in an all-electric way with the help of the antiferromagnetic tunnel junction based on a deep understanding of the manipulation of Mn2Au magnetic moments by electrical methods. The project intends to realize the magnetic switching of Mn2Au films by orientation and thickness related SOT combined with electric field, and then the switching signal is detected through anisotropic magnetoresistance. Based on an in-depth analysis of the intrinsic relationship among the microstructure of the films, the properties of the magnetoelectric transport, the distribution of antiferromagnetic moments and the evolution of antiferromagnetic domains, we can grasp the rules and the dynamic process of Mn2Au antiferromagnetic moment switching. Afterwards, we can clarify the physical mechanisms of efficient manipulation of antiferromagnetic moments by electric current and field. Finally, a new kind of antiferromagnetic tunnel junction device based on electrical manipulation of Mn2Au will be fabricated, where significant tunnel anisotropic magnetoresistance will be obtained above room temperature. This study will provide scientific basis and prototype devices for the development of high-density and low-consumption magnetic memories.

反铁磁替代铁磁作为隧道结的功能层，由于不会产生杂散场、本征频率高和抗外场干扰，有望大幅提高磁存储的密度、速度和数据稳定性。但是，反铁磁对外磁场不敏感且净磁矩为零，也使得反铁磁磁矩的操控和探测面临极大挑战。Mn2Au是目前仅有的两种有望实现电流驱动反铁磁翻转的材料之一，因而在深刻理解用电流和电场操控Mn2Au磁矩的基础上构造反铁磁隧道结对实现全电学方法的信息写入与读出具有重要价值。本项目拟通过Mn2Au薄膜取向和厚度相关的SOT以及电场来驱动磁翻转，并利用各向异性磁电阻探测翻转信号。在深入分析薄膜微结构、磁电输运性能、磁矩分布和磁畴演化之间内在联系的基础上，掌握Mn2Au磁矩翻转的规律和动态过程，阐明电流和电场高效操控反铁磁磁矩的物理机制；制备出基于电学方法操控Mn2Au的反铁磁隧道结器件，在室温以上获得显著的隧道各向异性磁电阻效应，为发展高密度和低功耗的磁存储器提供科学依据与原型器件。

随着大数据和云计算的发展，数据量爆炸式增长，因此亟需发展高速、高密度、低功耗的非易失性存储器。磁随机存储器(MRAM)由于非易失性和速度快等优点，是国际上重点发展的一类新型存储器。目前主流的MRAM由铁磁材料组成，其存在静磁耦合干扰、功耗高、数据易被外磁场擦除等问题，限制了磁存储的进一步发展。反铁磁材料可解决以上问题，但相比于铁磁材料，其外磁场不敏感性且净磁矩为零的特点，也使得反铁磁磁矩的操控和探测面临极大挑战。反铁磁材料Mn2Au具有亚晶格对称性破缺的特点，是有望实现电学操控反铁磁磁矩翻转的材料之一。因此深刻理解电流和电场操控Mn2Au磁矩的物理机制，以及在此基础上构造隧道结器件具有重要价值。本研究组生长出高质量的Mn2Au薄膜，并利用X射线磁线二色谱解析了Mn2Au薄膜的磁各向异性及磁矩排布规律。一方面利用电流诱导的类场力矩实现了对Mn2Au磁矩的循环翻转，并通过霍尔电阻测量读出其翻转结果，发现了类场力矩可以驱动反铁磁奈尔矢量翻转到垂直电流方向，为科学认识电流操控反铁磁奠定基础。另一方面通过构建外延生长的Mn2Au/铁电异质结，利用电场引起的铁弹应变驱动了Mn2Au薄膜的单轴磁各向异性在面内翻转90°，总结出反铁磁奈尔矢量排布在压应变方向的规律，为构造兼具高密度和低功耗特征的反铁磁存储器提供了原型器件。基于以上电控反铁磁技术，我们在Mn2Au中成功观察到反铁磁自旋霍尔效应及其逆效应，这不仅为霍尔家族添加了新成员，而且为高效可控自旋流的产生和探测提供新思路。此外，本课题组建立了一套反铁磁自旋电子学材料与器件的理论研究体系和实验研究方法，在反铁磁Mn2Au、α-Fe2O3和人工反铁磁体系的电流/电场驱动（超快）磁化翻转，反铁磁绝缘体α-Fe2O3、Cr2O3中的电/磁场可控的磁振子输运，反铁磁金属Mn2Au、RuO2、Mn3SnN、FeRh中可控的电荷-自旋转化等研究内容上取得系列研究成果，为发展高密度和低功耗的信息存储器件提供了科学数据与技术储备。在Nature Materials（2篇）和Nature Electronics等期刊发表论文60篇，国际磁学大会等国际会议邀请报告十余次。