钙钛矿锰氧化物磁圆二色效应及磁晶各向异性研究

Perovskite manganese oxides are regarded as the most promising spintronic materials for their excellent properties of high Curie temperature and high spin polarization rate. The heterogeneous thin films composed of it have a wealth of physical phenomena and broad application prospect, so they have attracted widespread attention. However, the dead-layer at the interface of the La2/3Sr1/3MnO3/SrTiO3 (LSMO/STO) hetero-structure with degraded ferromagnetism affects the overall performance of the film as spintronics devices. The origin of the dead-layer has not been clearly expounded, and there are also many controversies about its magnetic properties and magnetic structures. The angle-dependent X-ray magnetic circular dichroism (XMCD) has become an important and powerful tool because it allows to study the element-specific orbit magnetic moments and their anistropy. Based on the XMCD setup at the 4B7B beamline of Beijing Synchrotron Radiation Facility (BSRF), this project is intended to study the interface magnetic properties and magnetocrystalline anisotropy of LSMO/STO heterostructures. The influence of the oxygen vacancies with different number and position on the sample magnetism can be research by this method. At the same time, the Mn orbit magnetic moments and corresponding anisotropy can be quantitative analyzed from the magnetocrystallis anisotropy aspect. Combination of the XMCD spectroscopy simulations and ab initio calculation, we probe into how about the Mn atomic orbital ordering and magnetic coupling at the interface. This reasearch will reveal the magnetic properties and the origin mechanism of the dead-layer, and provide the experimental and theory basis for optimizing the interface magnetic properties and developing the low-dimensional functional devices.

钙钛矿锰氧化物由于具有高居里温度和高自旋极化率等优异特性而被视为理想的自旋电子学材料，由其构成的异质薄膜具有丰富的物理现象和广阔的应用前景，因而受到人们广泛关注。但是在其异质结界面却存在磁性受到抑制的“死层”，目前人们对这种界面死层的磁学性质及其形成机制仍然存在诸多争议。本项目依据角度依赖的软Ｘ射线磁圆二色谱能够探测特定元素轨道磁矩及其各向异性的特点，依托北京同步辐射室4B7B软X射线光束线XMCD实验装置，拟研究La2/3Sr1/3MnO3/SrTiO3体系中氧空位数量、占位对薄膜磁性的影响，并从磁晶各向异性角度定量分析Mn原子轨道磁矩和角度的依赖关系，结合磁圆二色谱拟合计算和第一性原理计算明确界面Mn3+原子eg电子轨道序和界面磁耦合类型，深入探讨界面死层的磁学性质及形成机理。本项目的研究将为调控和优化钙钛矿锰氧化物的界面磁性以及实现磁性功能器件低维化积累实验和理论依据。

本项目依据软X射线磁圆二色谱能够探测特定元素轨道及自旋磁距的特点，依托北京同步辐射4B7B光束线XMCD实验装置，结合VASP第一性原理计算，研究了锰基磁性材料La2/3 Sr1/3MnO3和GaMnN中空位缺陷对磁性的影响。结果表明空位缺陷的存在会降低Mn元素的磁性，其原因在于材料电负性的增加会降低锰元素化学价态，同时破坏形成铁磁性的双交换相互作用。除此之外，本项目建立角度依赖的XMCD实验方法，并应用于研究FM/DMS双层膜磁性、界面磁耦合方式以及磁晶各向异性。研究结果对于应用磁近邻效应设计室温自旋电子学器件具有重要指导意义。