铋系铁磁/多铁性氧化物薄膜异质结的精细结构及序参量的同步辐射研究

Bismuth-based multiferroic thin films have rich physics and wide potential applications due to the coexistence of ferroelectric and (anti-)ferromagnetic orders and the strong coupling effect between them. Currently the key issues for mutiferroics are 1) to prepare high quality multiferroic materials with a strong magnetoelectric effect at room temperature and 2) to understand the magnetoelectric coupling mechanism. In this project we will prepare BiFeO3/BiMnO3 multiferroic films with Laser-molecular beam epitaxy technique, measure the accurate lattice constant and charge-, orbital-ordering using the XRD and XMCD techniques and reveal the origin of antiferromagnetism and ferroelectricity and the interplay mechanism between the order parameters. In combination with exchange bias at the interface and strain engineering, we will explore the ferromagnetism and stronger magnetoelectric coupling effect near the room temperature and achieve an electrical control of magnetism and a magnetic control of an electrical polarization. With the aids of the experimental and the theoretical understanding of ferroelectric, ferromagnetic and magnetoelectric coupling effect as well as the studied microscopic mechanism, the application of synchrotron radiation will be further employed in the strongly correlated oxide system.

铋系多铁氧化物薄膜材料，因其同时具有铁电和铁磁/反铁磁两种属性，且磁、电序间存在的耦合效应，从而具有丰富的物理内涵和广泛的潜在应用。制备出具有强磁电耦合的室温多铁材料及了解其磁电耦合机理，是当前需要解决的首要问题。本项目将利用激光-分子束外延技术，构建BiFeO3/BiMnO3异质结，通过X射线衍射技术、软X射线磁性圆/线二色谱，来表征BiFeO3/BiMnO3的精细结构以及电荷有序、自旋有序，研究反铁磁性、铁电性的起源，揭示序参量及其相互作用和体系宏观电磁特性之间的关系和调控规律；通过界面的交换偏置效应以及应变效应等，实现室温附近的强磁电耦合作用和电控磁。基于同步辐射研究，探索铁电、铁磁和磁电耦合效应产生以及可被调控的微观机理，进一步推动同步辐射在氧化物关联体系研究中的应用。

发展了同步辐射衍射表征技术：三维倒易空间扫描技术(3D-RSM)，可快速有效表征外延薄膜中复杂的晶体结构、畴结构及其相互关联；发展了晶体截断面倒易杆(CTR)表征及分析技术，可有效表征BFO二维薄膜系统的表界面，给出原子级空间分辨的结构成分信息，相关实验主要在上海同步辐射和美国APS完成。此外还利用北京同步辐射研究了LSMO氧化物界面电荷转移和磁性。在BMO的生长和物性表征上，探究了高质量的外延BiMnO3（BMO）单相多铁薄膜材料的生长条件（温度，激光能量和靶间距等）。研究发现外延BMO多铁薄膜材料的随着厚度变化表现的的结构相变。最后对BMO薄膜的微观铁电性和磁性能进行了表征。