报告题目：Revealing the hidden magnetic interfaces by polarized neutron reflectometry
报告人：郭尔佳博士（美国橡树岭国家实验室研究员）

主持人：吴真平

报告时间：2017年10月18日10：10~11：10

报告地点：主楼1504

报告摘要：

Since the nature of neutrons is highly penetrating and sensitive to the changes in nuclear and magnetic scattering length density of a material, polarized neutron reflectometry (PNR) has great success in revealing many intriguing interfacial magnetic phenomena in transition metal oxide heterostructures. This novel method is not only capable to probe the magnetic depth profile with nanometer resolution, but also can give the absolute value of magnetization for individual layers. In this talk, firstly, I will show the evolution of the magnetic moment at interfaces in the typical ferroelectric/ferromagnetic (PbZr0.2Ti0.8O3/La0.8Sr0.2MnO3, PZT/LSMO) oxide heterostructures using PNR. The magnetizations of LSMO at both surface and interface are deteriorated; however, such deterioration can be much improved by interfacing with a ferroelectric. Assisted by ionic liquids (ILs), the interfacial magnetization of LSMO can be reversibly controlled by electrically switching the ferroelectric polarization. The compelling results demonstrate the strong modulation of magnetization by charge density at the interface. The second part of my talk, I identify the large interfacial magnetization in BiFeO3 (BFO) layers only exists in close proximity (~ 3 - 4 unit cells) to the LSMO. The net magnetizations of BFO and LSMO are anti-parallel. The onset of net magnetization in BFO persists up to 200 K, which is significantly higher than previous reports. The enhanced magnetization in BFO is only observed in the [100]-orientation, however, is absent in the [111]-orientations. Moreover, the induced magnetic moment in BFO is proportional to the magnetization of the adjacent ferromagnet. We attribute the induced large net magnetization in BFO is a result of orbital reconstruction between Fe and Mn across the interface, which establishes an upper temperature limit for magnetic ordering temperature of BFO.

报告人简介：

郭尔佳，2012年于中国科学院物理研究所获得理学博士学位。后赴德国马丁路德大学/马克思普朗克微结构物理研究所和美因茨大学继续从事博士后研究。2015年至今在美国橡树岭国家实验室从事科研工作。主要研究方向为复杂氧化物薄膜和异质结的制备与物性表征，侧重于铁电和铁磁氧化物薄膜在异质界面、畴壁等受限局域系统中的物理性质及其外场调控特性，已发表学术论文54篇，包括两篇Nature Communications，两篇Advanced Materials，两篇Nano Letters，一篇 Physical Review X，一篇 Physical Review Letters 等。发表文章中，21 篇论文为第一作者，包含2 篇综述。截至2017年6月，论文被他人引用近600次。