报告时间：2017年10月27日（周五）下午14:00

报告地点：高等研究院会议室

报告人：郭尔佳

任　职：美国橡树岭国家实验室，博士后

题　目：Revealing the hidden magnetic interfaces by polarized neutron reflectometry

Abstract:

　　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. [1,2] 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.[3] Assisted by ionic liquids (ILs), the interfacial magnetization of LSMO can be reversibly controlled by electrically switching the ferroelectric polarization.[4] 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. [5]