报告人：叶峰    研究员

时间\地点：2016年6月8日15:30 \ 强磁场中心203学术报告厅

报告题目：多铁氧化物单晶的中子衍射和X-射线衍射研究

报告摘要：I will discuss the neutron and x-ray diffraction results ofmultiferroics Mn1-xCoxWO4 and Ca3Mn1.9Ti0.1O7. MnWO4 is a classic example of frustratedmagnets with coupled electric and magnetic properties.. The magnetic ground state arises from the competing long range interactions and is subjected to various external (magnetic field, pressure) and internal (chemical substitution) perturbation. We use hydrostatic pressure as a tuning parameter, to clarify how the balance between controlling the magnetic anisotropy and modifying the long range magnetic interactions determines the ground state spin order. The appearance of ferroelectricity in the Ruddlesden-Popper compounds Ca3M2O7 (M=Mn,Ti) is believed to arise from a novel microscopic mechanism.The instability of the polar phonon mode is driven by the simultaneous condensation of two nonpolar lattice modes associated with oxygen octahedron rotation and tilt modes, and is responsible for the polar symmetry We have used single crystal neutron and x-ray diffraction to investigate the temperature and pressure dependence of these oxygen octahedron distortions in Ca3Mn1.9Ti0.1O7 which has a structural transition at 365 K and antiferromagnetic order at 120 K. We observed a strong interplay between magnetism and the local oxygen distortion near the magnetic transition. The control of the magnetism through octahedron distortion is discussed.

报告人简介：

　　Education

　　B.S.   University of Science and Technology of China, 1996

　　M.S.   University of Science and Technology of China, 1999

　　Ph. D.  University of California, Santa Cruz, 2003

　　Professional Experience

　　1999-2003  Research Assistant, Department of Physics, UC Santa Cruz

　　2003-2008  Postdoctoral Research Associate, ORNL

　　2008-present  Research staff and Lead instrument scientist for Corelli, ORNL

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