主讲人：Javier Campo 西班牙国立阿拉贡纳米及材料研究所

题   目：Neutron Scattering Techniques to Understand the Multiferroicity in the Molecular Magnet (ND4)2FeCl5·D2O

日   期：2024年4月9日     时   间：15:00-16：00

地   点：哈尔滨工业大学（深圳）, 信息楼L-416

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摘   要：The number of magnetoelectric multiferroic materials reported to date is scarce, as magnetic structures that break inversion symmetry and induce an improper ferroelectric polarization typically arise through subtle competition between different magnetic interactions. The (NH4)2FeCl5·(H2O) compound is a rare case where such improper ferroelectricity has been observed in a molecular material. We have used single crystal and powder neutron diffraction to obtain detailed solutions for the crystal and magnetic structures of (NH4)2FeCl5·(H2O), from which we determined the mechanism of multiferroicity. From the crystal structure analysis, we observed an order-disorder phase transition related to the ordering of the ammonium counterion. We have determined the magnetic structure below TN, at 2 K and zero magnetic field, which corresponds to a cycloidal spin arrangement with magnetic moments contained in the ac-plane, propagating parallel to the c-axis. Also Neutron Spherical Polarimetry, which is uniquely sensitive to the absolute magnetic configuration and domain population, used in this work unambiguously prove the multiferroicity. The observed ferroelectricity can be explained, from the obtained magnetic structure, via the inverse Dzyaloshinskii-Moriya mechanism. Here, also we present a neutron diffraction study under external magnetic field, aimed at elucidating the evolution of the magnetic structure under applied magnetic field, and determine the mechanism of magneto-electric coupling, which allows us to describe an unprecedented change from spin current to spin-dependent p-d hybridization mechanism.

报告人简介：Javier Campo, 国际著名材料物理学家，西班牙国立阿拉贡纳米及材料研究所终身特聘教授，西班牙国家中子技术及大装置负责人，国家科技基础设施委员会主席及驻欧盟研究理事会代表，欧洲散裂中子源科学与技术委员会顾问。曾任欧洲中子研究学会副主席（2009-2014）和国立阿拉贡纳米与材料研究所所长（2012-2020）。长期从事金属和有机材料的磁性能、多铁性和磁手性方面的研究。领导了西班牙国家大型中子装备CRG的建设，设计安装了法国劳埃•朗芝万研究所新型中子探测器和新型热中子衍射仪XtremeD。主持了46项欧盟和西班牙科研项目，发表学术论文170篇。