非正规铁电体BaMF4的磁电耦合效应研究

The study of improper ferroelectrics is a frontier topic in condensed matter physics, because most of the them have magnetic orders and magnetoelectric coupling effects, with profound physics and great application value. In the passed decade, remarkable progresses have been made on transition metal oxides with improper ferroelectricity, but there are still many tough scientific problems, such as low transition temperatures and high leakage, which seriously restrict the applications of multiferroics. Trying to solve the problems, this project will focus on a class of improper ferroelectrics with quasi-two-dimensional structure, BaMF4 (M: 3d transition metals), whose magnetoelectricity will be systematically studied. On one hand, we will experimentally study their syntheses, crystal structures, and physical properties such as ferroelectricity, domain dynamics, magnetism, and magnetoelectric coupling effects. On the other hand, theoretical calculations will be performed to excavate new fluoride multiferroics, and further investigate the magnetoelectric physics. This project is expected to break through the research bottleneck of traditional oxides, and find multiferroic materials with strong magnetoelectric coupling effects near room temperature.

在凝聚态物理学中，非正规铁电体研究是一个重要的前沿课题。非正规铁电体通常伴随着磁有序和磁电耦合效应，具有深刻的物理内涵和巨大的应用价值。基于过渡金属氧化物的多铁性研究虽在过去十余年间取得了显著进展，但是尚存在不少难以解决的科学问题，例如磁转变温度低，绝缘性不高等，这严重限制了多铁材料走向应用。为了尝试解决上述问题，本项目另辟蹊径，将着重关注一类准二维结构的非正规铁电体BaMF4(M为3d过渡金属)，并对其磁电耦合效应进行系统研究。一方面，通过实验方法研究材料的合成、晶体结构、铁电性、畴结构动力学、磁有序、磁电耦合效应等等。另一方面，结合理论计算方法挖掘新型的氟化物多铁材料，深入研究其多铁性，以及氟化物非正规铁电体的磁电物理。本项目研究将有望突破传统氧化物多铁体系的研究瓶颈，获得室温附近具有强磁电耦合效应的多铁材料。

层状氟化物铁电体当中蕴藏了丰富的物理内涵例如本征铁电性及其与其它铁性之间的共存问题，在凝聚态物理研究领域当中的热点问题。今年来随着二维范德瓦尔斯铁电体 的不断出现，对单层铁电性、层与层之间的相互作用，层状铁电材料的铁电体效应等等逐渐开始占据广大研究者们的视野。在本项目的研究工作中我们对新型层状铁电体的本征铁电性进行了详细 研究，包括铁电性的温度依赖、铁电翻转动力学、铁电极化与离子缺陷之间的耦合关联，以及铁电畴结构的稳定性。目标是挖掘层状铁电体当中更加隐秘的物理特性。本项目的研究将有助于丰富多铁物理内涵并推动二维材料应用和铁电存储领域的发展。

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