CaMnO钙钛矿多铁性化合物与电控磁性的研究

The intrinsic electrical control of ferromagnetism in multiferroic compounds remains to be a major issue even though substantial effort in the past ten years, due to the fact that no dominant ingredient of physics associated with this control has been available to type-I and type-II multiferroics. This proposal stems from the recently predicted scenario in perovskite manganite Ca3Mn2O7 where the electric control of ferromagnetism is generated by the coexisting rotation and tilting modes of the oxygen octahedral. It is proposed that the electric control of ferromagnetism can be realized by multifold lattice distortion modes in perovskite oxides as a general mechanism. The CaMnO-based compounds will be focused and the microscopic mechanisms responsible for the ferromagnetism and its electric control will be revealed. Both theoretical and experimental investigations on novel CaMnO multiferroic materials with potential capability of electric control of ferromagnetism will be carried out, forging our understanding of the ferroelectric polarization and spin order on the lattice distortions. In consequence, one or two multiferroic materials offering representative and promising performance of electric control of ferromagnetism will be synthesized.

在单相多铁性体中实现本征电控磁性与铁磁性依然是一个尚待突破的课题，十年来几无进展，原因在于第I类和第II类多铁性机制中电控磁性的基本物理不多。本申请基于最近钙钛矿结构氧八面体旋转与倾斜畸变模式共存导致电控磁性的理论雏形，提出多重晶格畸变共存诱发铁磁性与电控磁性的思路，并选择类钙钛矿结构CaMnO化合物为研究对象，着重阐明多重晶格畸变诱发铁磁性与电控磁性的微观物理机制。通过理论预测和实验合成表征来筛选具有大的多重晶格畸变的体系，归纳铁电极化与自旋序对这些畸变模式的响应。在此基础上重点关注1-2种有代表性的化合物，实现较强的铁磁性与大的电控磁性效应，为发展电控磁性的物理与材料研究打下若干基础。

本项目核心目标是在钙钛矿结构化合物、特别是层状钙钛矿化合物中实现电控磁性并阐明其物理机制，关键物理思路是通过多重晶格畸变共存来寻找实现电控磁性的途径。总体目标是合成具有(1)大铁电极化、(2)铁磁性、(3)磁电互相调控和应用潜力的多铁性材料并提供物理基础。本项目根据钙钛矿氧化物氧八面体旋转和倾斜畸变模式预言，通过实验合成探索与第一性原理计算密切结合，设计与制备327CMO、Sr3NiTa2O9 (SNTO)、LiFe(WO4)2、(Lu,Sc)FeO3四个新材料体系，深入研究其结构畸变与铁电起源之间的关系，初步揭示了磁结构和磁相变的表征和磁致铁电性的机理，特别是晶格畸变、电子极化、磁致亚铁电等新机制的揭示有一定意义。与此同时，在327CMO中初步实现了电控磁性，在(Lu,Sc)FeO3中初步实现了磁电相互调控。项目基本实现了原定物理目标，但材料体系有所扩大和调整。包括上述几个方面的研究成果发表论文22篇，其中包括Phys. Rev. B论文4篇、Inorganic Chem.论文1篇、Phys. Chem. Chem. Phys.论文2篇。除此之外，项目署名资助其他论文19篇。项目取得的主要内容在国内外学术会议上做邀请报告8次。在项目部分支持下有8名博士生获得博士学位。