钙钛矿结构稀土锰氧化物的磁相互作用研究

钙钛矿结构稀土锰氧化物RMnO3具有复杂的磁性相图，其成因仍存在争议，目前主要有两种观点：（1）次近邻反铁磁耦合与最近邻铁磁耦合的竞争引起的；（2）最近邻eg电子间铁磁耦合与t2g电子间反铁磁耦合竞争的结果。核心问题是：Mn离子的次近邻交换是否起作用？目前理论结果较多，但尚缺乏相关实验数据的支持。难点在于：次近邻交换作用主要由O2-O4距离决定，而最近邻eg电子耦合与Jahn-Teller畸变密切相关，不容易实现单独调节一个变量而不影响另一个。这是解决以上争议的主要障碍。针对这一问题，本项目利用高压调节O2-O4距离，利用非磁性等价元素Ga替代Mn调节Jahn-Teller畸变，使两个变量解耦，测量RMnO3体系物性随两者变化的规律性，找出影响其磁性的主要因素，对以上两种观点进行评价。预期本项目研究结果对深刻理解RMnO3体系的相图、设计新型高性能多铁材料将起到积极的作用。

RMnO3 exhibits a complex magnetic phase diagram, whose origin is controversial. Two different models exist at present: (1) the competition between next-nearest-neighbor antiferromagnetic coupling and nearest-neighbor ferromagnetic one, (2) the competition between ferromagnetic eg coupling and antiferromagnetic t2g one of nearest neighbors, results in the magnetic features of RMnO3 system. The critical factor is whether Mn next-nearest-neighbor interaction is involved? Whereas lots of theoretic results were published, few experimental investigations were performed to test the two models. The next-nearest-neighbor interaction is mainly determined by O2-O4 distance，while the nearest-neighbor eg one is in close relation to Jahn-Teller distortion. However, it is difficult to tune one variable independently while keeping the other fixed. In this proposal, high pressure and isovalent nonmagnetic ion (Ga) doping will be adopted to tune O2-O4 distance and Jahn-Teller distortion, respectively, to decouple the two variables. By monitoring the variation of physical properties, the major variable could be found, and the two models could be evaluated. The results of this proposal will promote the understanding of the phase diagram of RMnO3, and the design of novel multiferroic materials with high performance as well.