多种有序钙钛矿结构的高压制备与特殊物性

High-pressure synthesis and special physical properties of several ordered perovskite structures

具有ABO_3钙钛矿或类似结构的强关联电子体系是凝聚态物理研究的重要前沿领域,而高压是制备新型钙钛矿特别是A位与/或B位有序钙钛矿材料的有效手段.在这些有序钙钛矿中,因A,B位可同时容纳过渡金属离子,因而可导致A-A,B-B,A-B等多种磁电相互作用的出现,进而诱导系列新颖有趣的物理现象.本文介绍高压下制备的几种化学式为AA'_3B_4O_(12)的新型A位有序钙钛矿以及化学式为AA'_3B_2B'_2O_(12)的A,B位同时有序的钙钛矿体系.在LaMn_3Cr_4O_(12)中发现了具有立方钙钛矿结构的磁电多铁性,为多铁新材料探索与新机理研究提供范例;在CaCu_3Fe_2Os_2O_(12)中发现了远高于室温的亚铁磁半导体行为,并指出A位磁性离子的引入可大大增加磁相互作用强度从而大幅度提高磁有序温度;在LaMn_3Ni_2Mn_2O_(12)中观察到A位磁性离子调控的B位Ni^(2+)/Mn^(4+)子晶格正交自旋有序结构.以上研究结果为探索新型磁电多功能钙钛矿材料提供了重要参考.

Strongly correlated electronic systems with ABO_3 perovskite and/or perovskite-like structures have received much attention. High pressure is an effective method to prepare perovskites, in particular A-site and/or B-site ordered perovskites. In these ordered perovskites, both A and B sites can accommodate transition-metal ions, giving rising to multiple magnetic and electrical interactions between A-A, B-B, and A-B sites. The presence of these new interactions can induce a wide variety of interesting physical properties. In this review paper, we will introduce an A-site ordered perovskite with chemical formula AA＇_3B_4O_（12） and two A- and B-site ordered perovskites with chemical formula AA＇_3B_4O_（12）. All of these compounds can be synthesized only under high pressure. In the A-site ordered LaMn_3Cr_4O_（12） with cubic perovskite structure, magnetoelectric multiferroicity with new multiferroic mechanism is found to occur. This is the first observation of multiferroicity appearing in cubic perovskite, thereby opening the way to exploring new multiferroic materials and mechanisms. In the A- and B-site ordered perovskite CaCu_3Fe_2Os_2O_（12）, a high ferrimagnetic Curie temperature is observed to be around 580 K. Moreover, this compound exhibits semiconducting conductivity with an energy band gap of about 1 e V. The CaCu_3Fe_2Os_2O_（12） thus provides a rare single-phase ferrimagnetic semiconductor with high spin ordering temperature well above room temperature as well as considerable energy band gap. Moreover,theoretical calculations point out that the introducing of A＇-site Cu^（2＋） magnetic ions can generate strong Cu-Fe and Cu-Os spin interactions. As a result, this A- and B-site ordered perovskite has a much higher Curie temperature than that of the B-site only ordered perovskite Ca_2FeOsO_6（~320 K）. In addition, we also for the first time prepare another A- and B-site ordered perovskite LaMn_3Ni_2Mn_2O_（12）. In the reported ordered perovskites with Mn^（3＋） at the A＇site, the A＇-B intersite spin interaction is usually negligible. In our LaMn_3Ni_2Mn_2O_（12）, however, there exists the considerable A＇-B interaction, which is responsible for the rare formation of B-site orthogonal spin structure with net ferromagnetic moment.