稀土基过渡金属氧化物RCrO4(R=Gd,Ho,Dy)的磁热效应研究

Rare earth based transitional metal oxides possess magnetoelectric effect, giant magnetoresistance effect and other excellent physical properties, which have shown great prospects in the field of new magnetoelectric devices, high-performance information storage and etc. Rare earth based chromates RCrO4 as an important branch, exhibit high-quality magnetocaloric properties at the aspect of low-temperature magnetic refrigeration, and have great research value. At present, the research on this kind of material is still in the initial stage, and the exploration space is very broad. For the purpose of searching for excellent low-temperature magnetic refrigeration materials, the project focuses on three representative compounds RCrO4(R=Gd,Ho,Dy). Based on the established theoretical model, the first principles calculations are employed to obtain the model parameters. Then by using the mean field approximation and Monte Carlo simulation, we will detailedly explore the influences of spin exchange coupling, magnetocrystalline anisotropy, temperature and magnetic field on the magnetic phase transition and magnetocaloric properties of the system. And the dependences of magnetic entropy change, refrigeration capacity, etc., on the above key factors will be established. On the basis of this, by comparison the results of three compounds, we will analyze the mechanism of 4f-3d spin interactions under different environment of rare earth ions, and the universal law will be extracted. Finally, the microscopic mechanism of the giant magnetocaloric effect will be clarified. We believe that these results will provide theoretical support for designing and development of novel rare-earth based refrigeration materials.

稀土基过渡金属氧化物由于具有磁电、巨磁阻等优异的物理特性而在新型磁电器件、高性能信息存储等领域展现出巨大的应用前景。稀土基铬酸盐RCrO4作为其中重要分支，在低温磁制冷方面表现出优质的磁热性能，研究价值极大。目前关于该类材料的研究尚处于起步阶段，探索空间非常广阔。本项目立足于探寻优质的低温磁制冷材料，拟选取具有代表性的RCrO4(R=Gd,Ho,Dy)化合物作为研究对象，构建微观物理模型，结合第一原理计算实现模型参数初始化。采用平均场近似和蒙特卡罗模拟等计算方法，细致研究自旋交换耦合、磁晶各向异性、温度、磁场等因素对体系磁相变和磁热性质的影响，建立磁熵变、制冷能力等与以上关键要素间的依赖关系及变化规律。在此基础上，通过三种化合物对比研究和交叉验证，解析不同稀土离子环境4f与3d自旋的作用机理，提炼普适性规律，最终阐明显著磁热效应的微观机制，为新型稀土磁制冷材料的设计和研发提供理论支撑。

稀土基铬酸盐RCrO4展现出显著磁熵变，大绝热温变以及优异制冷能力，在低温磁制冷领域极具应用潜力。本项目针对具有锆石型结构RCrO4(R=Gd,Ho,Dy)化合物的磁学行为和磁热性质展开了细致的理论研究。基于该类化合物晶体结构，解析了内部可能的复杂超交换作用路径，构建了相应的微观自旋模型。通过蒙特卡罗模拟，探讨了不同交换耦合作用、温度及外磁场的影响。研究结果显示，过渡金属铬离子间的交换耦合决定了体系的铁磁-顺磁转变温度，为稀土离子在转变温度以下的自旋极化提供了有效内场。稀土(4f)-过渡金属(3d)离子间相互作用则直接促进了稀土离子有序度的提升和体系磁热效应的增强。研究还发现适当削弱稀土-过渡金属离子间耦合强度，更加有利于外场诱导稀土离子自旋极化行为，进而提升体系的磁热性能。通过对稀土Ho，Dy离子固有各向异性的研究，发现其对转变温度以下的磁熵变起抑制作用。此外，利用项目开展过程中积累的计算经验和数值研究手段对相关前沿课题进行了适当的延伸和拓展。课题负责人与大连理工大学极端条件凝聚态物理团队合作，开展了关于二维磁性材料的相关研究工作，设计并系统考察了二维草酸盐基金属有机框架Ni2(C2O4)3、Re2(C2O4)3化合物以及二维本征铁磁材料FenGeTe2(3≤n≤7)的电学和磁学特性，为新型自旋电子学器件的设计提供一定思路。