基于A位离子尺寸失配构筑镍锰基双钙钛矿多铁材料及其磁电耦合性能

Multiferroic materials have simultaneous magnetic and ferroelectric long-range orders. Because of the multiple ordering and magnetoelectric property induced by the coupling between the ordering parameters, they have a wide range of applications in memory devices, sensors, spintronics, and so on. However, in single-phase materials ferroelectricity and magnetism have contradicting requirements. Thus, multiferroics are rarely realized in single-phase materials. In this project, we will use the size-mismatch effect at A site to generate ferroelectricity, which do not need ions such as Bi3+ and Pb2+ with 6s lone pair electrons. Magnetic ordering with higher transition temperature is driven from Ni2+-O-Mn4+ superexchange interaction. Based on this strategy, a series of multiferroic materials will be designed and synthesized. We will use chemical strategy to adjust the micro-structure of the materials, such as the size and level of size-mismatch at A site, degree of ordering at B site, which have substantial influence on magnetic and electric properties. Moreover, we will uncover the mechanism of multiferroicity and magnetoelectric coupling and the key factor that they depend on. This project is expected to reveal the relationship between synthesis, microstructure and multiferroicity, and provide theoretical and experiment basis for the design of multiferroic and magnetoelectric materials.

多铁材料同时具有铁电性和长程磁有序，而且磁和电之间的耦合可以衍生出磁电效应，这些特点使得多铁材料在信息存储、感应元件、自旋电子学等方面有着广泛的应用。然而由于单相材料中铁电性和磁性之间的互斥性，造成了单相多铁材料数量非常稀少。.本项目以镍锰基双钙钛(R,R’)2NiMnO6作为设计单相多铁性的原型材料，铁电性的构建基于A位尺寸失配的稀土离子，不依赖于Bi3+、Pb2+等离子的孤对电子；磁有序基于Ni2+-O-Mn4+超交换作用，具有较高的转变温度。我们拟建立相应的化学合成策略对A位离子尺寸大小和失配程度、B位有序度等与磁电性能直接相关的微结构进行调控，探索多铁性和磁电耦合性能的产生机制及核心影响因素。通过本项目的实施，将建立合成-微结构-多铁性、磁电耦合性能之间对应关系，为多铁和磁电耦合材料的设计奠定实验和理论基础。

近年来，由于在磁性随机存储器等方面的潜在应用，多铁材料受到了广泛的关注。然而由于铁电性和磁有序的互斥性，如何在同一材料中同时实现磁有序和电有序一直是一项具有挑战性的工作。本项目基于A位离子尺寸失配效应来构筑多铁性镍锰基双钙钛矿材料，以实现磁有序和铁电性的共存，并建立相关的合成策略，阐明影响材料磁电性能的因素。（1）我们用水热法合成了Lu2-xYxNiMnO6(x=0，0.2，0.6,1，1.4，1.8，2)和SmYNiMnO6双钙钛矿。用粉末X射线衍射、拉曼光谱、透射和球差电镜对样品的微结构进行了表征。样品中Ni和Mn的价态分别为2+价和+4价。热力学分析表明，水热较低的反应温度有利稳定Ni2+/Mn4+。（2）HAADF-STEM清楚地表明了Ni2+和Mn4+在B位有序排布,然而A位离子的有序排布没有实现。磁性分析结果表明样品实现了磁有序，这主要归于样品较高的有序度。（3）对于Lu2-xYxNiMnO6样品，其居里温度T随着A位离子半径减小而线性减小，表明样品的结构畸变逐渐增大。拉曼分析结果也表明随着A位离子半径减小样品的八面体转动和结构畸变也逐渐增强。因而，可以通过A位离子的半径来调控样品的微结构和磁性。（4）在磁有序温度附近发现了介电异常，表明磁和电之间存在耦合作用。磁介电效应在磁有序温度附近也表现出最大值。