钙钛矿结构Cr基氧化物单晶的制备和磁电效应研究

The multiferroic materials with the ferroelectricity arising from magnetic order exhibit strong magnetoelectric coupling. This kind of multiferroics have recently attracted much attention due to their potential application in information storage as well as the rich fundamental physics. Among all the multiferroics, the chromites ACrO3 with perovskite structure were found to exhibit relatively high multiferroic transition temperature, large electric polarization and strong magnetoelectric coupling. But the multiferroic origin in these materials are still not known. Therefore, the chromites are ideal materials to explore new mechanism of multiferroicity and to study the mutual control among the lattice (structure), spin (magnetism) and charge (ferroelectricity). The single crystalline chromites ACrO3 (A=Y, La, Nd, Gd) will be selected as the object of the study in the present proposal. We plan to investigate the relation between magnetism and ferroelectricity via element substitution tunned magnetic interaction. It is well known that the infrared and Raman spectra are sensitive to the change of microstructure in materials. Hence, we also plan to use the infrared and Raman spectra to study the modes that are related to the ions with respect to ferroelectricity under high pressure or in high magnetic fields. Besides, the magnetic, ferroelctric, dielectric and magnetoelectric properties will also be included to systematically study the mechanism of the multiferroiciy and magnetoelectric effect in the chromites ACrO3. This project can provide some experimental and theoretical help in exploring new applicable multiferroic materials with strong magnetoelectric coupling.

铁电性源于磁有序的多铁性材料由于存在较强的磁电耦合效应，不仅在信息存储领域存在着广泛的应用前景，而且蕴含着丰富的物理问题，从而备受人们关注。其中钙钛矿结构铬基氧化物ACrO3体系由于具有较高的多铁性转变温度、大的电极化和磁电耦合效应，同时其多铁性起源尚不清楚，因而是探索新的多铁性机制和研究晶格(结构)、自旋(磁性)及电荷(铁电)等自由度(参量)之间相互调控的理想材料。本项目拟选取ACrO3(A=Y、La、Nd、Gd等)体系的单晶作为研究对象，通过元素掺杂或替代调控体系的磁相互作用，利用对材料微结构敏感的红外及拉曼光谱，分析体系中与产生电极化的离子相关的振动模式在外加高压或强磁场下的变化规律，结合磁性、铁电、介电和磁电效应的物性测量结果，建立体系的磁性与铁电性之间的关联，认识ACrO3体系中多铁性及磁电效应的演变规律，并建立其微观物理机制，为探索新的具有强磁电效应的多铁性材料提供实验依据。

多铁性磁电材料由于磁性与铁电性之间强的耦合作用使其在信息存储、传感器等领域有着潜在的应用前景，近年来受到人们的普遍关注。本项目选择钙钛矿结构Cr基氧化物RCrO3及其掺杂体系单晶作为研究对象，系统研究了稀土离子R-R之间、R-Cr之间及Cr-Cr之间的磁相互作用，对该体系的磁行为、介电、多铁性、磁电效应等物性的影响。我们发现R-R、R-Cr、Cr-Cr磁相互作用使该体系表现出温度/磁场诱导的自旋重取向及磁矩跳跃、巨磁热效应、强磁电耦合效应等丰富的物理现象。通过对该体系单晶的磁、本征磁电效应等的各向异性的研究，我们对这些现象的微观物理机制给出了相应的解释。此外，实验结果还表明Cr位Mn掺杂可在该体系可诱导出多铁性。我们在DyCrO3单晶观测到了量子顺电行为，进一步的实验结果及理论计算表明其电极化可能起源于Cr3+离子偏离中心对称位置的位移。相关的研究结果主要以论文的形式发表。到目前为止，已在Appl. Phys. Lett.、J. Mater. Chem. C、J. Appl. Phys.等SCI期刊上发表论文4篇，另有1篇论文正在审稿。本项目的成功执行不仅对理解钙钛矿结构Cr基氧化物中发现的诸如磁矩跳跃、磁电效应等新物理现象的微观机制具有重要意义，而且为在该体系以及其它钙钛矿结构材料中寻找新型磁性及磁电材料提供了思路。