软铋矿型手性磁材料的结构设计、晶体生长及磁光与电光性能研究

Magneto-optical devices play an important role in next generation information technologies of optic communication, optical information processing, smart power grids and so on. Chiral magnetic material is the ideal dependency for developing new magneto-optical devices to realize a combination of multiple functions in one material. The strong electro-optic effect can be observed on the sillenite-type chiral crystals such as Bi12SiO20. But their magneto-optical properties are poor due to their weak magnetism, and the comprehensive performance is not ideal. How to improve the magneto-optical performance of crystals is the key to develop multifunctional magneto-optical devices. It can be considered that a higher concentration of magnetic ions should be introduced into the crystal to enhance the magnetism, which greatly improves the magneto-optical performance. Therefore, the crystal structure design combining with the quantum theory calculation is adopted to research the influence of magnetic ions on structure, magnetic properties, magneto-optical, and electro-optical properties of crystal in this project. On these bases, the structure and the composition of crystal will be optimized, and the crystal growth method and the defect formation mechanism will be studied. Then the chiral magneto-optical crystals with good magneto-optical and electro-optical comprehensive performance will be obtained, which provide strong support for the development of new multifunctional magneto-optical devices and the promotion of information technology. Simultaneously, the research on the chiral structure design, quantum theory calculation, and the structure-activity relationship also provide the beneficial references for exploring other chiral magnetic materials.

磁光器件在光通讯、光信息处理、智能电网等下一代信息技术中扮演着重要作用。手性磁材料可以实现同一材料中多种功能复合，是开发新型多功能磁光器件所需的理想材料。Bi12SiO20等软铋矿型手性晶体拥有较强的电光效应，但因磁性太弱而致磁光性能差，综合性能不理想。如何提高晶体磁光性能是开发多功能磁光器件的关键。本课题设想在晶体中引入较高浓度的磁性离子来增强磁性，进而大幅提升磁光性能。为此，项目计划结合晶体结构设计和量子理论计算，研究磁性离子引入对晶体结构稳定性、晶体的磁性、磁光、电光等性质的影响机理和变化规律。在此基础上优化晶体的结构和成分，探讨晶体生长方法与缺陷形成机理，获得磁光、电光综合性能强的手性磁光晶体，为开发新型多功能磁光器件，促进信息技术发展提供有力支持。同时，本项目在手性结构设计、量子理论计算、构效关系探讨等方面研究还可为探索新型磁光晶体提供新思路，为其他手性磁材料研究提供有益参考。

Bi25FeO40软铋矿晶体含有高浓度能极大增强磁光效应的Bi3+离子，且具有电光、旋光、压电等多种功能，可用于开发新颖多功能磁光器件。但该晶体磁性很弱，如何提升磁性以提升磁光性能是其走向应用的关键。.本课题结合软铋矿晶体的结构设计和理论计算，通过引入高浓度磁性离子来增强磁光效应，以获得高性能手性磁光晶体。采用熔盐自发成核法和水热法生长了Bi26-x-yCoxFeyO40、Bi26-x-yNixFeyO40和Bi26-x-yMxFeyO40 (M = Co, Ni)微晶，获得目前已知磁性最强的Bi10.4Co8.6Fe7.0O40软铋矿型微晶。其饱和磁化强度达15.69 emu/g，远大于Bi25FeO40晶体的0.02emu/g。其MCD值与磁性成正相关，也远高于Bi25FeO40晶体，说明Bi10.4Co8.6Fe7.0O40也具有极强的磁光效应。晶体结构解析和XPS谱分析表明，钴离子掺杂浓度低时铁离子占据2a格位，高时则由钴离子占据；晶体中钴离子存在+3和+4两种价态。分别以Bi2O3、Bi2O3-BiF3、K2MoO4-MoO3和Bi2(MoO4)3为助溶剂，采用顶部籽晶法生长掺杂软铋矿晶体。在Bi2O3助溶剂中生长获得厘米级、质量较高的Bi26-x-yCoxFeyO40 单晶，但磁性离子掺杂浓度低，且易出现尖晶石杂相。Bi2O3-BiF3助溶剂能有效降低熔体粘度和生长温度，并实现更高浓度的磁性离子掺杂。在Bi2(MoO4)3助溶剂中生长的晶体磁性离子掺杂浓度最高，值得深入研究晶体生长工艺，以获得高质量、强磁光的掺杂软铋矿单晶。.基于密度泛函理论第一性原理计算了晶体掺杂形成能和电子结构，发现双掺磁性离子能有效降低形成能、提高结构稳定性，磁性离子掺杂还增大了导带与价带之间不同自旋电子跃迁几率的差异，提升晶体磁光性能。.项目还开展了掺杂软铋矿磁光薄膜的制备与性能研究。Bi18.6Co2.8Fe4.6O40/FTO薄膜的MCD值达6658 deg/cm@706 nm，表现出优异的磁光性能。在薄膜中引入Au或Ag纳米粒子，借助表面等离子体共振效应，磁光性能得以进一步大幅提升。借助金属/半导体界面的内建电场， Au/Bi19Ni2.8Fe4.2O40/FTO复合薄膜的压电效应明显增强，并实现电场调制磁光效应，有望用于构建新颖多功能磁光器件。