交换弹性复合硬磁铁氧体的微磁结构和磁性能研究

Synthesizing the hard/soft magnetic composite ferrites with exchange spring behavior is an important way to improve the magnetic properties of widely-used hexagonal hard magnetic ferrites. However, the improvement of magnetic properties is limited in current reports. Moreover, it still lacks the study of magnetic properties and the nature of exchange spring in composite ferrites in the view of magnetic microstructures, both experimentally and theoretically. In this project, in order to improve the magnetic properties of practical hard magnetic ferrites, we are intended to prepare hard/soft magnetic composite M-type Sr ferrites via a hydrothermal method and a novel sol-gel method using egg white as metal ion complex, and a series of Ni-Zn ferrites or Fe-B compounds with high saturation magnetization will be introduced as the soft magnetic phases. Combined with the magntic force microscopy, the exchange coupling interaction, magnetic properties, magnetic microstructures and their relationships will be systematically analyzed experimentally, and the changes of magnetic properties and the nature of exchange coupling in composite Sr ferrites will also be investigated in the view of micromagnetics in theory as well as experiments. We hope it can further lay a foundation for the improvement of magnetic properties of hard magnetic ferrites, both experimentally and theoretically.

六角晶系硬磁铁氧体目前有着广泛的应用，利用硬磁/软磁相的交换耦合作用制备交换弹性复合铁氧体是提高其磁性能的重要途径。但是，现有相关报导不但其磁性能提升十分有限，而且无论是从实验还是理论上，都缺乏从微磁学角度出发对复合铁氧体的磁性能和交换弹性的本质的研究。本项目拟以提高实用硬磁铁氧体的磁性能为出发点，拟引入高饱和磁化强度的NiZn系铁氧体或者Fe-B系化合物等作为软磁性相，采用水热法和新颖的以鸡蛋蛋清为金属离子配合物的溶胶-凝胶法制备硬磁/软磁复合M型Sr铁氧体，结合磁力显微学系统地实验研究硬磁/软磁交换弹性复合Sr铁氧体的交换耦合作用、磁性能、微磁结构以及它们的相互关系；并专门针对交换弹性复合铁氧体，从微磁学角度出发理论模拟结合实验研究对其磁性能的变化和交换耦合的本质进行解释，以期能为我国硬磁铁氧体性能的提高进一步奠定实验和理论基础。

本项目成功采用水热法和以鸡蛋蛋清为金属离子配合物的溶胶凝胶法制备了SrFe12O19等铁氧体，并针对SrFe12O19基软、硬磁复合材料的关键科学问题，主要对不同软磁性相对复合材料的磁性能和交换耦合作用的影响进行了系统的研究。研究表明，对SrFe12O19基软硬磁复合材料而言，CoFe2O4是一种比(Ni,Zn)Fe2O4更好的“软磁性相”；而如果要采用Fe-B作为软磁性相，则只能在低于500ºC的烧结温度下才能制备出SrFe12O19/Fe-B复合物，而高于此温度将引起复杂的相变。研究还有如下新发现：1) 在SrFe12O19/(Ni,Zn)Fe2O4烧结块体中发现了多存在于垂直磁化薄膜中的条形畴结构；2)简单的研磨即可实现SrFe12O19和CoFe2O4或者Fe-B之间的交换耦合作用。通过这些研究工作，发表项目相关SCI收录论文11篇，申请相关国家发明专利6项(已授权3项)，为SrFe12O19及其复合铁氧体性能的进一步提高提供了更多的实验和理论依据。