SiC中缺陷的铁磁性以及反铁性耦合机理的研究

Recently, defect induced ferromagnetism in SiC becomes a hot spot in magnetism and spintronics. However some reports point out that the variation of saturation magnetization is nearly independent of the implanted fluence. So, to understand the mechanism of ferromagnetic coupling is a key issue for future applications. Based on our previous research, the ferromagnetic samples also contain a paramagnetic phase which probably is produced by single defects. In addition, all the ferromagnetic samples have the paramagnetic phase which contains the similar number of paramagnetic centers. This project aims to establish a relation between paramagnetic centers and saturation magnetization. Firstly, we plan to use electron paramagnetic resonance (EPR), positron annihilation spectroscopy (PAS), Monte Carlo method and first-principles calculation to build the exchanging model for investigating coupling mechanism of defect induced ferromagnetism in SiC. Secondly, Superconducting Quantum Interference Device (SQUID) is preformed to test the exchange bias effect. From this effect we hope to evaluate the influence of antiferromagnetism on ferromagnetism. In summary, this project can promote the research on the mechanism of magnetic ordering in defective SiC and therefore extend the application of SiC.

近些年在SiC中发现离子注入的缺陷能够在注入区域内诱发高磁饱和强度铁磁性耦合的现象（d0磁性），这一现象已经就成为自旋电子学和磁学研究的热点。但是一些实验指出d0磁性的磁饱和强度随注入剂量的变化很小，于是研究产生铁磁耦合的机理就成为实用化d0磁性的首要问题。我们发现大部分离子注入产生的缺陷磁性样品能够被分成为顺磁相、和铁磁相贡献，且所有铁磁样品中的顺磁相含有顺磁性中心数目相近。基于上述成果本项目旨在首先通过定量研究顺磁性中心数目随铁磁性磁饱和强度的变化来定量研究铁磁相和顺磁相间的相互作用，通过电子顺磁共振、正电子湮灭技术、蒙特卡洛和第一性模拟建立磁性缺陷之间相互作用的模型，进而研究铁磁作用机理。其次通过超导量子干涉器件（SQUID）交考察换偏置效应的测试反铁磁性的作用。本项目能在探索d0磁性SiC中铁磁耦合的物理机制方面做出创新性成果，为进一步推进SiC应用做出贡献。

本次研究了缺陷铁磁SiC的交换偏置效应。交换偏置的两个典型特征：磁滞随磁场冷却的变化和训练效应。采用核壳形态粒子模型定量分析了交换偏置场与冷却场的关系。基于该模型，计算出的各向异性常数为2.5 × 105 erg/cm3。Training effect 可用经典交换偏置系统的Kolmogorov-Avrami模型来描述。交换偏置的出现是铁磁和反铁磁层或核/壳之间存在界面的特征。