磁电多铁性材料Z型铁氧体的磁介电效应研究

Magnetodielectric (MD) effect has attracted great attention due to the renaissance of research on multiferroic materials involving magnetoelectric coupling. The study of MD effect is important regarding not only fundamental interest but also potential applications. One of the interesting scenarios is the correlation between change of dielectric constant and the magnetization (Δε∝ M2), which was derived within the framework of Ginzburg-Landau theory for the second-order phase transition in ferroelectromagnet. This scenario has been used to interpret the MD effect in a number of ferromagnetic systems. Even for antiferromagnetic systems, this scenario is valid for the MD effect induced by external magnetic field. However, it was shown that this scenario does not work for Mn3O4, which is believed to be due to some complex spin-spin correlation in the magnetically ordered phase. Therefore, it is interesting to examine the validity of this scenario in other systems, especially those with complicated spin structures. In this project, the temperature and frequency dependences of MD effect will be investigated in Z-type hexaferrite SCFO. The mechanism of MD effect and the role of the spontaneous magnetization will be explored in order to establish a general theoretical model suitable for all kinds of magnetic structures. This work helps to deepen the understanding of the correlation between magnetization and MD and will also contribute to practical applications of the mutual control of magnetic and electric properties of the Z-type hexaferrite SCFO.

由于与磁电耦合密切相关的多铁材料研究的复兴，磁介电效应也引起了人们广泛的关注，它在基础研究和应用方面都具有重要的意义。根据铁电磁体的Ginzburg-Landau二级相变理论，介电常数的变化和磁化强度的平方成正比关系，它可以解释共线磁结构体系中的磁介电效应，但对于具有复杂的自旋结构的四氧化三锰体系并不适用。目前这一关系在其它具有复杂的自旋结构的体系是否有效尚不清楚。 本项目拟系统研究不同温度及频率(包括低频和高频)下具有复杂磁结构的Z型铁氧体SCFO的磁介电效应和磁性，通过对不同颗粒度样品的详细研究，揭示介电常数的变化和磁化强度之间的关系及磁电耦合的物理机制，为建立适合于各种磁结构的理论模型提供依据。这一工作有助于深化对磁介电和磁化强度间关联的认识，为Z型铁氧体SCFO在磁电调控方面的应用研究提供有意义的参考。

由于与磁电耦合密切相关的多铁材料研究的复兴，磁介电效应也引起了人们广泛的关注，它在基础研究和应用方面都具有重要的意义。根据铁电磁体的Ginzburg–Landau二级相变理论，介电常数的变化和磁化强度的平方成正比关系，它可以解释共线磁结构体系中的磁介电效应，但对于具有复杂的自旋结构的四氧化三锰体系并不适用。目前这一关系在其它具有复杂的自旋结构的体系是否有效尚不清楚。 制备了400 nm、5 um、20 um几种不同粒径的Z相单相样品，对不同粒径Z 型铁氧体MH、CH、CT 曲线的测量，研究了它在300K 时的磁性和磁介电效应与粒径大小的关系，观察到了相对比较大的负的磁电容，并且在室温附近且低频情况下最明显，低场部分不满足Δε∝M2源于磁畴和畴壁的运动。这一工作有助于深化对磁介电和磁化强度间关联的认识，为Z型铁氧体SCFO在磁电调控方面的应用研究提供有意义的参考。在项目的资助下，发表论文8篇，其中被SCI收录6篇，申请专利3项，取得了圆满成功。