Research for Physical Properties and Applications to Electronic Devices in Ferromagnetic and Ferroelectric Oxide Films Prepared by Sputtering

在rf反应溅射制备的Bi_2O_3-Fe_2-O_3-PbTiO_3体系薄膜中，施加磁场H后，介电常数实部ε_r′发生了变化。在不同温度下退火后薄膜的Δε_r′vs. H曲线与薄膜的磁化性能密切相关。|Δε_r”(H)/ε_r’|的最大相对值可达1.0%。ε_r”(H)曲线可以用一个基于均匀磁化旋转的简单模型重建。接下来，我们测量了ε_r′和Δε_r′(H)的温度依赖关系，两者在50℃以上迅速增加，这表明在该温度下，介电基质的玻璃网络发生软化，促进电荷位移，导致介电极化。此外，我们还测量了位移电流Jd(H)对磁场的依赖关系，以确定磁导率随磁场Δε_r”(H)的变化是否是本征的。发现Jd(H)也会以类似Δε_r’(H)的方式发生变化，说明确实发生了H辅助的电荷位移。最后，我们观察了在室温下施加一个小的交流磁场所引起的介电极化。这被认为是一种新型的电磁效应。为了解释实验结果，我们提出了一个基于分散在介电玻璃基体中的铁磁纳米团簇磁化旋转的简单模型。

In Bi_2O_3-Fe_2-O_3-PbTiO_3 system thin films prepared by rf-reactive sputtering, ε_r' the real part of dielectric permittivity, was changed by applying a magnetic field H. The Δε_r' vs. H curves of the films subjected to annealing at various temperatures were strongly correlated with their magnetization properties. The maximum relative value of |Δε_r''(H)/ε_r'| reached as much as 1.0%. A ε_r''(H) curve can be reconstructed by a simple model based on uniform magnetization rotation. Next, we measured the temperature dependence of ε_r' and Δε_r'(H)- Both quantities increase rapidly above 50℃, which suggests that softening of the glass network of the dielectric matrix takes place at this temperature to promote the charge displacement giving rise to the dielectric polarization. In addition, we measured the magnetic field dependence of the displacement current Jd(H) to confirm whether the permeability change with magnetic field Δε_r''(H) is intrinsic. It was found that Jd(H) is also subject to change in a similar manner to Δε_r'(H), indicating that the charge displacement assisted by H really occurs. Finally, we observed the dielectric polarization induced by applying a small ac magnetic field at room temperature. This is considered to be a new type of electromagnetic effect. To explain the experimental results, we propose a simple model based on magnetization rotation of ferromagnetic nano-clusters dispersed in a dielectric glassy matrix.