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

在射频反应溅射制备的Bi_2O_3-Fe_2-O_3-PbTiO_3系薄膜中，施加磁场H改变了介电常数的真实的部分ε_r '。在不同温度下退火的薄膜的Δ ε r '-H曲线与其磁化强度有很强的相关性。的最大相对值|Δ ε_r "（H）/ε_r"|达到了1.0%。ε_r "（H）曲线可以通过基于均匀磁化旋转的简单模型来重建。然后，我们测量了ε_r '和Δ ε_r'（H）的温度依赖性。这两个量在50 ℃以上迅速增加，这表明在此温度下介质基体的玻璃网络发生软化，促进电荷位移，引起介质极化。此外，我们还测量了位移电流Jd（H）的磁场依赖性，以确认磁导率随磁场的变化Δ ε_r "（H）是否是本征的。发现Jd（H）也以类似于Δ ε r '（H）的方式变化，表明H辅助的电荷位移确实发生了。最后，我们观察到在室温下施加一个小的交流磁场诱导的介电极化。这被认为是一种新型的电磁效应。为了解释实验结果，我们提出了一个简单的模型的基础上分散在介电玻璃基质中的铁磁纳米团簇的磁化旋转。

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.