Development of high frequency soft magnetic thin films consisting of ferromagnetic alloy/ferromagnetic insulator multi-phase granular materials

在磁性器件小型化、高频化的今天，制备高饱和磁化强度、高电阻率的磁性薄膜是磁性材料研究领域的重要课题。到目前为止，由磁性金属和非磁性绝缘体组成的纳米颗粒薄膜已经被研究，并获得了较好的软磁性能(电阻率Rho=100-500µOMEGAcm，饱和磁化强度Bs-10 kg)。本课题研究了铁磁合金/铁磁绝缘体多相颗粒薄膜的软磁性能和电阻行为，采用铁磁合金和铁磁绝缘体复合靶材溅射法制备了颗粒薄膜样品，并对其微观结构、电阻率和磁性能进行了测试。通过对多种铁磁合金和铁磁绝缘体组合的系统研究，发现控制铁磁绝缘体在薄膜表面的表面反应是非常重要的。此外，我们还发现Fe-MgFe_2O_4和Ni-MgFe_2O_4系统是具有高饱和磁化强度和高电阻率的很好的软磁薄膜的候选者。对于Fe-Mg-O多相颗粒系统，在优化的溅射条件下，获得了Rho=100-400和B_s=12-16 kg的良好结果。此外，还获得了具有很高饱和磁化强度(B_s=19 kg)的Co-Fe-Al-O软磁薄膜，尽管其电阻率很低(R_o=100µOMEGAcm)。认为Co-Fe-Al-O薄膜可用于高密度磁记录头。

As small sizing and high frequency use of magnetic devices are extensively required nowadays, it is an important subject in the research field of magnetic materials to fabricate magnetic thin films with high saturation magnetization and high electrical resistivity. Nanogranular thin films consisting of magnetic metal and nonmagnetic insulator have been investigated so far, and fairly good soft magnetic properties (resistivity rho=100-500 muOMEGAcm, saturation magnetization Bs-10 kG) were achieved. However, further investigation and development of soft magnetic thin films with high electrical resistivity are currently required for applications such as high density magnetic recording heads etc. In this research project, we have investigated soft magnetic properties and electrical resistivity behavior of ferromagnetic alloy/ferromagnetic insulator multi-phase granular thin films.Granular thin film samples were prepared by a sputtering technique with composite targets of ferromagnetic alloy and ferromagnetic insulator, and microstructure, electrical resistivity and magnetic properties were examined. From a systematic investigation for many kinds of combinations of ferromagnetic alloys and ferromagnetic insulators, we found that it is important to control surface reaction of ferromagnetic insulator on the film surface. Also, we found that Fe-MgFe_2O_4 and Ni-MgFe_2O_4 systems are candidates for very good soft magnetic thin films with high saturation magnetization and high electrical resistivity. For Fe-Mg-O multi-phase granular systems, good results, such as rho=100-400 and Bs=12-16 kG,were obtained in the optimized sputtering condition.In addition to the results mentioned above, soft magnetic thin films of Co-Fe-Al-O exhibiting very high saturation magnetization (Bs=19 kG) has been achieved although its resistivity is fairly low( rho=100 muOMEGAcm) . It is considered that the Co-Fe-Al-O film can be used for application of high density magnetic recording heads.