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

随着磁性器件的小型化和高频化的发展，制备具有高饱和磁化强度和高电阻率的磁性薄膜是磁性材料研究领域的重要课题。迄今为止，已经研究了由磁性金属和非磁性绝缘体组成的纳米颗粒薄膜，并且获得了相当好的软磁性能（电阻率ρ =100-500 μ OMEGAcm，饱和磁化强度Bs-10 kG）。然而，目前需要进一步研究和开发具有高电阻率的软磁薄膜，以用于高密度磁记录头等应用。在本研究项目中，研究了铁磁合金/铁磁绝缘体多层复合材料的软磁性能和电阻率行为，采用铁磁合金和铁磁绝缘体复合靶溅射技术制备了颗粒状薄膜样品，检测电阻率和磁性。通过对铁磁合金和铁磁绝缘体的多种组合的系统研究，我们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。Fe-MgFe_2 O_4和Ni-MgFe_2 O_4体系是制备高饱和磁化强度和高电阻率软磁薄膜的理想材料。对于Fe-Mg-O多相颗粒体系，在优化的溅射条件下，获得了rho=100-400，Bs=12-16 kG的良好结果，此外还获得了电阻率较低（rho=100 μ OMEGAcm），但饱和磁化强度（Bs=19 kG）很高的Co-Fe-Al-O软磁薄膜。认为Co-Fe-Al-O薄膜可用于高密度磁记录磁头。

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.