Giant Magnetoimpedance Effect And High Frequency Properties Of Soft Magnetic Films

The rapid development of electronic and information industry has improved the core role of the dimensional soft magnetic films in magnetic sensors and high frequency devices, due to the advantage of miniaturization, integration and standardization in practical electromagnetic devices. For magnetic sensing technology, giant magnetoimpedance effect (GMI), an electromagnetic phenomenon with high signal intensity and field sensitivity, has potential applications. For high frequency electromagnetic devices, soft magnetic films with higher permeability in high operation frequency range are demanded. Hence, soft magnetic films with high saturation magnetization and high in-plane uniaxial anisotropy field have become very important research materials in high frequency applications.In this dissertation, FeNi/Cu/FeNi sandwich films without and with one or two 65 nm NiZn-ferrite spacers were prepared by radio frequency magnetron sputtering on Si(111) substrates, and thin NiZn-ferrite layers were fabricated on the free surface of Fe-based amorphous ribbons for the research of giant magnetoimpedance effect. Fe75.5Cu1Nb3Si3.5B7 films were deposited by oblique sputtering with different incidence angles, and uniform Fe75.5Cu1Nb3Si3.5B7 films with different thickness were fabricated under the application of an external magnetic field along the film plane during sputtering. And their high frequency magnetic properties were studied. Main results of these studies are as follows:1. Influence of NiZn-ferrite spacers on GMI in FeNi/Cu/FeNi sandwich films.An enhanced GMI effect is observed in the multilayer film with one NiZn-ferrite spacer. The highest GMI ratio in the FeNi/NiZn-ferrite/Cu/FeNi multilayer film reaches up to 36% at 10 MHz, which is a relatively high value for a nanometer film. This ratio is about 1.25 times larger than that of the FeNi/Cu/FeNi sandwich film (-16% at 30 MHz), while the GMI is not evidently enhanced in the FeNi/NiZn-ferrite/Cu/NiZn-ferrite/FeNi multilayer film. These results indicate that inserting one NiZn-ferrite spacer to a sandwich film is a simple and effective way to improve the GMI in the nano- film systems.2. Influence of NiZn-ferrite spacers on GMI in Fe-based amorphous ribbons.After the thin NiZn-ferrite layer coating on the free surface of a Fe-based amorphous ribbon, an enhanced GMI effect has been observed in the NiZn-ferrite modified ribbon at all measured frequencies. The largest GMI ratio up to 80% is about 2.6 times as large as that of the ribbon without any coating.3. Adjust of in-plane uniaxial magnetic anisotropy of Fe75.5Cu1Nb3Si3.5B7 films.Methods of oblique sputtering and sputtering with an external magnetic field applied in the film plane were used to induce in-plane magnetic anisotropy in the films. From the static measurements of in-plane magnetic hysteresis loops and the angular dependence of remanent magnetization, it is concluded that films deposited for 23 min with different oblique angles show in-plane anisotropy and the largest anisotropy appears at the angle of 19°. From the ferromagnetic resonance (FMR) measurement, it is found that there exist double resonance peaks at two different resonance fields. Further analyses of in-plane angular dependence of FMR reveal that these two peaks correspond to two phases in the Fe75.5Cu1Nb3Si3.5B7 films, and for the one with lager saturation magnetization Ms, the in-plane magnetic anisotropy field Hk and Ms roughly increase with increasing oblique angles, while these two quantities of the other basically show a downward trend. Additionally, for the films deposited for different time of 17, 23, and 35 min by normal sputtering under the application of an external magnetic field, no visible presence of in-plane anisotropy is obtained in Fe75.5Cu1Nb3Si3.5B7 films.4. Adjust of magnetic damping in obliquely sputtered Fe75.5Cu1Nb3Si3.5B7 films.For the films deposited for 23 min with oblique angle θ ranging from 3° to 32°, the effective damping parameter extracted from the magnetic permeability spectrum is increased with increasing oblique angle, and it is increased from 0.026 to 0.051 (0=32°). The intrinsic damping parameter extracted from the angular dependence of FMR, basically maintains the value of about 0.016 in the range of 3° to 26°, and the enhancement of effective damping is attributed to the extrinsic damping. But when the oblique angle is 32°, the intrinsic damping parameter reaches 0.037, and the main contribution to the effective damping is from intrinsic damping.