Preparation And High-frequency Soft Magnetic Performances Of Co-based Half-metal Heusler Alloy Films

With the rapid development of mobile and satellite communication technology, the requirements for the miniaturization, high frequency, integration of electronic devices are increasingly desire. The main factor for limiting the miniaturization and high frequency of electronic devices is the large dimension of micromagnetic inductors and other magnetic devices. In order to satisfy with the requirements of miniaturization of integrated circuits, it becomes a hot point to explore the soft magnetic films with high saturation magnetization, low coercivity and high ferromagnetic resonance frequency. Comparing with the magnetization, which has a limited enhancing possibility, the uniaxial magnetic anisotropy (UMA) of soft magnetic films (SMFs) may increase by1or2orders, some efforts therefore are focused on exploring the SMFs with high UMA. hi this thesis, Co-based half-metal Heusler alloy SMFs were prepared by an oblique sputtering method in magnetron sputtering devices. Microwave ferromagnetic properties and microstructure of the SMFs were investigated. The main research results were summarized as follows:(1) Co2FeSi alloy films were prepared by a RF oblique sputtering method at room temperature. The effect of sample position and sputtering power on the microwave ferromagnetic properties of CoaFeSi alloy films were systematically studied. It is revealed that the microwave ferromagnetic properties of Co2FeSi films are sensitive to the sample position and the sputtering power. It is exciting that the as-deposited films without any magnetic annealing exhibit high in-plane uniaxial magnetic anisotropy field Hk up to330Oe, and low coercivity in range of5-28Oe. As a result, high self-biased ferromagnetic resonance frequency up to4.75GHz is achieved in as-deposited oblique sputtered films. These results indicate that Co2FeSi Heusler alloy films are promising candidate for high-frequency applications.(2) The Co2FeSi Heusler alloy films with Al2O3doping were deposited on Si (100) substrates using oblique sputtering method at room temperature. It is revealed that microwave ferromagnetic properties of thin films can be effectively improved by Al2O3 doping, the as-deposited films exhibit a very high in-plane UMA HK up to360Oe and low coercivity of8Oe. Consequently, a very high self-bias ferromagnetic resonance frequency in excess of5.02GHz was obtained in as-deposited Co2FeSi films without any annealing. The good microwave ferromagnetic performances and the integrated circuits compatible fabrication process of Co2FeSi films make possible application in RF/microwave devices.(3) Co2FeAl0.3Si0.7alloy films with/without Cr buffer layer were prepared on Si (100) substrates at room temperature. It is revealed that the Hk only slightly increases, while the coercivity along hard and easy axis increases significantly for the sputtering time of Cr films from0to7.5min, implying Cr buffer layer isn’t a good choice to improve the soft magnetic properties of thin films.