Preparation And Magnetic Performances Of The NiO/NiFe Multilayer Thin Films

With the rapid development of the communication industry, the microwave devices with high working frequency, bandwidth and integration degrees are required. Magneto-electric components is one of the important part of the microwave devices, it must meet to the above requirements and development towards high frequencies and miniaturization, for which excellent property of magnetic materials are required. To satisfy the applied demand, a great deal of research efforts should be devoted to exploring advanced magnetic materials or structures with high frequencies, bandwidth and thin-film integratable. Metallic soft magnetic thin films with high saturation magenticzaiton are widely used in high frequency microwave devices. The ferromagnetic resonance frequency can be continusly improved by using the multilayer structure with antiferromagentic layers. The surface spin of ferromagnetic layer will be pinned by using of the antiferromagentic layer which can improves the effective exchange field of ferromagnetic film,therefore, the ferromagnetic resonance frequency is increased with proper structure. In view of the background application of the ferromagnetic/antiferromagentic multilayer structures in high frequency microwave devices, antiferromagnetic NiO film and multilayer NiO/NiFe films and NiO/NiFe/NiO films are fabricated using magnetron sputtering. In order to find the thin film with optimal performance, the effects of preparation process on characterictics are studied.Antiferromagentic NiO thin films are farbricated by DC magnetron reactive sputtering, influence of sputting pressure, oxygen content, sputting power, substrate heating temperature and target magnetic field strength on the texture and surface morphology have been investigated. The results show NiO thin film grows with(220) preferred orientation with lower oxygen content at fiexd sputting power and pressure. However, when the oxygen content equal or larger than 8%, the NiO thin film turns to(111) preferred orientation. The desirable substrate temperatures can promote the crystallization of the NiO thin film and enhanced the preferred orientation. It is also found that a larger target magnetic field is conductive to the NiO(200) plane preferential orientation.Ferromagnetic NiFe thin films are farbricated by magnetron sputting, and the static magnetic properties dependent on film thickness are studied. The best soft magnetic properties are obtained in single layer NiFe thin film at 50 nm thickness. By using 40 nm thickness NiO buffer layer, the saturation magnetizaiton of NiO/NiFe film is greatly improved, and the remanence ratio decreased. When a 25 nm thickness NiO thin film as cover layer deposited on NiFe film, both the saturation magnetization and remanence ratio are slightly decrease. The saturation magnetization shows a maximum value when introducing 30 nm thickness NiO films as cover layer and buffer layer. In addition, the exchange bias effect has been observed in the three type layered structures which discussed above, and the coercive force are increased.The angular dependent of the ferromagnetic resonance of NiO/NiFe thin film on the sputting pressure and preferred orientation of NiO and thickness of NiFe has been studied. The results shown that both the resonance bandwidth and damping factor of NiO/NiFe with NiO(220) preferred orientation are smaller than NiO(200) preferred orientation. Thus, the high frequency magnetic performance of the former is better than the later. The g factor first increases and than decreases with increasing sputting pressure, but the damping factor has show an opposite trends. For the NiO/NiFe film with different thickness of NiFe layer, the resonance bandwidth, g factor and damping factor are decreases with the increase of NiFe thickness.