Sudies On The Static And Dynamic Magnetic Properties Of FeCo Based Alloy Thin Films

With the rapid development of electronics and information industry, the electronic components are urgently required to the direction of the miniaturization, high-frequency, and integrated. As the core of electronic components, magnetic materials are put forward higher requirements. Nowadays, Soft magnetic thin films have been studied intensively because of their potential applications in highly integrated devices, such as magnetic inductors, transformers, and magnetic recording heads. The basic demands for these films are high saturation magnetization4nMs, low coercivity Hc, high electric resistivity p, and appropriate anisotropy field Hk. Among various materials, FeCo alloys are important materials for their high saturation magnetization. However, it is difficult for FeCo alloys thin fims to achieve low coercivity and in-plane uniaxial magnetic anisotropy due to its high magnetocrystalline anisotropy and saturation magnetostriction constant. Therefore, it is important and essential to improve the soft magnetic properties and high-frequency characteristics of the FeCo alloy thin films.In this thesis, a series of FeCo based alloy thin films were prepared by adding third element. The static and dynamic properties of these films were investigated, respectively. The main conclusions are as follows:Ⅰ. FeCoAlO and FeCoAlN thin filmsFor FeCoAlO and FeCoAIN thin films, the Al-O and Al-N elements added by using Al2O3and AlN ceramic chips could successfully optimize the soft magnetic properties of FeCo alloy thin films. The good soft magnetic properties can be attributed to the refine of grain size in both kinds of the films. The permeability spectra almost exhibited a relaxation characteristic and the real part of the permeability,μ',had a high value at low frequency region.(1) FeCoAlO thin films showed good soft magnetic properties with increasing of Al content. As the Al content changed from11.8to18.5at.%, a low coercivity Hc of3-6Oe was obtained. These films possessed a well defined in-plane uniaxial magnetic anisotropy(Hk～50Oe). When the Al content was11.8at.%, the film showed high saturation magnetization (4nMs=21.1kG) and low coercivity (Hce=5.2Oe, Hch=3.6Oe Hc).(2) FeCoAlN thin films also showed good soft magnetic properties with increasing of Al content. As the Al content changed from13.8to31.0at.%, a low coercivity Hc of5-8Oe was obtained. The in-plane anisotropy of the film changed while the Al content was21.9and28.8at.%.Ⅱ. FeCoAlO gradient composition thin filmsIn order to get good frequency performance, the FeCoAlO gradient composition thin films fabricated by composite target with Al2O3ceramic chips arrayed in one half of sputtering area were introduced.(1) By using the asymmetric target, the Al-O composition gradient was introduced into the FeCoAlO thin films to induce the stress anisotropy. The excellent high frequency characteristics of the gradient composition thin films were much improved compared with that of the uniform composition thin films.(2) The permeability spectra of the FeCoAlO gradient composition films exhibited three different features with the number of the Al2O3ceramic chips: relaxation characteristic (4,8pcs), resonance characteristic (12,16pcs), and absorptive characteristic in GHz region (20,24chips).(3) The FeCoAlO gradient composition films showed very high resonance frequency of beyond3.0GHz at Ar gas flow rate of7.5-15sccm and the real permeability μ' had a high value of～200at low frequency side. In particular, a resonance frequency of4.0GHz was obtained at the Ar gas flow rate of15sccm. When the Ar gas flow rates were equal or more than12.5seem, the easy axis was perpendicular to the applied external magnetic field.(4) The FeCoAlO gradient composition thin films also showed good high frequency response when the applied external magnetic field was removed. (5) A large in-plane uniaxial magnetic anisotropy (Hk>100Oe) were obtained at Ar depositing pressure of4-12mTorr.III. FeCoAlON and FeCoZr stripe domain thin filmsThe static and dynamic properties of the FeCoAlON and FeCoZr thin films with stripe domain structure were investigated. The appearance of the stripe domain structure needs to reach a certain element content, and the film thickness must be grater than a critical value. For both kinds of the films, the multiple resonances occurred in the permeability spectra.(1) The stripe domain structure was observed in210nm thick FeCoAlON (the nitrogen partial of5%) and150nm thick FeCoZr (the Zr content of11.2at.%) thin films, it is a critical thickness for two kinds of the films, respectively.(2) For the films with stripe domain structure, the residual magnetization ratio of the in-plane hysteresis loops could reflect the angle between the orientation of magnetic moment and film plane. The smaller the residual magnetization ratio, the bigger the angle is, and the more obvious the perpendicular magnetic anisotropy is.