Investigation On Properties Of FeCo Based Alloy Films With Al-O,C And N Doped

Recently, soft magnetic thin film has been increasingly applied in industry accompanying the rapid development of electronic information. When the soft magnetic thin films were used as perpendicular magnetic recording head or magnetic induction devises, high saturation magnetization, low coercive force, good high frequency response characteristics were desired. So, it is necessary and significant to study and improve the soft magnetic properties and high frequency response characteristics of soft magnetic thin films. FeCo alloy has been studied systematically because of its highest saturation magnetization. However, it is difficult to obtain excellent soft magnetic properties in FeCo alloy due to its large magnetocrystalline anisotropy constant and saturation magnetostriction coefficients. Therefore, it is one important challenge to improve the soft magnetic properties of FeCo alloy films while maintain its high saturation magnetization. Using suitable underlayers between the substrate and the FeCo films and adding the third element to FeCo alloy films are the proper methods.In this thesis, three series of FeCo-based thin films were prepared by RF magnetron sputtering. The influence of adding Al-O, C, and N to FeCo films on soft magnetic properties and high frequency characteristics were sudied. The main results are as follows:Ⅰ. FeCoAlO films1) The FeCoAlO films have high saturation magnetization and good soft magnetic properties:Hce=5.2Oe, Hch=3.6Oe,4πMs=21.3kG. The improvement of soft magnetic proerties can be attributed to the refine of grain size in FeCoAlO films. The amorphous Al-O matrix lies at the boundary of FeCo crystalline granules and limits the grains growing, consequently, enhancing the exchange coupling among grains and reducing the effective anisotropy.2) The soft magnetic properties of FeCoAlO films are intimately correlated with the sputtering condition. The best sputtering condition:sputtering power P=400W; sputtering pressure PAr=4mTorr;film thickness t=500nm. 3) The dynamical magnetizing model of FeCoAlO films is traditional damping model. As the content percent Al% increases from 6% to 14.6%, the cut-off frequency increases from 0.6 GHz to 1.0 GHz, and meanwhile, the permeability decreases slightly.Ⅱ. FeCoAlOC films1) If C element was introduced into FeCoAlO films by sputting inorganic graphite, large clusters mixing with FeCo granules were formed in films, resluting in large stress and deteriorated soft magnetic properties.2) If C element was introduced into FeCoAlO films by sputting organic epoxy resin, the nanocrystalline structure was formed when Sc%(?)0.42%, and at the same time, high saturation magnetization, good soft magnetic properties and high frequency characteristics were obtained. When Sc%=0.28%, FeCoAlOC nanocrystalline films show best soft magnetic properties:Hce=1.7Oe, Hch=2.1Oe;47πMs=20kG;fr=2.8GHz,μ'=300.3) High frequency curves of FeCoAlOC nanocrystalline films show obvious resonance characteristics. The simulation results of high frequency curves by LLG equation agree well with the experiment results.4) With the increase of C, amorphous FeCoAlOC films were obtained. The coercivities decrease further because the grain boundary disappearances. Nevertheless, the magnetic moments of Fe and Co in amorphous films are lower than that in crystalline films. So, the saturation magnetization of amorphous films drastically drops. Although the resistivity of amorphous films is high, the permeability and cut-off frequency are lower due to the disappearance of in-plane uniaxial anisotropy and the increase of natural resonance loss.5) The amorphous FeCoAlOC films were annealled by slow and rapid speed thermal process, respactively. It is expected that the amorphous FeCoAlOC films could be crystallized and smaller grain size of nanocrystalline could be obtained in thermal process. It is found out that grain growth was inevitable in slow speed thermal process while a new chemical compound was generated in rapid speed thermal process. Both results will lead to the deterioration of soft magnetic properties. Ⅲ. FeCoAlON films1) When the nitrogen partial pressure is low (N2%(?)0.2%), the saturation magnetization of FeCoAlON films is high (about 20kG) and the coercivity is low (3-4Oe). The microstructure indicates that adding N is beneficial to the refinement of grain size, which result in the improvement of soft magnetic properties.2) With the increasing of nitrogen partial pressure (N2%(?)0.4%), strip domain were formed in FeCoAlON films. The magnetization has perpendicular component alone the normal direction of film plane and the magnetoelastic anisotropy energy is high, which leads to the deterioration of soft magnetic properties and the disappearance of in-plane uniaxial anisotropy.3) The dynamic magnetizing model of FeCoAlON thin films with low nitrogen is conventional damping model. The permeability at low frequency is high (about 600) while the cut-off frequency is low (0.5GHz).4) The dynamic magnetizing process of FeCoAlON thin films with high nitrogen contents is complicated, showing natural resonance characteristics. Furthermore, more than one resonance peaks along both the hard and the easy axis were observed.