Studies Of Magnetic Thin Film Materials For High Density Magnetic Recording

Three kinds of film materials which related to the magnetic recording have been investigated in this work. The research contains three parts:(1) FeCoN soft magnetic thin films for the write heads;(2) L10phase FePt alloy films for perpendicular recording media;(3) FeCoN synthetic antiferromagnetic coupling multilayer films for the underlayer of perpendicular recording media. The detailed results are shown as follows:Ⅰ. Investigation of structure and magnetic properties of FeCoN thin films which used for write head. When sputtering, different flux ratio of N2are used in working gas for importing N. Excellent soft magnetic properties realized in FeCoN thin films. The in-plane uniaxial anisotropy is enhanced by using the inclined sputtering and deformation of the substrate. The main conclusions are as follows:1. When sputtering, using different flux ratio of N2in the working gas could improve the soft magnetic performance. The magnetic properties of the thin films changed along with N2flux ratio. When the N2flux ratio raises from0to9%, the coercivity along easy (Hce) and hard (Hch) axes are decrease. When the N2flux ratio is10%, it has the best properties:4πMs～20kG, Hce～4.5Oe, Hch～1Oe, Hk～90Oe. When the N2flux ratio is10%, it has the lowest coercivity:Hce～3Oe, Hch～0.45Oe. N2flux ratio raise from9%to18%, FeCoN thin film keeps excellent soft magnetic properties, and the coercivity on the hard axis keeps about1Oe. When the N2flux ratio is11%, the film has the lowest coercivity:Hce～3Oe, Hch～0.45Oe. The saturation magnetization of the film decreases with the increase of N2flux ratio.2. The addition of N element into FeCo thin film causes FeCo lattice expansion and grains refining. When the N2flow ratio is10%, grain size of the film is about10nm. Although FeCoN films have large magnetic anisotropy and magnetic anisotropy, there are still very good soft magnetic properties, since the films'grain sizes are much smaller than the size of critical exchange. Strong intergranular exchange coupling effect will average the effective magnetocrystalline anisotropy and magnetoelastic anisotropy in the FeCoN film, and the effective magnetic anisotropy can be greatly reduced.3. With the N2flux ratio increases, the cutoff frequency decreases, because of the reduction of the saturation magnetization and the anisotropy field of the FeCoN film. Oblique sputtering method and deformation of the substrate improves the FeCoN films'in-plane uniaxial anisotropy field and its cutoff frequency. Using both two ways will greatly improve FeCoN film in-plane uniaxial anisotropy field and the cutoff frequency.II. Investigation of the microstructure and magnetic properties of L10phase FePt alloy thin films for perpendicular magnetic recording media. A series of [Fe/Pt]n (n=4,8,16,20,32) films are prepared. The Fe layer and Pt layer are alternately sputtering on a glass substrate with the temperature of480℃. The total thickness is fixed at40nm. Structure and magnetic properties of thin films are investigated. The sources of perpendicular anisotropy of FePt alloy films are investigated by using micromagnetic method. The main conclusions are as follows:1. All of the FePt alloy thin films'parallel and perpendicular coercivity are higher than10kOe. FePt thin film has formed a stable L10phase with such high coercivity. XRD patterns show that all of the FePt alloy films' preferred orientations are (111).2. In general,(111) texture of the L10phase of FePt thin films easy magnetization axis (c axis) and the angle of the film surface is about36°. Therefore,(111) texture of FePt thin films'effective magnetization vector perpendicular to the film surface direction should be significantly less than the component parallel to the film surface, but our experimental results are different. When the number of cycles n≤8, the remanence ratio parallel to the film surface are higher than that perpendicular to the film surface. When the number of cycles n≥16, the remanence ratio perpendicular to the film surface are still higher than that parallel to the film surface. It means that when the number of cycles n≥16, samples showing a certain degree of perpendicular anisotropy.3. By using X-ray electro-optical sub-spectrometry analysis of [Fe(5.2nm)/Pt(4.8nm)]4, Fe-rich composition interfaces are found in the film.4. The enhanced perpendicular magnetic anisotropy in the films prepared by sequential sputtering are related with the component interface, because the structure symmetric is broken in the interface of the films, which leads to an interface anisotropy.5. By investigating the δM(H) curve of FePt thin films, the exchange coupling between grains of FePt film prepared alternately sputtering is lower than the co-sputtering FePt film. The greater the number of cycle, the smaller of the exchange coupling.III. Investigation of the FeCoN sandwich-type anti-ferromagnetic coupling multilayer film The FeCoN film prepared when the N2flux ratio is5%is used as the magnetic layer, Ru as the nonmagnetic metal intermediate layer, FeCoN/Ru/FeCoN sandwich structure prepared a series of anti-ferromagnetic coupling multilayers. The influences of structures and preparation conditions on magnetic propertise have been investigated. The main conclusions are as follows:1. The SAF film's anisotropy field increases due to the exchange anisotropy energy(Kex). The anisotropy field in the SAF multilayer films increased with increasing the exchange coupling field. The exchange coupling field, anisotropy field and the cut-off frequency can be tune by changing the thickness of Ru layer and FeCoN layer.2. When the thickness of FeCoN layer is fixed, the exchange coupling field(Hex) and anisotropy field (Hk) increases with the decrease of the thickness of Ru layer. When the Ru layer thickness is less than one atomic layer thickness (0.35nm), the hard axis have larger remanence.3. Exchange coupling field and the anisotropy field increase with the decrease of the thickness of FeCoN layer. When the thickness of FeCoN layer is less than20nm, the anisotropy is becoming not obvious, however, when the thickness is less than10nm, the film is almost become isotropic.4. By smoothing, defect-less magnetic layer can get higher exchange coupling field, anisotropy field and cutoff frequency. By using oblique sputtering, the oblique sputtering anisotropy energy (shape anisotropy) is introduced in the multilayer, resulting in the exchange coupling field, anisotropy field, as well as cutoff frequency are greatly enhanced, while the coercivity of the films did not increase significantly.