( FeCo/Co–M ) n soft magnetic multilayers with uniaxial anisotropy and very high saturation magnetization

Abstract

Nanocrystalline (FeCo/CoNbZr)n and (FeCo/CoZr)n uniaxial-anisotropy soft magnetic multilayers with saturation flux density up to 22.5 kG were prepared by rf sputtering. Magnetic and microstructural properties of these films were studied before and after magnetic annealing. Cross-sectional transmission electron microscopy study showed that the soft magnetic Co–M (M=Zr, Nb, etc.) amorphous layers act as grain refiners as well as soft magnetic grain-boundary materials for the FeCo layers. The resultant multilayer films exhibit excellent uniaxial-anisotropy soft magnetic properties with small coercivity, high anisotropy field Hk, and excellent thermal stability after magnetic field annealing, which are very attractive for applications in thin-film heads for ultrahigh-density magnetic recording. The origin of the soft magnetism was discussed in the light of the random anisotropy model. The improvement of soft magnetic properties of the laminated films is closely associated with the reduction in grain size of the FeCo layers due to lamination. Qualitative agreement between the experimental data and theoretical calculations can be established. Magnetic field annealing was very effective in improving the soft magnetic properties of the films. However, further study is required in order to understand the mechanism. The saturation magnetization of the film follows a simple summation function of the saturation magnetization of the two sublayer materials, with a maximum achievable value of 22.5 kG within the uniaxial-anisotropy regime.