Substrate Influence on the Magnetization Dynamics of Ni-Fe Thin Films

This paper describes the variation of the damping constant $\alpha $ of Ni-Fe films with various thicknesses deposited on the soda-lime glass, quartz, and thermally resistant glass (Tempax). Both the surface roughness and the in-plane average grain size are independent of film thickness, while they vary with the kind of substrates, that is, both the surface roughness and the grain size of the films on Tempax are larger than those on either the soda-lime glass or the quartz, and its value is $\sim 0.60$ and 30 nm, respectively. The changes in $\alpha $ with thickness are independent of the kind of substrates, but their values depend on the substrate: each value for the soda-lime glass substrate is smaller than those for the other substrates and is very close to the typical Ni-Fe film value. This means that the extrinsic damping is weakened by both the weak anisotropy dispersion for the soda-lime glass and the lower structural inhomogeneity, as the grain size, for the glass. Therefore, it is pointed out that $\alpha $ of the ultra-thin films sensitively varies with the substrate and can be effectively controlled by suppressing both the structural inhomogeneity, such as the grain size, and the magnetic inhomogeneity, such as the anisotropy dispersion.