Thickness dependence of dynamic magnetic properties of soft (FeCo)-Si alloy thin films

Abstract

${\mathrm{Fe}}_{69}{\mathrm{Co}}_{26}{\mathrm{Si}}_{5}$ alloy thin films of various thicknesses were deposited on MgO(100) single crystal substrates by magnetron sputtering at $230{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ substrate temperature. The thickness dependence of the dynamic magnetic properties was investigated using broadband ferromagnetic resonance (FMR). The x-ray diffraction results indicate that all films are of the bcc structure with an in-plane epitaxial alignment of ${[100]}_{\mathrm{FeCoSi}}//{[110]}_{\mathrm{MgO}}$. The exchange constant was determined from the field shift between the uniform precession FMR mode and the first order perpendicular standing spin wave resonance mode in the FMR spectra. The effective damping parameter decreases dramatically with increasing film thickness up to 16 nm due to the decrease of the spin pumping contribution and then remains relatively constant as the film thickness increases. In-plane angle dependent FMR measurements reveal that the in-plane anisotropy of these films is dominated by a fourfold magnetic anisotropy, which increases sharply with increasing film thickness up to 16 nm and then shows a slightly decreasing trend as the film thickness increases. In-plane angular dependence of the FMR linewidth shows a strong two-magnon scattering contribution.