FMR Study of ZnFe₂O₄ Thin Films in Varied Growth Environments

Abstract

The quest for improved ferrimagnetic insulators has garnered significant research interest for spintronic devices due to their low damping constants. In this work, we investigated the growth and frequency-dependent microwave properties of sputtered ZnFe2O4 thin films grown under different gaseous environments and substrate temperatures ( $T_{\text {S}}$ ). While an argon environment promotes (111) textured ZnFe2O4 growth at intermediate $T_{\text {S}}$ , an oxygen environment produces amorphous ZnFe2O4 regardless of $T_{\text {S}}$ . A reasonably high effective magnetization, $4\pi M_{\mathbf {eff}} = \sim 0.3$ –3.7 kG, and effective anisotropy were estimated by ferromagnetic resonance (FMR) using Kittel equations in both gaseous environments at intermediate $T_{\text {S}}$ . The lowest Gilbert damping constant ( $\alpha ~\approx ~4.18\times 10^{-3}$ ) and inhomogeneous broadening ( $\Delta H_{0} =318$ Oe) were observed at the highest $T_{\text {S}}$ in the argon environment. Landau-Lifshitz damping plus inhomogeneous broadening alone cannot describe the damping in all ZnFe2O4 thin films; a low-field-loss effect has to be considered to describe the entire frequency dependence of the linewidth.