FMR Study of ZnFe₂O₄ Thin Films in Varied Growth Environments

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 (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{\text {S}}$ </tex-math></inline-formula>). While an argon environment promotes (111) textured ZnFe2O4 growth at intermediate <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{\text {S}}$ </tex-math></inline-formula>, an oxygen environment produces amorphous ZnFe2O4 regardless of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{\text {S}}$ </tex-math></inline-formula>. A reasonably high effective magnetization, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\pi M_{\mathbf {eff}} = \sim 0.3$ </tex-math></inline-formula>–3.7 kG, and effective anisotropy were estimated by ferromagnetic resonance (FMR) using Kittel equations in both gaseous environments at intermediate <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{\text {S}}$ </tex-math></inline-formula>. The lowest Gilbert damping constant (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha ~\approx ~4.18\times 10^{-3}$ </tex-math></inline-formula>) and inhomogeneous broadening (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta H_{0} =318$ </tex-math></inline-formula> Oe) were observed at the highest <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{\text {S}}$ </tex-math></inline-formula> 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.