Evolution of the spin wave dynamics of Fe 0.89 Ga 0.11 thin films driven by varying argon sputtering pressure

Abstract

In this work we have investigated the influence of Ar sputtering pressure (𝑃Ar) on the spin-wave dynamics of Fe1-xGax thin films. The evolution of the magnetic anisotropies and exchange stiffness constant was studied for increasing 𝑃Ar as a result of the incorporation of impurities that modify the magnetic structure of the samples. While the perpendicular magnetic anisotropy shows only a slight evolution within the measured range, the observation of standing spin waves by ferromagnetic resonance (FMR) reveals a clear evolution of the spinwave regime with 𝑃Ar. Films grown at low 𝑃Ar exhibit a behavior consistent with the model proposed by Kittel, indicating a homogeneous magnetization across the film thickness and rigid spin pinning at the samplesurfaces. This regime is supported by the power-law dependence of the resonance fields, with an exponent of 1.7, close to the quadratic dependence expected within the Kittel standing spin-wave model. In contrast, films grown at higher 𝑃Ar show a progressive deviation from this behavior, consistent with partial spin relaxation at the interfaces and a non-uniform magnetization profile across the film thickness, as described by the Portis model. In this regime, the mode dependence becomes closer to linear, with exponents decreasing to 1.05 and 1.18 for the intermediate- and high-pressure films, respectively, and the estimated magnetization gradients reach 4.3% and 17%. These results demonstrate that controlling 𝑃Ar provides an effective route to tune the exchange stiffness and spin-wave characteristics of Fe-Ga thin films, which is relevant for the optimization ofmagnetostrictive materials in magnonic applications.