Ferromagnetic and Spin-Wave Resonance on Heavy-Metal-Doped Permalloy Films: Temperature Effects

Broadband ferromagnetic resonance (FMR) spectroscopy is used to study the temperature (T) and dopant-concentration dependence of the magnetodynamic properties of Permalloy (Py = Ni80Fe20) and Py100-xMx films, where the dopant M = Pt, Au, and Ag. The saturation magnetization (MS) and Gilbert damping constant (α) are determined from the uniform FMR mode, while the spin wave stiffness (D) is extracted using the first perpendicular standing spinwave mode. The temperature dependence of D is best described by a T2 law, which suggests a noticeable effect of the itinerant character of the electrons. The spin wave stiffness is also estimated using Bloch's law and the two methods are compared. The results strongly imply that not only spin wave and Stoner excitations, but also other mechanisms contribute to the reduction of MS. The damping increases with T for all samples, but the enhancement is most pronounced for Py doped with 30 at.% Au.