Intrinsic Gilbert damping constant in Co₂MnAl Heusler alloy films

Intrinsic α-damping constants of Co₂MnAl Heusler alloy films prepared by magnetron sputtering were investigated. After deposition of Co₂MnAl films, the films were annealed at 200-400°C to control the crystal structure and the atomic order between Co, Mn, and Al sites. Ferromagnetic resonance (FMR) technique was used to obtain α values of Co₂MnAl films in this study. Out-of-plane angular dependences of the resonance field (H_R) and line width (ΔH_pp) of FMR spectra were measured and fitted using the Landau-Lifshitz-Gilbert (LLG) equation. The authors were able to fit all experimental results well because of the lack of inhomogeneities in prepared Co₂MnAl films. The α-damping constants obtained from the fitting results decreased with increasing annealing temperature and showed a minimum value of 0.007 at 300°C. It was found that a degree of B2 structure order can sensitively affect α-damping constants of Co₂MnAl films.