FeAl films*

Half-metallic Heusler compounds are predicted to have low intrinsic damping due to the suppression of spin-flip scattering. Here, we measure the damping constant in epitaxial MgO(001)/Co₂FeAl Heusler films using broadband (0-40 GHz) ferromagnetic resonance (FMR). For in-plane FMR, the linewidth (~hundreds of Oe) is a nonlinear function of frequency and anisotropic, smaller for magnetization along CFA<110> and larger for magnetization along CFA <100>. A much narrower linewidth (~tens of Oe) is found for out-of-plane FMR, constraining the intrinsic damping value α≤10-3. The in-plane behavior of the FMR linewidth is attributed to an anisotropic two-magnon scattering mechanism. We follow the Krivosik’s approach (P. Krivosik et al. JAP 101, 083901 (2007)) to fit our in-plane linewidth data with a self-consistent two-magnon linewidth calculation and obtain an inhomogeneity correlation length of ~70nm with an intrinsic damping α≤10-3, which is consistent with the out-of-plane measurement. We discuss how the presence of low intrinsic damping enhances the two-magnon linewidth, explaining common reports of large two-magnon FMR linewidths in Heusler compounds.