Large anisotropy of Gilbert damping constant in L21-ordered Co2FeSi film

We experimentally demonstrated anisotropic damping of the magnetization dynamics in a highly ordered Heusler compound Co3−xFexSi (x = 1.0, 2.0, and 3.0). The field-swept ferromagnetic resonance linewidth as a function of the resonant frequency was measured to exclude extrinsic contributions from two-magnon scattering and inhomogeneous line-broadening. In L21-ordered Co2FeSi film, a wide variation in the intrinsic Gilbert damping constant from 0.0023 to 0.0061 was clearly observed in the (111) plane, where a weak uniaxial magnetic anisotropy was formed via low-temperature epitaxial growth. The large anisotropy of the Gilbert damping constant was suppressed by increasing x, which suppresses the half-metallicity in Co3−xFexSi films.