Magnetic Damping Properties of Single-Crystalline Co₅₅Mn₁₈Ga₂₇ and Co₅₀Mn₁₈Ga₃₂ Films

We investigate the structural, static magnetic and damping properties in two Mn-deficient magnetic Weyl semimetal Co-Mn-Ga (CMG) alloy films, i.e., Co₅₅Mn₁₈Ga₂₇ (CMG1) and Co₅₀Mn₁₈Ga₃₂ (CMG2), which were epitaxially grown on MgO (001) substrates. CMG1 has a mixing phase of B₂ and L2₁, larger saturation magnetization (M_s ∼ 760 emu/cm³), stronger in-plane magnetic anisotropy. CMG2 has an almost pure B2 phase, smaller M_s (∼ 330 emu/cm³), negligible in-plane magnetic anisotropy. Time-resolved magneto-optical Kerr effect results unambiguously demonstrate an obvious perpendicular standing spin wave (PSSW) mode in addition to the Kittel mode for both of the CMG films. The intrinsic damping constant is about 0.0055 and 0.015 for CMG1 and CMG2, respectively, which are both significantly larger than that of the stoichiometric CMG (i.e., Co₂MnGa) film reported previously. In combination with the first-principles calculations, the intrinsic damping properties of the Mn-deficient CMG films can be well explained by considering the increase of density of states at the Fermi level, reduction of M_s, and excitation of the PSSW mode. These findings provide a new clue to tuning the magnetic damping of the magnetic Weyl semimetal film through slight off-stoichiometry.