Low magnetic damping for equiatomic CoFeMnSi Heusler alloy

Magnetic materials with low Gilbert damping and low magnetization are necessary for the realization of faster or more energy-efficient spintronic devices based on spin-transfer-torque. Here, we report Gilbert damping in epitaxially grown equiatomic quaternary CoFeMnSi Heusler alloy films. The 10 nm-thick films show a saturation magnetization of M_S = 630 emu cm^-3 and a Gilbert damping constant of , which are relatively small values among transition metal ferromagnets, in addition to its soft magnetic properties. The physical origin of the relatively low damping and the possibility of a further reduction of α to the ultra-low damping regime ∼10^-4 are discussed in terms of the spin-gapless-like electronic structure and the effect of the chemical order computed from first principles.