Off-Stoichiometry Effect On Magnetic Damping In Thin Films Of Hensler Alloy Co2mnsi

We investigated the effect of off-stoichiometry on the Gilbert magnetic damping constant (alpha) of Heusler alloy Co2MnSi (CMS) thin films by employing time-resolved magneto-optical Kerr effect (TR-MOKE) measurements along with first-principles calculations based on the linear-response theory for magnetic damping. Because of the contribution of extrinsic damping arising from two-magnon scattering, the effective alpha (alpha(eff)) extracted from the TR-MOKE responses showed dependences on the in-plane magnetic-field angle (theta(H)) and the field strength (H). Then, we obtained the smallest alpha(eff) (alpha(0)) for each sample under the most reduced contribution from two-magnon scattering realized through varying theta(H) and H values, which is the closest value to alpha. The thus obtained a o values of epitaxially grown off-stoichiometric Co2Mn beta Si gamma (gamma = 0.82) films with various (Mn + Si) compositions, (beta + gamma), decreased with increasing (beta + gamma)) from alpha(0) = 0.0057 for (Mn + Si)-deficient (beta + gamma) = 1.44 to alpha(0) = 0.0036 for (beta + gamma) = 1.90 being close to the stoichiometric one of (beta + gamma) = 2.0 at 300 K. It was also demonstrated that a half-metallic (Mn+Si)-rich CMS film with beta = 1.30 and gamma = 0.90 showed a low alpha(0) of 0.0035. The dependence of alpha(0 ) on (beta + gamma) in Co(2)MnpSi, (gamma = 0.82) was well explained by the first-principles calculations. Through the systematic investigations of off-stoichiometric CMS with various values of (beta + gamma), it was clarified that the total density of states (DOS) at the Fermi level, D(E-F), plays the key role for determining the damping constant of CMS. Furthermore, it was revealed that the reduced minority-spin DOS at E-F, caused by decreasing harmful Co-Mn antisites, is essential for reducing the damping constant of CMS. These findings demonstrate that appropriately controlling off-stoichiometry and film composition is thus promising for achieving half-metallicity and a low alpha simultaneously for CMS thin films.