Influence of thickness-dependent structural evolution on ultrafast magnetization dynamics in Co2Fe0.4Mn0.6Si Heusler alloy thin films

We experimentally investigate thickness (t)-dependent evolution of structural and magnetic properties in Co2Fe0.4Mn0.6Si (CFMS) thin films and correlate them with ultrafast demagnetization time (tau(d)) and relaxation time (tau(1)) as well as the Gilbert damping coefficient alpha). Structural ordering and magnetic parameters, including alpha, exhibit a nonmonotonic variation with increasing t. A remarkably low value of alpha of 0.009 is obtained for the CFMS film with t = 20 nm without any buffer layers, which helps to avoid possible diffusion of the buffer layer into CFMS. Highest saturation magnetization, lowest coercivity, and the alpha value imply CFMS film with t = 20 nm is most suitable for integrated spintronics devices, viz. low-current switched spin transfer torque, and magnetic tunnel junction with a high tunnel magnetoresistance ratio at room temperature. Despite the presence of strain, a lower degree of chemical ordering in the low-t regime, and increased defect density in the high-t regime, we obtained a reasonably low value of damping. In addition to the intrinsic fourfold magnetocrystalline anisotropy, an induced uniaxial anisotropy is found, which also varies nonmonotonically with t. Finally, unique band structure controlled demagnetization and fast relaxation in half-metallic CFMS is correlated to alpha.