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

Abstract

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 (τd) and relaxation time (τ1) as well as Gilbert damping coefficient (α). Structural ordering and magnetic parameters, including α, exhibit a non-monotonic variation with increasing t. A remarkably low value of α of 0.009 is obtained for the CFMS film with t = 20 nm without any buffer layers, which helps to avoid possible diffusion of buffer layer into CFMS. Highest saturation magnetization, lowest coercivity and α value imply CFMS film with t = 20 nm is most suitable for integrated spintronics devices viz. low current switched spin transfer torque, magnetic tunnel junction with high tunnel magnetoresistance ratio at room temperature. Despite the presence of strain, lower degree of chemical ordering in low t regime, increased defect density in high t regime, we obtained a reasonably low value of damping. In addition to the intrinsic four-fold magneto-crystalline anisotropy, an induced uniaxial anisotropy is found, which also varies non-monotonically with t. Finally, unique band structure controlled demagnetization and fast relaxation in half-metallic CFMS is correlated to α.