Role of the Cr Buffer Layer in the Thickness-Dependent Ultrafast Magnetization Dynamics of Co2Fe0.4Mn0.6Si Heusler Alloy Thin Films

Abstract

The epitaxial growth of Co2Fe0.4Mn0.6Si (CFMS) Heusler alloy on MgO with high crystal orientation requires the use of buffer layer. The utilization of Cr buffer layer in a controlled manner without hampering the intrinsic CFMS properties remains a challenge. Here, we have epitaxially grown the CFMS films on Cr buffered MgO substrate and investigated the thickness (t)-dependent variation in structural ordering, and its impact on magnetic Gilbert damping and magnetic anisotropy. We observed a regular improvement in the crystal structure with increasing t, which caused similar increasing trend in saturation magnetization and magneto-crystalline anisotropy (MCA). Interestingly, we achieved a very low t-independent value of Gilbert damping parameter (α) of ~ 0.0045 because of unaltered atomic site ordering which indicates different origin of MCA and α in this system. Notably, α also remains nearly independent of frequency (f) for lower thickness regime in these CFMS films. The observation of t-independent and f-independent value of α strongly suggests the suitability of thinner CFMS film for device applications in broadband frequency regime.