Significant modulation of Gilbert damping in ultrathin ferromagnetic films by altering the surface magnetic anisotropy

The ability to control the Gilbert damping which determines the lifetime of spin information is crucial for designing spintronic and magnonic devices. Thus, controlling the Gilbert damping parameter alpha has been a significant research target for several decades. Although numerous approaches have been explored to control alpha, few reports of large changes of this parameter have been presented. Herein, we demonstrate significant change of alpha in 2-nm-thick Co25Fe75 films originating from uniaxial surface magnetic anisotropy, which affects the two-magnon scattering. We report a change in alpha by approximately 0.02, or 300%. The value for alpha and its change are comparable to those observed in a previous study using a film that is one order of magnitude thicker. Our results achieved with Co25Fe75 can be directly transferred to other ultrathin ferromagnetic materials, which are a promising platform for spin information processing, and thus represents a versatile approach to modulate the Gilbert damping.