Control of perpendicular magnetic anisotropy and spin pumping damping in MgO/CoFeB/ Ta/Pt structures

Abstract

The perpendicular magnetic anisotropy (PMA) and spin pumping induced magnetic damping of CoFeB films can be significantly tuned by the adjacent nonmagnetic layer (Ta or Pt). For the CoFeB/Pt(t Pt) structure, both PMA strength and magnetic damping increase with t Pt, due to the enhanced interfacial orbital hybridization and spin pumping effects, respectively. By inserting a thin Ta interlayer between CoFeB and Pt, the magnetic easy axis immediately turns into in-plane direction. Meanwhile, time-resolved magneto-optical Kerr effect measurement shows an obvious reduction in the magnetic damping, which can be explained as the increase of spin current backflow and the decrease of interfacial spin-mixing conductivity. As the Ta interlayer thickness (t Ta) increases, the effective damping parameter α s measured at saturation field initially decreases and eventually reaches a constant value of 0.027. The α s value at t Ta > 5 nm does not change regardless of the top Pt layer, implying the influence of Pt is completely isolated and the spin diffusion length of Ta is around 5 nm. Our findings provide more insights into the control of PMA strength and spin pumping contribution to magnetic damping.