Electric-field effects on magnetic anisotropy and damping constant in Ta/CoFeB/MgO investigated by ferromagnetic resonance

We investigate electric-field effects on the effective magnetic anisotropy energy density K-eff and the Gilbert damping constant alpha in Ta/CoFeB/MgO structures with CoFeB thickness t ranging from 1.4 to 1.8 nm by ferromagnetic resonance. The electric field-induced modulation ratio of the areal energy density K(eff)t does not depend on the CoFeB thickness, indicating that the electric-field effect on the magnetic anisotropy originates from the modulation of CoFeB/MgO-interfacial magnetic anisotropy. A clear electric-field modulation of alpha is observed for the structure with t = 1.4 nm, and almost no modulation for the structures with t >= 1.5 nm. (C) 2014 AIP Publishing LLC.