Effect of oxygen migration on magnetic anisotropy and damping constant in perpendicular Ta/CoFeB/Gd/MgO/Ta multilayers

By inserting a Gd layer with strong oxygen-affinitive property, the effect of interfacial oxygen migration on the perpendicular magnetic anisotropy (PMA) and damping constant was investigated in perpendicular Ta/CoFeB/Gd/MgO/Ta multilayers. The overoxidation of CoFeB was greatly suppressed by inserting a thin Gd layer at CoFeB/MgO interface, leading to an O-poor status at interface. Different oxygen migration behavior in samples without and with Gd was observed during the thermal annealing. By optimizing Gd thickness, the effective damping constant of 0.029 and 0.037 was obtained with 0.6 nm Gd layer in out-of-plane and in-plane configuration, respectively. This value was decreased by 70% and 46% with respect to that without Gd layer. More importantly, the PMA can be well maintained when Gd thickness was increased to 1.2 nm. This effective modification of magnetic properties based on oxygen migration provides a promising pathway for spintronic applications.