Standing wave hard X-ray photoemission study of the structure of the interfaces in Ta/Co2FeAl/MgO multilayer

Abstract

Interfaces of the magnetic layer in the heterostructure Ta/Co2FeAl/MgO have been studied using hard X-ray photoelectron spectroscopy (HAXPES). Depth-selective information with sub-nanometer resolution is obtained using X-ray standing waves. It is found that the two magnetic species namely, Co and Fe behave very differently at the interfaces; 54% of Fe in the magnetic layer gets either oxidised or alloyed with Ta at the interfaces, as against 48% of Co. Oxidation state of both Co and Fe decreases, as one moves away from the MgO interface. On the average about 0.36 nm of Co2FeAl gets oxidised at MgO interface and 0.66 nm gets alloyed with Ta at the bottom interface. Thermal annealing at 200℃ results in further oxidation of Fe, accompanied by a partial reduction of Co. It is suggested that this opposite behaviour of Fe and Co at the MgO interface may be the cause of the thermal annealing induced shift of the centroid of Fe distribution towards MgO layer, as observed in some STEM studies in such heterostructures.