The effect of capping layer Ta on magnetic behaviour for multilayers Ta/Co/Co3O4/Ta

Ta/Co/Co3O4/Ta and Ta/Co/Co3O4 multilayers were fabricated in a magnetron sputtering system under the same experimental conditions. The exchange bias field HE of Ta/Co/Co3O4/Ta was found obviously higher than that of Ta/Co/Co3O4. The results of XPS showed that some Ta atoms of capping layer in Ta/Co/Co3O4/Ta diffused into Co3O4 layer and reduced most of Co3O4 to CoO and a minor part to metallic Co, and introduced some non-magnetic defects of Ta oxide into the AFM layer. The effective thickness of interfacial layer CoO was evaluated according to the finite-size effect. Two possible reasons of enhancement of HE by Ta capping layer were proposed. The dilution of the AFM layer by Ta oxide may lead to the formation of AFM domains and some surplus magnetization to enhance HE. The metallic Co enchased in CoO matrix may lead to an increase of FM-AFM interface for the enhancement of HE.