Exchange Bias in NiFe/IrMn/CoFeB Antidot Arrays

A study was made of the exchange bias effect in a structure of SiO₂/Ta (5 nm)/NiFe (7 nm)/IrMn (10 nm)/CoFeB (7 nm)/Ta (5 nm) with nanoscale antidot arrays. The nanostructure comprised rhomboid lattice antidot arrays with antidot diameters from 150 to 300 nm and a rhomboid lattice period of 500 nm. Enhancements of exchange bias H_EX and coercivity HC were observed in the nanostructure antidot arrays compared to continuous film. These effects were mainly ascribed to the physical limitations on ferromagnetic and antiferromagnetic layers due to the presence of antidots. In antidot arrays, due to the presence of nonmagnetic holes, the ferromagnetic-ferromagnetic interactions in FM layer are reduced, leading to smaller ferromagnetic domains and larger exchange bias with the random-field model. In this paper, the relation between the antidot diameter size and exchange bias was studied.