Probing the exchange bias in Co/CoO nanoscale antidot arrays using anisotropic magnetoresistance

Abstract

The dependence of exchange bias in polycrystalline Co/CoO nanoscale antidot arrays on temperature and Co layer thickness tCo has been systematically probed using the anisotropic magnetoresistance technique. Our experimental results reveal a relatively small degree of asymmetry in the magnetization reversal process of the antidot arrays as compared to a continuous film of identical composition, attributable to the configurational anisotropy of the antidot arrays and the competition between interfacial ferromagnetic-antiferromagnetic (FM-AFM) exchange anisotropy and FM uniaxial anisotropy. The strong interplay between thermal activation effects and AFM domain size confinement in the antidot arrays results in the exchange bias field HE being either smaller or larger than the continuous film depending on the temperature. Furthermore, with increasing tCo, the asymmetry in the magnetization reversal of the antidot arrays increases monotonously due to enhancement in the FM anisotropy. This enhancement is accompanied by a reduction in the magnitudes of HE and coercive field HC with increasing tCo at all temperatures. © 2009 The American Physical Society.