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 ${t}_{\text{Co}}$ 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 ${H}_{E}$ being either smaller or larger than the continuous film depending on the temperature. Furthermore, with increasing ${t}_{\text{Co}}$, 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 ${H}_{E}$ and coercive field ${H}_{C}$ with increasing ${t}_{\text{Co}}$ at all temperatures.