The asymmetric magnetization reversal in exchange biased granular Co/CoO films

Abstract

A special kind of asymmetric magnetization reversal characterized by a sharp step in the second quadrant of the hysteresis loop has been investigated in the exchange biased Co/CoO films. This asymmetry only exists in the film where the small clusters grow to form islands. A bimodal distribution of the first-order reversal curves diagram demonstrates that the irreversible magnetization reversal is composed of the free part and exchange biased part, originating from the grains smaller and larger than 6 nm in the film, respectively. The finite-size effect of the antiferromagnetic anisotropy in the ultrafine grains is responsible for this asymmetry.