Abstract
Coexistence of exchange bias (H <sub>E</sub> ) and magnetization (M) shift was observed in as-grown and field-annealed MnO <sub>x</sub> /Ga <sub>0.95</sub> Mn <sub>0.05</sub> Asbilayers. It was found that H <sub>E</sub> initially decreases with the annealing time t <sub>a</sub> and then increases when t <sub>a</sub> >30min, while the M shift remains almost unchanged with t <sub>a</sub> . X-ray photoelectron spectroscopy (XPS) analysis reveals that MnO <sub>x</sub> is composed of MnO and Mn <sub>3</sub> O <sub>4</sub> , and the volume amount ratio of Mn <sub>3</sub> O <sub>4</sub> to MnO increases with increasing t <sub>a</sub> . A simple model based on a uniform MnOMn <sub>3</sub> O <sub>4</sub> interface with constant pinned uncompensated interfacial spins is proposed to account for the observed exchange-biased phenomena in the bilayers. © 2011 IOP Publishing Ltd.