Exchange bias and asymmetric magnetization reversal in ultrathin Fe films grown on GaAs (001) substrates

Magnetization measurements on a series of Fe films grown by molecular beam epitaxy on GaAs (001) substrates and capped with a thin Au layer reveal interesting exchange bias (EB) properties at low temperatures. The observed exchange bias decreases rapidly with increasing temperature, and completely disappears above 30K. While the Fe samples were not grown with an intentionally deposited antiferromagnetic (AFM) layer, X-ray reflectometry, X-ray absorption near-edge spectroscopy carried out near the L-edge of Fe, and comparison with similar Fe/GaAs samples capped with Al, which do not show exchange bias, suggest that the exchange bias in the GaAs/Fe/Au multilayers is caused by an AFM Fe oxide at the Fe/Au interface formed by penetration of oxygen through the Au capping layer. The observed exchange bias is accompanied by a strikingly asymmetric magnetization reversal of the Fe films occurring when the magnetic field is applied at angles away from the easy axis of the film. The observed asymmetry can be interpreted in terms of a competition between cubic, uniaxial, and unidirectional magnetic anisotropy characteristic of the exchange-biased Fe film. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4798515]