Exchange bias in a thin film dispersion of MnO nanocrystallites in Co

Unusually large magnetization loops shifts along the field axis, of the same order as those observed in the archetypical exchange biased system Co/CoO, have been measured in a Co/MnO thin film made using reactive ion beam assisted deposition. These large loop shifts are unexpected for a system with an antiferromagnetic anisotropy that is two orders of magnitude less than that of CoO. This magnetic behavior is attributed to the nanoscale nature of the crystallites that constitute the film, where the surface area to volume ratio is large enough so that a sizable surface magnetic contribution provides the necessary antiferromagnet to ferromagnet coupling for the large measured exchange bias.