Exchange anisotropy in metal-evaporated tapes

The hysteretic properties of commercial Metal Evaporated tapes, consisting of one or three layers of Co-Ni-O, have been analysed at low temperature. When the tapes are cooled from room temperature in the saturation remanence, or in presence of a strong applied field, the hysteresis loops at low temperature are displaced, with dissymmetrical values of the coercive fields. Also the rotational hysteresis has an anomalous behaviour with a monotonic increase with the applied field. These effects are due to the interface action between the ferromagnetic Co and the antiferromagnetic CoO, which, at low temperatures, gives rise to the unidirectional exchange anisotropy