Inverted hysteresis in magnetic systems with interface exchange

The effects of interface exchange on magnetic hysteresis are considered for a variety of situations in a two-phase model in which the phases are coupled antiferromagnetically. This work is motivated by studies of Co-CoO nanophase systems where inverted hysteresis loops, a phenomenon closely related to shifted hysteresis loops, are obtained. Some previous examples of systems with inverted hysteresis loops are reviewed and a two-phase model with uniaxial anisotropy and interface exchange is considered. It should be emphasized that this model cannot completely explain inverted hysteresis loops, but it does show that partially inverted loops can be obtained. Cases where H is not along an anisotropy axis are discussed; it was concluded that some alignment of H with the axis of the stronger anisotropy phase is necessary to obtain partially inverted hysteresis.