Metastable states in layered antiferromagnetic structures causing giant magnetoresistance

Abstract

Metastable states in a spin system with antiferromagnetic and ferromagnetic interactions and a possible local energy minimum have been studied. The antiferromagnetic state of this sort of system with zero magnetization is shown to be stable to the action of an external magnetic field. Within a certain range of external magnetic field amplitudes this state becomes a local energy minimum separated from the global minimum by a big energy barrier. Only when the external field is strong enough, the local energy minimum disappears and an abrupt transition to a ferromagnetic state occurs. Analytical expressions explaining this behavior are obtained in terms of the mean field approximation. A layered lattice with a finite interaction radius is used for computer simulation whose results agree with conclusions of the mean field approximation.