Magnetoresistance of Co-EuS, a macroscopic ferrimagnet

Abstract

Macroscopic ferrimagnets are materials consisting of two magnetic phases with a negative magnetic exchange at the phase boundary. A prototypical example is the Co-EuS system which consists of {approx}10 nm particles of EuS in a matrix of metallic cobalt. The EuS is exchange coupled antiferromagnetically to the cobalt at least at the Co/EuS interface. Because of the small size of the EuS particles, a large fraction of the EuS is in close proximity to the interface and thus influenced by the strong Co/EuS exchange. These materials have been shown to have unusual magnetic and magneto-optical properties including magnetic compensation points depending on the mole fraction of EuS. Magnetization and Kerr hysteresis loops have confirmed the macroscopic ferrimagnetic model for these systems. The Co/EuS exchange in these systems is sufficiently weak that it can be overcome at high fields of order 2 T leading to alignment of the Co and EuS moments with the applied field. This magnetic transition is well above the coercive field and technical saturation of the film. In the same field range they observe a large negative magnetoresistance. They believe this effect is related to the giant negative magnetoresistance observed in granular solids consisting of magnetic precipitatesmore » in a conductive nonmagnetic matrix. The Co-EuS system differs in that both the conductive matrix and the particles are magnetic.« less