Exchange bias in a ferromagnet/antiferromagnet system with TC≪TN

Abstract

This paper reports experimental results obtained on an unconventional exchange bias (EB) system where the ferromagnetic layer, Ni0.75Cu0.25, has lower ordering temperature (TC) than that (TN) of the antiferromagnetic one, NiO, with emphasis on modifying EB through either magnetic annealing or light-ion irradiation. Samples were cooled from temperatures higher than TN or in between TC and TN to room temperature with magnetic field applied in different in-plane directions. Upon ion irradiation, magnetic fields, parallel or antiparallel to the orientation of the field present during the films deposition, were applied to explore different effects on EB. We found that the EB direction can be completely reversed by means of either annealing or ion bombardment; however, both postdeposition treatments provide very little variation of the EB field value over that produced during the film’s growth. The importance of the annealing field strength was also discussed. The results were interpreted based on a mechanism which assumes that the interfacial moments adjacent to the antiferromagnetic layer are responsible for establishing the exchange biasing in the paramagnetic state.