The influence of the cooling field on the exchange bias in ferromagnet/antiferromagnet bilayers system

Abstract

The ferromagnetic domainwall model is used to investigate the influence of the cooling field （including its magnitude and orientation） on the exchange bias（hE） in ferromagnet/antiferromagnet bilayers with uncompensated interface. The results show that hE is independent of the magnitude of the cooling field when it is applied parallel to the easy axis of the antiferromagnet. When the cooling field deviates from the easy axis direction, hE changes slowly with increasing field angle, but a sudden change is observed when the angle goes up to a critical angle γc, which γc increases with the cooling field increaseing. Especially, hE has a transition from negative to positive when the field angle is beyond γc, and the transition point also relates to the magnitude of the cooling field. Moreover, the thickness dependence of the exchange bias exhibits a liner dependence on the inverse ferromagnet layer thickness, but yields a crossover from hE∝N-1F to hE∝N-λF at a certain thickness （here λ>1）. This behavior is strongly dependent on the ferromagnet thickness, the magnitude and the angle of the cooling field.