Investigating the exchange bias in multilayer triangular nanorings

Abstract

Exchange bias effects have been systematically investigated in individual spin valve triangular rings using the synchronous transport measurement technique. Preferential pinning of antiferromagnetic (AFM) layer and ferromagnetic (FM) layer domain walls at the corners of the ring results in stronger interface coupling leading to higher blocking temperatures in the ring structure compared to the continuous film of the same film composition. At low temperature, the competition between unidirectional anisotropy and configurational anisotropy results in the formation of large domains at the corners of the ring, which results in lower values of exchange bias in the ring as compared to the continuous film. The effect of cooling field direction was also studied. We observed that the magnitude of bias obtained for negative field cooling direction is larger than that obtained for positive field cooling direction with sweeping field always starting from negative saturation. This observation has been ascribed to the dominance of FM domain magnetization determined by the external magnetic field over the cooling field which defines the AFM-FM interface coupling.