Exchange Bias Effect Determined by Anisotropic Magnetoresistance in CoxNi1−xO/Ni0.8Fe0.2 Bilayer System

We prepared bilayer systems composed of the ferromagnetic (FM) layer Ni_0.8Fe_0.2 and the anti-FM (AFM) layer Co_xNi_1-xO (x = 0.3, 0.4, 0.5, and 0.6) using the dc/RF magnetron sputtering methods. Coercive field H_C and exchange bias field H_E, the shift field in hysteresis loop, were observed in all the Ni_0.8Fe_0.2/Co_xNi_1-xO bilayer systems after field cooling. The changes of H_C and H_E were explicitly studied for various parameters, such as the composition of AFM material x, the measured temperature T, and the direction of applied magnetic field. Measured anisotropic magnetoresistance (AMR) was analyzed to extract the H_C and H_E, since the peaks (maximum or minimum) in AMR do not appear exactly at the coercive field H_C of the magnetic hysteresis measurement. We propose a new approach for the analysis of AMR to determine H_C and H_EB along the field angle θ with respect to the field-cooling direction. The results were compared with the variations of H_EB and H_C reported earlier.