Temperature dependence of the AMR curve in NiO/NiFe bilayers

The temperature dependence of the anisotropic magnetoresistance (AMR) curves was measured as a function of the angle between the applied field H and the exchange coupling field H_ex in NiO(30 nm)/NiFe(t) (t = 5, 10 and 30 nm) bilayers, and the data were compared with calculated results using the single-domain model with the crystalline anisotropy field as fitting parameter. The AMR curves for H ≤ H_ex are asymmetrical with respect to θ = 0° in the t = 10 nm sample, and the angles for maximum resistance, θ_m, are located at the negative field region for the measurement temperature T = 300 K. As temperature decreases, the AMR curve becomes nearly symmetric at T = 100 K, and then again asymmetric with positive θ_m. A comparison of these results with the calculated AMR has suggested that the crystalline anisotropy field increases with decreasing temperature, but its angle decreases.