Exchange biasing in NiO spin valves

Abstract

We have investigated the effects of crystal texture, deposition condition and interfacial roughness on exchange biasing field H ex and coercive field H c in NiO spin valves to understand the exchange biasing mechanism at the NiO/NiFe interfaces. The H ex of the NiO/NiFe bilayers epitaxially deposited on MgO(1 1 1), (1 1 0), and (1 0 0) substrates were independent from the crystallographic orientation of NiO films. For a better understanding of the interfacial roughness effect, the H ex and H c of the NiO spin valves, deposited over differently etched glass substrates and glass/Si 3N 4 buffer layers, were measured. The magnetoresistance (MR) ratio, H ex and H c were not changed by variation of etching time, despite the increase of rms roughness from 4.7 to 33 Å. However, the MR ratio and these fields increased according to an increase of the Si 3N 4 buffer thickness, even when the rms roughnesses had almost the same values. The H ex and H c increased with deposition rate of the NiO layer, even if the rms roughnesses of the NiO films deposited at the rate of 6 and 30 Å/min were similar. To explain this ambiguous dependence of rms roughness, we considered an average slope of roughness instead of rms roughness in the AFM image. The short-range roughness with a steep slope played an important role in H ex and H c of NiO spin valves due to an increase in magnetostatic energy and the decrease in antiferromagnetic domain size.