Effect of roughness slope on exchange biasing in NiO spin valves

Exchange biasing field Hex and coercive field Hc of the exchange-biased NiO spin valves deposited over differently etched glass substrates and glass Si3N4 buffer layers were measured in order to investigate the effect of roughness at the NiO/NiFe interfaces. The magnetoresistive (MR) ratio, Hex, and Hc were not influenced by etching time, even though the rms roughness Rrms increased from 4.7 to 33 Å. However, the MR ratio, Hex, and Hc increased with Si3N4 buffer thickness, even when the Rrms had almost the same values. To explain this ambiguous dependence of Rrms, we consider an effect of the average slope of roughness instead of Rrms in an atomic force microscope image. The steep slope of roughness played an important role in Hex and Hc in NiO spin valves due to an increase in magnetostatic energy and the decrease in antiferromagnetic domain size.