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.