Probing the Effect of Structural Roughness on Domain Wall Formation in Spin Valves Using the Offspecular Reflectivity Technique

A previous polarized neutron reflectivity study of IrMn-based spin valves demonstrated that domain wall formation during training is influenced by the thickness of the ferromagnetic pinned layer. However, magnetoresistance measurements and x-ray reflectivity of spin valves with the same nominal structure revealed that sample roughness may also affect the characteristics of the exchange bias, and thus the type of domain walls that develop. To probe the interplay between structural roughness and domain formation, we measured diffuse neutron scattering from a sample with a thick pinned layer (15 nm) and extracted the field evolution of the in-plane correlation length. At saturation, the correlation length was estimated to be 750 plusmn 50 nm and originates from magnetic roughness. The correlation length at intermediate fields decreases to 340 nm or less and signifies the formation of in-plane domains. These results suggest that structural roughness enhances the formation of perpendicular domain walls during training.