Exchange coupling of NiFe/CrMnPtx bilayers prepared by a substrate bias sputtering method

Publisher Website
Google Scholar
Abstract
We have investigated the unidirectional exchange anisotropy between a ferromagnetic Ni 81 Fe 19 film and a disordered antiferromagnetic CrMnPt x (x=3, 6, or 9) film prepared by substrate bias sputtering. A hysteresis loop with the shape predicted by the planar domain-wall model was found in the sample without substrate bias, suggesting that the interfacial exchange coupling energy between the Ni 81 Fe 19 and CrMnPt x layers is comparable to the antiferromagnetic domain-wall energy. The substrate bias on the Ni 81 Fe 19 underlayers improved the texture of the CrMnPt x layers but also increased the interface roughness. The substrate bias effect on the exchange bias can be understood in terms of the planar domain-wall model. The interface roughness reduces the interfacial exchange coupling by introducing defects and disordering the antiferromagnetic moments at the interface. This leads to a triangular hysteresis loop. The texture improvement increases the exchange bias by increasing the domain-wall energy of the antiferromagnet. The differences between these substrate bias effects and those observed in the Ni 81 Fe 19 /Fe 50 Mn 50 bilayer system are also discussed.