Influence of different stoichiometric Cr-oxides created via oxygen ion-beam bombardment on the magnetism of the NiFe/Cr-oxide exchange-biased systems

In exchange-biased systems, antiferromagnetic Cr₂O₃ has drawn intensive attention because of its highly anisotropic structure. However, other Cr-oxide phases can be formed during fabrication. The influence of different stoichiometric Cr-oxides on the magnetism of the NiFe/Cr-oxide bilayers was studied. We find that paramagnetic CrO₃ grains could promote the formation of domain states in the Cr-oxide layer by magnetically isolating antiferromagnetic domains. These domain states gave rise to an excess of irreversible magnetic moments at the NiFe/Cr-oxide interface, causing a nontrivial increase in the exchange bias. The presence of ferromagnetic CrO₂ grains in the Cr-oxide layer introduced abundant magnetic disorders. These magnetic disorders acted as pinning sites and impeded the domain-wall motion, which resulted in an increase of the coercivity. These results indicate that the magnetism of the NiFe/Cr-oxide bilayers can be remarkably affected by different Cr-oxide phases, enabling control of both the coercivity and exchange bias and providing a possible route to improve the performance of exchange-biased devices.