Effect of field cooling process and ion-beam bombardment on the exchange bias of NiCo/(Ni, Co)O bilayers

•Strong angular dependence was observed in the exchange bias of NiCo/(Ni, Co)O bilayers.•The field cooling process resulted in negative exchange bias.•Moderate ion-beam bombardment on (NiCo)O layers enhanced exchange bias at 298 K.•High-energy ion bombardment strengthened the exchange coupling in field cooled bilayer.•The structural deformation was responsible for the change in magnetic properties.

The research on exchange coupled ferromagnetic/antiferromagnetic (FM/AF) bilayers has been the foundation of spintronic applications such as hard disk reading heads and spin torque oscillators. In order to further explore the exchange bias behavior of NiCo/(Ni, Co)O bilayers, effect of field cooling process, magnetic angular dependence, and ion-beam bombardment was investigated. The difference in film composition resulted in remarkable distinction in crystalline structures and domain patterns. The exchange bias field (Hex) in the bilayer systems exhibited a strong angular dependence. The negative Hex after a field cooling process indicated that the polarity of Hex can be defined by aligning the magnetization orientation of the FM NiCo layer with the applied field. Moreover, enhanced exchange bias effect was observed in the NiCo/(Ni, Co)O bilayers that resulted from the surface of the (Ni, Co)O layers bombarded with different Ar+ ion-beam energies using End-Hall voltages from 0 V to 150 V. The interface spin structures as well as the surface domain patterns were altered by the ion-beam bombardment process. These results indicated that the exchange bias field of NiCo/(Ni, Co)O bilayer systems could be tailored by field cooling process, angular dependence of magnetic properties, and post ion-beam bombardment.