Surface spin orientation of NiO(100) and interfacial coupling of Fe/NiO(100) revisited with soft X-ray spectromicroscopy

Accurate retrieval of spin-axis orientation at the antiferromagnetic (AFM) surface requires involved consideration of the crystal field effect in X-ray magnetic linear dichroism (XMLD), which was neglected until recently. Here, we present a unique determination of surface spin-axes of the prototype antiferromagnet NiO(100) from detailed angular-dependent measurements using different polarizations of incident light by considering the recently developed angular dependence of the XMLD effect. The bulk twin domains terminating on the (100) surface have also been determined from the angular dependence of the experimental contrast at the oxygen K edge. The effect of Fe deposition on the AFM domain pattern was followed in situ and the interfacial exchange coupling of as-deposited Fe/NiO(100) has been explored using the recent formalism of XMLD. Unlike Co/NiO(100), we realize only the rough perpendicular coupling between Fe moments and compensated Ni spin-axes. The uncompensated spins (UCS) at the interface were also characterized and a mechanism of interfacial coupling is suggested.