Anti-ferromagnetic contrast in NiO (0Â 0Â 1) studied with threshold photoemission electron microscopy

 A detailed study is presented of the potential of threshold photoemission electron microscopy (PEEM) for the imaging of anti-ferromagnetic (AF) domains of NiO (0 0 1). Characteristic patterns with large asymmetry have been observed experimentally. Upon heating the sample to temperatures significantly above the Néel temperature, the patterns clearly remain visible and a magnetic origin can therefore be excluded. The patterns probably originate in polishing damage, with the bright areas corresponding to areas with a high oxygen deficiency (with enhanced electron emission). After sputter cleaning the sample, thereby removing the dominant patterns, no significant asymmetries in electron emission remain. Obviously, for our samples the AF asymmetries as measured with threshold PEEM are less than the detection limits of our setup of 0.5%. The conclusion is supported by model calculations, which show that the asymmetry should have a distinct angular dependence and which give an estimate of the maximum asymmetry of below 1%.