Magnetic moments at the surface of antiferromagnetic NiO(100)

The orientation of magnetic moments at the (100) surface of antiferromagnet ic NiO single crystals is studied by x-ray linear magnetic dichroism in pho toemission microscopy. T domains are observed terminating at the surface, w ith domain boundaries running mostly along in-plane [10] directions. From t he detailed polarization dependence we find that the magnetic surface struc ture of a cleaved crystal is bulk terminated. This is in contrast to sputte red surfaces, where magnetic moments lie within the surface plane, forming a magnetically relaxed structure. These findings are of importance for unde rstanding the exchange bias phenomenon.