Magnetic Moments at the Surface of Antiferromagnetic NiO(100)

The orientation of magnetic moments at the $\left(100\right)$ surface of antiferromagnetic NiO single crystals is studied by x-ray linear magnetic dichroism in photoemission microscopy. $T$ domains are observed terminating at the surface, with domain boundaries running mostly along in-plane $\left[10\right]$ directions. From the detailed polarization dependence we find that the magnetic surface structure of a cleaved crystal is bulk terminated. This is in contrast to sputtered surfaces, where magnetic moments lie within the surface plane, forming a magnetically relaxed structure. These findings are of importance for understanding the exchange bias phenomenon.