Influence of surface roughness and chemisorption on magnetic hysteresis curves of a Ni(110) surface observed by spin-resolved inverse photoemission

Using the high spin asymmetry in inverse photoemission of the Ni d-band just above the Fermi level as an indicator of surface magnetization, we have measured hysteresis curves of the (110) surface of nickel. Nearly rectangular hysteresis loops indicate a well-defined behavior of the surface magnetization of the picture-frame single crystal with sides along 110 directions. The influence of geometrical order and chemisorption of O, S, and CO on the shape of the hysteresis loops has been investigated. We found a significant reduction of the coercive force (about 10%) if the clean high-quality (110) surface is disordered on an atomic scale by ion bombardment or low-coverage chemisorption.