Tight-binding study of the CO chemisorption effect on cobalt magnetization

By using a semiempirical self-consistent tight-binding scheme we study the effect of O and CO chemisorption on the Co(0001) surface magnetization. Similar calculations are performed for the Co₁₃ and Co₅₅ clusters of high symmetry. The CO molecule in the atop position, but not in the bridge geometry, is effective in local magnetization quenching. In clusters magnetic phase transitions are observed as the Co-CO separation varies. When the separation is more than about 1.8 {}, the Co magnetization remains strong. The character of phase transitions conforms to the formal predictions based on the Landau theory.