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. Sim ilar calculations are performed for the CO13 and Co-55 clusters of high sym metry. 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 separati on is more than about 1.8 Angstrom, the Co magnetization remains strong. Th e character of phase transitions conforms to the formal predictions based o n the Landau theory. [S0163-1829(99)10705-7].