DYNAMIC EVOLUTION OF THE MAGNETIC-ANISOTROPY OF ULTRATHIN CO CU(110) FILMS/

We have studied the magnetic properties of the Co/Cu(110) system (5 ML < d(Co) < 40 ML) at 300 K, using the magneto-optic Kerr effect. The m agnetic easy axis is found to switch through 90 degrees for a constant Co thickness, typically over a period of one hour. We attribute this behavior to the reversal in sign of the effective in-plane uniaxial an isotropy constant, due to the adsorption of submonolayer quantities of residual CO gas in the UHV chamber. Scanning tunnel microscope images reveal the growth of elongated island structures preferentially orien ted along the [001] direction providing edges for gas adsorption.