The evolution of magnetic properties of ultrathin Co/Cu(111) films with Ag overlayer has been investigated using the surface magneto-optical Kerr effect. In general, the easy axis of the magnetization is in-plane for a Co/Cu(111) system. However, a small longitudinal coercive force (one order smaller than that in polar case) has been observed for films with Co thickness roughly between 1.5 and 10 monolayers. With an Ag overlayer on the top of films, the orientation of the easy axis does not change. Ag-induced oscillation of the polar coercive force shows that it is dominated by the complete or incomplete Ag atomic layers. The oscillation phenomenon decreases with increasing the thickness of the Co layer, from 2.3 to 4.6 ML.
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