Direct observation of the stabilization of ferromagnetic order by magneticanisotropy

We have engineered an experimental realization of an isotropic two-dimensio nal XY magnet by depositing submonolayer coverages of Cu onto a CO exposed 5 ML Co/Cu(110) film with zero cubic anisotropy component K-1 at room tempe rature. For a Cu coverage of 1.02 ML, the uniaxial anisotropy component van ishes also, and we observe a corresponding loss of ferromagnetic order at r emanence. Further Cu deposition restores the uniaxial anisotropy and the ma gnetic order.