Direct observation of the stabilization of ferromagnetic order by magnetic anisotropy

We have engineered an experimental realization of an isotropic two-dimensional 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 temperature. For a Cu coverage of 1.02 ML, the uniaxial anisotropy component vanishes also, and we observe a corresponding loss of ferromagnetic order at remanence. Further Cu deposition restores the uniaxial anisotropy and the magnetic order.