We have studied the effect of depositing submonolayer quantities of Cu onto the CO exposed Co/Cu͑110͒ system at room temperature using the magneto-optic Kerr effect. Cu overlayers are found to completely reverse the in-plane 90°easy axis switch caused by the CO adsorption, for all Co thicknesses studied up to 40 ML. The Cu reverses the sign of the effective in-plane uniaxial anisotropy K U eff thereby switching the easy axis from the ͓1-10͔ to the ͓001͔ direction. Two modes of switching are observed depending on the magnitude of the cubic magnetocrystalline anisotropy constant K 1 which is in turn dependent on the thickness of the Co films. For sufficiently thick Co films (d Co Ͼ15 ML), the easy axis is found to shift gradually from the ͓1-10͔ to the ͓001͔ direction due to the competition between the cubic and effective uniaxial anisotropy contributions. Therefore, we are able to controllably engineer the direction of the easy axis in this system as a function of Cu overlayer thickness. For thin Co films (d Cu Ͻ15 ML) K 1 tends to zero as revealed by BLS measurements of Hillebrands et al. and the easy axis switch is abrupt. 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/Cu͑110͒ film with a 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. Therefore we have directly observed the stabilization of ferromagnetic order by magnetic anisotropy in an ultrathin magnetic film, as theoretically predicted.
The correlation between the structure and magnetic properties of ultrathin Mn overlayers grown on fcc Co/Cu͑001͒ was studied using low-energy electron diffraction and the magneto-optic Kerr effect in situ. A two-dimensional magnetic c͑2ϫ2͒ Mn-Co͑001͒ surface alloy was found to be stabilized in the range 0.3-0.8 ML Mn overlayer thickness. Within this thickness range Mn is ferromagnetically coupled to the fcc Co͑001͒ underlayer. Above one monolayer of Mn, the c͑2ϫ2͒ surface reconstruction fully disappears and the Mn overlayers are no longer ferromagnetically ordered. Furthermore, it is shown that the Kerr signal, magnetic anisotropy strength, and coercivity are correlated with the stabilization of the MnCo surface alloy and growth conditions. ͓S0163-1829͑99͒02709-5͔
The structure and magnetic properties of epitaxially grown Mn on fcc Co/Cu(001) are studied using in situ magneto-optical Kerr effect and low-energy electron diffraction. A two-dimensional c(2×2) Mn–Co(001) surface alloy stabilizes in the range of 0.3–0.8 ML of Mn, in which Mn is ferromagnetically coupled to the fcc Co(001). Above one monolayer of Mn, the c(2×2) superstructure disappears and the Mn overlayer no longer has long range ferromagnetic order. Furthermore, it is shown that the strengths of the magnetic anisotropies and magneto-optic response are correlated with the MnCo surface alloy formation.
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