Magnetic properties of Mn/Cu(001) and Mn/Ni(001)c(2×2) surface alloys

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Abstract
Solid phase epitaxy was used to grow two-dimensional, ordered alloys of MnCu and MnNi on the surface of Cu(100) and Ni(100) crystals. These surface alloys, which have structures that are not present in the bulk phase diagram, result in highly corrugated surface layers with a c(2×2) periodicity. The large outward relaxation of Mn atoms has been predicted theoretically to be due to magnetism of the Mn atoms. Using a combination of soft-x-ray absorption spectroscopy and x-ray magnetic circular dichroism, we have found an enhanced local magnetic moment and long-range magnetic ordering in these surface alloys. We find that Mn is in a high-spin ground state, which stabilizes the surface reconstruction, but that long-range magnetic ordering is not always present. Compositionally ordered MnNi films, with the same c(2×2) surface periodicity, show ferromagnetic coupling of Mn atoms, unlike the antiferromagnetic ordering found in the bulk alloy.