We have studied ultrathin ${\mathrm{Fe}}_x{\mathrm{Mn}}_{1-x}$ films on Cu(100) for Fe contents ranging from 45% to 80%. In the bulk the fcc structure displays antiferromagnetic order in this concentration regime. The growth was investigated via reflection high energy electron diffraction and structural properties were investigated with low energy electron diffraction. From lattice mismatch arguments one would have expected to observe a $p(1\mathrm{}\times 1)$ pattern. However we find a $c(2\mathrm{}\times 2)$ structure for thicknesses below 5 ML. Above this coverage it transforms into a $p(1\mathrm{}\times 1)$ structure. The $c(2\mathrm{}\times 2)$ structure is not present when the alloys are grown on a Co/Cu(100) surface. With the use of Auger spectroscopy we find clear evidence of Fe surface segregation. At 54% Fe content we estimate an enhancement of the surface content of Fe by $\sim 10\%.$ The amount of excess Fe agrees well with the observation of ‘uncompensated’ Fe spins in ${\mathrm{C}\mathrm{o}/\mathrm{F}\mathrm{e}}_{50}{\mathrm{Mn}}_{50}$ structures. Further we were able to detect magnetic signals for coverages below $\sim 5\mathrm{ML}.$

• Received 24 September 2003

DOI:https://doi.org/10.1103/PhysRevB.69.054411