Structure and magnetic properties of thin Mn/Cu(001) and CuMn/Cu(100) films

The structure and magnetic properties of Mn and CuMn overlayers on Cu(001) are investigated within the generalized-gradient approximation of density-functional theory via ab-initio calculations based on the ultra-soft pseudo-potential method. For a one monolayer (1 ML) Mn film, we predict in-plane c(2 x 2) antiferromagnetism with large moments, as slight outward relaxation and almost no buckling. For a 2ML Mn film, we find layered antiferromagnetism, a modest outward relaxation of both overlayers and again no buckling. For a c(2 x 2) 1 ML CuMn surface alloy, we iind a high-moment (m(Mn)=4.09 mu(B)) ferromagnetic ground-state with a pronounced buckling of 0.26 Angstrom. A c(2 x 2) 2 ML CuMn alloy film is antiferromagnetic (m(Mn1) = 4.13 mu(B) and m(Mn2) = - 3.66 mu(B) in the first and second layer, respectively), with strong outward relaxation and buckling of the top layer. The surface alloy is found to be energetically more favourable than an overlayer. The predicted relaxation and buckling are shown to be driven by magnetic effects. It is shown that the strong enhancement of the magnetic moments in the surface alloy is also reflected in a large exchange splitting in the Mn-d band. (C) 1999 Elsevier Science B.V. All rights reserved.