Structural, electronic, and magnetic properties of thin Mn/Cu(100) films

Abstract

The atomic structure, electronic, and magnetic properties of thin Mn films epitaxially grown on Cu(100) substrates have been investigated by ab initio density-functional studies. Because the local-density approximation leads to a rather poor description of the magnetostructural properties of bulk Mn, a detailed study of the effect of generalized gradient corrections (GGC) to the exchange-correlation functional on the structure and magnetism of Mn in three and two dimensions has been performed. For the bulk we find that the GGC's lift the almost-degeneracy between the competing magnetic configurations and lead to a large magnetovolume effect, in much better agreement with experiment. For free-standing Mn monolayers the effect of the GGC's is even more pronounced: the relative stability of square and hexagonal layers is inverted, antiferromagnetic ordering leads to a large increase of the equilibrium distances. Therefore all investigations of Mn films on Cu substrates have been performed in the generalized gradient approximation. The results demonstrate that homogeneous Mn overlayers are unstable against interdiffusion and the formation of ordered surface alloys. At a coverage of $\ensuremath{\Theta}=0.5$ Mn monolayers, an ordered ferromagnetic $c(2\ifmmode\times\else\texttimes\fi{}2)$ surface alloy is formed. The same atomic structure is assumed at a coverage of $\ensuremath{\Theta}=1$ and leads to an antiferromagnetic coupling between the CuMn alloy layers. In both homogeneous alloy layers and in the surface alloys, Mn is in a high-spin state with a magnetic moment close to $4{\ensuremath{\mu}}_{B}.$ The large atomic volume of magnetic Mn leads an outward relaxation of the Mn atoms and a pronounced buckling of the surface. Detailed comparisons of the calculated atomic structure with low-energy electron diffraction and photoelectron diffraction experiments and of the electronic structure with photoemission and inverse photoemission spectroscopies are reported.