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 configu
rations and lend 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 layer
s is inverted. antiferromagnetic ordering leads to a large increase of the
equilibrium distances. Therefore all investigations of Mn films on Cu subst
rates have been performed in the generalized gradient approximation. The re
sults demonstrate that homogeneous Mn overlayers are unstable against inter
diffusion and the formation of ordered surface alloys. At a coverage of The
ta =0.5 Mn monolayers, an ordered ferromagnetic c(2x2) surface alloy is for
med. The same atomic structure is assumed at a coverage of Theta = I and le
nds 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 s
tate with a magnetic moment close to 4 mu(B). The large atomic volume of ma
gnetic Mn leads an outward relaxation of the Mn atoms and a pronounced buck
ling of the surface. Detailed comparisons of the calculated atomic structur
e with low-energy electron diffraction and photoelectron diffraction experi
ments and of the electronic structure with photoemission and inverse photoe
mission spectroscopies are reported.