Coherent epitaxy and magnetism of face-centred-cubic Fe films on Cu(100)

The epitaxy of face-centred-cubic (fcc) Fe layers on a Cu(001) substrate has been investigated by means of ab initio local spin-density calculations (including generalized gradient corrections) as a function of the thickness of the film. Fe films with a thickness varying between one and three monolayers (ML) adopt a ferromagnetic (FM) ground state. For thicker films with even numbers of Fe layers (4 ML, 6 ML and 8 ML), bilayer antiferromagnetic (AF) structures develop, while for odd numbers of Fe layers (5 ML, 7 ML and 9 ML), a variety of energetically almost degenerate spin structures each with a ferromagnetically coupled bilayer at the free surface are found. The magnetic structures of the films are strongly coupled to their crystal structures: the interlayer distance between ferromagnetically coupled layers is expanded, while that between antiferromagnetically coupled layers is reduced compared to the layer distance in the substrate and in ideal fcc Fe films. Our results explain the observed change from a tetragonally distorted structure in the ferromagnetic regime to thicker films that are almost fcc (on average) due to the antiferromagnetism in the deeper layers.