Noncollinear magnetism in rough ultrathin γ-Fe films

In ultrathin face-centered cubic Fe films on Cu(100) substrates only the surface and subsurface layers are ferromagnetically coupled, while the interior of the films shows various antiferromagnetic configurations, depending on the thickness of the films. We show using ab initio local-spin-density calculations that for films with more than four monolayers this leads to a frustration of the magnetic interactions in the vicinity of a step and hence to a noncollinear magnetic structure. As a consequence rough ultrathin γ-Fe films cannot be characterized by a simple uniaxial magnetic anisotropy.