Ultrathin Mn films on Cu(111) substrates:: Frustrated antiferromagnetic order

Using local-spin density calculations performed in the generalized-gradient approximation we have examined the possibility that Mn monolayers epitaxially grown on Cu(111) substrates represent a physical realization of the frustrated antiferromagnetic planar (AFP) model. Indeed, we find that the noncollinear ground state of the AFP model with +/- 120 degrees orientations of the nearest-neighbors is also the ground state of Mn/Cu(111). However, due to the rather long-range antiferromagnetic interactions, the energetic preference over a raw-wise antiferromagnetic order is only very weak.