Ab initio calculation of Heisenberg parameters in thin magnetic films

We present first principles calculations of the Heisenberg exchange parameters (J ij ) in thin films on top of a disordered local moment description of the paramagnetic state and also from the magnetically ordered ground state. For Co and Ni films on a Cu(001) substrate ferromagnetic nearest-neighbour (NN) and next-nearest-neighbour (NNN) interactions play throughout a dominating role. Furthermore, J ij 's display significant dependence on the layer positions, giving a typical maximum for layers near the surface of the film as well as the interface with the substrate. As presented for the case of the Fe5/Cu(001) overlayer system, the long-ranged behaviour of the exchange pair interactions has to be ultimately taken into account in order to recover the antiferro-magnetic ground states of thin Fe films on Cu(001) obtained by total energy calculations. Theoretical Curie temperatures (T C) calculated within a simple statistical mean-field approach follow qualitatively well the trends against the film thickness observed in the experiments.