Ab initio calculation of Heisenberg parameters and Curie temperatures in thin magnetic films

We present first principles calculations of the Heisenberg exchange parameters, J(ij) in thin Co and Ni films on a Cu(0 0 1) substrate. Two methods are compared, relying either on a disordered local moment description of the paramagnetic state or on the magnetically ordered ground state. Ferromagnetic nearest-neighbor and next-nearest-neighbor interactions are found to play a dominating role throughout. Furthermore, J(ij)s display significant dependence on the layer positions, having a typical maximum for layers near the surface of the film as well as at the interface with the substrate. The Curie temperatures calculated within a simple statistical mean-field approach follow qualitatively well the trends against the film thickness observed in the experiments. (C) 1999 Elsevier Science B.V. All rights reserved.