Correlation between magnetism and structure in ultrathin Fe/Cu3Au(001) films

We have studied the correlation between the magnetic properties and the structure of ultrathin ferromagnetic Fe/Cu3Au(001) films for thicknesses up to 15 angstrom. We have found that two different face centered tetragonal structural phases coexist within the film in the thickness range 5-15 angstrom. The coexistence of the two structural phases induces an anomalous thickness dependence of the Curie temperature of the films. We ascribe this thickness dependence to a difference in the exchange coupling between the two phases. The irreversible modifications of the magnetic properties of the films after a mild thermal treatment are discussed on the basis of the corresponding changes of the structure and the morphology.