Nanostructure and magnetic properties of Fe0.56Cu0.44 films

X-ray diffraction, high-resolution transmission electron microscopy, Mossbauer effect and magnetisation investigations have been performed on sputtered Fe0.56Cu0.44 thin films, in which the Fe concentration is near the percolation threshold. Segregation into FCC-Cu rich and BCC-Fe rich phases takes place in the as-deposited film. This state is described in terms of the interfacial transient concentration and ferromagnetism, which originate from the ferromagnetic BCC-Fe in the centre of the individual grains, the iron-rich crystalline Fe(Cu) alloy lying near the interface and the paramagnetic copper-rich FCC-Cu(Fe) matrix. Annealing effects cause not only the evolution of the grain size of the BCC-nanocrystalites, but also the enrichment of Fe in this phase, leading to an increase of the interfacial sharpness. In addition, the magnetic coercive field is found to be enhanced. The coercivity shows a value as large as 24.2 mT for the sample annealed at 400degreesC. A contribution of the positive surface magnetic anisotropy (K-S = +0.1 mJ/m(2)) to the coercivity is deduced. (C) 2003 Elsevier Science B.V. All rights reserved.