Structural and magnetic properties of granular (Ni0.84Fe0.16)54(alumina)46 sputtered thin films

The microstructure and magnetic properties of sputtered (Ni0.84Fe0.16)(54)(alumina)(46) (at%) thin films have been investigated by X-ray diffraction, electron microscopy, Mossbauer spectroscopy and magnetic measurements. The microstructure of the as-sputtered film is constituted of 4 nm large Ni(Fe) nanoprecipitates in an amorphous alumina matrix. This film exhibits a ferromagnetic character due to the existence of interactions between magnetic Ni(Fe) nanoprecipitates. Its Mossbauer spectrum consists of a magnetic broadened sextet indicating a large distribution of iron atom environment probably due to the chemical disorder on the Ni(Fe) lattice. One hour annealing heat treatments were applied to the films at temperatures ranging from 573 to 773 K. The annealing resulted in a simultaneous dewetting of the film, and coarsening of the nanoprecipitates. It was shown to be associated with an increase of the saturation magnetization of the films and a refinement of the Mossbauer spectrum. (C) 2010 Elsevier By. All rights reserved.