Structural and magnetic properties of Fe-x-C1-x nanocomposite thin films

Iron-carbon nanocomposite thin films with iron concentrations ranging from 12 to 74 at. % were grown by ion-beam sputtering codeposition at different substrate temperatures. The microstructure of the films was characterized b y transmission electron microscopy, atomic force microscopy, extended x-ray absorption fine structure, and grazing incidence small-angle x-ray scatter ing. A granular morphology consisting of body-centered-cubic iron-rich nano particles (2-5 nm in diameter and 3-8 nm in height with a relatively sharp size distribution) regularly distributed within a more or less graphitic ma trix was obtained. Structural properties as well as magnetic ones were foun d to depend strongly on composition, substrate temperature, and postdeposit ion treatments (annealing or Ar+ irradiation). The temperature dependence o f the susceptibility exhibited a superparamagnetic response with blocking t emperature in the range of 13-180 K. The maximum low-temperature (5 K) coer civity value obtained in this study was 850 Oe for the film with the lowest iron content (x = 0.12). The saturation magnetization was found to be redu ced compared to the corresponding bulk value for pure alpha-Fe, and increas ed with increasing substrate temperature. Otherwise, when increasing the ir on content, a decrease in coercivity was observed in correlation with an in crease in remanent magnetization. (C) 2000 American Institute of Physics. [ S0021-8979(00)05407-4].