Magnetic, structural and microstructural properties of FePt/M (M = C, BN) granular films

Nanocomposite FePt/C and FePt/BN thin films have been fabricated by dc and rf magnetron sputtering on naturally-oxidized Si (100) substrates. Particles consisting of the highly anisotropic tetragonal L1(0) FePt phase were obtained by annealing the as-made multilayers by a conventional vacuum furnace in the temperature range of 500 to 800 degreesC. By controlling the annealing conditions, samples with grain size in the range of 3 to 20 nm were obtained, with coercivities between 2 and 16 kOe. The evolution of crystal structure during annealing at 600 degreesC was studied in FePt/C and the dependence of a, c and c/a on annealing time were determined. These data were used to estimate the degree of ordering which was found to increase with aging, but with a maximum value less than the bulk value, explaining thus the lower H-C in the nanoparticles.