Magnetic properties of granulated SiC _xN _y:Fe films with different structure of α-Fe nanoclusters

We report the modification of magnetic properties due to variation of the structure of Fe-contain granules in SiC _xN _y:Fe films grown by chemical vapor deposition at different temperatures from various gaseous mixtures. It was shown that formation of large composite Fe-granules in the case of structures created using hexamethyldisilazane as source of Si, C, and N atoms results in the hysteresis loop in the magnetization curve appeared only at low temperature (5 K). The ESR spectra are characterized by many ESR lines with sharp asymmetrical shapes and different line widths. The samples with a dense arrays of small homogeneously distributed α-Fe granules, obtained with hexamethylcyclotrisilazane, demonstrate the large saturation magnetization, the hysteresis loop (~135 Oe at 300 K and ~680 Oe at 5 K) and the collective ferromagnetic resonance signal. The pronounced magnetic properties are explained by the formation of the single magnetic domain due to quantum-mechanical tunneling between small coupled α-Fe clusters. Conductivity measurements confirm the existence of the tunneling coupling between Fe-granules even in case of lowest Fe concentration in the samples under study.