| Nanocrystalline (TiCx + SiC)/C (sample 1) and TiC0.3N0.7 + SiC + Si3N4 (sample 2) materials were prepared by the non-hydrolytic sol-gel method. Sample 2 was obtained from sample 1 by annealing in an NH3 atmosphere at 1623K. It was composed of aggregates of cubic SiC+TiCxN1-x nanoparticles (10 to 30 nm in size) with a small amount of Si3N4 nanofibers. A very narrow electron paramagnetic resonance (EPR) line arising from magnetic localized centers could be observed in both samples. An analysis of the temperature dependence of the EPR parameters (g-factor, linewidth, integrated intensity) unveiled the existence of three different temperature ranges. At low temperature, in particular, spin reorientation processes plausibly influencing the character of magnetic interaction were registered. The thermal annealing, on the other hand, was recognizable as a modifier of magnetic transition within the nanocomposite, as well as of the prevailing interaction mechanism for each major temperature regime. The model of exchange coupled two spin systems (localized defects and conduction electrons) in the bottleneck regime was applied to explain the observed behavior of the EPR signal. |
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