We present the results of magnetoresonance investigations for Ni nanoparticles embedded into a nanoporous carbon matrix (NPC). First, the NPC was prepared from polycrystalline powder of Mo₂C and then impregnated by Ni from NiCl₂.
At room temperature the as grown powder NPC: Ni samples demonstrate wide (ΔHpp = 2.7 kG) almost unstructured line of magnetoresonance absorption (ν=9.3 GHz). Intensity and width of the line increase sharply on cooling up to about T=50 K due to dipole coupling induced magnetic ordering in the interactive ensemble of Ni nanoparticles. Such ordering could be stimulated more probably by influence of mesopores as well as presence Ni on the granule surface.
Separation of granules from each other change drastically the magnetoresonance absorption spectra. Intensity of the ferromagnetic resonance line as well as coercive force (measured separately) at room temperature drop more than one order of magnitude. At the same time a new narrow resonance line ( ΔHpp = 350 G) appears. g-factor of the line (g=2.19) is close to the one of Ni. The new line is determined by resonance magnetic response of superparamagnetic particles above their blocking temperature. Temperature behavior of the narrow line was measured and analyzed starting from dispersion of blocking temperature due to size dispersion of Ni nanoparticles.

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