Here, we report on the synthesis and magnetic resonance study of Co nanoparticles, encapsulated in nanoporous carbon (NPC). NPC powder samples were prepared from carbide Mo₂C using the chemical removal of non-carbon carbide forming atoms. Size of nanopores was estimated as 1-7 nm. Impregnation of Co into was done from CoCl₂ during 48 hours at T = 980 C.
At room temperature the as grown powder samples of NPC: Co show magnetoresonance responce ( ν=9.3 GHz) represented by two superposed lines, a broad and a narrow ones, with effective g-factor close to g=2.0.
The sample with separated granules of NPC: Co demonstrate only one almost symmetric line of absorption (ΔHpp = 340 G at T=300 K) determined by magnetic response of superparamagnetic Co particles above their blocking temperature. The resonance field corresponds to g-factor of g=2.22, which is close to the one of Co. As temperature decrease, parameters of the line change sufficiently being an evidence for a spectrum anisotropy. Such anisotropy could be interpreted as anisotropic superparamagnetic resonance, taking into account both anisotropy energy of the nanoparticles and effective magnetization of the non-spherical form of nanoparticles in a disordered system. Using the value of blocking temperature (about 70 K) estimated from our measurements, mean size of Co nanoparticles was obtained as 5 nm.

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