Carbon nanocapsules with a ferromagnetic core of single-crystalline Fe3O4 are demonstrated to be effectively synthesized and collected separately from the other nano-carbon products of the low-temperature reaction of catalytic disproportionation of carbon monoxide. HRTEM demonstrated a defect-free crystalline structure of the Fe3O4 nanoparticles. The encapsulating carbon shells of the Fe3O4 nanoparticles are stable in air at room temperature, but do not prevent them at high temperatures. Accordingly, these nanoparticles may also act as catalysts for the corresponding production of carbon nanomaterials via carbon monoxide disproportionation. In particular, we demonstrate the corresponding transformation of a Fe3O4 core to an iron carbide nanoparticle with simultaneous formation of additional encapsulating carbon layers. Characterization of the synthesized materials by DC magnetization represents clearly resolved hysteresis loops. However characteristic S-shape of the loops (magnetization is still not saturated at 16 kOe) points out some superparamagnetic effects driven by the nano-size origin of the samples. Analysis of the sample's EPR spectra provides an additional insight to the coexistence of several magnetic phases in the synthesized nanomaterials.