Graphitic shells coated ferromagnetic cobalt nanoparticles (C-Co-NPs) with diameters of around 7-9 nm cubic crystalline structures were synthesized by catalytic chemical vapor deposition (CCVD). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis indicated that the Co-NPs inside the carbon shells were preserved in the metallic state. Confocal microscope images revealed effective penetrations of C-Co-NPs through plasmatic membranes into the nucleus of the cultured HeLa cancerous cells. Low RF radiation of 350 kHz triggered the cell death, process that was found to be dependent on the NPs concentration and application time. Compared to carbon nanostructures such as single wall carbon nanotubes, super paramagnetic cobalt nanoparticles demonstrated higher specificity for RF absorption and heating. This work indicates a great potential of a new technology for tumor thermal ablation.