The embodiments of the present disclosure relate to a method, system and composition producing a magnetic carbon nanomaterial product that may comprise carbon nanotubes (CNTs) at least some of which are magnetic CNTs (mCNTs). The method and apparatus employ carbon dioxide (CO2) as a reactant in an electrolysis reaction in order to make mCNTs. In some embodiments of the present disclosure, a magnetic additive component is included as a reactant in the method and as a portion of one or more components in the system or composition to facilitate a magnetic material addition process, a carbide nucleation process or both during the electrosynthesis reaction for making magnetic carbon nanomaterials.