Superconductivity and magnetism in tantalum–graphite multilayers based on natural graphite

DC magnetization and AC magnetic susceptibility of Ta–graphite (Ta–G) based on natural graphite (NG) have been measured using a SQUID magnetometer. In this system, Ta multilayers sandwiched between adjacent graphite layers would be periodically stacked along the c axis. Each Ta layer is composed of Ta nanoparticles in the form of either one-dimensional chains or two-dimensional platelets. An irreversible effect of magnetization is observed around 10 K, suggesting the occurrence of a spin-glass like behavior reflecting the frustrated nature of Ta nanoparticles as localized spins. A Meissner-like behavior is also observed below 10 K. The superconducting property of Ta–G (NG) is similar to that of tantalum carbide (TaC) nanoparticles based on carbon nanotubes, suggesting the existence of TaC nanoparticles in Ta–G (NG) as a minority phase.