Coexistence of superconductivity and ferromagnetism in the graphite-sulfur system

Abstract

Superconducting characteristics such as the Meissner-Ochsenfeld state, screening supercurrents and hysteresis loops of type-II superconductors were observed from the temperature and magnetic field dependences of the magnetic moment, m(T, H), in graphite powders reacted with sulfur for temperatures below 9.0 K. The temperature dependence of the lower critical field Hc1(T) was determined and the zero-temperature penetration depth, lambda(0), was estimated (lambda (0) = 227 nm). The superconductivity was observed to be highly anisotropic and to coexist with a ferromagnetic state that has a Curie temperature well above room temperature. A continuous transition from the superconducting state to the ferromagnetic state could be achieved by simply increasing the applied magnetic field.