Coexistence of superconductivity and ferromagnetism in the graphite–sulphur 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 sulphur for temperatures below 9.0K. The temperature dependence of the lower critical field H _cl (T) was determined and the zero-temperature penetration depth λ(0) was estimated (λ(0) = 2270 Å). 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.