Coexistence of ferromagnetism and superconductivity in CeO0.3F0.7BiS2

Neutron scattering measurements have been performed on a polycrystalline sample of the newly discovered layered superconductor CeO0.3F0.7BiS2 with or without a magnetic field. This system exhibits the rare and interesting case of the coexistence of ferromagnetism and superconductivity, which is hardly realized in the conventional phonon mediated superconductors due to their antagonistic nature. The crystal and magnetic structures was investigated together with the spin fluctuations, and the spin Hamiltonian describing the spin dynamics in this system was determined. In addition, we examined the external magnetic field dependence of both magnetic structure and its excitation. It seems that superconductivity is robust against a magnetic field and there is no direct relationship between magnetism and superconductivity in this system.