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

Bulk magnetization, transport and neutron scattering measurements were performed to investigate the electronic and magnetic properties of a polycrystalline sample of the newly discovered ferromagnetic superconductor, CeO0.3F0.7BiS2. Ferromagnetism develops below T\textunderscore \textbraceleft FM\textbraceright $=$ 6.54(8) K and superconductivity is found to coexist with the ferromagnetic state below T\textunderscore \textbraceleft SC\textbraceright $=$ 4.5 K. Inelastic neutron scattering measurements reveal a very weakly dispersive magnetic excitation at 1.8 meV that can be explained by an Ising-like spin Hamiltonian. Under application of an external magnetic field, the direction of the magnetic moment changes from the c-axis to the ab-plane and the 1.8 meV excitation splits into two modes. A possible mechanism for the unusual magnetism and its relation to superconductivity is discussed.