Coexistence of itinerant ferromagnetism and superconductivity in ZrZn2

A microscopic coexistence of itinerant ferromagnetism and superconductivity is studied in a single- band homogeneous system, using an equation of motion method and Green's function technique. Self-consistent equations for the superconducting order parameter Delta and magnetization m are derived. It is shown that there generally exists coexistent (Delta not equal 0 and m not equal 0) solutions to the coupled equations of the order parameters in the temperature range 0 < T < min(T-c ,T-FM ), where T-c and T-FM are respectively the superconducting and ferromagnetic transition temperatures. The expressions for specific heat, density of states, free energy, and critical field are also derived. The theory is applied to explain the observations in ZrZn2. The agreement between the theory and experimental observations is quite satisfactory.