Phenomenological Theory of Ferromagnetic Superconductivity

It is argued that the pairing symmetry realized in a ferromagnetic superconductor ${\mathrm{UGe}}_2$ must be a nonunitary triplet pairing. This particular state is free from the Pauli limitation and can survive under a huge internal molecular field. To check our identification we examine its basic properties and several experiments are proposed. In particular, the external field is used to raise $T_c$ by controlling the internal spontaneous dipole field.