Meissner Superconductivity in Itinerant Ferromagnets

Recent results about the coexistence of ferromagnetism and uncon- ventional superconductivity with spin-triplet Cooper pairing are reviewe d on the basis of the quasi-phenomenological Ginzburg-Landau theory. The super- conductivity in the mixed phase of coexistence of ferromagnetism and uncon- ventional superconductivity is triggered by the spontaneous magnetization. The mixed phase is stable, whereas the other superconducting phases that usually exist in unconventional superconductors are either unstable or metasta ble at rel- atively low temperatures in a quite narrow domain of the phase diagram and the stability properties are determined by the particular values of Landau para me- ters. The phase transitions from the normal phase to the phase of coexistence is of first order while the phase transition from the ferromagnetic phase to the coexistence phase can be either of first or second order depending o n the con- crete substance. The Cooper pair and crystal anisotropies are releva nt to a more precise outline of the phase diagram shape and reduce the degeneration of the ground states of the system. The results are discussed in view of applicatio n to itinerant ferromagnetic compounds, such as UGe2, ZrZn2, URhGe.