Superconductivity in uranium ferromagnets

The theoretical description and survey of the physical properties of superconducting states in uranium ferromagnetic materials are presented. On the basis of microscopic theory, we show that the coupling between electrons in these ferromagnetic metals by means of magnetization fluctuations gives rise to a triplet-pairing superconducting state, and establish the general form of the order parameter dictated by symmetry. The theory allows explaining some specific observations, including the peculiar phenomenon of reentrant superconductivity in URhGe in a magnetic field perpendicular to the spontaneous magnetization direction. In addition, we describe several particular topics related to uranium superconducting ferromagnets: (i) critical magnetic relaxation in dual localized–itinerant ferromagnets, (ii) phase transition to the ferromagnetic state in a Fermi liquid and UGe$_2$, (iii) superconducting ordering in ferromagnetic metals without an inversion center.