Field-induced phenomena in ferromagnetic superconductors UCoGe and URhGe

Aoki, Dai*; Taupin, M.*; Paulsen, C.*; Hardy, F.*; Taufour, V.*; Kotegawa, Hisashi*; Hassinger, E.*; Malone, L.*; Matsuda, Tatsuma; Miyake, Atsushi*; Sheikin, I.*; Knafo, W.*; Knebel, G.*; Howald, L.*; Brison, J. P.*; Flouquet, J.*

We review our recent studies on ferromagnetic superconductors, UGe2, URhGe, and UCoGe. We focus on experimental results of URhGe and UCoGe in which the superconductivity occurs already at ambient pressure. The huge upper critical field on UCoGe for the field along the hard magnetization axis (-axis) is confirmed by the AC susceptibility measurements by the fine tuning of field angle. Contrary to the huge along the hard-magnetization axis, along the easy-magnetization axis (-axis) is relatively small in value. However, the initial slope of , namely / (0) both in UCoGe and in URhGe indicates the large value, which can be explained by the magnetic domain effect detected in the magnetization measurements. The specific heat measurements using a high quality single crystal of UCoGe demonstrate the bulk superconductivity, which is extended under magnetic field for the field along -axis.