Anisotropic Magnetic Fluctuations And Superconductivity In Ferromagnetic Superconductor Ucoge

We have performed Co-59 NQR / NMR measurements on the single-crystalline UCoGe, in order to investigate the relationship between ferromagnetism and superconductivity. The measurements of Knight-shift and nuclear spin-lattice relaxation rate provide clear evidence that both static and dynamic susceptibilities are ferromagnetic with Ising anisotropy. In addition, H-c2 also shows extremely large anisotropy which cannot be explained by the GL model with anisotropy of effective mass. These data suggest intimate relationship between Ising magnetization and anisotropic superconductivity in UCoGe.