The Coexistence of Superconductivity and Ferromagnetism in (Ce_1−xGd_x)Ru₂ —Self-Induced Vortex State—

Abstract

Electric resistivity, a.c. magnetic susceptibility, magnetization and ¹⁵⁷Gd NMR measurements have been performed in (Ce_1−xGd_x)Ru₂ for x=0.12 and 0.13. The resistivity measurement determines the superconducting transition temperature for x=0.12 and 0.13 to be 4.85 K and 4.4 K, respectively, though both the susceptibility and magnetization show no diamagnetism. An internal field associated with the ferromagnetic order appears in ¹⁵⁷Gd NMR, where the nuclear spin-lattice relaxation time for x=0.12 below 100 mK shows a characteristic temperature dependence for the superconductivity. From these results, it is concluded that the compound with x=0.12 is microscopically in a coexistent state of the superconductivity and the ferromagnetism at low temperature, forming a self-induced vortex state.