⁷³Ge-nuclear magnetic resonance/nuclear quadrupole resonance investigation of magnetic properties of URhGe

We report on the ⁷³Ge-nuclear magnetic resonance (NMR)/nuclear quadrupole resonance (NQR) results for the ferromagnetic (FM) superconductor URhGe. The magnitude and direction of the internal field, H_int, and the parameters of the electric field gradient at the Ge site were determined experimentally. By using powdered polycrystalline samples oriented by different methods, the field dependences of NMR shift and nuclear spin relaxation rates for H₀ ∥ c (easy axis) and H₀ ∥ b were obtained. From the NMR shifts for H₀ ∥ b, we confirmed a gradual suppression of the Curie temperature and observed a phase separation near the spin reorientation. The observation of the phase separation gives microscopic evidence that the spin reorientation under H₀ ∥ b is of first order at low temperatures. The nuclear spin-lattice relaxation rate 1/T₁ indicates that the magnetic fluctuations are suppressed for H₀ ∥ c, whereas the fluctuations remain strongly for H₀ ∥ b. The enhancements of both 1/T₁T and the nuclear spin-spin relaxation rate 1/T2 for H₀ ∥ b toward the spin reorientation field suggest that the field-induced superconductivity in URhGe emerges under the magnetic fluctuations along the b- and c-axes.