Search for the Field-induced Magnetic Instability around the Upper Critical Field of Superconductivity in Hallel c in CeCoIn5

We present nuclear spin-lattice relaxation rate (1/T₁) at the Co site and ac-susceptibility results in the normal and superconducting (SC) states of CeCoIn₅ for H\parallel c near the SC upper critical field H_c2 above 0.1 K. At 4.2 T, 1/T₁ rapidly decreases below the SC transition temperature, consistent with the previous reports. Although the field dependence of 1/T₁T at 0.1 K shows a peak at 5.2 T above H_c2, the temperature dependence of 1/T₁T at 5.2 T is independent of temperature below 0.2 K, showing a Fermi-liquid behavior. In addition, we found no NMR-spectrum broadening by the appearance of internal fields around H_c2 at 0.1 K. We could not detect any field-induced magnetic instability around H_c2 down to 0.1 K although the remarkable non-Fermi-liquid behavior towards H_c2 was observed in various physical quantities.