Magnetization study of the heavy fermion superconductor CeCoIn5 Original Research Article

We report the high-resolution dc magnetization measurements in the heavy fermion superconductor CeCoIn5 at very low temperatures down to 50 mK in fields up to 125 kOe. A clear magnetization jump is observed at the upper critical field Hc2 for both H‖a and c axes in the isothermal magnetization curve below 0.7 K, indicating the existence of a first-order phase transition at Hc2. It is likely that the first-order phase transition is ascribed to a strong Pauli paramagnetic suppression in the even-parity pairing. In the normal state above Hc2 we found non-Fermi liquid behavior in the temperature dependence of the magnetization down to 150 mK, suggesting the presence of antiferromagnetic fluctuations.