Unconventional heavy-fermion superconductor CeCoIn5:: dc magnetization study at temperatures down to 50 mK -: art. no. 180504

dc magnetization measurements on CeCoIn5 reveal a first-order phase transition at H-c2 for both Hparallel toa and c axes in the isothermal magnetization M(H) below 0.7 K, indicating a strong Pauli paramagnetic suppression in the even-parity pairing. M(T) in the normal state above H-c2 exhibits non-Fermi-liquid behavior down to 150 mK, implying the existence of antiferromagnetic fluctuations behind the unconventional superconductivity. We observed an unusual peak effect for Hparallel toc in fields 5-30 kOe below 150 mK(=0.06T(c)), whose anomalous temperature dependence cannot be simply explained by ordinary mechanisms.