Ferromagnetic interaction and superconductivity of CeCu2Si2 Original Research Article

We have recently reported our finding of a weakly ferromagnetic phase and two superconducting phases in the Cu-deficient and Cu-rich region of the homogeneity range, respectively, for the heavy-electron compound CeCu2Si2. We herein report more detailed results of the specific heat, magnetic susceptibility, resistivity (R), magnetoresistance (ΔR) and thermopower for many different compositions. We confirmed the slightly re-entrant behavior in the Hc2(T) curve and a change of regime in the ΔR at about 0.35 K above Hc2(T) for the low-Tc phase. Above about 0.75 K, the normal state of this phase exhibited no magnetoresistance up to 70 kOe, while that of high-Tc phase and the weakly ferromagnetic phase did a slightly positive ΔR. These differences in the three phases may provide an important clue to better understanding of the heavy-electron superconductivity of CeCu2Si2.