Magnetic and Superconducting Phase Diagram of Heavy Fermion Superconductors Ce_1−xTh_xCu_2.2Si₂ —Cu NMR and NQR Study—

Abstract

The magnetic and superconducting phase diagram of Th-doped Ce_1−xTh_xCu_2.2Si₂ has been established by Cu NMR and NQR technique and is compared with that of CeCu_2.02Si₂. Static magnetic ordering with T_N=2.4 K and 4.5 K for x=0.08 and 0.12, respectively, is evidenced by a pronounced broadening of the ⁶³Cu-NQR and -NMR spectra and a pronounced anomaly in the specific heat. In contrast, for the lightly Th-doped compounds with x≤0.064, there has been observed neither a signature of a broadening of the NQR and NMR spectra nor an anomaly of the specific heat, but a dramatic reduction of the NMR and NQR intensities below a temperature ranging from 0.9 K to 1.3 K upon increasing Th-content. It is emphasized that the unusual “magnetic transition” found in undoped and lightly Th-doped CeCu_2.2Si₂ should be distinguished from the static magnetic ordering in the heavily Th-doped systems.