Magnetic Properties of RCoGe₃ (R: Ce, Pr, and Nd) and Strong Anisotropy of the Upper Critical Field in Non-centrosymmetric Compound CeCoGe₃

Abstract

We grew single crystals of RCoGe₃ (R: La, Ce, Pr, and Nd) by the Bi-flux method, and studied the magnetic properties of PrCoGe₃ and NdCoGe₃ and the pressure-induced superconducting property of CeCoGe₃. These compounds crystallize in a non-centrosymmetric tetragonal structure. PrCoGe₃ and NdCoGe₃ were found to be a paramagnet and an antiferromagnet with the Néel temperature T_N=3.8 K, respectively. Crystalline electric field (CEF) schemes were proposed for PrCoGe₃ and NdCoGe₃. The magnetic property of a pressure-induced superconductor CeCoGe₃ is highly different from those of PrCoGe₃ and NdCoGe₃, or a similar pressure-induced superconductor CeIrSi₃. This was discussed in connection with the superconductivity of CeCoGe₃. We clarified the upper critical field H_c2 for H||[001] and [100] by measuring the electrical resistivity under pressure P in magnetic fields: H_c2(0)\\simeq24 T for H||[001] and H_c2(0)\\simeq3.1 T for H||[100] at 0 K at P=7.1 GPa. A huge H_c2(0) value for H||[001] is a combined phenomenon between the Rashba-type antisymmetric spin–orbit interaction and the electronic instability, as observed in CeIrSi₃.