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

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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 $T_{\text{N}} = 3.8$ 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 $H_{\text{c2}}$ for $H \parallel [001]$ and [100] by measuring the electrical resistivity under pressure $P$ in magnetic fields: $H_{\text{c2}}(0) \simeq 24$ T for $H \parallel [001]$ and $H_{\text{c2}}(0) \simeq 3.1$ T for $H \parallel [100]$ at 0 K at $P = 7.1$ GPa. A huge $H_{\text{c2}}(0)$ value for $H \parallel [001]$ is a combined phenomenon between the Rashba-type antisymmetric spin–orbit interaction and the electronic instability, as observed in CeIrSi3.
2009-12-15