Superconducting, Fermi surface, and magnetic properties in SrTGe^sub 3^ and EuTGe^sub 3^ (T: transition metal) with the Rashba-type tetragonal structure

We succeeded in growing single crystals of SrTGe3 (T: transition metal) by the In-flux method and measured the electrical resistivity, specific heat, and de Haas-van Alphen (dHvA) effect. We confirmed superconductivity in SrPdGe3 and SrPtGe3, which was previously observed using polycrystal samples, and also found superconductivity for SrRhGe3, SrIrGe3, and SrNiGe3. Furthermore, from the results of dHvA experiments and energy band calculations, Fermi surfaces of SrIrGe3 are found to split into two similar Fermi surfaces, reflecting the Rashba-type non-centrosymmetric tetragonal structure. We also grew single crystals of EuTGe3 by the same In-flux method and studied magnetic properties, especially focusing on magnetism of EuIrGe3 with a Néel temperature TN=12.2 K and a successive magnetic transition TN=7.3 K. The magnetic phase diagram of EuIrGe3 is found to consist of three antiferromagnetic phases named AF1, AF2, and AF3. A critical field Hc reaching a saturated moment of 7 µB/Eu is determined as Hc≂ 160 kOe from a high-field magnetization curve. We proposed a simple helical magnetic structure based on the Dzyaloshinskii-Moriya interaction.