Magnetic and superconducting properties of the Ir – rich compounds MIr₃ (M=Ce, Th and Nd)

Recently we have synthesized and studied CeIr₃, NdIr₃ and ThIr₃ compounds that are members of the RE_2m+nT_4m+5n family (m, n > 0). The bulk nature of the superconducting transitions for CeIr₃ and ThIr₃ are evident from the visible anomalies at T_c = 2.5 K and 4.4 K, respectively. The heat capacity experiment revealed that CeIr₃ is a weak-coupling BCS superconductor and ThIr₃ is a moderately coupled type-II superconductor. Theoretical calculations indicate a multi-band character for the Fermi surfaces, with the dominating contribution to the density of states at the Fermi level coming from the 5d states of Ir.
In the case of NdIr₃, our measurements indicate a ferromagnetic ground state with the Curie temperature T_C = 10.6 K. The heat-capacity anomaly confirms the bulk nature of the transition, though C_p = 11.7 J mol⁻¹K⁻¹ is lower than expected for J = 9/2 and instead close to that of a J = 1/2 system. This suggests that the Nd ions are subject to a crystalline electrical field that removes spin degeneracy and leaves the Nd ions in a doublet ground state.