Crystal structure, and physical properties of the novel compounds EuRh_3Ge_7 and EuIr_3Ge_7

摘要

Two novel compounds, EuRh_3Ge_7 and EuIr_3Ge_7, have been synthesized by arc melting of the elements and subsequent annealing at 800℃. X-ray structure analyses confirmed for both compounds isotypism with the crystal structure of the ScRh_3Si_7-type (R3c): SC-data for EuRh_3Ge_7 (a = 0.78918(2), c = 2.07179(5) nm, R_F = 0.0130) and Rietveld powder data for EuIr_3Ge_7 (a = 0.788399(5), c = 2.07583 (2) nm, R_F = 0.0501).Magnetization, heat capacity, thermal expansion and electrical resistivity at various magnetic fields were measured revealing second order phase transitions at 20 K for EuRh_3Ge_7, and 87 K for EuIr_3Ge_7, respectively. While this transition is clearly antiferromagnetic in the case of EuRh_3Ge_7, the nature of this transition remains unclear for EuIr_3Ge_7. The evaluation of magnetic susceptibility as well as heat capacity data reveals an intermediate valence state of Eu-ions in both compounds.