Magnesium-rich Intermetallics RE3RuMg7 (RE = Y, Nd, Dy, Ho) – Rows of Condensed Ru@RE6/2 Octahedra in Magnesium Matrices

The magnesium-rich intermetallic phases RE₃RuMg₇ (RE = Y, Nd, Dy, Ho) have been synthesized from the elements in sealed niobium ampoules and subsequently characterized by powder X-ray diffraction. The structure of the dysprosium compound was refined on the basis of single-crystal X-ray diffractometer data: Ti₆Sn₅ type, P6₃/mmc, a = 1019.1(2), c = 606.76(9) pm, wR2 = 0.0159, 439 F² values, 19 variables. The Mg3 site shows a small degree of Mg3/Dy mixing, leading to the composition Dy_3.03RuMg_6.97 for the investigated crystal. The striking structural motifs in the Dy₃RuMg₇ structure are rows of face-sharing Ru@Dy₆ octahedra and corner-sharing Mg2@Mg₈Dy₄ icosahedra. The rows of octahedra form a hexagonal rod-packing, and each rod is enrolled by six rows of the condensed icosahedra. Temperature-dependent magnetic susceptibility measurements of Dy₃RuMg₇ show Curie–Weiss behavior with an experimental magnetic moment of 10.66(1) μ_B per Dy atom. Antiferromagnetic ordering is detected at T_N = 27.5(5) K. The 5 K isotherm shows a metamagnetic transition at a critical field of H_C = 40 kOe.