Intermetallic magnesium compounds <i>RE</i> ₂RuMg₃ (<i>RE</i> = Dy, Ho, Er, Tm, Lu) and <i>RE</i> ₃Ru₂Mg (<i>RE</i> = Sc, Er, Lu) with <i>bcc</i> Superstructures

Abstract

Abstract The intermetallic magnesium compounds RE 2 RuMg 3 ( RE = Dy, Ho, Er, Tm, Lu) and RE 3 Ru 2 Mg ( RE = Sc, Er, Lu) were synthesized from the elements in sealed niobium tubes in muffle or induction furnaces using different annealing sequences. The polycrystalline RE 2 RuMg 3 and RE 3 Ru 2 Mg samples were characterized through Guinier powder patterns. The structures of Er 2 RuMg 3 and Sc 3 Ru 2 Mg were refined on the basis of single-crystal X-ray diffractometer data: new type, P 4/ mmm , a = 336.71(9), c = 1234.6(7) pm, wR = 0.0327, 240 F val­ues, 12 variables for Er 2 RuMg 3 and a = 324.67(6), c = 1077.2(3) pm, wR = 0.0345, 273 F values, 12 variables for Sc 3 Ru 2 Mg. The Er 2 RuMg 3 and Sc 3 Ru 2 Mg structures are i3 superstructures of the CuAu type and thus belong to the large family of ordered bcc derivatives. The fundamental building units are distorted ErRu, ScRu, ScMg, and ErMg cubes. The magnesium-rich phase Er 2 RuMg 3 has a pronounced Mg substructure (314–337 pm Mg–Mg) with distorted cuboctahedral coordination. This sub­structure is compared to other magnesium-rich compounds. Temperature dependent magnetic susceptibility studies show Curie-Weiss paramagnetism for RE 2 RuMg 3 ( RE = Dy, Ho, Er, Tm) with experimental magnetic moments close to the RE 3+ free ion values. The compounds exhibit antiferromagnetic ordering at Néel temperatures of 6.5(1), 3.6(5), 3.5(5), and 5(1) K, respectively. Metamagnetic transitions underline the stable antiferromagnetic ground states. Lu 2 RuMg 3 is a Pauli paramagnet.