Magnesium-rich intermetallic compounds RE 3Ag4Mg12 (RE = Y, La–Nd, Sm–Dy, Yb) and AE 3Ag4Mg12 (AE = Ca, Sr)

Abstract

The magnesium-rich intermetallic compounds RE₃Ag₄Mg₁₂ (RE = Y, La–Nd, Sm–Dy, Yb) and AE₃Ag₄Mg₁₂ (AE = Ca, Sr) were synthesized from the elements in sealed tantalum ampoules through heat treatment in an induction furnace. X-ray powder diffraction studies confirm the hexagonal Gd₃Ru₄Al₁₂ type structure, space group P6₃/mmc. Three structures were refined from single crystal X-ray diffractometer data: a = 973.47(5), c = 1037.19(5) pm, wR2 = 0.0296, 660 F² values, 30 variables for Gd₃Ag_3.82(1)Mg_12.18(1), a = 985.27(9), c = 1047.34(9) pm, wR2 = 0.0367, 716 F² values, 29 variables for Yb₃Ag_3.73(1)Mg_12.27(1) and a = 992.41(8), c = 1050.41(8) pm, wR2 = 0.0373, 347 F² values, 28 variables for Ca₃Ag_3.63(1)Mg_12.37(1). Refinements of the occupancy parameters revealed substantial Ag/Mg mixing within the silver-magnesium substructure, a consequence of the Ag@Mg₈ coordination. The alkaline earth and rare earth atoms build Kagome networks. Temperature dependent magnetic susceptibility measurements indicate diamagnetism/Pauli paramagnetism for the compounds with Ca, Sr, Y and Yb^II, while the others with the trivalent rare earth elements are Curie-Weiss paramagnets. Most compounds order antiferromagnetically at T _N = 4.4(1) K (RE = Pr), 34.6(1) K (RE = Gd) and 23.5(1) K (RE = Tb) while Eu₃Ag₄Mg₁₂ is a ferromagnet (T _C = 19.1(1) K). ¹⁵¹Eu Mössbauer spectra confirm divalent europium (δ = −9.88(1) mm s⁻¹). Full magnetic hyperfine field splitting (18.4(1) T) is observed at 6 K. Yb₃Ag₄Mg₁₂ shows a single resonance in its ¹⁷¹Yb solid state NMR spectrum at 6991 ppm at 300 K indicating a strong, positive Knight shift.