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 RE 3Ag4Mg12 (RE = Y, La–Nd, Sm–Dy, Yb) and AE 3Ag4Mg12 (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 F 2 values, 30 variables for Gd3Ag3.82(1)Mg12.18(1), a = 985.27(9), c = 1047.34(9) pm, wR2 = 0.0367, 716 F 2 values, 29 variables for Yb3Ag3.73(1)Mg12.27(1) and a = 992.41(8), c = 1050.41(8) pm, wR2 = 0.0373, 347 F 2 values, 28 variables for Ca3Ag3.63(1)Mg12.37(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 YbII, 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.

On the Ytterbium Valence and the Physical Properties in Selected Intermetallic Phases

“…The room temperature value of 7.2 × 10 –6 emu mol –1 for Yb 5 Cu 2 Zn indicates Pauli paramagnetism . In contrast, in Yb 3 Ag 4 Mg 12 the intrinsic diamagnetism is not as strongly overcompensated by the Pauli contribution, leading to a room temperature value of −4.61 × 10 –4 emu mol –1 . The susceptibility increases in the low-temperature regimes (the so-called Curie tails), which originates from traces of paramagnetic impurities.…”

“…The resonance of the strongly broadened spectrum recorded under static conditions applying the WURST-CPMG pulse sequence is found to be between 6800 and 7000 ppm, indicating a strong positive Knight shift. Between 200 and 300 K, the temperature dependence of the resonance shift was negligible, suggesting a strong orbital contribution to the Knight shift …”

“…Temperature dependence of the magnetic susceptibility χ of Yb 3 Ag 4 Mg 12 and Yb 5 Cu 2 Zn, measured at 10 kOe.…”