Structure and ferromagnetism of the rare-earth zintl compounds:: Yb14MnSb11 and Yb14MnBi11

Rare-earth transition metal compounds Yb14MnSb11 and Yb14MnBi11 have been prepared by heating stoichiometric amounts of the elements at 1000-1200 degrees C. These compounds are isostructural with the Zintl compound Ca14AlSb11 and crystallize in the tetragonal space group I4(1)/acd (Z = 8). Single-crystal X-ray data (143 K) were refined for Yb14MnSb11 [a = 16.615(2) Angstrom, c = 21.948(4) Angstrom, V = 6059(2) Angstrom(3), and R1/wR2 (0.0299/0.0479)] and Yb14MnBi11 [a = 17.000(3) Angstrom, 22.259(6) Angstrom, V = 6433(2) Angstrom(3), R1/wR2 (0.0631/0.133)]. Structural analysis is consistent with Yb2+. Temperature-dependent magnetic susceptibility data show that Yb14MnSb11 orders ferromagnetically at 56 K and Yb14MnBi11 has a ferromagnetic transition at 58 K and another transition at 28 K. High-temperature magnetic susceptibility data can be fit with a modified Curie-Weiss law and give mu(eff) = 4.92(2)mu(B) and mu(eff) = 4.9(1)mu(B) for the Sb and Bi compounds, respectively. This result is consistent with the assignment of Mn3+ (d(4)) and Yb2+ (f(14)). Single-crystal magnetic data provide additional evidence for the magnetic transitions and show that the compounds are magnetically anisotropic.