Abstract
The three title compounds crystallize in the monoclinic system, with
unit cell parameters (at 4.95 K): Li2TbF6: a = 7.5643(3) Angstrom, b =
4.9372(3) Angstrom, c = 11.0710(4) Angstrom, beta = 107.012(3)degrees,
space group P2(1)/c (ndegrees 14), K2TbF6: a = 6.5909(2) Angstrom, b =
11.4135(4) Angstrom, c = 7.1235(2) Angstrom, beta = 90.502(2)degrees,
space group C2/c (ndegrees 15), and Rb2TbF6: a = 6.8298(2) Angstrom, b
= 11.8385(5) Angstrom, c = 7.2013(2) Angstrom, beta = 91.358(2)degrees,
space group C2/c (ndegrees 15). Neutron diffraction study down to 1.4 K
revealed an antiferromagnetic ordering for the three compounds,
occurring at T-N = 2.02(1), 1.60(5) and 2.10(5) K for Li, K and Rb
representatives, respectively. All the magnetic structures are
incommensurate and square-modulated with extremely long periods at 1.40
K. While the magnetic structure of Li2TbF6 is characterized by a
propagation vector k = (0, 0.01617(7), 0), those of the potassium and
rubidium representatives exhibit propagation vectors k = (0.0073(2), 0,
0) and k = (0.01039(8), 0, 0), respectively, these three propagation
vectors corresponding to the direction of the shortest interchain
distances. This singular magnetic behaviour will be correlated with the
nuclear structures and the potential competition between magnetic
interactions occurring in these M2TbF6 compounds and will be discussed
in the light of a fine topological analysis. (C) 2003 Elsevier B.V. All
rights reserved.
