Noncollinear two- and three-dimensional magnetic ordering in the honeycomblattices of ErX3 (X=Cl,Br,I)

Unusual magnetic ordering phenomena have been observed in the three title c ompounds in the milli-Kelvin temperature range. The ratio of interlayer to intralayer coupling and thus the critical behavior and the nature of the ma gnetic order can be tuned by chemical variation. In all three lattices the two-dimensional (2D) magnetic order within the layers is a two sublattice 1 20 degrees antiferromagnetic order with an infinite rotational degeneracy, The ordered magnetic moments increase from 3.3 to 4.7 and 5.5 mu(B)/Er3+ fo r ErCl3, ErBr3, and Erl(3), respectively. ErCl3 shows a transition to 3D ma gnetic order at 350 mK with a k vector of (2/3, 0,-1/12) ErBr3 and ErI3 are the first examples of rare-earth trihalides displaying short-range 2D magn etic order from 400 mK up to several Kelvin, long-range 2D order between 28 0 mK and 400 mK, long-range 2D and short-range 3D order with k=(1/3,1/3,0), and a correlation length of 15 Angstrom below 280 mK. The differences are attributed to the different layer stackings in ErCl3 and ErBr3/ErI3 as well as the variation of interlayer distances, [S0163-1829(99)50530-4].