  The manganese tellurate Li2MnTeO6 consists of trigonal spin lattices made up
of Mn4+ (d3, S = 3/2) ions. The magnetic properties of this compound were
characterized by several experimental techniques, which include magnetic
susceptibility, specific heat, dielectric permittivity, electron spin resonance
(ESR), nuclear magnetic resonance (NMR) and neutron powder diffraction (NPD)
measurements, and by density functional calculations (DFT). The magnetic
susceptibility chi(T) demonstrates very unusual behavior. It isdescribed by the
Curie-Weiss law at high temperature with Curie-Weiss temperature of Theta = -74
K, exhibits no obvious anomaly indicative of a long-range magnetic ordering at
low magnetic fields. At high magnetic fields, however, the character of chi(T)
changes showing a maximum at about 9 K. That this maximum of chi(T) reflects
the onset of an antiferromagnetic order was confirmed by specific heat
measurements, which exhibit a clear lambda-type anomaly at TN around 8.5 K even
at zero magnetic field, and by 7Li NMR and dielectric permittivity
measurements. The magnetic structure of Li2MnTeO6, determined by neutron powder
diffraction measurements at 1.6 K, is described by the 120-degree non-collinear
spin structure with the propagation vector k = (1/3, 1/3, 0). Consistent with
this finding, the spin exchange interactions evaluated for Li2MnTeO6 by density
functional calculations are dominated by the nearest-neighbor antiferromagnetic
exchange within each triangular spin lattice. This spin lattice is strongly
spin frustrated with f = |Theta|/TN around 8 and exhibits a two-dimensional
magnetic character in a broad temperature range above TN.
