ИСТИНА

The static and dynamic magnetic properties of a new quasi-two-dimensional magnet with a triangular lattice Li2MnTeO6 are investigated. The data on the specific heat and low-temperature neutron diffraction reveal the onset of long- range magnetic order, despite the absence of any pronounced features on the temperature dependence of magnetic susceptibility in weak magnetic fields upon cooling to 2 K and essentially reduced magnetic moment as determined from neutron studies (hidden magnetic order effect). The temperature dependence of the magnetic susceptibility obeys the Curie-Weiss law at high temperatures but involves a wide range of short-range magnetic correlations and a relatively large negative Weiss temperature, which indicates the predominance of antifer- romagnetic exchange interactions and a noticeable spin frustration. With an increase in the magnetic field, the behavior of the temperature dependence of the magnetic susceptibility changes noticeably, and a characteristic maximum is observed at the Neel temperature. The magnetic structure of Li2MnTeO6, determined by neutron powder diffraction measurements at 1.6 K, is described by the 120° 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.