  MnSnTeO6, a new chiral antiferromagnet, was prepared both by topotactic
transformation of the metastable rosiaite-type polymorph and by direct
synthesis from coprecipitated hydroxides. Its structure, static and dynamic
magnetic properties were studied comprehensively both experimentally (through
X-ray and neutron powder diffraction, magnetization, specific heat, dielectric
permittivity and ESR techniques) and theoretically (by means of ab initio
density functional theory (DFT) calculations within the spin-polarized
generalized gradient approximation). MnSnTeO6 is isostructural with MnSb2O6
(space group P321) and does not show any structural transition between 3 and
300 K. The magnetic susceptibility and specific heat exhibit an
antiferromagnetic ordering at TN=9.8 K, which is confirmed by low-temperature
neutron data. At the same time, the thermodynamic parameters demonstrate an
additional anomaly on the temperature dependences of magnetic susceptibility
chi(T), specific heat Cp(T) and dielectric permittivity epsilon(T) at T*=4.9 K,
which is characterized by significant temperature hysteresis. Clear enhancement
of the dielectric permittivity at T* is most likely to reflect the coupling of
dielectric and magnetic subsystems leading to development of electric
polarization. It was established that the ground state of MnSnTeO6 is
stabilized by seven exchange parameters, and neutron diffraction revealed
incommensurate magnetic structure with propagation vector k= (0, 0, 0.183)
analogous to that of MnSb2O6. Ab initio DFT calculations demonstrate that the
strongest exchange coupling occurs between planes along diagonals. All exchange
parameters are antiferromagnetic and reveal moderate frustration.
