PbMnTeO6: a chiral quasi 2D magnet with all cations in octahedral coordination and the space group problem of trigonal layered A2+M4+TeO6

Abstract

Antiferromagnetic PbMnTeO₆, also known as mineral kuranakhite, has been reported recently to have all three cations in trigonal prismatic coordination, which is extremely unusual for both Mn(4+) and Te(6+). In this work, the phase was reproduced with the same lattice parameters and Néel temperature T_N = 20 K. However, powder neutron diffraction unambiguously determined octahedral (trigonal antiprismatic) coordination for all cations within the chiral space group P312. The same symmetry was proposed for SrMnTeO₆ and PbGeTeO₆, instead of the reported space groups P2m and P31m, respectively. PbMnTeO₆ was found to be a robust antiferromagnet with an assumingly substantial scale of exchange interactions since the Néel temperature did not show any changes in external magnetic fields up to 7 T. The determined effective magnetic moment μ_eff = 3.78μ_B was in excellent agreement with the numerical estimation using the effective g-factor g = 1.95 directly measured here by electron spin resonance (ESR). Both specific heat and ESR data indicated the two-dimensional character of magnetism in the compound under study. The combination of chirality with magnetic order makes PbMnTeO₆ a promising material with possible multiferroic properties.