Hidden Magnetic Order in Triangular-Lattice Magnet Li2MnTeO6

TL;DR

This study reveals the presence of hidden magnetic order in Li2MnTeO6, a triangular-lattice magnet, showing antiferromagnetic order at low temperatures with a non-collinear spin structure and strong spin frustration.

Contribution

The paper provides experimental and theoretical evidence of a non-collinear antiferromagnetic order in Li2MnTeO6, highlighting its spin frustration and two-dimensional magnetic behavior.

Findings

Antiferromagnetic transition at around 8.5 K confirmed by specific heat.

Neutron diffraction reveals a 120-degree non-collinear spin structure.

Density functional calculations show dominant nearest-neighbor antiferromagnetic exchange.

Abstract

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.