Anisotropic Triangular Lattice Realized in Rhenium Oxychlorides A3ReO5Cl2 (A = Ba and Sr)

TL;DR

This study synthesizes and characterizes new quantum antiferromagnets A3ReO5Cl2 (A=Sr, Ba) with anisotropic triangular lattices, revealing gapless spin liquid behavior due to geometrical frustration, expanding understanding of 5d quantum magnetism.

Contribution

First synthesis and analysis of A3ReO5Cl2 compounds showing anisotropic triangular lattice and gapless spin liquid state, highlighting 5d mixed-anion compounds' potential in quantum magnetism.

Findings

Re6+ ions form anisotropic triangular lattice with S=1/2 spins.

Magnetic interactions J and J' are estimated as 19.5/44.9 K and 9.2/19.3 K.

Compounds exhibit gapless spin liquid behavior with no long-range order above 2 K.

Abstract

We report the synthesis, crystal structure, and magnetic properties of two new quantum antiferromagnets A3ReO5Cl2 (A = Sr and Ba). The crystal structure is isostructural with the mineral pinalite Pb3WO5Cl2, in which the Re6+ ion is square-pyramidally coordinated by five oxide atoms, and forms an anisotropic triangular lattice (ATL) made of S = 1/2 spins. The magnetic interactions J and J' in the ATL are estimated from magnetic susceptibilities to be 19.5 (44.9) and 9.2 (19.3) K, respectively, with J'/J = 0.47 (0.43) for A = Ba (Sr). For each compound, heat capacity at low temperatures shows a large T-linear component with no signature of long-range magnetic order above 2 K, which suggests a gapless spin liquid state of one-dimensional character of the J chains in spite of the significantly large J' couplings. This is a consequence of one-dimensionalization by geometrical frustration in the ATL magnet; a similar phenomenon has been observed in two compounds with slightly smaller J'/J values: Cs2CuCl4 (J'/J = 0.3) and the related compound Ca3ReO5Cl2 (0.32). Our findings demonstrate that 5d mixed-anion compounds provide a unique opportunity to explore novel quantum magnetism.