beta-Cu2V2O7: a spin-1/2 honeycomb lattice system

TL;DR

This paper investigates the magnetic properties of beta-Cu2V2O7, demonstrating it as a prime experimental realization of the spin-1/2 honeycomb lattice Heisenberg model through detailed band structure calculations and modeling.

Contribution

It provides a comprehensive microscopic model of beta-Cu2V2O7, revealing its anisotropic honeycomb lattice structure and magnetic interactions, and compares computational approaches for exchange coupling evaluation.

Findings

Beta-Cu2V2O7 exhibits a spin-1/2 honeycomb lattice with coupling J1=60-66 K.

The material shows long-range magnetic order at TN~26 K.

The simulated ordering temperature closely matches experimental data.

Abstract

We report on band structure calculations and a microscopic model of the low-dimensional magnet beta-Cu2V2O7. Magnetic properties of this compound can be described by a spin-1/2 anisotropic honeycomb lattice model with the averaged coupling \bar J1=60-66 K. The low symmetry of the crystal structure leads to two inequivalent couplings J1 and J1', but this weak spatial anisotropy does not affect the essential physics of the honeycomb spin lattice. The structural realization of the honeycomb lattice is highly non-trivial: the leading interactions J1 and J1' run via double bridges of VO4 tetrahedra between spatially separated Cu atoms, while the interactions between structural nearest neighbors are negligible. The non-negligible inter-plane coupling Jperp~15 K gives rise to the long-range magnetic ordering at TN~26 K. Our model simulations improve the fit of the magnetic susceptibility data, compared to the previously assumed spin-chain models. Additionally, the simulated ordering temperature of 27 K is in remarkable agreement with the experiment. Our study evaluates beta-Cu2V2O7 as the best available experimental realization of the spin-1/2 Heisenberg model on the honeycomb lattice. We also provide an instructive comparison of different band structure codes and computational approaches to the evaluation of exchange couplings in magnetic insulators.