Eur. Phys. J. B 55, 219-228 (2007)
https://doi.org/10.1140/epjb/e2007-00056-0

Quenching of the Haldane gap in LiVSi₂O₆ and related compounds

¹ Laboratorium für Festkörperphysik, ETH-Hönggerberg, 8093,  Zürich, Switzerland
² The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA, 92037, USA
³ Institut für Theoretische Physik III, Universität Stuttgart, Pfaffenvaldring 57, 70550,  Stuttgart, Germany
⁴ Laboratory for Neutron Scattering, PSI, 5232 Villigen PSI, Switzerland
⁵ Crystal Chemistry Laboratory, Inorganic Chemistry Division, Chemical Departement, Moscow State University, Leninskie Gory, 119992 Moscow, Russia

Corresponding author: ^a pedrini@scripps.edu

Received: 5 June 2006
Revised: 6 November 2006
Published online: 21 February 2007

Abstract

We report results of susceptibility χ and ⁷Li NMR measurements on LiVSi₂O₆. The temperature dependence of the magnetic susceptibility χ(T) exhibits a broad maximum, typical for low-dimensional magnetic systems. Quantitatively it is in agreement with the expectation for an S=1 spin chain, represented by the structural arrangement of V ions. The NMR results indicate antiferromagnetic ordering below T_N=24 K. The intra- and interchain coupling J and J_p for LiVSi₂O₆, and also for its sister compounds LiVGe₂O₆, NaVSi₂O₆ and NaVGe₂O₆, are obtained via a modified random phase approximation which takes into account results of quantum Monte Carlo calculations. While J_p is almost constant across the series, J varies by a factor of 5, decreasing with increasing lattice constant along the chain direction. The comparison between experimental and theoretical susceptibility data suggests the presence of an easy-axis magnetic anisotropy, which explains the formation of an energy gap in the magnetic excitation spectrum below T_N, indicated by the variation of the NMR spin-lattice relaxation rate at T≪T_N.