In2VO5, containing magnetically frustrated zig-zag chains, shows a remarkable magnetic crossover at 120 K between paramagnetic states with positive (17 K) and negative (-70 K) Weiss temperatures. Magnetic moment and entropy data show that the V4+ S = 1/2 spins condense into S = 1 triplet dimers below the crossover. A further freezing of the antiferromagnetically coupled triplet dimers into a global singlet state is observed at 2.5 K, with no long range magnetic order down to 0.42 K and in fields up to 9 T. No structural V-V dimerization is observed by high-resolution X-ray diffraction down to 10 K, but a subtle lattice anomaly evidences a spin-lattice coupling in the triplet dimer state. This is assigned to longitudinal oxygen displacement modes that reduce frustration within the chains and so couple to the spin dimer fluctuations.
@article{arxiv.0708.2550,
title = {Triplet Dimerization Crossover Driven by Magnetic Frustration in In2VO5},
author = {S. A. J. Kimber and M. A. de Vries and J. Sanchez-Benitez and K. V. Kamenev and J. P. Attfield},
journal= {arXiv preprint arXiv:0708.2550},
year = {2009}
}