Quadratic heat capacity and high-field magnetic phases of V5S8

TL;DR

This paper investigates the unusual quadratic temperature dependence of heat capacity in V5S8, revealing an unconventional phonon spectrum and a novel high-field magnetic transition linked to frustrated spin interactions.

Contribution

It reports the discovery of quadratic heat capacity behavior and a new high-field magnetic phase in V5S8, supported by a model of frustrated spin sublattices.

Findings

Quadratic temperature dependence of heat capacity in V5S8.

Unconventional phonon spectrum with linear and quadratic dispersion.

Observation of an intermediate magnetic transition at high fields.

Abstract

We report the observation of an unexpected quadratic temperature dependence of the heat capacity in the vanadium sulphide metal V5S8 at low temperatures which is independent of applied magnetic field. We find that the behaviour of the heat capacity is consistent with an unconventional phonon spectrum which is linear in wavevector in the c direction but quadratic in the a-b plane, indicating a form of geometrical elastic criticality. In the case of V5S8 we also observe an unusual intermediate transition at high magnetic fields between the expected spin-flop and spin-flip transitions. We demonstrate that the intermediate field-induced transition is in agreement with a model of two sublattices with frustrated inter- and intra-sublattice spin couplings.