Eur. Phys. J. B 59, 9-17 (2007)
https://doi.org/10.1140/epjb/e2007-00262-8

Equilibrium low temperature heat capacity of the spin density wave compound (TMTTF)₂Br: effect of a magnetic field

¹ Institut NEEL, CNRS, & Université Joseph Fourier, BP 166, 38042 Grenoble Cedex 9, France
² Institut für Festkörperphysik, IFP, Technische Universität Dresden, 01062 Dresden, Germany

Corresponding authors: ^a sahling@physik.tu-dresden.de - ^b lasjaunias@grenoble.cnrs.fr

Received: 6 March 2007
Revised: 3 August 2007
Published online: 5 October 2007

Abstract

We have investigated the effect of the magnetic field (B) on the very low-temperature equilibrium heat capacity c_eq of the quasi-1 D organic compound (TMTTF)₂Br, characterized by a commensurate Spin Density Wave (SDW) ground state. Below 1 K, c_eq is dominated by a Schottky-like A_ST^-2 contribution, very sensitive to the experimental time scale, a property that we have previously measured in numerous DW compounds. Under applied field (in the range 0.2–7 T), the equilibrium dynamics, and hence c_eq extracted from the time constant, increases enormously. For B ≥ 2–3 T, c_eq varies like B², in agreement with a magnetic Zeeman coupling. Another specific property, common to other Charge/Spin density wave (DW) compounds, is the occurrence of metastable branches in c_eq, induced at very low temperature by the field exceeding a critical value. These effects are discussed within a generalization to SDWs in a magnetic field of the available Larkin-Ovchinnikov local model of strong pinning. A limitation of the model when compared to experiments is pointed out.