J. Phys. I France
Volume 6, Numéro 12, December 1996
Page(s) 1745 - 1752
DOI: 10.1051/jp1:1996186
J. Phys. I France 6 (1996) 1745-1752

Evidence from $\mathsf{^1}$H-NMR for a Crossover from "Local-Moment" Antiferromagnetism to Spin-Density Wave in (TMTTF) $\mathsf{_2}$Br with Application of Pressure

B.J. Klemme1, S.E. Brown1, P. Wzietek2, D. Jérome2 and J.M. Fabre3

1  Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA
2  Laboratoire de Physique des Solides, Université de Paris-Sud, 91405 Orsay Cedex, France
3  Laboratoire de Chimie Organique Structurale, Université des Sciences et Techniques du Languedoc, 34060 Montpellier, France

(Received 27 June 1996, received in final form 26 August 1996, accepted 27 August 1996)

We have made measurements of the proton spin-lattice relaxation in the low-temperature antiferromagnetic ground state of (TMTTF) 2Br at different pressures. At ambient pressure, the relaxation rate 1/T1 is peaked at the transition temperature with isotropic critical fluctuations apparent over a wide temperature range. 1/T1 declines monotonically as the temperature is lowered. Application of hydrostatic pressure results in additional relaxation, very likely from collective excitations, in the ordered phase. The results taken together imply the system is driven from commensurability at a very low pressure ( <4 kbar). The behavior is summarized in a P-T phase diagram.

© Les Editions de Physique 1996

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