J. Phys. IV France 114 (2004) 111
Anomalous thermal expansion behavior in (TMTTF) 2PF 6 and (TMTSF) 2PF 6 around 100 K: Indications for a strong spin-phonon interaction?M. Lang1, J. Müller2, F. Steglich2, A. Brühl1, B. Wolf1 and M. Dressel3
1 Institute of Physics, J.W. Goethe-University Frankfurt, 60054 Frankfurt (M), Germany
2 Max-Planck-Institut for Chemical Physics of Solids, 01187 Dresden, Germany
3 Institute of Physics I, University of Stuttgart, 70550 Stuttgart, Germany
High-resolution measurements of the coefficient of thermal expansion along the b axis, , on the quasi-1D Spin-Peierls and spin-density-wave systems (TMTTF) 2PF 6 and (TMTSF) 2PF 6, respectively, reveal an anomalous (T) contribution around 100 K. This feature, which is most strongly pronounced in the SP system, is reminiscent of the magnetic contribution observed in low-dimensional spin systems with a strong spin-lattice interaction such as CuGeO 3. Remarkably enough, the position of the anomalies for both compounds almost coincide with the temperatures where the thermal conductivity shows a distinct minimum [T. Lorenz et al., Nature 418 (2002) 614]. Our observation indicates a significant role of the spin-lattice interaction for these systems. Key words. Spin - phonon interaction, thermodynamic properties.
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