Abstract
We have conducted comprehensive electron spin resonance (ESR) investigations on single crystals of the one-dimensional organic compounds and in the temperature range from 4 to 500 K and additionally, and at room temperature. In contrast to the selenium analogs TMTSF which are one-dimensional metals, the sulfur salts are semiconductors with localized spins on the TMTTF dimers. Taking into account the thermal expansion of the crystals at high temperature the ESR intensity of all sulfur compounds can be described as a spin-1/2 antiferromagnetic Heisenberg chain with exchange constants Although the TMTSF compounds are one-dimensional organic metals down to 10 K, the temperature dependence of the spin susceptibility can also be described within the framework of the Hubbard model in the limit of strong Coulomb repulsion with By modeling as an alternating spin chain, the change of the alternation parameter at the first-order phase transition indicates a tetramerization of the chain. undergoes a spin-Peierls transition at which can be well described by Bulaevskii’s model with a singlet-triplet gap We find evidence of antiferromagnetic fluctuations at temperatures well above the magnetic ordering in and which follow the critical behavior expected for three-dimensional ordering. and show one-dimensional lattice fluctuations.
- Received 22 April 1999
DOI:https://doi.org/10.1103/PhysRevB.61.511
©2000 American Physical Society