J. Phys. IV France 114 (2004) 57
Magnetic and optical studies of spin and charge ordering in (TMTTF) 2AsF 6M. Dumm1, 1, B. Salameh1, M. Abaker1, L.K. Montgomery2 and M. Dressel1
1 Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany
2 Department of Chemistry, Indiana University, Bloomington, IN 47405, USA
We studied the magnetic and electronic properties of the insulating charge-transfer salt (TMTTF) 2AsF 6 by electron spin resonance (ESR), SQUID magnetometer and optical conductivity measurements. For the first time, the lattice dynamics was investigated in the vicinity of the charge order transition. We found a splitting of the electron-molecular-vibration coupled totally symmetric intramolecular a mode below the charge-order transition at 100 K. From this result a charge disproportionation on the TMTTF molecular stacks of about 2:1 can be estimated. The spin degrees of freedom were investigated by ESR and SQUID. At high temperatures (TMTTF) 2AsF 6 behaves like a antiferromagnetic S=1/2 Heisenberg chain. Below 13 K, we observed an exponential decrease of the spin susceptibility indicating the phase transition into the spin-Peierls ground state. Key words. charge-transfer salts - charge order - spin order - optical properties - magnetic properties.
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