Abstract
We studied the magnetic and electronic properties of the insulating charge-transfer salt (TMTTF)2AsF6 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$_{g}(\nu _{3})$ 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)2AsF6 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.