J. Phys. IV France
Volume 114, April 2004
Page(s) 57 - 60

J. Phys. IV France
114 (2004) 57
DOI: 10.1051/jp4:2004114010

Magnetic and optical studies of spin and charge ordering in (TMTTF) 2AsF 6

M. 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 $_{g}(\nu _{3})$ 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) 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.

© EDP Sciences 2004