Electronic Properties of a TMTTF-Family Salt, (TMTTF)₂TaF₆: New Member Located on the<i>Modified</i>Generalized Phase-Diagram

Abstract

A new TMTTF (tetramethyl-tetrathia-fulvalene)-family salt, (TMTTF) 2 TaF 6 , which has the largest octahedral ( O h ) symmetry counter anion among the various salts in the TMTTF family, was prepared. X-ray, static magnetic susceptibility, electron spin resonance (ESR) and nuclear magnetic resonance (NMR) measurements were carried out in order to investigate the electronic state of (TMTTF) 2 TaF 6 . The unit-cell volume of (TMTTF) 2 TaF 6 is larger than that of (TMTTF) 2 M F 6 ( M =P, As, and Sb). (TMTTF) 2 TaF 6 shows the highest charge-ordering phase transition temperature ( T CO ∼175 K) among TMTTF salts with the O h -symmetry counter anion. These facts indicate that (TMTTF) 2 TaF 6 is located on the most negative side in the generalized phase-diagram for TMT C F family salts. (TMTTF) 2 TaF 6 undergoes an antiferromagnetic transition around 9 K. It turned out the phase diagram needs to be modified.