Magnetic susceptibility studies of tetrathiofulvalene-tetracyanoquinodimethan (TTF) (TCNQ) and related organic metals

Abstract

The complete temperature dependence of the magnetic susceptibility is reported for pure (TTF)(TCNQ), (ATTF)(TCNQ), and (TMTTF)(TCNQ), [(tetrathiofulvalene-, cis (trans)-dimethyl tetrathiofulvalene-, and tetramethyltetrathiofulvalene-tetracyanoquinodimethan)]. The nonmagnetic ground state and absence of localized-moment formation imply that electron-electron Coulomb interactions are not dominant. The results are analyzed in terms of a two-chain model with a mean-field Peierls-Fröhlich transition temperature $T_p\simeq 450$ K associated with one set of chains, while the second set behaves as a simple metal above 60 K. The susceptibility above 60 K is analyzed in terms of the proposal of Lee, Rice, and Anderson. The transition to a small-band-gap semiconductor at 60 K is interpreted as the onset of three-dimensional ordering. The experimental results show (TTF)(TCNQ) and its dimethyl and tetramethyl derivatives to be a family with quite similar electronic properties.