ESR studies of organic conductors with bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF), (BEDT-TTF)2ClO4(C2H3Cl3)0.5, and (BEDT-TTF)3(ClO4)2, and their two-dimensionality

Abstract

The magnetic properties of two (BEDT-TTF)-${\mathrm{ClO}}_4$ radical salts, (BEDT-TTF${)}_2$ ${\mathrm{ClO}}_4$(${\mathrm{C}}_2$ ${\mathrm{H}}_3$ ${\mathrm{Cl}}_3$ ${)}_{0.5}$ and surements. For the former (2:1:0.5)-phase crystal, the susceptibility shows a nesting transition at 20 K, which is affected by the degree of the incompleteness in the ordering of the ${\mathrm{C}}_2$ ${\mathrm{H}}_3$ ${\mathrm{Cl}}_3$ molecules below 200 K. The large linewidth suggests two-dimensionality, consistent with the low $T_c$ of the nesting instability and the small anisotropy in the resistivity in the a-c plane. In the case of the latter (3:2)-phase crystal, the susceptibility shows a metal-insulator transition at 150 K. Below $T_c$, an insulating state with a spin singlet is stabilized after the displacement of the BEDT-TTF [(${\mathrm{C}}_5$ ${\mathrm{H}}_4$ ${\mathrm{S}}_4$ ${)}_2$] molecules in a one-dimensional chain through the Peierls instability. The large linewidth also suggests two-dimensionality.