Metal-insulator transition and antiferromagnetic order in bis(ethylenedithio)tetrathiafulvalene tetracyanoquinodimethane (BEDT-TTF)(TCNQ)

Electrical and magnetic properties have been investigated for (BEDT-TTF)(TCNQ) which is composed of BEDT-TTF sheets and TCNQ columns. The metal-insulator transition temperature ${\mathit{T}}_{\mathrm{MI}}$, 330 K at ambient pressure, decreases down to 40 K by applying hydrostatic pressure, which may be ascribed to the change in both the intermolecular transfer energy and the band filling (molecular valence). Measurements of EPR and magnetic susceptibility indicate that the low-temperature states of BEDT-TTF sheets and TCNQ columns are magnetic insulators, perhaps due to strong electron correlation. An anomalous broadening of EPR linewidth observed below 35 K at ambient pressure suggests an occurrence of magnetic order in BEDT-TTF sheets. A subsequent antiferromagnetic order of TCNQ columns has been found at ${\mathit{T}}_{\mathit{N}}$=3.0±0.1 K from the anisotropic magnetic susceptibility.