Pressure Effect on Insulating State in Ferrimagnetic π− d System (EDT-TTFVO)2 FeBr4

To explore novel physical phenomena related to strong π−d interaction, we measured the resistivity (ρ) and magnetoresistance of the first organic ferrimagnetic π−d system, (EDT-TTFVO)₂FeBr₄ under high pressures up to 8 GPa, where EDT-TTFVO denotes ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide. At ambient pressure, ρ(T) exhibits resistivity minimum near T_min ~ 170 K followed by a gradual increase below it. With increasing pressure, T_min abruptly decreases till 4 GPa, beyond which it slightly increases. The increase of T_min above 4 GPa is discussed in terms of the enhancement of the π−d interaction by applying pressure.