ESR studies of (BEDT-TTF)(ClMeTCNQ) under pressure

(BEDT-TTF)(ClMeTCNQ), one of mixed-stack charge-transfer (CT) compounds located on the boundary of a neutral (N) phase and an ionic (I) phase, shows a pressure or temperature induced NI phase transition. Magnetic properties associated with the transition were investigated using electron spin resonance (ESR) under hydrostatic pressure. The NI phase transition temperature was determined as the peak temperature (Tp) of the electronic spin susceptibility derived from the ESR intensity under several pressures. The susceptibility increases as the temperature goes down near Tp. This increase is interpreted as the growth of the ionic domain in the neutral phase.