Metal–insulator transitions in magnetic conductor λ-(BEDT-TSF)2FeCl4 studied by 1H and 77Se NMR

We have performed 1H and 77Se NMR measurements on a π–d organic metal λ-(BEDT-TSF)2FeCl4 containing paramagnetic ions Fe3+. It is found from 1H NMR measurements that the resonance line starts to split around TFM=70 K, just a temperature where a ferroelectric-like transition occurs, and with further decreasing temperature, the spectrum becomes significantly broad near the metal–insulator transition TMI=8.3 K. From 77Se NMR measurements, near the phase boundary between the forced-ferromagnetic metallic state and the canted antiferromagnetic insulating state at 1.6 K and 11.67 T, a single peak becomes split with two new peaks emerging at the both sides of the zero-shift.