Evidence for Strong π–d Interaction in β-(EDT-DSDTFVSDS)₂FeBr₄

Abstract

Electronic properties of the π–d system β-(EDT-DSDTFVSDS) 2 FeBr 4 are investigated, where EDT-DSDTFVSDS = ethylenedithiodiselenadithiafulvalenothioquinone-1,3-diselenolemethide. Clear contrast between the FeBr 4 salt and the nonmagnetic anion analogue salt, β-(EDT-DSDTFVSDS) 2 GaBr 4 , was observed in the electrical resistance and magnetoresistance (MR). The FeBr 4 salt exhibits a giant negative MR of 85% at 0.7 K and 14 T. Furthermore, MR of the FeBr 4 salt has a deep and sharp dip anomaly associated with the spin flop of the d spin at around 1.8 T below Néel temperature T Nd = 3.3 K. A model calculation, based on the assumption that antiferromagnetic arrangement of the d spins enhances an insulating state, qualitatively reproduced the experimental result. These results demonstrate the strong π–d interaction in the FeBr 4 salt. Further, it is remarkable that in the higher angle of magnetic field from the easy axis, two anomalies associated with spin flop were observed. This behavior is neither explained by the conventional three-dimensional Ising nor XY models. The magnetic susceptibility of the FeBr 4 salt obeys the Curie–Weiss law without a peak, which is characteristic of the usual low-dimensional antiferromagnet at higher temperature than Néel temperature.