Antiferromagnetic ordering and estimation of the exchange interaction in the π−d system λ−(BEDSe−TTF)2FeCl

Abstract

We performed 13 C NMR measurements on λ-(BEDSe-TTF) 2 FeCl 4 [BEDSe-TTF = bis(ethylenediseleno) tetrathiafulvalene] to investigate the antiferromagnetic transition in this material and evaluate the exchange interaction J π d between the donor molecules and FeCl − 4 anions. Based on the NMR spectrum and the nuclear spin-lattice relaxation rate, we determined that the antiferromagnetic transition in the donor layers occurs at 25 K. The structure of the NMR spectra in the antiferromagnetic phase resembles that of λ-(BEDSe-TTF) 2 GaCl 4 . We used the angle dependence of the NMR shift in the paramagnetic phase and the experimentally determined demagnetization factor to estimate J π d of λ-(BEDSe-TTF) 2 FeCl 4 as 3.4(7) T/µ B . This result shows that the π -d interaction of λ-(BEDSe-TTF) 2 FeCl 4 is weaker than that of λ-(BETS) 2 FeCl 4 . The different signs of J π d between λ-(BEDSe-TTF) 2 FeCl 4 and λ-(BETS) 2 FeCl 4 could be attributed to the different paths for the π -d interaction in the two systems.