ESR Study on Molecular Salt (Benzo-TTFVS)2MBr4 (M = Fe, Ga)

Electron spin resonance (ESR) experiments on (Benzo-TTFVS)2MBr4 (M = Fe, Ga) have been done with 15.4 GHz microwaves, where Benzo-TTFVS denotes a new donor molecule substituted with a benzo group, benzotetrathiafulvalenothioquinone-1,3-dithiolemethide. The temperature and the magnetic-field-direction dependencies of the effective g-value and the linewidth are obtained. In (Benzo-TTFVS)2GaBr4 (Ga salt), the ESR signals are due to π-electrons while they originate from d-electrons at the Fe3+ ion in the case of (Benzo-TTFVS)2FeBr4 (Fe salt). The g-value and the linewidth for the direction of the π-d correlation are di erent from those for other directions in the Fe salt. A strong antiferromagnetic fluctuation related to the π-d correlation is observed in the Fe salt. On the other hand, in the Ga salt, the magnetic- eld-direction dependencies of the g-value and the linewidth re ect the anisotropy of the one-dimensional conduction band. The importance of the π-d correlation is proved by comparing the ESR results for the Fe salt with those for the Ga salt.