Antiferromagnetic ordering of organic Mott insulator λ-(BEDSe-TTF)2GaCl4

概要

The band structure and magnetic properties of organic charge-transfer salt λ−(BEDSe-TTF)2GaCl4 [BEDSe-TTF: bis(ethylenediseleno)tetrathiafulvalene; abbreviated as λ-BEDSe] are investigated. The reported crystal structure is confirmed using x-ray diffraction measurements, and the transfer integrals are calculated. The degree of electron correlation U/W (U: on-site Coulomb repulsion, W: bandwidth) of λ-BEDSe is larger than one and comparable to that of the isostructural Mott insulator λ−(ET)2GaCl4 (ET: bis(ethylenedithio)tetrathiafulvalene, abbreviated as λ-ET), whereas the U/W of the superconducting salt λ−(BETS)2GaCl4 [BETS: bis(ethylenedithio)tetraselenafulvalene] is smaller than one. 13C-NMR and μSR measurements revealed that λ-BEDSe undergoes an antiferromagnetic (AF) ordering below TN = 22 K. In the AF state, discrete 13C-NMR spectra with a remaining central peak are observed, indicating the commensurate AF spin structure also observed in λ-ET. The similarity between the structural and magnetic properties of λ-BEDSe and λ-ET suggests that both salts are in the same electronic phase, i.e., the physical properties of λ-BEDSe can be understood by the universal phase diagram of bandwidth-controlled λ-type organic conductors obtained by donor molecule substitution.

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