Antiferromagnetic ordering of organic Mott insulator $λ$-(BEDSe-TTF)$_2$GaCl$_4$

Abstract

The band structure and magnetic properties of organic charge-transfer salt λ-(BEDSe-TTF)2GaCl4 (BEDSe-TTF: bis(ethylenediseleno)tetrathiafulvalene, abbreviated as λ-BEDSe) were investigated. The reported crystal structure was confirmed by the X-ray diffraction measurement, and the transfer integrals were 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 isostructural Mott insulator λ-(ET)2GaCl4 (ET: bis(ethylenedithio)tetrathiafulvalene, abbreviated as λ-ET), whereas U/W of superconducting salt λ-(BETS)2GaCl4 (BETS: bis(ethylenedithio)tetraselenafulvalene) is smaller than one. 13 C-NMR and µSR measurements revealed that λ-BEDSe undergoes an antiferromagnetic (AF) ordering below TN = 22 K. In the AF state, discrete 13 C-NMR spectra with a remaining central peak were observed, indicating the commensurate AF spin structure also observed in λ-ET. The similarity between structural and magnetic properties of λ-BEDSe and λ-ET indicates that both salts are in the same electronic phase, namely, physical properties of λ-BEDSe can be understood by the universal phase diagram of bandwidthcontrolled λ-type organic conductors by donor molecule substitution. Furthermore, polymorphism was not obtained in the synthesis of this material, unlike for many other λ-type salts. The absence of polymorphism will allow us to construct electronic phases next to the superconducting phase, where a strange paramagnetic insulating phase is sandwiched between superconducting and antiferromagnetic phases.

Magnetic state in the quasi-two-dimensional organic conductor λ−(BEST)2FeCl4 and the path of π−dSaito1, Iida2, Kobayashi3 et al. 2022Phys. Rev. B3080View full textAdd to dashboardCite

“…Considering that the temperature in λ-(STF) 2 FeCl 4 corresponded to the AFM transition temperature in the donor layer [19], λ-(BEST) 2 FeCl 4 undergoes a magnetic transition at around 26 K in the donor layer. Because λ-(BEST) 2 GaCl 4 shows an AFM transition at 22 K, as confirmed by 13 C NMR [23], the FeCl 4 and GaCl 4 compounds of the BEST salts in the λ-type family show an AFM transition. To determine the accurate transition temperature and confirm the TABLE III.…”

“…ET and BEST salts are also on the negative-pressure side of STF salts and insulators at all temperatures [21,22]. Recently, it was reported that λ-(BEST) 2 GaCl 4 undergoes an AFM transition at 22 K, and the preparation of λ-(BEST) 2 FeCl 4 has already been reported [22,23]. However, λ-(ET) 2 FeCl 4 has not been reported, whereas λ-(ET) 2 GaCl 4 undergoes the AFM transition at 13 K [24].…”