Magnetic state in the quasi-two-dimensional organic conductor λ−(BEST)2FeCl4 and the path of π−d

Abstract

Studies of the quasi-two-dimensional organic conductors λ-(D) 2 MCl 4 [D = donor molecules, M = Ga, Fe] have shown that λ-(BETS) 2 GaCl 4 [BETS = bis(ethylenedithio)tetraselenafulvalene] undergoes an unconventional superconducting transition and λ-(BETS) 2 FeCl 4 undergoes a field-induced superconducting transition. In λ-type salts, the interactions between donor molecules and FeCl − 4 (π -d interactions) are important.To investigate π -d interaction, a pair of magnetic M = Fe and nonmagnetic M = Ga salts which have the same ground state in the donor layer is desired. However, no such pair has been found, and few experimental studies have considered π -d interaction paths. λ-(BEST) 2 MCl 4 [BEST = bis(ethylenediseleno)tetrathiafulvalene] are obtained for both anions, and M = Ga salt shows an antiferromagnetic transition, but the ground state has not been analyzed in M = Fe salt. We perform x-ray diffraction, magnetic susceptibility measurement, and Mössbauer spectroscopy in λ-(BEST) 2 FeCl 4 . We find that a magnetic transition is observed at around 26 K. The λ-(BEST) 2 MCl 4 system is a system in which both FeCl − 4 and GaCl − 4 salts show antiferromagnetic transitions. In addition, the ethylene motions observed at room temperature are ordered around 108 K, resulting in the establishment of the π -d interaction path between chalcogens and the anion, and low-field magnetization suggests that the π -d interaction in λ-(BEST) 2 FeCl 4 is smaller than that in λ-(BETS) 2 FeCl 4 . Our results show that the inner chalcogen of donor molecules is important as the path of the interaction.

Antiferromagnetic ordering and estimation of the exchange interaction in the π−d system λ−(BEDSe−TTF)2FeClSaito, Kobayashi, Taniguchi et al. 2023Phys. Rev. BSelf Cite0000View full textAdd to dashboardCite

“…13 C NMR measurements on λ-(BEDSe-TTF) 2 GaCl 4 showed that the AF transition occurred at 22 K [19]. We have reported 57 Fe Mössbauer measurements and magnetic susceptibility measurements on λ-(BEDSe-TTF) 2 FeCl 4 [20]. Although the Mössbauer measurements indicated multistep development of the internal field exerted on Fe sites below 26 K, the magnetic susceptibility measurements did not indicate a magnetic anomaly at this temperature.…”

“…In a previous study, we compared the strengths of the π -d interaction between λ-(BEDSe-TTF) 2 FeCl 4 and λ-(BETS) 2 FeCl 4 [20]. We observed weak anisotropy of the magnetic susceptibility in λ-(BEDSe-TTF) 2 FeCl 4 [20]. By contrast, clear anisotropy was reported for λ-(BETS) 2 FeCl 4 and λ-(STF) 2 FeCl 4 [3,11].…”

“…It is important to evaluate the coupling parameter between the π and 3d spins, J πd , to understand the π -d interaction. In a previous study, we compared the strengths of the π -d interaction between λ-(BEDSe-TTF) 2 FeCl 4 and λ-(BETS) 2 FeCl 4 [20]. We observed weak anisotropy of the magnetic susceptibility in λ-(BEDSe-TTF) 2 FeCl 4 [20].…”

“…Figure 5 shows the temperature dependence of the hyperfine fields obtained by 13 13 C NMR and 57 Fe Mössbauer measurements [12,13,20]. λ-STF (#1) and λ-STF (#2) are different samples of the same compound.…”

“…Hence, we used the mean H dip (θ ) over four sites as H dip (θ ). We assumed M d follows the Curie's law with S = 5/2 [20]. Using M d = 0.4761 µ B at 100 K, we calculated H dip (θ ) with a standard deviation as the average of the dipole fields exerted on the four crystallographically nonequivalent 13 C sites shown in the inset of Fig.…”