Ferromagnetism in a π–d electron system at 1 K

Interplay of strongly correlated electrons and localized Ising moments in one dimension

“…The electrons coupled to localized spins have been a long studied issue from Kondo chains in heavy fermionic systems 1 , double exchange systems(DEX) in manganites 2 to π-d systems of molecular solids 3,4,5,6 . Particularly, the negative giant magnetoresistance effect in DEX system had been a highlight which provided a mechanism of tuning the electronic degrees of freedom by the magnetic field 2,7 .…”

New aspects of π–d interactions in magnetic molecular conductors

“…The Arrott method is suitable for high T C , but not for a ferrimagnet with low T C and a small hysteresis loop. Therefore, a resonant circuit method developed by Noguchi et al is employed, which can sensitively detect the jump in M in a small hysteresis loop caused by ferromagnetic or ferrimagnetic ordering [20]. As shown in figure 6(b), an oscillation initially appears below 1 K, when H changes sign, and the magnitude of oscillation increases as T decreases.…”

High field magnetization of (Benzo-TTFVS)2FeBr4and (Benzo-TTFVO)2FeBr4

“…We have extensively developed new charge-transfer salts composed of bent donor molecules and magnetic counter anions. We have found a ferromagnetic semiconductor based on a 2:1 salt (EDT-TTFVO) 2 FeBr 4 , in which the π electrons and the d spins significantly interact with each other, giving rise to a ferrimagnetic ordering at 1 K [1][2][3]. Subsequently we have synthesized a 1:1 salt (BEDT-TTFVS)FeBr 4 , which exhibits a semiconducting behavior and a ferromagnetic ordering at 1.8 K [4,5].…”

“…(Benzo-TTFVS) 2 FeBr 4 and (Benzo-TTFVO) 2 FeBr 4 are recently developed by our group with bent donor molecules of benzotetrathiafulvalenothioquinone-1,3-dithiolemethide (Benzo-TTFVS) [6] and benzotetrathiafulvalenoquinone-1,3-dithiolemethide (Benzo-TTFVO) [7], respectively. The (Benzo-TTFVS) 2 FeBr 4 salt shows a semiconducting behavior below 100 K with small activation energy of < 30 meV and an antiferromagnetic ordering at T N = 5.8 K. The ESR experiment by Hayakawa et al suggests that the strong fluctuation is coupled with the π-d correlation along the b-direction for which donor molecules and counter anions are stacked alternately [8].…”

“…The (Benzo-TTFVS) 2 FeBr 4 salt shows a semiconducting behavior below 100 K with small activation energy of < 30 meV and an antiferromagnetic ordering at T N = 5.8 K. The ESR experiment by Hayakawa et al suggests that the strong fluctuation is coupled with the π-d correlation along the b-direction for which donor molecules and counter anions are stacked alternately [8]. The (Benzo-TTFVO) 2 FeBr 4 salt, on the other hand, exhibits a clear metal-to-insulator transition at 166 K accompanied by a onedimensional structural phase transition of the donor-stacked columns [7]. An antiferromagnetic ordering occurs at T N = 9.3 K, which means that the exchange interaction between d spins for (Benzo-TTFVO) 2 FeBr 4 is larger than that for (Benzo-TTFVS) 2 FeBr 4 .…”