Abstract
Thermodynamic investigation using the relaxation calorimetry technique and the microchip calorimetry technique is performed to clarify low-temperature behaviors of a radical cation salt consisting of a donor molecule of bispropylenedithiotetrathiafulvalene (BPDT-TTF) and a linear anion of \({{\text{ICl}}_{2}^{-}}\). This compound has a layered structure similar to numerous BEDT-TTF compounds. The donor molecules form a dimerized arrangement in the layer. Temperature dependence of heat capacity obtained by the relaxation technique shows a broad hump structure around 20–25 K corresponding to the temperature where the magnetic susceptibility shows a drastic decrease due to the formation of the singlet spin state. The microchip calorimetry technique detected a step-like anomaly around 23 K in the temperature dependence of C p T −1 of which entropy is evaluated as only few % of Rln2 corresponding to the full entropy of localized π-electrons located on each dimer unit. The negligibly small T-linear term in the low-temperature heat capacity and absence of magnetic fields dependence below 3.2 K predict opening of rigid gap structure in the spin excitations, which is consistent with a spin-singlet formation due to the formation of spin-Peierls type ordering or charge ordering state.
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This work was supported in part by Grant-in-Aid for Scientific Research (Nos. 23110717 and 22340098) from the MEXT and JSPS.
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Guan, G., Fukuoka, S., Yamashita, S. et al. Magnetic transition in dimerized radical cation salt of (BPDT-TTF)2ICl2 studied by heat capacity measurements. J Therm Anal Calorim 113, 1197–1201 (2013). https://doi.org/10.1007/s10973-013-3015-5
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DOI: https://doi.org/10.1007/s10973-013-3015-5