Spin ordering and enhancement of electronic heat capacity in an organic system of (DI-DCNQI)2(Ag1−xCux)

Thermodynamic measurements on the organic system of (DI-DCNQI)2(Ag1−xCux) (x = 0,0.05, 0.71, 0.90) were performed to study the change from the charge-ordered (CO) insulating state to the π–d hybridized metallic state. A thermal anomaly associated with the antiferromagnetic transition that occurred in the charge-ordered lattice was observed at 6.2 K from the temperature dependence of the heat capacity of (DI-DCNQI)2Ag. We have found that the magnetic entropy around the peak is only 1.5% of Rln2, corresponding to the full entropy expected for the formula unit of (DI-DCNQI)2Ag. This anomaly is suppressed down to about 3 K in the x = 0.05 sample owing to the disorders induced in the CO lattice. In the metallic concentration of x = 0.90, the low-temperature electronic heat capacity coefficient, γ was found to be enhanced by up to about 63.6 mJ K−2 mol−1 probably owing to the cooperative effect of π–d hybridization and intersite Coulomb interaction (V).

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