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2017 | 131 | 4 | 925-927
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Magnetic Specific Heat of Anion-Radical Salt [Ni(bipy)₃](TCNQ)₄·(CH₃)₂CO at Very Low Temperatures

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Thermodynamic studies of the anion-radical salt system [Ni(bipy)₃](TCNQ)₄·(CH₃)₂CO, where TCNQ is 7,7',8,8'-tetracyano-quinodimethane, are reported. The anion-radical salt systems based on TCNQ belong to a material class in which the arrangement of the anion-radical salt has considerable impact on the charge transfer and magnetic properties. The crystal structure of the studied compound consists of [Ni(bipy)₃]⁺² cations containing Ni⁺² ions and four types of crystallographically independent anion-radicals TCNQ^{·-} (A, B, C and D). These TCNQ^{·-} radicals form two different types of TCNQ^{·-} stacks (AABB and CCDD), where a strong exchange interaction is expected. The temperature dependence of the specific heat of a single crystal was studied in magnetic fields up to 5 T and in the temperature range from 0.4 K to 30 K. The temperature dependence of specific heat displays a broad Schottky-like maximum above 0.4 K. Using a single-ion approximation, the analysis of the temperature dependence of the specific heat below 10 K yields values for the anisotropy parameters, D/k_{B}=-1.95 K and E/k_{B}=0.3 K. These results suggest that the observed maximum in the specific heat originates from Ni⁺² ions while the exchange interaction between the transition metal ions and the TCNQ is negligible.
  • Institute of Physics, Faculty of Sciences, P.J. Šafárik University, Park Angelinum 9, 041 54 Košice, Slovakia
  • Institute of Physics, Faculty of Sciences, P.J. Šafárik University, Park Angelinum 9, 041 54 Košice, Slovakia
  • Applied Chemistry Department, V.N. Karazin Kharkiv National University, Svobody Sq. 4, 61022 Kharkiv, Ukraine
  • Institute of Chemistry, Jan Kochanowski University of Humanities and Sciences, Świętokrzyska 15G, 25-406 Kielce, Poland
  • Institute of Physics, Faculty of Sciences, P.J. Šafárik University, Park Angelinum 9, 041 54 Košice, Slovakia
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