One- and two-dimensional S=12 Heisenberg antiferromagnetism in Cu(C5H5NO)6 (ClO4)2 and Cu(C5H5NO)6 (BF4)2, respectively |
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| Affiliation: | 1. College of Chemistry and Chemical Engineering, Shanghai University of Engineering Science, Shanghai 201620, China;2. Department of Chemistry and Biochemistry, Wichita State University, Wichita, KS 67260, United States;3. State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China |
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| Abstract: | Specific-heat data on CuL6(ClO4)2 and CuL6(BF4)2 in the temperature range 0.05 < T < 20 K are presented (L ≡ C5H5NO). The magnetic contributions are found to have the form of broad maxima, occurring near 1 K. Small χ-type anomalies are observed at Tc = 0.62 ± 0.01 K and 0.142 ± 0.002 K for CuL6(BF4)2 and CuL6(ClO4)2, respectively. The analyses show the magnetic structure to be an assembly of weakly coupled antiferromagnetic chains or layers for CuL6(ClO4)2 and CuL6(BF4)2, respectively. For CuL6(ClO4)2 the intrachain exchange constant is J/K = -1.02 ± 0.02 K, for CuL6(BF4)2 the intralayer exchange constant is J/K = -1.10 ± 0.02 K. Additional evidence for the lower-dimensional magnetic structures is obtained from the temperature dependences of the antiferromagnetic susceptibilities. The data on CuL6(BF4)2 clearly indicate the absence of a divergence in the specific heat for the quadratic-layer Heisenberg antiferromagnet, and provide an estimate for the specific heat for this model. A comparison is made with the corresponding result for the ferromagnetic Heisenberg layer. |
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