Condensed Matter Physics, 2012, vol. 15, No. 1, 13706: 1-10
DOI:10.5488/CMP.15.13706           arXiv:1009.4078v4

Title: The high-temperature expansion of the classical Ising model with $S_z^2$ term
  M.T. Thomaz (Instituto de Física, Universidade Federal Fluminense, Av. Gal. Milton Tavares de Souza s/no, CEP 24210-346, Niterói-RJ, Brazil) ,
  O. Rojas (Departamento de Ciências Exatas, Universidade Federal de Lavras, Caixa Postal 3037, CEP 37200-000, Lavras-MG, Brazil )

We derive the high-temperature expansion of the Helmholtz free energy up to order β17 of the one-dimensional spin-S Ising model, with single-ion anisotropy term, in the presence of a longitudinal magnetic field. We show that the values of some thermodynamical functions for the ferromagnetic models, in the presence of a weak magnetic field, are not small corrections to their values with h=0. This model with S=3 was applied by Kishine et al. [J.-i. Kishine et al., Phys. Rev. B, 74 (2006) 224419] to analyze experimental data of the single-chain magnet [Mn (saltmen)]2 [Ni(pac)2 (py)2] (PF6)2 for T<40 K. We show that for T<35 K the thermodynamic functions of the large-spin limit model are poor approximations to their analogous spin-3 functions.

Key words: quantum statistical mechanics, one-dimensional Ising model, spin-S models, large-spin limit Ising model, single-chain magnets.
PACS: 75.10.Jm, 05.30.-d, 75.50.Xx

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