Callen-like method for the classical Heisenberg ferromagnet |
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Authors: | L.S. CampanaA. Cavallo L. De Cesare U. EspositoA. Naddeo |
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Affiliation: | a Dipartimento di Scienze Fisiche, Università degli Studi di Napoli “Federico II”, Piazzale Tecchio 80, I-80125 Napoli, Italyb Dipartimento di Fisica “E.R. Caianiello”, Università degli Studi di Salerno, via Ponte don Melillo, I-84084 Fisciano (Salerno), Italyc CNISM, Unità di Salerno, I-84084 Fisciano (Salerno), Italy |
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Abstract: | A study of the d-dimensional classical Heisenberg ferromagnetic model in the presence of a magnetic field is performed within the two-time Green function’s framework in classical statistical physics. We extend the well known quantum Callen method to derive analytically a new formula for magnetization. Although this formula is valid for any dimensionality, we focus on one- and three- dimensional models and compare the predictions with those arising from a different expression suggested many years ago in the context of the classical spectral density method. Both frameworks give results in good agreement with the exact numerical transfer-matrix data for the one-dimensional case and with the exact high-temperature-series results for the three-dimensional one. In particular, for the ferromagnetic chain, the zero-field susceptibility results are found to be consistent with the exact analytical ones obtained by M.E. Fisher. However, the formula derived in the present paper provides more accurate predictions in a wide range of temperatures of experimental and numerical interest. |
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Keywords: | Classical statistical mechanics Magnetism Green functions |
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