THERMODYNAMICS OF THE 2-DIMENSIONAL HEISENBERG CLASSICAL HONEYCOMB LATTICE

In this article we adapt a previous work concerning the two-dimensiona l (2D) Heisenberg classical square lattice [Physica B 245, 263 (1998)] to the case of a honeycomb lattice. Closed-form expressions of the ma in thermodynamic functions of interest are derived in the zero-field l imit. Notably, near absolute zero (i.e., the critical temperature), we derive the values of the critical exponents alpha = 0, eta = -1, gamm a = 3, and nu = 1, as for the square lattice, thus proving their unive rsal character. A very simple model allows one to give a good descript ion of the low-temperature behaviors of the product chi T. For 2D-comp ensated antiferromagnet, we derive simple relations between the charac teristics of the maximum of the susceptibility curve T(chi(max)) and c hi(max) and the involved exchange energies. Therefore, owing to the kn owledge of T(chi(max)) and chi(max), one can directly obtain the respe ctive values of these energies. Finally, we show that the theoretical model allows one to fit correctly experimental susceptibility data of the recently synthetized compound Mn-2(bpm)(ox)(2). 6H(2)O characteriz ed by a 2D classical honeycomb lattice (where ''bpm'' and ''ox'' are t he abbreviations for the ligands bipyrimidine and oxalate, respectivel y). [S0163-1829(98)04434-8].