Journal of Physical Studies 13(1), Article 4007 [11 pages] (2009) DOI: https://doi.org/10.30970/jps.13.4007 THE EQUATION OF STATE OF A THREE-DIMENSIONAL ISING-LIKE SYSTEM M. P. Kozlovskii1, R. V. Romanik2 1Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii St., 79011 Lviv, Ukraine, e-mail: mpk@icmp.lviv.ua 2Lviv National University, Faculty of physics, 1 Universytetska St., 79000 Lviv, e-mail: romanikroma@gmail.com

The free energy $F$ and the order parameter $M$ are calculated near the phase transition point for a 3D Ising-like system in the temperature region $T < T_c$. An explicit expression for free energy as a function of temperature and field is obtained at arbitrary values of the latter. Hamiltonian parameters dependence of coefficients of the free energy expression is found. Expression for the model's magnetization as a function of temperature and field is derived by direct differentiation of $F$ with respect to external field. It is shown that in the case of small fields the behavior of magnetization is determined by the critical exponent $β\, (M=M_{0τ}(-τ)^{β}$), and in the case $T = T_c$ we have the field dependence ($M=M_{0h}h^{1/δ}$).

PACS number(s): 05.50.+q, 64.60.Fr, 75.10.Hk

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