09-07E

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 $T < T_c$. Explicit expression for the 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 $\beta $ ($M=M_{0\tau }(-\tau )^{\beta }$), in the case $T = T_c$ we have the field dependence ($M=M_{0h}h^{1/\delta }$).