2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/27825The paper presents new method for calculating the low-temperature asymptotics of free energy of the 3D Ising model in external magnetic field $(H\neq 0)$. The results obtained are valid in the wide range of temperature and magnetic field values fulfilling the condition: $[1-\tanh(h/2)]\simε,$ for $ε\ll 1$, where $h=βH$, $β$ - the inverse temperature and $H$ - external magnetic field. For this purpose the method of transfer-matrix, and generalized Jordan-Wigner transformations, in the form introduced by the author in $\cite{mkoch95}$, are applied.12 pages, REVTEX, submitted to J. Math. PhysStatistical Mechanicstext