Free Energy of Three-Dimensional Uniaxial Magnet in the Higher Non-Gaussian Approximation and in the Presence of an External Field

摘要

A three-dimensional Ising-like system in a homogeneous external field isstudied on the basis of the higher non-Gaussian measure density (theρ6model). Thepresented solutions of recurrence relations for the coefficients of the effective measuredensities and the generalized point of exit of the system from the critical regime are usedfor calculating the free energy of the system at temperaturesT>Tc(Tcis the phase transitiontemperature in the absence of an external field). A calculation technique isbased on the first principles of statistical physics and is naturally realized without anygeneral assumptions and without any adjustable parameters. The obtained expressionfor the free energy does not involve series expansions in the scaling variable and isvalid near the critical point not only in the regions of the so-called weak and strongexternal fields, but also in the crossover region between these fields, where power seriesin the scaling variable are not effective.