On the adiabatic approximation in statistical mechanics

The description of an adiabatic process by means of the quasiequilibrium canonical density matrix is discussed for the case of an isolated magnetic spin system. It is shown that the compatibility condition for the various equations for the reciprocal temperature implies constancy of the heat capacity of the system in the adiabatic process. Allowance for the compatibility condition also enables one to find the explicit form of the nonlinear adiabatic response of the system without recourse to the high-temperature approximation. The expressions obtained can be verified experimentally.