The Calculation of Phase Equilibrium Between Structural Phases with a Magnetic Transition by the Cluster Variation Method

The phase equilibrium between structural phases with a magnetic transition is investigated using the CV-pair approximation of the cluster variation method (CVM). By the geometric analysis of the grand potential, it is demonstrated that the grand potential and effective chemical potential of the different structural phases with a magnetic transition can be separated into paramagnetic and magnetic terms. In addition, the molar grand potential-effective chemical potential curve can be obtained from the relevant molar energy diagram. A calculation method for the phase equilibrium between structural phases with a magnetic transition is proposed; this method is applied to the a/y phase equilibrium in the Fe-Mn binary system, and the calculated phase diagram closely approximates the experimental diagram.