Critical Point in the Curve of First-Order Magnetic Phase Transition

A magnetic state diagram for ferromagnets exhibiting a first-order phase transition in a magnetic field has been calculated. Calculations have been made using the exchange-striction model of a ferromagnet. It has been shown that the curve of first-order magnetic phase transition ends up at a critical point (H-cr, T-cr) that is similar to the critical point of the liquid-gas transition on the (T, P) plane. Analytical expressions for thermodynamic quantities, namely, magnetic susceptibility, specific heat, and compressibility, which anomalously grow near the critical point, have been derived. Calculation results have been compared with available experimental data for La(Fe0.88Si0.12)(13) ferromagnet, which experiences the first-order magnetic phase transition.