Heat capacity, entropy and volume change near phase transition temperature in La1−xCaxMnO3

The two-level semiempirical model of the ferromagnetic ordering in the La1−xCaxMnO3 (x≈0.2–0.33) crystals is described. The partition function for the ferromagnetic to paramagnetic phase transition is determined and the Curie temperature, TC, is expressed in terms of the model parameters. Since around TC the partition function undergoes an abrupt drop, the crystal exhibits unusual changes in its properties at this temperature. The change of the specific heat capacity, entropy and volume is calculated. The influence of magnetic field on the heat capacity is discussed.