Magnetocaloric effect and heat capacity in the phase-transition region

The behavior of the magnetic-field and temperature-dependent heat capacity C(H,T) and the magnetocaloric effect Delta T(Delta H,T), in the vicinity of magnetic phase transitions is discussed. A simple model allowing calculation of the peak value of the magnetocaloric effect is developed from general principles of thermodynamics. It is shown that a characteristic temperature Theta(H) where the heat capacity of the magnetic material is independent of the magnetic field, can be defined. The peak value (maximum or minimum) of the magnetocaloric effect occurs near the Theta(H). Both Theta(H) and peak value of the magnetocaloric effect approach the magnetic ordering temperature. Experimental measurements of the heat capacity and the magnetocaloric effect of several high-purity lanthanide magnetic materials agree well the theoretical model. [S0163-1829(99)07101-5].