Magnetocaloric effect and heat capacity in the phase-transition region

Abstract

The behavior of the magnetic-field and temperature-dependent heat capacity $C(H,T)$ and the magnetocaloric effect $\ensuremath{\Delta}T(\ensuremath{\Delta}H,T),$ 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 $\ensuremath{\Theta}(H)$ 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 $\ensuremath{\Theta}(H).$ Both $\ensuremath{\Theta}(H)$ 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.