Adiabatic magnetocaloric temperature change in polycrystalline gadolinium – A new approach highlighting reversibility

Abstract

The adiabatic temperature change (ΔT) during the magnetization and demagnetization processes of bulk gadolinium is directly measured for several applied magnetic fields in the temperature range 285 K to 305 K. During the magnetization process, ΔT measurements display the same maximum for each applied field when plotted against the initial temperature (Ti). However, during the demagnetization process, the maximum ΔT varies for each applied field. This discrepancy between the magnetization and demagnetization measurements appears inconsistent with the reversibility of the magnetocaloric effect. A new approach is undertaken to highlight the reversibility of the magnetocaloric effect by plotting ΔT against the average temperature change (Tavg) instead of Ti. The value of Tavg which corresponds to the maximum ΔT is found to increase linearly with the applied magnetic field, consistently for both the magnetization and demagnetization measurements. Solving the linear-fitting equations of these measurements gives a new, and more precise, Curie temperature measurement. This new approach confirmed that the relationship between the maximum adiabatic temperature change (ΔTpeak) and the applied magnetic field is perfectly linear.