Magnetocaloric effect of (ErxR1-x)CO2 (R = Ho, Dy) for magnetic refrigeration between 20 and 80 K

Two series of RCo2 compounds, (ErxHo1-x)Co-2 and (EryDyl-y)Co-2, were investigated as magnetic refrigerants for hydrogen liquefaction. A large magnetocaloric effect (MCE) was observed just above the Curie temperature (T-c) of these compounds which both undergo a first-order magnetic transition. The isothermal entropy change Delta S and the adiabatic temperature change Delta T-ad of these compounds were larger than those of other Laves-phase materials such as RAl2 and RNi2. However, the temperature range of the large MCE for these compounds was limited. It has been shown that T-c increases almost linearly against the de Gennes factor, and can be controlled by changing the concentration of the rare earth elements while maintaining a first-order transition. By measuring the magnetization and heat capacity, we obtained temperature entropy (T-S) diagrams, which are essential for analyzing the magnetic refrigeration cycle. Both series of compounds showed high potential for use in a regenerative thermal cycle, especially as a combination of several compositions to cover a wide temperature range. (C) 2011 Elsevier Ltd. All rights reserved.