Magnetocaloric effect of (ErxR1−x)Co2 (R = Ho, Dy) for magnetic refrigeration between 20 and 80 K

Two series of RCo2 compounds, (ErxHo1−x)Co2 and (EryDy1−y)Co2, were investigated as magnetic refrigerants for hydrogen liquefaction. A large magnetocaloric effect (MCE) was observed just above the Curie temperature (Tc) of these compounds which both undergo a first-order magnetic transition. The isothermal entropy change ΔS and the adiabatic temperature change ΔTad 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 Tc 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.

► Large magnetocaloric effect of (ErxHo1−x)Co2 and (EryDy 1−y)Co2 was observed.
► Magnetization and specific heat were measured.
► Entropy temperature diagrams were determined.
► Transition temperature was controlled by changing the rare earth concentration.