The recent literature concerning the magnetocaloric effect (MCE) has been reviewed. The MCE properties have been compiled and correlations have been made comparing the behaviours of the different families of magnetic materials which exhibit large or unusual MCE values. These families include: the lanthanide (R) Laves phases (RM 2 , where M = Al, Co and Ni), Gd 5 (Si 1−x Ge x) 4 , Mn(As 1−x Sb x), MnFe(P 1−x As x), La(Fe 13−x Si x) and their hydrides and the manganites (R 1−x M x MnO 3 , where R = lanthanide and M = Ca, Sr and Ba). The potential for use of these materials in magnetic refrigeration is discussed, including a comparison with Gd as a near room temperature active magnetic regenerator material.

New erbium-based regenerator materials have been developed as a replacement for lead in low temperature cryocoolers. These alloys have volumetric heat capacities which are 20 to 185% larger than that of lead from 10 to 80 K. These magnetic, ductile, oxidation resistant erbium alloys are more than 10 times stronger than lead and have a thermal conductivity ~10 times lower than lead. The alloys can easily be fabricated into spheres, foils, ribbons, and wires, and are environmentally friendly, non-toxic materials. A layered regenerator composed of three different erbium alloy compositions is recommended as the most efficient system to improve the cryocoolers' performance to "get the lead out."

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