Magnetic refrigeration materials (invited)

Research on the magnetocaloric effect and its application for cooling near room temperature over the past few years has helped to move this phenomenon from a scientific curiosity to an emerging technology. Two of the most important advances include the demonstration which proved that it is possible to obtain significant cooling powers (600 W) at high Carnot efficiencies (60%) and with a large coefficient of performance (15) near room temperature in moderately strong magnetic fields $\text{(⩽5}$ T); and the discovery of the giant magnetocaloric effect in the ${\mathrm{Gd}}_{\mathrm{5}}({\mathrm{Si}}_x{\mathrm{Ge}}_{\text{1−x}}{)}_{\mathrm{4}}$ series of alloys. Also, new knowledge about the magnetocaloric effect has been gained. This includes: the relationship between the nature of the magnetic transformation(s) and the temperature dependence of the magnetocaloric effect, the entropy utilized in the magnetocaloric process, and the role of impurities on the giant magnetocaloric effect.