Energy storage is one of the most important issues for using renewable energy resources. Although liquid hydrogen is expected as a main energy storage carrier, at the present, a gas compression cycle cooling technique for liquefaction of hydrogen requires high operation costs. Magnetic refrigeration using magnetocaloric effects is known as an alternative refrigeration technique. In this review, we introduce the principle of magnetocaloric effects caused by magnetic entropy changes with varying a magnetic field. Next, the features of magnetocaloric effects in paramagnets are outlined as refrigerants for adiabatic demagnetization refrigerator working at very low temperatures. Then we note the characteristics of magnetocaloric effects in ferromagnets as refrigerants for air-conditioner operating at room temperatures. The potential of magnetocaloric effects induced by spin rearrangement transitions in various magnetic materials is considered as refrigerants for hydrogen liquefiers working in the intermediate temperature range. As an example, we describe the highly efficient cooling using pure holmium metal where small magnetic field oscillation superimposed on a static bias magnetic field are applied around its metamagnetic transitions. Finally, we summarize the future prospects of magnetic refrigeration efficiently utilizing magnetocaloric effects.
Keywords:magnetic refrigeration, magnetocaloric effect, metamagnetic transition, liquefaction of hydrogen