Thermal expansion and thermal conductivity of RT₂ (R: Gd, Dy, Er; T: Al, Ni) intermetallic compounds for magnetic refrigerator

Highly efficient hydrogen liquefaction is required for upcoming hydrogen energy society. Magnetic refrigeration is expected as a method to realize efficient hydrogen liquefaction, and the performance depends on properties of magnetic materials. RT ₂ (R: rare-earth; T: Al, Ni) Laves phase intermetallic compounds with a second-order magnetic phase transition are one of the promising magnetocaloric materials. Thermal expansion, magnetostriction, and thermal conductivity of ErAl₂, DyNi₂, DyAl₂ and GdNi₂ were measured in magnetic fields using polycrystalline samples because of the important properties for practical use in a magnetic refrigerator. Thermal expansions showed anomalies at the magnetic transition temperature. However, those in 0 T were nearly the same as copper. Magnetostriction were not as large as magnetocaloric materials with a first-order magnetic phase transition such as TbMn₂. Thermal conductivities in 0 T were almost in agreement with the literature data, and magnetic field dependence was small. These results indicate that RT ₂ compounds are suitable as magnetic refrigerants for hydrogen liquefaction in practical use. (paper)