Thermal and electrical conductivity of magnetic refrigerant holmium diboride for magnetic refrigerator application

• The thermal conductivity and electric resistivity of HoB 2 were measured and evaluatted as magnetic material for magnetic refrigerators. • HoB 2 was confirmed to have large magneto-caloric effect at the transition temperature of 15 K by magnetization and specific heat . • Material size was discussed from the good heat transfer point of view. • Eddy current power dissipation was evaluated to be negligibly smaller than the cooling power of magnetic refrigerator. • HoB 2 is excellent magnetic refrigerant due to transport properties and large magneto-caloric effect. Intermetallic compound holmium diboride, HoB 2 is a promising refrigerant in magnetic cooling systems. It is particularly well-suited for hydrogen liquefaction. It was confirmed that HoB 2 had large magneto-caloric effect because of a magnetic phase transition from a paramagnetic to a ferromagnetic state at the transition temperature T c of 15 K by magnetization and specific heat. From the standpoint of magnetic refrigerator, the thermal and electrical conductivity of polycrystal HoB 2 in magnetic fields were reported in the present work. The thermal conductivity was found to increase with magnetic field around T c . In electric resistivity measurements, a characteristic kink was observed at T c in zero field, and this kink was suppressed in magnetic fields. The transport properties of HoB 2 were analyzed using these data. Evaluated thermal diffusion coefficient and eddy current power dissipation showed that HoB 2 with submillimeter size has good heat transfer and negligible eddy current power dissipation compared with the cooling power, in practical magnetic refrigeration cycles. These results show that HoB 2 is an excellent magnetic refrigerant for use in the lowest temperature stage of hydrogen liquefaction.