Magnetic properties of terbium dihydrides

Magnetization measurements of terbium dihydride samples with different hydrogen concentration, TbH1.92, TbH1.99, TbH2.03 and TbH2.09, in the temperature range from 1.8 to 300 K and at an applied field of 1 kOe are reported. Two first-order antiferromagnetic transitions have been registered in the narrow temperature range between 15–18 K for all hydride compositions. Isothermal magnetization ( σ ( H ) T = const ) measurements at several temperatures in the vicinity of magnetic transitions have been carried out and used for the magnetic-entropy change, Δ S σ , calculations. The magnetic-entropy changes have negative values, and in an applied magnetic field of 5 T they reach 2.5 J/kg K, which is only about 26% of the Δ S σ ( H ) value expected from thermal measurements. A much larger magnetic field must be applied for terbium hydrides to be used as refrigerant materials for low-temperature needs.