Large magnetocaloric effects of RFeSi (R = Tb and Dy) compounds for magnetic refrigeration in nitrogen and natural gas liquefaction

Magnetic properties and magnetocaloric effect (MCE) of intermetallic RFeSi (R = Tb and Dy) compounds have been investigated systematically. The RFeSi compounds undergo a second-order magnetic transition from ferromagnetic to paramagnetic states with the variation of temperature. The Curie temperatures determined from magnetization measurements are 110 K and 70 K for TbFeSi and DyFeSi, respectively, which are quite close to the liquefaction temperatures of natural gas (111 K) and nitrogen (77 K). Both compounds exhibit nearly same large MCE around their respective ordering temperatures. For a low magnetic field change of 1 T, the maximum values of magnetic entropy change -ΔS_M and adiabatic temperature change ΔT_ad are 5.3 J/kg K and 2.1 K for TbFeSi, 4.8 J/kg K and 1.7 K for DyFeSi, respectively. Furthermore, a composite material based on (Tb_1-xDy_x)FeSi compounds is designed theoretically by using a numerical method, and it exhibits a constant -ΔS_com of ∼1.4 J/kg K for a field change of 1 T in the wide temperature range of 67-108 K, satisfying the requirement of Ericsson-cycle magnetic refrigeration over the liquefaction temperatures of nitrogen and natural gas.