Crystal Structure, Magnetic Phase Transitions and Magnetocaloric Effect of DyCo_2−xGe_x Compounds

The crystal structure, magnetic phase transitions and magnetocaloric effect of DyCo_2−xGe_x (x = 0.0–0.2) compounds were studied. X-ray diffraction coupled with Rietveld analysis shows that all DyCo_2−xGe_x samples maintain the cubic Laves structure (MgCu₂-type, Fd-3 m space group), and the lattice parameter increases as x increases. Under an applied field change of 0–5 T, the maximum magnetic entropy change of DyCo_2−xGe_x (x = 0.0, 0.05, 0.15 and 0.2) compounds are 10.4, 10.3, 7.3 and 6.3 J/kg K, and the values of relative cooling power are 290.6, 309.6, 290.4 and 271.8 J/kg, respectively. According to Arrott plots and the Inoue-Shimizu model, DyCo₂ and DyCo_1.95Ge_0.05 compounds still maintain the first-order magnetic phase transition. But when the Ge content exceeds 0.05, a magnetic phase transition from first-order to second-order occurs. Magnetic measurement reveals that the Ge content increases the Curie temperature from 151 (for x = 0.0) to 179 K (for x = 0.2). This suggests that the DyCo_2−xGe_x compounds are candidate materials for cryogenic magnetic cooling, which can be used in natural gas liquefaction, biological organ storage in medicine and quantum computer heat dissipation.