Magnetic and magnetocaloric properties of Dy1−xErxNi2 solid solutions and their promise for hydrogen liquefaction

Abstract

Magnetic cooling is perceived as an enticing option for the liquefaction of hydrogen. Compared to the currently employed method, it offers significantly enhanced efficiency. However, further research is needed to identify refrigerants suitable for low-temperature applications. Rare-earth nickel, RNi₂, intermetallic compounds based on heavy rare earth elements have garnered considerable attention owing to their unique properties linked to highly localized magnetic moments that emanate from the incompletely filled 4f-electron shell of the R atoms. In this work, the impact of simultaneous substitution within the rare earth sublattice on the magnetic and magnetocaloric properties of Dy_1−xEr_xNi₂ (x = 0.25, 0.5, 0.75) Laves phase solid solutions has been studied and the critical behavior around ferromagnetic–paramagnetic phase transition was analyzed. The samples were synthesized by arc melting and tested in a wide magnetic field range of up to 14 T. Both direct and indirect methods were used to characterize magnetocaloric properties. Experimental data were compared with theoretical results obtained in the frame of the microscopic model that considers exchange magnetic interaction and crystal electric field anisotropy. At temperatures below 20 K, all samples studied are ferromagnets. As the erbium content increases, Curie temperatures and magnetic entropy changes decrease while temperature changes remain stable. With an increasing magnetic field, the peak value of magnetic entropy change shifts to higher temperatures. At a magnetic field change of 14 T, the largest observed magnetic entropy and temperature changes are equal to 32 J kg⁻¹ K⁻¹ and 13 K, respectively, demonstrating that these solid solutions have high potential for low-temperature applications.