Influence of interstitial and substitutional atoms on magnetocaloric effects in RNi compounds

Highlights: • New (GdDy)NiH₃ hydrides were obtained. • In Dy-rich compounds, the hydrogenation leads to a change of a crystal structure. • Hydrogenation leads to an extremely large reduction of the Curie temperature. • The (GdDy)NiH3 hydrides obey high values of the plateau-like magnetocaloric effect. The effects of substitutional and interstitial atoms on the magnetic and magnetocaloric properties are investigated for RNi (R is rare earth) compounds attractive for magnetic solid-state cooling at cryogenic temperatures. We focused on combining weakly and highly anisotropic rare earth compounds and obtained Gd_xDy_1-xNi (x = 0.1 and 0.9) compounds and their Gd_xDy_1-xNiH₃ hydrides. We observed a considerable decrease in Curie temperatures (T_C) in the hydrides Gd_xDy_1-xNiH₃ compared to their parent alloys. The magnetocaloric effect (MCE) values of Gd_xDy_1-xNiH_y (y = 0 and 3) in the vicinity of T_C were obtained and compared with literature data for the final GdNi and DyNi compounds. The maximum specific isothermal entropy changes -Δs_T at μ₀ΔH = 5 T were 14.5, 17, and 17.5 J kg⁻¹K⁻¹ for GdNi, Gd_0.9Dy_0.1Ni, and Gd_0.9Dy_0.1NiH₃, respectively. For DyNi, Gd_0.1Dy_0.9Ni, and Gd_0.1Dy_0.9NiH₃, they were -Δs_T = 18, 15.5, and 12.5 J kg⁻¹K⁻¹ at μ₀ΔH = 5 T, respectively. -Δs_T(H) in Gd_0.9Dy_0.1NiH₃ at T = T_C linearly increased in fields up to 7 T, while Gd_0.1Dy_0.9NiH₃ at T ≥ T_C showed a plateau-like magnetocaloric effect at μ₀ΔH = 5 and 7 T. The observed effects were explained based on altered exchange and magnetocrystalline interactions in the modified compounds.