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

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 GdxDy1-xNi (x = 0.1 and 0.9) compounds and their GdxDy1-xNiH3 hydrides. We observed a considerable decrease in Curie temperatures (TC) in the hydrides GdxDy1-xNiH3 compared to their parent alloys. The magnetocaloric effect (MCE) values of GdxDy1-xNiHy (y = 0 and 3) in the vicinity of TC were obtained and compared with literature data for the final GdNi and DyNi compounds. The maximum specific isothermal entropy changes -ΔsT at μ0ΔH = 5 T were 14.5, 17, and 17.5 J kg−1K−1 for GdNi, Gd0.9Dy0.1Ni, and Gd0.9Dy0.1NiH3, respectively. For DyNi, Gd0.1Dy0.9Ni, and Gd0.1Dy0.9NiH3, they were -ΔsT = 18, 15.5, and 12.5 J kg−1K−1 at μ0ΔH = 5 T, respectively. -ΔsT(H) in Gd0.9Dy0.1NiH3 at T = TC linearly increased in fields up to 7 T, while Gd0.1Dy0.9NiH3 at T ≥ TC 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. •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.