Broad table-like magnetocaloric effect in the full hydrogen liquefaction range in Gd3Ni6XY

Gd 3 Ni 6 SiAl, Gd 3 Ni 6 SiGa, and Gd 3 Ni 6 AlGa (Ce 3 Ni 6 Si 2 -type, Im -3 m , N 229, cI 44) present a broad table-like magnetocaloric effect in the full hydrogen liquefaction range (20–77 K) with a real plateau wide enough to be competitive for refrigeration devices based on the Ericsson cycle. The characterization of the magnetocaloric variables ( |ΔS M pk |= 6.60 J/kgK, TEC(10)= 6.44 J/kgK for Gd 3 Ni 6 SiGa, |ΔS M pk |= 6.05 J/kgK, TEC(10)= 6.01 J/kgK for Gd 3 Ni 6 SiAl, all at μ 0 ΔH =5 T) state that they are among the best of table-like magnetocaloric materials in this temperature range. The physical origin of this smooth and wide table-like effect is the combination of a spin reorientation transition (which appears in Gd 3 Ni 6 XY when Si or Ga is introduced) with the paramagnetic to ferromagnetic transition, close to each other. The application of the Banerjee criterion and the evolution of the critical exponent with temperature n(T) confirm that both transitions are second order, which is extremely relevant for real applications. From the study of the magnetic properties it has been inferred that the introduction of Si induces a magnetic ground state with combined ferromagnetic and antiferromagnetic components which turns to fully ferromagnetic at very low field. The critical exponents ( β , γ , δ , n ) have been found for the paramagnetic to ferromagnetic transitions; the values of γ (from 1.22 to 1.36) suggest that the magnetic interactions are short-range, though the ensembles do not correspond to any particular universality class. • Ce3Ni6Si2-type Gd3Ni6SiAl, Gd3Ni6SiGa and Gd3Ni6AlGa show ferromagnetic ordering. • There is a broad and flat table-like magnetocaloric effect over 20–77 K. • Spin reorientation transition and PM-FM close enough to sustain the MCE. • Competitive for refrigeration devices based on the Ericsson cycle. • Critical exponents for the PM-FM transition point to short-range magnetic interactions.