Crystal structure, magnetic properties and magnetocaloric performance of RE₅Rh₂In₄ (RE = Gd-Tm) compounds

Polycrystalline samples of the RE₅Rh₂In₄ (RE = Gd--Tm) intermetallics have been investigated by means of X-ray diffraction (XRD) as well as by DC and AC magnetometric measurements. The XRD data confirm that the compounds crystallize with the orthorhombic Lu₅Ni₂In₄-type structure (space group Pbam, No. 55). With decreasing temperature, RE₅Rh₂In₄ spontaneously order magnetically with the critical temperatures of magnetic order equal to 10.6, 14.2, 15.4, 7.2, 5.9 and 4.9 K for RE = Gd, Tb, Dy, Ho, Er and Tm, respectively. The compounds have complex magnetic properties, showing features characteristic of both ferro- and antiferromagnetic orderings. Moreover, the magnetic properties change with increasing number of the 4f electrons from predominantly ferromagnetic in Gd₅Rh₂In₄ to predominantly antiferromagnetic in Tm₅Rh₂In₄. The magnetic data indicate that only the rare earth atoms carry magnetic moments. The maximum magnetic entropy change (-Δ SMᵐᵃˣ) at the 0-9 T magnetic flux density change (Δ μ₀ H) equals 12.4 J·kg⁻¹·K⁻¹ at 17 K for Gd₅Rh₂In₄, 11.3 J·kg⁻¹·K⁻¹ at 28 K for Tb₅Rh₂In₄, 13.1 J·kg⁻¹·K⁻¹ at 19 K for Dy₅Rh₂In₄, 16.4 J·kg⁻¹·K⁻¹ at 12 K for Ho₅Rh₂In₄, 15.3 J·kg⁻¹·K⁻¹ at 8 K for Er₅Rh₂In₄ and 12.6 J·kg⁻¹·K⁻¹ at 6.5 K for Tm₅Rh₂In₄. For a selected rare earth element (RE), the member of the RE₅Rh₂In₄ family of compounds reaches the highest -Δ SMᵐᵃˣ value, when compared with its RE₅T₂In₄ (T = Ni, Pd, Pt) isostructural analogues, making the RE₅Rh₂In₄ intermetallics a good choice for application in low-temperature magnetic refrigeration.