An excellent cryogenic magnetic cooler: magnetic and magnetocaloric study of an inorganic frame material

Abstract

The cryogenic magnetic coolers based on the magnetocaloric effect (MCE) of paramagnetic compounds usually need relatively large fields to realise a practical cooling performance. Thus, it is of significance to search for molecule-based cryogenic magnetic coolers with high performance of the MCE under low fields (smaller than 2 T), considering the ready availability of low fields by commercial Nd–Fe–B permanent magnets. In this work, the crystal structure, magnetic susceptibility and isothermal magnetization for the inorganic compound Gd(OH)SO₄ (1) have been investigated. The title compound exhibits a 3D structure with Gd-oxygen chains as the supramolecular building units. Magnetic characterisations indicated that adjacent Gd^III ions show weak magnetic couplings in 1. Because of the integration of large metal/ligand mass ratio, weak magnetic couplings and a dense framework, the observed maximum entropy change (−ΔS^max_m) for 1 was up to 53.5 J kg⁻¹ K⁻¹ or 276 mJ cm⁻³ K⁻¹ for ΔH = 7 T and T = 2 K, comparable to the performance of commercial gadolinium gallium garnet Gd₃Ga₅O₁₂ (GGG, −ΔS^max_m = 38.4 J kg⁻¹ K⁻¹ or 272 mJ cm⁻³ K⁻¹ with ΔH = 7 T). Notably, the −ΔS^max_m of 1 still reaches 27.5 J kg⁻¹ K⁻¹ at T = 2 K and ΔH = 2 T, and 38.3 J kg⁻¹ K⁻¹ at T = 2 K and ΔH = 3 T, which already surpasses GGG (about 24 J kg⁻¹ K⁻¹ with ΔH = 3 T) and makes 1 a superior cryogenic magnetic cooler for low-temperature applications, even in low fields.