NaGdS₂: A Promising Sulfide for Cryogenic Magnetic Cooling

Abstract

The development of effective and eco-friendly cooling technology demands an investigation of new magnetocaloric materials. Compounds containing gadolinium are one of the best candidates due to the large spin-only magnetic moment of Gd 3+ ion. This work reports on the magnetocaloric properties of the AGdS2 family (A = Li, Na, K, Rb) in relation to crystal chemistry of these compounds. These sulfides crystallize in two different structure-types: NaCl (A = Li) and -NaFeO2 (A = Na, K, Rb). Although one would expect the larger magnetocaloric effect to be associated to LiGdS2 due to its higher magnetic/non-magnetic mass ratio, our study demonstrates that the NaGdS2 member leads to the best properties among the investigated series. The change of structure from the 3D NaCl structure of LiGdS2 to the layered -NaFeO2 structure of NaGdS2 drastically improves the magnetocaloric properties.Hence, thanks to its structural features associated to negligible exchange interactions, NaGdS2 exhibits a magnetic entropy change up to 54 J kg -1 K -1 at 2.5 K for µ0H = 5 T, which is comparable to the top ranked inorganic Gd-based materials operating in the cryogenic temperature range. These magnetocaloric figures of merit provide evidence that Gd-based sulfides are promising materials for magnetic refrigeration and, more broadly, this highlights the potential of sulfides in that field.

Free-Spin Dominated Magnetocaloric Effect in Dense Gd3+ Double Perovskites

“…This is rationalized by differences in the exchange interaction and the onset of ordering at higher temperatures in LiGdS 2 . At high temperatures, T > 2 K, a similar effect is not observed in the A 2 GdSbO 6 double perovskites but may result in significant differences in the magnetocaloric effect closer to the ordering temperature in Ca 2 GdSbO 6 …”

“…At high temperatures, T > 2 K, a similar effect is not observed in the A 2 GdSbO 6 double perovskites but may result in significant differences in the magnetocaloric effect closer to the ordering temperature in Ca 2 GdSbO 6 . 44 …”

High-pressure synthesis, spin-glass behaviour, and magnetocaloric effects in FexTi2S4 heideite sulphides

“…For instance, FeCr 2 S 4 presents a reversible MCE around a FiM transition (T N = 167 K) with maximum magnetic entropy change = 3.72 J.kg -1 .K -1 for ΔH = 50 kOe, along with 𝛥𝑆 𝑚𝑎𝑥 a cusp-like anomaly around 70 K 4 . Recently, Delacotte et al 19 showed a larger MCE for NaGdS 2 that presents very weak local AFM interactions because of its negligible exchange interactions. Such a compound exhibits a up to 54 J kg -1 K -1 at 2.5 K for μ 0 ΔH = 5 T, being then suggested 𝛥𝑆 𝑚𝑎𝑥 𝑀 as a promising material for Cryogenic Magnetic Cooling.…”

Free-spin dominated magnetocaloric effect in dense Gd$^{3+}$ double perovskites

“…At high temperatures, T > 2 K, a similar effect is not observed in the A 2 GdSbO 6 double perovskites but may result in significant differences in the magnetocaloric effect closer to the ordering temperature in Ca 2 GdSbO 6 . 44 The fcc materials presented here, Ba 2 GdSbO 6 and Sr 2 GdSbO 6 , are likely able to cool below the industry standard, Gd 3 Ga 5 O 12 (which has a lower cooling limit of ∼ 0.8 K due to spin-spin correlations 45 ), into the temperature regime of paramagnetic salts (∼ 100 mK or less 46 ) based on their minimal superexchange. This presents a possible significant advancement as the frus-trating lattice should have a better per unit volume magnetic entropy change than a Gd 3+based paramagnetic salt.…”