Exceptional Magnetocaloric Responses in a Gadolinium Silicate with Strongly Correlated Spin Disorder for Sub‐Kelvin Magnetic Cooling

Abstract

The development of magnetocaloric materials with a significantly enhanced volumetric cooling capability is highly desirable for the application of adiabatic demagnetization refrigerators in confined spatial environments. Here, the thermodynamic characteristics of a magnetically frustrated spin‐7/2 Gd9.33[SiO4]6O2 is presented, which exhibits strongly correlated spin disorder below ≈1.5 K. A quantitative model is proposed to describe the magnetization results by incorporating nearest‐neighbor Heisenberg antiferromagnetic and dipolar interactions. Remarkably, the recorded magnetocaloric responses are unprecedentedly large and applicable below 1.0 K. It is proposed that the S = 7/2 spin liquids serve as versatile platforms for investigating high‐performance magnetocaloric materials in the sub‐kelvin regime, particularly those exhibiting a superior cooling power per unit volume.

Accurate Prediction of the Magnetic Ordering Temperature of Ultralow-Temperature Magnetic Refrigerants

“…As the volumetric −Δ S m (mJ cm –3 K –1 ) values of magnetic refrigerants are more important than their gravimetric −Δ S m (J kg –1 K –1 ) values for practical applications, the volumetric −Δ S m values of some representative magnetic refrigerants are compared. ,,,− Owing to the high T 0 of 1.25 K in GdF 3 , a sharp decrease in its −Δ S m values below 1.5 K leads to its remarkable −Δ S m values not being applicable in the 1–4 K range . Consequently, GdF 3 is excluded from the scope of the following comparison.…”

Achieving Magnetic Refrigerants with Large Magnetic Entropy Changes and Low Magnetic Ordering Temperatures

“…To assess the magnetic refrigeration efficacy of 3 and 4 , they are compared with selected representative magnetic refrigerants that are currently deemed suitable for the fourth stage in the CADR. As shown in Figures S12 and Table S5, ,,− although the −Δ S m values of 3 are smaller than that of the best magnetic refrigerant of Gd(OH)F 2 , the −Δ S m values of 4 under 2 T surpass those of all the representative magnetic refrigerants in 1–4 K, demonstrating that weak antiferromagnetic coupling and a large spin ground state have a positive effect on the large entropy changes at low magnetic fields. Notably, the −Δ S m values for 4 under a 2 T magnetic field are 19–52% greater than those of the existing commercial LiGdF 4 , signifying that 4 stands out as the prime candidate for the fourth stage in the CADR system.…”