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.
ABSTRACT
Searching for working refrigerant materials is the key element in the design of magnetic cooling devices. Herein, we report on the thermodynamic and magnetocaloric parameters of an X1 phase oxyorthosilicate, Gd2SiO5, by field-dependent static magnetization and specific heat measurements. An overall correlation strength of |J|S2 ≈ 3.4 K is derived via the mean-field estimate, with antiferromagnetic correlations between the ferromagnetically coupled Gd-Gd layers. The magnetic entropy change -ΔSm is quite impressive, reaches 0.40 J K-1 cm-3 (58.5 J K-1 kg-1) at T = 2.7 K, with the largest adiabatic temperature change Tad = 23.2 K for a field change of 8.9 T. At T = 20 K, the lattice entropy SL is small enough compared to the magnetic entropy Sm, Sm/SL = 21.3, which warrants its potential in 2 -20 K cryocoolers with both the Stirling and Carnot cycles. Though with relatively large exchange interactions, the layered A-type spin arrangement ultimately enhances the magnetocaloric coupling, raising the possibilities of designing magnetic refrigerants with a high ratio of cooling capacity to volume.
