Strong Magnetocaloric Coupling in Oxyorthosilicate with Dense Gd³⁺ Spins

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 X 1 phase oxyorthosilicate, Gd2SiO5, by field-dependent static magnetization and specific heat measurements. An overall correlation strength of |J|S 2 ≈ 3.4 K is derived via the mean-field estimate, with antiferromagnetic correlations between the ferromagnetically coupled Gd–Gd layers. The magnetic entropy change −ΔS m 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 T ad = 23.2 K for a field change of 8.9 T. At T = 20 K, the lattice entropy S L is small enough compared to the magnetic entropy S m, S m/S L = 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.

Magnetocaloric Properties in Rare-Earth-Based Metal–Organic Frameworks: Influence of Magnetic Density and Hydrostatic Pressure

“…The RCP data has been successfully adjusted to the power-law RCP ≈ ⟨ d Gd ⟩ q (i.e, ⟨ d Gd ⟩ is the Gd-relative density per molecular weight), yielding q = 0.92 ± 0.03, and demonstrating an almost linear relationship with the Gd-density. This RCP max value is higher than the one recently observed for Gd 2 SiO 5 (649.5 J/kg) . The divergence between Δ S M max and RCP is due to the larger δ T fwhm for Gd-UiO-66 compared to Gd-LRH, which induces an enhancement of the RCP value.…”

“…However, this is not the case for the total angular momentum ( J ), as it does not display any trend depending on the rare-earth ion (see Figure ). Specifically, the highest −Δ S M max , which corresponds to Gd-RPF-4, is due to the particularity of the large spin ground state with zero orbital moment ( S = 7/2 and L = 0, i.e., J = 7/2), where Gd 3+ has a spherically symmetric ground state of 8 S 7/2 which provides the largest entropy per single ion, and an overall crystal field splitting of 1 K magnitude. , Moreover, its weak superexchange interactions result in low-lying excited spin states . On the other hand, even if the Ho ion has a greater J = 8 ( S = 2 and L = 6), the corresponding MOF only yields a −Δ S M max of 3.71 J/kg·K at 17 K. Thus, from the magnetization point of view, we observed that PM moment and M S play an important role in enhancing the magnetic entropy change values in the α-RPF-4 series.…”

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

“…We then adopt a nearest‐neighbour Heisenberg model to characterize the bulk magnetic behaviour, by writing the spin Hamiltonian $$$$\begin{equation} \mathcal{H}={J}_{1}\sum _{<i,j>}{S}_{i}\cdot {S}_{j}+{H}_{\mathrm{dip}} \end{equation}$$$$of which J 1 represents the Heisenberg exchange interactions between the nearest neighbour spin pairs, and H dip denotes the magnetic dipolar interactions. [ 7,16,19 ] Although the magnetic anisotropy is considered important in some Gd 3+ clusters, we exclude the single‐ion anisotropy term for the eightfold degenerate spin multiplet of Gd 3+ ( L = 0, S = J = 7/2) here, following a similar approach employed in studies on garnet GGG and tripod kagome magnet Mg 2 Gd 3 Sb 3 O 14 . [ 20 ] The relevant dipolar energy scale is D dip = 0.65 K, using the crystallographic Gd 3+ …Gd 3+ separation in triangle Gd 1.00 −(6 h ) chain, accounts for no more than 29% of the antiferromagnetic couplings.…”

“…[2b-d,3] The spinonly Gd 3+ compounds, with large J = S = 7/2 and g J = 2, then become rather appealing, as in the case of the benchmark refrigerant Gd 3 Ga 5 O 12 (GGG), and the alternative dipolar antiferromagnet LiGdF 4 . [2f,3b,4] Many other potential working materials, including the GdPO 4 , [5] NaGdS 2 , [6] Gd 2 SiO 5 , [7] Sr 2 GdSbO 6 , [8] Gd(HCOO) 3 , [9] Gd(OH)CO 3 , [10] GdF 3 [11] and Gd(OH)F 2 , [12] as well as the molecular {Gd 12 Na 6 } quadruplewheel are identified. [13] In most cases, the volume of refrigerant dominates the magnet system and the associated shielding, which must be minimized during space missions, thereby posing a challenge in identifying magnetocaloric materials with a large volumetric cooling capability.…”

“…[ 2 , 3 ] The spin‐only Gd 3+ compounds, with large J = S = 7/2 and g J = 2, then become rather appealing, as in the case of the benchmark refrigerant Gd 3 Ga 5 O 12 (GGG), and the alternative dipolar antiferromagnet LiGdF 4 . [ 2 , 3 , 4 ] Many other potential working materials, including the GdPO 4 , [ 5 ] NaGdS 2 , [ 6 ] Gd 2 SiO 5 , [ 7 ] Sr 2 GdSbO 6 , [ 8 ] Gd(HCOO) 3 , [ 9 ] Gd(OH)CO 3 , [ 10 ] GdF 3 [ 11 ] and Gd(OH)F 2 , [ 12 ] as well as the molecular {Gd 12 Na 6 } quadruple‐wheel are identified. [ 13 ]…”