High-Performance Magnetic Refrigerant Featuring One-Dimensional Gd-O Chains and O-Gd3 Triangles

Gd3 TeBO9 : A Rare-Earth Borate with Significant Magnetocaloric Effect

Magnetic refrigeration technology based on Gd-based paramagnets is expected to be applied to refrigeration in extremely low temperatures, thereby reducing the consumption of liquid helium. Here, we obtained a compound, Gd3 TeBO9 with high Gd3+ concentration through element substitution. The Gd3+ concentration in this compound is as high as 2.4×1024  ions/kg, which is 33 % higher than the commercial Gd3 Ga5 O12 (GGG), and further magnetic tests show that Gd3 TeBO9 has a large magnetic entropy change (57.44 J/(kg K) and 408 mJ/(cm3  K) at 2.6 K and 7 T), which is 1.5 times that of GGG, implying the possibility of its further development as an potential magnetocaloric material.

Gd(OH)F2: A Promising Cryogenic Magnetic Refrigerant

Magnetic refrigerants with a large magnetocaloric effect (MCE) in a wide temperature range and low magnetic ordering temperature (T_o) in the sub-kelvin temperature region are not only crucial for adiabatic demagnetization refrigeration but also open up a broader parameter space for the optimal design of adiabatic demagnetization refrigerators. However, such magnetic refrigerants are extremely rare because they require magnetic materials to simultaneously satisfy three conditions: low T_o, weak magnetic interaction, and high magnetic density. Here, we report the syntheses, heat capacities, and magnetic properties of Gd(OH)_3-xF_x (1: x = 1, 2: x ≈ 1.5, and 3: x = 2), demonstrating for the first time that the introduction of fluoride anions into antiferromagnetic Gd(OH)₃ can effectively regulate its T_o. Significantly, 3 not only has a T_o of 0.5 K but also exhibits a large MCE in the temperature range from 0.5 to 4 K, representing the best magnetic refrigerant reported to date in the temperature range of 0.5-4 K from the viewpoint of the MCE.

3-Pyridylacetic-Based Lanthanide Complexes Exhibiting Magnetic Entropy Changes, Single-Molecule Magnet, and Fluorescence

Four complexes from lanthanides, 3-pyridylacetate, and 1,10-phenanthroline, formulated as [Ln2(3-PAA)2(μ-Cl)2(phen)4](ClO4)2 [Ln = Gd(1), Dy(2), Eu(3), Tb(4), 3-PAA = 3-pyridylacetic acid, phen = 1,10-phenanthroline], were obtained. The four compounds were characterized by IR spectra, thermogravimetric analyses, powder X-ray diffraction, and single-crystal X-ray diffraction. Compounds 1-4 are isomorphous, and they have a dinuclear structure. Magnetic studies reveal that 1 shows the magnetocaloric effect with -ΔS m max = 19.03 J kg-1 K-1 at 2 K for ΔH = 5 T, and 2 displays a field-induced single-molecule magnet with U eff = 19.02 K. The photoluminescent spectra of 3 and 4 exhibit strong characteristic emission, which demonstrate that the ligand-to-EuIII/TbIII energy transfer is efficient.

Magnetocaloric Effect and Thermal Conductivity of a 3D Coordination Polymer of [Gd(HCOO)(C2O4)]n

A 3D coordination polymer, [Gd(HCOO)(C₂O₄)]_n was prepared. Its magnetocaloric effect (MCE) (32.7 J K^-1 kg^-1 at 2 K and 2 T) is significantly larger than that of commercial Gd₃Ga₅O₁₂ (GGG) (14.6 J kg^-1 K^-1 at 2 K and 2 T), while its thermal conductivity (9.9 W m^-1 K^-1 at 3 K) is comparable to that of the commercial GGG (about 10 W m^-1 K^-1 at 3 K).

Large Magnetocaloric Effect in Li3K9Gd3(BO3)7 Crystal Featuring Sandwich-Like Three-Dimensional Framework

A new Gd-based borate crystal, Li₃K₉Gd₃(BO₃)₇, has been successfully obtained via the high-temperature solution method using Li₂O-K₂O-B₂O₃ self-flux. It crystallizes in monoclinic space group P2/n (no. 10) with lattice parameters a = 11.3454(6) Å, b = 9.9881(4) Å, c = 11.4467(7) Å, α = γ = 90 ^o, β = 114.782(7) ^o, and Z = 2. Li₃K₉Gd₃(BO₃)₇ exhibits an intriguing sandwich-like three-dimensional (3D) framework constructed from [Gd-B-O]_∞ layers, KO_n (n = 6 and 8) polyhedra, and LiO₄ tetrahedra, in which [Gd-B-O]_∞ layers are built from two types of GdO₈ polyhedra and triangular BO₃ units. Magnetic measurements showed that Li₃K₉Gd₃(BO₃)₇ exhibits a large magnetocaloric effect with -ΔS_m = 39.3 J kg^-1 K^-1 at 2.0 K for ΔH = 7 T, which is slightly higher than that of the commercial gadolinium gallium garnet under the same conditions. The powder X-ray diffraction, infrared spectrum, and UV-vis-NIR diffuse reflectance spectrum were also performed to characterize Li₃K₉Gd₃(BO₃)₇. The electronic band structures, partial density of states, and refractive indices of Li₃K₉Gd₃(BO₃)₇ were investigated via the first-principle calculations.

Gadolinium-Rich Borate Gd17.33(BO3)4(B2O5)2O16 Exhibiting a Magnetocaloric Effect

A gadolinium-rich borate Gd_17.33(BO₃)₄(B₂O₅)₂O₁₆ was successfully grown by the high-temperature solution method using the Rb₂O-B₂O₃ flux. The crystal crystallizes in centrosymmetric space group C2/m with lattice constants a = 18.4300(2) Å, b = 3.7400(4) Å, c = 14.2047(16) Å, and β = 119.8550(12)°. Two different honeycomb-like [GdO] layers alternately arrange in the order ABAB forming the three-dimensional framework, in which the isolated [B₂O₅] and [BO₃] units fill in channels of the 12-membered and 10-membered [GdO] polyhedral rings, respectively. The UV cutoff edge of Gd_17.33(BO₃)₄(B₂O₅)₂O₁₆ is less than 240 nm. The maximum -ΔS_m,max is 26.53 J kg^-1 K^-1 or 174.70 mJ cm^-3 K^-1 (T = 4.4 K and ΔH = 7 T) as investigated by the isothermal magnetization method.