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There is an urgent demand for the development of new resource-saving and high-efficiency cryogenic refrigeration technologies against the historical backdrop of increasing scarcity of resources and energy. Magnetic refrigeration technology based on the magnetocaloric effect (MCE) of magnetic materials is a promising approach to address helium resource constraints and improve energy efficiency. Here, a brilliant cryogenic magnetic refrigerant with a large low-field MCE and excellent refrigeration performance is presented. Benefiting from the enhanced ferromagnetism and low saturation magnetic field, the peaks of magnetic entropy change, refrigeration capacity, and adiabatic temperature change of Eu(Ti,Nb,Zr)O3 compounds reach 19.6 J·kg−1·K−1, 87.6 J·kg−1, and 5.5 K, respectively, for a field change of 0−1 T. Magnetic refrigeration experiments on a Gifford‒McMahon (GM)/magnetic hybrid refrigerator further demonstrated that EuTi0.8375Nb0.0625Zr0.1O3 is an excellent magnetic refrigerant operating near the liquid helium temperature. An appropriate amount of this magnetic refrigerant can significantly improve the refrigeration performance of the hybrid refrigerator. The cooling power in hybrid refrigeration mode is improved by a maximum of 52% over that in pure GM/HoCu2 mode at 4.2 K and 0.5 Hz. In addition, the cooling efficiency at 4.2 K is more than 40% greater than that of the pure GM/HoCu2 refrigerator.

Herein, as the fabrication of the microchannels for fluid flow using La(Fe,Si)13 magnetic refrigerant material is required while maintaining its superior magnetocaloric performance, sinter molding of the microchannel-designed La(Fe,Si)13 was investigated using a dissolutive mold comprised of NaCl to develop a molding process without contamination by carbon and other light elements. In addition, to avoid the thermal decomposition of fine particles of La(Fe,Si)13, a solid-state reaction was conducted during sintering using a mixture of α-Fe and La-rich compounds as the initial powder. After sintering, the sample shape exhibited channel widths and depths of 200 μm and pillar widths of 300 μm, which were originally designed for the NaCl dissolutive mold. The metallographic microstructure mostly comprised the La(Fe,Si)13 phase, and the volume fractions of the extra phases, such as α-Fe and La2O3, were suppressed to 1.1 % and 3.2 %, respectively. The maximum of the magnetic entropy change in a single pillar reached −19 J/kg K. Direct observation of magnetic nucleation/growth confirmed the smooth emergence of the first-order transitions in multiple pillars. Consequently, this fabrication approach promoted micro-channel-designed La(Fe,Si)13Hy while maintaining a large magnetocaloric effect via low carbon contamination.

Two structurally dissimilar 3d-4f cages having the formulae [(CoIII)3Gd4(μ3-OH)2(CO3) (O2CtBu)11(teaH)3]·5H2O (1) and [(CoIII)3Dy3(μ3-OH)4(O2CtBu)6(teaH)3]·(NO3)2·H2O (2) have been isolated under similar reaction conditions and stoichiometry of the reactants. The most important factor for structural diversity seems to be the incorporation of one μ3-carbonate anion in 1 and not in 2. Co atoms are in a +3 oxidation state in both complexes, as shown by the Bond Valence Sum (BVS) calculations and bond lengths, and as further supported by magnetic measurements. Co3Gd4 displays a significant magnetocaloric effect (−∆Sm = 25.67 J kg−1 K−1), and Co3Dy3 shows a single molecule magnet (SMM) behavior.

A metal-organic framework (MOF) based on gadolinium ion (Gd 3+ ) and tricarboxylate ligand, [Gd(BTPCA)(H 2 O)]·2DMF·3H 2 O ( Gd-BTPCA ) (H 3 BTPCA =1,1′,1′-(benzene-1,3,5-triyl)tripiperidine-4-carboxylic acid; DMF=dimethylformamide), was synthesized and structurally characterized. The adjacent Gd 3+ ions are intraconnected by the carboxylate groups of the BTPCA 3- ligands to form a 1D Gd 3+ ion chain. The 1D Gd 3+ ion chains are interconnected by the BTPCA 3- ligands, giving rise to a 3D framework with 1D open channel. The magnetic studies indicate that Gd-BTPCA exhibits weak ferromagnetic interactions, and acts as a cryogenic magnetic refrigerant having the magnetic entropy change (−Δ S m ) of 20.40 J kg −1 K −1 for ΔH =7 T at 3 K. [ABSTRACT FROM AUTHOR]

The parent La 0.8 Ce 0.2 Fe 11.47 Mn 0.23 Si 1.3 were prepared by induction furnace and annealed at 1363 K for 144 h, then milled to powder and hot pressed into cylindrical block at723 K, 873 K, 1023 K and 1173 K respectively under the pressure of 30Mpa for 15min. The hot pressing samples were cut into thin plates and hydrogenated. The structure and morphology were tested by XRD and SEM method, the magnetic property were tested by VSM. The experimental results show that the structure of sample is more compact and the magnetocaloric effects increase with the increase of the hot pressing temperature. The max magnetic-entropy change ΔS M is 10.99 J/kgK (66.53 mJ/cm 3 K), max adiabatic temperature change ΔT ad is 2.5 K under a magnetic field change of 1.5 T for the sample hot pressed at 1173 K. The max bending strength is 113.6 Mpa and the thermal conductivity is 7.3w/mk. [ABSTRACT FROM AUTHOR]

Highlights: [•] The single-phase formation process of La(Fe0.89Si0.11)13 was investigated. [•] The NaZn13-type single-phase is obtained by annealing for 300h at 1323K. [•] The Curie temperature is increased by annealing due to compositional homogenization. [•] The isothermal magnetic entropy change was related to the microstructure. [•] The peak position of the isothermal magnetic entropy change is affected by annealing. [Copyright &y& Elsevier]

Abstract: Magnetic field dependence of the magnetic entropy change (ΔS M) is the key for magnetic refrigeration. A large magnetic entropy change (ΔS M) associated with the ferromagnetic-paramagnetic transition in Ce-doped La0.7Sr0.3MnO3 material has been observed. It is shown for (La0.56Ce0.14)Sr0.3MnO3 composition at the Curie temperature of 357K, that the maxima of the magnetic entropy changes upon variation of the applied magnetic field at 1 and 5T are about 1.55 and 4.78Jkg−1 K−1, respectively. Due to the large (ΔS M) and high Curie temperature, the (La0.56Ce0.14)Sr0.3MnO3 perovskite is suggested to be used as potential magnetic refrigerants for magnetic refrigeration technology above room temperature. [Copyright &y& Elsevier]

Two structurally dissimilar 3d-4f cages having the formulae [(CoIII)3Gd4(μ3-OH)2(CO3) (O2CtBu)11(teaH)3]·5H2O (1) and [(CoIII)3Dy3(μ3-OH)4(O2CtBu)6(teaH)3]·(NO3)2·H2O (2) have been isolated under similar reaction conditions and stoichiometry of the reactants. The most important factor for structural diversity seems to be the incorporation of one μ3-carbonate anion in 1 and not in 2. Co atoms are in a +3 oxidation state in both complexes, as shown by the Bond Valence Sum (BVS) calculations and bond lengths, and as further supported by magnetic measurements. Co3Gd4 displays a significant magnetocaloric effect (−∆Sm = 25.67 J kg−1 K−1), and Co3Dy3 shows a single molecule magnet (SMM) behavior. [ABSTRACT FROM AUTHOR]

Abstract: Polycrystalline samples of potassium doped lanthanum manganites having nanometric crystallite size have been synthesized by pyrophoric method. The Curie temperature (T C) of the prepared samples is found to be strongly dependent on K content and spans between 260 and 309K. Close to T C, large change in magnetic entropy has been observed in all the samples. The maximum magnetic entropy change observed for samples with different concentration of K, exhibits a linear dependence with the applied magnetic field. Adiabatic temperature change at T C at 1T also increases with K doping and attains a maximum of 2.1K for La0.85K0.15MnO3. Estimated relative cooling power of La1−x K x MnO3 compounds is nearly one-third of pure Gd. In addition to the tuneability of T C between 260 and 310K, higher chemical stability, lower eddy current heating and inexpensive preparation technique; the magnetic entropy change in La0.85K0.15MnO3 compound at 1T magnetic field is found to be 3.00J/kgK and is ∼89% to that known for the prototype magnetic refrigerant (pure Gd). Our result on magnetocaloric properties suggests that La1−x K x MnO3 compounds are attractive as a possible refrigerant for near room temperature magnetic refrigeration. [Copyright &y& Elsevier]

Abstract: The series of strontium-substituted calcium La0.5Ca0.5−x Sr x MnO3 has been studied and show the effect of strontium substitution. Magnetic studies on La0.5Ca0.5−x Sr x MnO3 compounds are reported. The substitution of a bigger cation, Sr2+ for Ca2+ enhances the Curie temperature (T C) from 228K (x =0) to 335K (x =0.5) and we have found a value of T C around room temperature (273K) for x =0.15. Maximum magnetic-entropy change (ΔS M) and relative cooling power (RCP) are discussed for La0.5Ca0.35Sr0.15MnO3 compound. The magnetic-entropy change is ∼0.615J/(kgK) at T C (273K) for a magnetic field of 2T and the RCP is 36.5J/kg, which suggests La0.5Ca0.35Sr0.15MnO3 compound a possible candidate for magnetic refrigerants near room temperature. [Copyright &y& Elsevier]

Abstract: The rare earth mononitride, ErN, has been synthesized by the carbothermic reduction and hot isostatic press methods. The magnetocaloric effect of ErN has been evaluated by calculating the magnetic entropy changes, ΔS, from the magnetization data sets and from the heat capacity measured at various temperatures and applied fields. The two results are in good agreement with each other. The ΔS value of ErN is the highest at 7.5K and higher than that of ErNi2 reported as the candidate material for the magnetic refrigerant of cryogenic technology. Heat capacity curve against temperature of ErN has a peak at 4.4K at zero-field. The peak value of the heat capacity of ErN is 507kJK−1 m−3. This value is larger than those of Er3Ni used commercially as a magnetic regenerator for the Gifford–McMahon refrigerator. The present results indicate that ErN is a promising material for the magnetic refrigerant and regenerator of cooling systems working above the boiling temperature of helium. [Copyright &y& Elsevier]

Abstract: We have synthesized Gd x Tb1−x N and Tb x Ho1−x N (x =0, 0.25, 0.5, 0.75 and 1) by the carbothermic reduction performed in a nitrogen gas stream. GdN and TbN have been completely miscible with each other as well as TbN and HoN. As x was changed from 0 to 1, the Curie temperature increased monotonously from 18.5 to 43.8K for Tb x Ho1−x N and from 43.8 to 61.2K for Gd x Tb1−x N. The magnetocaloric effects have been evaluated by calculating the magnetic entropy changes from the magnetization data sets measured at different applied fields and temperatures. In any composition x, the magnetocaloric effects of Gd x Tb1−x N and Tb x Ho1−x N are larger than those of Gd x Dy1−x N. Therefore, Gd x Tb1−x N and Tb x Ho1−x N are promising magnetic refrigerant materials for hydrogen liquefying system working below liquid nitrogen temperature. [Copyright &y& Elsevier]

Abstract: To obtain large magnetocaloric effects (MCEs) due to the itinerant-electron metamagnetic (IEM) transition in , the Curie temperature has been controlled by hydrogen absorption. In compounds,  K for increases with increasing hydrogen concentration, resulting in  K for . Furthermore, the magnetic moment is also stabilized against temperature by hydrogen absorption. Since the IEM transition is preserved after hydrogenation, large MCEs of the magnetic entropy change and the adiabatic temperature change have been observed around room temperature. A large value of has been confirmed by a direct measurement in adiabatic magnetic field change for the ( and 1.6). Consequently, the compounds and their hydrides are promising as high-performance magnetic refrigerants working in a wide range of temperature covering room temperature in relatively low applying magnetic fields. [Copyright &y& Elsevier]

Polycrystalline samples of La0.67-xCa0.33MnO3 (x=0.00, 0.02, 0.06, and 0.10) with different La site vacancies have been prepared by the sol–gel method. The grain sizes of the samples are observed by SEM. XRD results show that the samples are single phase of perovskite-type oxides. The Curie temperatures and the magnetic entropy changes of the samples are measured on a vibrating sample magnetometer (VSM). The influence of the vacancy concentration in the La site on their magnetocaloric properties has been investigated. A large magnetic entropy change (∼2.78 J/kg K) is obtained in the sample La0.67-xCa0.33MnO3 (x=0.02) at its Curie temperature (277 K) in an applied magnetic field of 1 T. Results of magnetic measurement show that these materials with La site vacancies can be used as candidates for magnetic refrigerants near room temperature. [Copyright &y& Elsevier]