Room-temperature magnetic refrigeration is a new type of solid-state refrigeration technology. As refrigerants, La (Fe, Si)13-based alloys have become candidate refrigeration materials because of their considerable magnetocaloric effect and adjustable Curie temperature, but their inherent brittleness yields severe limitations. Selective laser melting (SLM) technology in additive manufacturing could solve the problems associated with the formation and processing of materials. In this study, La(Fe, Al, Si)13 alloys were prepared via SLM technology, and the effects of different scanning strategies on the surface morphology, microstructure, magnetocaloric properties and mechanical properties were systematically analysed. The results revealed that the content of the 1:13 main phase is highest in the sample formed through the interlayer rotation 67 degrees scanning strategy, the maximum magnetic entropy change can reach 8.07 J/(kg & sdot; K), and the compressive strength and hardness are greatest. This strategy provides a shorter laser scanning path and easily achieves a consistent solidification rate, thus effectively reducing stress concentration, which is conducive to the application of magnetic refrigeration technology.

In this study, a series of polycrystalline La 0.65 Ca 0.35- x Ba x MnO 3 ( x = 0,0.1,0.2,0.3) samples were synthesized through high-pressure heat treatment processing. Their magnetic properties, magnetocaloric effects, and critical behaviors associated with phase transitions were investigated. The substitution of Ba2+ for Ca2+ resulted in lattice expansion, which in turn increased the Mn-O-Mn bond angle and enhanced the double-exchange interaction within the system. It was revealed by experimental magnetic studies and Density functional theory calculations that the magnetic interactions, dominated by Mn-3d in the ferromagnetic ground state, were strengthened, leading to an increase in the Curie temperature from 219 K (x = 0) to 249 K (x = 0.1), 272 K (x = 0.2) and 300 K (x = 0.3). Under a magnetic field of 7 T, the maximum magnetic entropy change was found to be 4.47 J & sdot; kg- 1 & sdot; K- 1 (x = 0), 4.25 J & sdot; kg- 1 & sdot; K- 1 (x = 0.1), 3.60 J & sdot;kg- 1 & sdot;K-1 (x = 0.2) and 3.28 J & sdot; kg- 1 & sdot; K- 1 (x = 0.3), respectively. Notably, compared to solid-state reaction method samples, the refrigerating temperature range broadened by 131.25 %, 57.44 %, and 47.45 % for x = 0, 0.1, and 0.2, respectively, using high-pressure heat treatment. Additionally, the x = 0.1 sample exhibited a first-to-second-order phase transition. Analysis of Arrott plots confirmed the first-order phase transition in the parent sample and the second-order phase transition in the doped samples. Furthermore, the Modified Arrott plot, Kouver-Fisher, and local exponent methods revealed that, as the Ba content increased, the critical exponents beta, gamma, and delta of the samples with second-order phase transition characteristics (doped samples) approached 0.5, 1.0, and 0.667, respectively. The introduction of Ba was found to facilitate the establishment of a second-order phase transition pattern that is more consistent with the mean- field theory model.

Thus far, metal-bonding has presented high efficacy in improving the mechanical, thermal conductive, and anti-corrosion properties of La(Fe,Si)13-based hydrides. However, to ensure high performance, the proportion of metal bonders has to be as high as 20 wt%, thereby significantly weakening the magnetocaloric effect (MCE). In this work, small amounts of graphene nanosheets (up to 2 wt%) with high thermal conductivity and specific surface area were incorporated into the La0.8Ce0.2Fe11.7Si1.3Hy matrix through a cold-pressing and sintering process. X-ray diffraction analysis indicates that carbon from graphene can easily diffuse into the lattice of La(Fe,Si)13 main phase as an interstitial atom, resulting in a significant increase of the lattice constant accompanied by a significant decrease of the Curie temperature and H content of the composites. While 0.3 wt% graphene doping only has minor improvements in the thermal conductivity λ and corrosion resistance of the parent La0.8Ce0.2Fe11.7Si1.3Hy, further increase of graphene content to 1 wt% causes a significant increase of λ from 1.4 W/(m·K) for the parent material to ∼2 W/(m·K) and a decrease of corrosion current density from 1.43×10‒5 to 9.63×10‒6 A/cm2. When the graphene content is lower than 0.3 wt%, the large MCE does not significantly deteriorate. In 0–1.5 T, the maximal magnetic-entropy change ΔSm of 11.5 J/(kg·K) at 336 K for the parent material decreases to 8.2 J/(kg·K) at 306 K for the 2 wt% graphene-doped composite.

In this paper, Gd20Tb20Er20Cu20M20 (M = Fe, Co) high entropy metallic glasses (HE-MGs) are designed, and their microstructure, magnetic behavior, magnetocaloric effect (MCE) and critical behavior are studied in detail. All prepared alloy ribbons exhibit the feature of disordered structure. Two samples exhibit distinct spin glass behavior at 62 K and 37 K, respectively. Two HE-MGs undergo the second-order phase transition (SOPT) from ferromagnetic state to paramagnetic state at 113 K and 77 K, which are near liquid hydrogen temperature. The remarkable MCEs are achieved by two HE-MGs through the combination of SOPT and spin glass behavior. Under the applied magnetic field of 0-7 T, the peak isothermal magnetic entropy change (|-Delta SMmax|) and RCP are 6.7 J & sdot;kg- 1 K- 1 and 900.9 J & sdot; kg- 1 (for M = Fe), 8.5 J & sdot; kg- 1 K- 1 and 763.7 J & sdot; kg- 1 (for M = Co). Due to spin behavior and complicated compositions, the phase transition temperature span (Delta TFWHM) of the Gd20Tb20Er20- Cu20M20 is exceeding 130 K under 0-7 T. The microstructure fluctuations and chemical short-range order cause respective phase transition deviate from mean field model. The Gd20Tb20Er20Cu20M20 (M = Fe, Co) HE-MGs show excellent MCE properties and can be manufactured easily, making them promising for cryogenic temperature magnetic refrigerant applications.

Magnetic refrigeration technology is a green refrigeration technology with the potential to replace traditional gas compression refrigeration. Selective laser melting (SLM) is a processing technique for preparing magnetic refrigerants with complex geometric shapes. In this work, La(Fe,Al,Si)13 alloy samples were prepared via SLM. The effects of heat treatment on the microstructure, magnetocaloric effect, and mechanical properties of the samples were systematically investigated. The relationship among structure, heat treatment, magnetic properties, and mechanical properties was revealed. Based on the experimental results, when the heat treatment time was 72 hours, the main phase and the magnetic entropy change were the greatest. With increasing heat treatment time, the lattice constant decreases and the volume shrinks. At the same time, the overlap of the 3d electron wave function of Fe is increased, resulting in a decrease in the Curie temperature. In addition, the increase in heat treatment time released the tensile stress caused by the rapid cooling in the SLM process, eliminated the local misorientation, and was conducive to the movement of the magnetic domain; however, the coarse grains increased the brittleness of the material. The compressive strength of the sample after heat treatment was 29 % lower than that of the sample without heat treatment, and the hardness was 43 % greater. Furthermore, a porous magnetic refrigerant was prepared, and the refrigeration utilization rate was determined to be 0.94 via finite element simulation; Therefore, the comprehensive performance shows that the alloy prepared in this work has better magnetic refrigeration application potential.

Magnetic refrigeration in the liquid-helium temperature region plays a significant role in many technological fields. In this work, the crystal structure, magnetic properties, and magnetocaloric effect (MCE) of commercial Yb2O3 and a series of (Yb1-xHox)2O3 (x = 0, 0.1, 0.2) compounds prepared by a feasible high-energy ball milling method were systematically investigated. The crystallography results demonstrate that these Yb2O3-based compounds have a cubic bixbyite structure with space group Ia3, and the lattice constant increases with the increase of Ho3+ ions content. Commercial Yb2O3 shows antiferromagnetic (AFM) ordering at 2.35 K, and ballmilled (Yb1-xHox)2O3 (x = 0, 0.1, 0.2) compounds have lower AFM ordering temperatures of RE3+ moments of 2.30 K, 2.15 K and below 2 K for x = 0, x = 0.1 and x = 0.2 samples, respectively. Thermomagnetic behavior under high magnetic fields exhibited the existence of ferromagnetic (FM) correlation in these compounds, and a high magnetic field could induce an AFM to FM transition. The magnetization of Yb2O3 increases with the increase of Ho3+ ions content due to the increase of the effective magnetic moments. The maximum magneticentropy change GSM and relative cooling power RCP of (Yb0.8Ho0.2)2O3 are 11.1J/kg center dot K and 123.2 J/kg, respectively under 5 T, which are 19.4 % and 67.6 % larger than those of commercial Yb2O3. The (Yb1-xHox)2O3 (x = 0, 0.1, 0.2) compounds have a large MCE under moderate magnetic field changes and there is no thermal and magnetic hysteresis, which is beneficial for application as a promising refrigerant near the liquid-helium temperature range.

La(Fe, Si)(13) hydrides suffer from intrinsically poor mechanical, anti-corrosive and thermally conductive properties, which impede their implementation as efficient regenerators. The current improvement strategies are faced with difficult trade-offs among these properties. In this work, we developed a facile chemical vapor deposition (CVD) method for low-temperature in-situ deposition of a thin graphitic layer of similar to 200 nm on La0.8Ce0.2FexMn0.215Si1.3 plates of 0.5-1 mm thickness by evaporating polyethylene glycol (PEG) polymer as a solid carbon source. These plates could be machined directly from their casting ingot due to the mechanical property enhancement from similar to 3-6 wt% alpha-Fe. Favorably, these graphite-coated plates could be successfully fully hydrogenated at atmospheric pressure for room-temperature application. The similar to 0.03 wt% graphite coating could endow the composites with striking anti-corrosive properties with the sum of the film resistance and the charge transfer resistance increasing from 105 (for the graphite-free hydride) to 11298 Omega center dot cm(2) by more than two orders of magnitude. Moreover, these graphite composites exhibit large room-temperature magnetic entropy change Delta S-M of 8.7 J/kg center dot K in 0-1.5 T and high thermal conductivity lambda of 7.9-8.6 W/Km compared with the corresponding values of 3.5 J/kg center dot K and 9.5 W/Km for the prototype room-temperature magnetocaloric material Gd. The intriguing functionality of the graphite coating may advance the practical application of La(Fe, Si)(13)-based materials.

Rare earth-rich NaZn13-type La-Fe-Si-based alloys are promising candidates for near-room-temperature magnetocaloric applications. However, their poor corrosion resistance limits practical applications. The microstructure, corrosion behavior and magnetic entropy change of La0.8Ce0.2Fe9.2Co0.6Si1.2 alloys after annealing were systematically investigated. Annealing treatments were conducted at 1423 K for durations of 4–24 h. As annealing time increased, the α-Fe phase content decreased monotonically from ~7.81wt% to ~2.92wt%, accompanied by significant microstructural evolution. For the 4 h-annealed sample, extensive and large corroded spots were observed, attributed to micro-galvanic corrosion where the α-Fe phase (cathode) and 1:13 matrix phase (anode) formed active electrochemical pairs. Prolonged annealing reduced the corrosion current density by ~50%, directly correlating with the α-Fe phase reduction and improved microstructural homogeneity. Notably, corrosion exhibited a negligible effect on the magnetic entropy change of the alloys. This study confirms that optimizing annealing time to decrease α-Fe content and enhance microstructural uniformity represents an effective strategy to improve corrosion resistance without compromising magnetocaloric performance.

La0.7Sr0.3MnO3 polycrystalline samples were prepared using a two-step process (high-temperature solid-phase reaction method and high-pressure heat treatment) under different pressures. The magnetocaloric properties of the samples exhibited a significant dependence on pressure. The nonlinear changes in average bond length with pressure were defined in two stages: 0-2 GPa (S1) and 2-4-6 GPa(S2). S1: The double-exchange interaction was weakened and the Curie temperature was decreased from 367 K to 338 K due to negative volume compressibility, while the peaks of magnetic entropy change were reduced. S2: The rate of linear increase in Curie temperature induced by normal cell contraction is 5.6 K·GPa-1. Maximum magnetic entropy change and refrigeration temperature span varied at the rates of 0.29 J·kg-1·K-1·GPa-1 and -5.37 K·GPa-1, respectively. All the samples exhibited a second-order ferromagnetic-paramagnetic transitions with critical behavior evolving from mean-field model adherence (S1) to deviation (S2). The magnetocaloric properties of La0.7Sr0.3MnO3 can be effectively regulated by pressure.

Due to the larger magnetic entropy change Delta S-M and the much lower raw material cost, La(Fe, Co, Si)(13) materials have the potential to replace the room-temperature magnetic refrigeration prototype material Gd. In this work, we have developed a simple chemical vapor deposition (CVD) method for in situ graphite deposition on the surface of La(Fe, Co, Si)(13)B-0.2. Facilitated by the decomposition of the solid carbon-source polyethylene glycol (PEG), the CVD process could be carried out at a low temperature of 400 degrees C and in a short duration of 20 min, which ensures no alpha-Fe precipitation from and carbon atom diffusion into the La-Fe-Si material. These 400-700 nm-thick coatings could significantly enhance the anti-corrosive property with a positive shift of corrosion potential E-corr from -788 to -600 mV and a reduction of the corrosion current density I-corr from 1.67x10(-5) to 9.14x10(-6) A/cm(2), accompanied by a concurrent enhancement of the thermal conductivity. More favorably, a large Delta S-M of similar to 4 J/kg.K at 286 K and a relative cooling power (RCP) value of similar to 98 J/kg in 0-1.5 T were maintained

Defect engineering is an effective means to improve the electronic structure and physicochemical properties of materials. In this work, the cryogenic magnetocaloric effect (MCE) of commercial Tm2O3 was significantly improved by the introduction of oxygen vacancy (OV) defects. A series of monocrystalline Tm2O3 powders (cubic structure, Ia 3 space group) with high-level OV content was obtained by ball-milling (BM) the commercial counterpart for 3-12 h. Of these samples, the 9 h-ball milled Tm2O3 sample (Tm2O3-9) has the highest ratio value of oxygen atoms near OV (Onear OV) of 15.79 % and largest effective magnetic moment (mu eff) of Tm3+ ion of 6.8 mu B compared with the corresponding values of 8.06 % and 6.32 mu B for the commercial Tm2O3. Consistently, Tm2O3- 9 has the best MCE performance with the maximal magnetic-entropy change (GSM) and the refrigerant capacity (RC) of 7.0 J center dot kg-1 center dot K-1 and 96.8 J center dot kg-1 in 0-5 T, respectively as compared to 4.2J center dot kg-1 center dot K-1 and 66.9 J center dot kg-1 for the commercial Tm2O3. Further increasing the BM time to 12h, the OV content almost remains unchanged, accompanied by a minor reduction of GSM and RC due to the decrease of grain size. This work provides a novel approach for enhancing the MCE of rare earth-based oxides.

Heavy rare-earth (RE)-based oxides possessing large magnetocaloric effect (MCE) have great application prospects in ultra-low-temperature magnetocaloric cooling. However, their large MCE based on the antiferromagnetic (AFM) ordering of heavy RE ions were generally obtained under high magnetic field changes. In this work, light RE-based tetragonal NaNd1-xEuxO2 (x = 0, 0.05, 0.1) compounds (I41/amd space group) were prepared by a facile ball-milling assisted sintering method. These oxides exhibit a second-order ferromagnetic (FM) to paramagnetic transition (PM) transition at the Curie temperature (TC) of 2.4 K to below 2 K, which is accompanied by an excellent low-field magnetocaloric cooling performance. In 0-1 T, a large magnetic entropy change GSM of 7.7, 7.6 and 7 J kg-1 K-1 was obtained at 2.5 K in NaNd1-xEuxO2 for x = 0, 0.05 and 0.1, respectively. These values are approximately twice as much as that for the commercial gallium gadolinium garnet (GGG) material (3.9 J kg-1 K-1, at 2 K). More favorably, these compounds show negligible coercivity and hysteretic loss, indicating reversibility of the large MCE. Eu3+ doping leads to a decrease of both the lattice constants and lengths of the Nd-O and Na-O bonds, accompanied by a lowering of TC and a decrease of effective magnetic moments of the RE3+. The excellent low-field MCE in the light RE-based FM oxides provides a novel insight for exploring suitable cryogenic magnetic refrigeration materials.

Ni44.1Fe33.2Ga22.8 (NFG) Heusler alloy nanowires were fabricated using a pulsed electrodeposition method. The challenge of co-depositing the Ga element in ternary alloy nanowires was addressed by employing dual complexing agents, high current, and high Ga ion concentrations. The nanowire structure was confirmed to be the B2 phase through XRD and TEM analyses. Furthermore, elemental mapping and multiple-point EDS measurements verified the homogeneous composition distribution within the nanowires. The nanowires exhibited diameters of approximately 70 nm and lengths ranging from 3 to 5 μm. The magnetic properties, including M-H and M-T dependencies, Landé g-factor, and saturation magnetization (Ms), were characterized using a vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) techniques. No martensitic transformation was observed in the nanowires within the temperature range of 80 to 370 K. Ultimately, this work provides a fabrication strategy for the co-deposition of elements with significant potential differences in multi-component alloy electrodeposition systems.

Rare-earth (RE) based oxides have presented great application prospects in low-temperature magnetic refrigeration technology. Thus far, studies on magnetic and especially magnetocaloric properties of alkali-metal RE oxides are limited, largely due to the difficulty in synthesizing these oxides. In this work, NaREO2 (RE = Er, Ho) compounds with both the rhombohedral (R 3 m space group) and cubic (Fm 3 m space group) structures were prepared by a facile ball-milling-aided sintering approach. The cubic structural compounds exhibit a spherical microstructure composed of vertically-grown irregular hexahedra, which sharply contrast with a loose lamellar microstructure of the rhombohedral structural compound. The as-prepared NaHoO2 or NaErO2 compound exhibits an antiferromagnetic ordering of RE3+ moments at a temperature of 2.4 K or lower than 2 K respectively. An excellent comprehensive magnetic refrigeration performance at cryogenic temperatures in a low magnetic field change of 0-20 kOe was obtained in these compounds, including a complete reversibility of the magnetocaloric effect, a maximal magnetic-entropy change Delta SM at 2 K of 12 J/kg center dot K for the rhombohedral NaErO2 and a relative cooling power (RCP) of 79.7 J/kg for the cubic NaHoO2.

La(Fe,Si)13 is a candidate room temperature magnetic refrigeration material owing to its large magnetocaloric effect and an adjustable Curie temperature. The structure, magnetocaloric effect, and mechanical properties of La(Fe,Si)13 strongly depend on its microscopic atomic environment. Proportional doping of magnetic or ductile elements can improve its magnetocaloric and mechanical properties. Here, magnetocaloric effect, and mechanical properties of Al-doped La(Fe,Si)13 alloys were studied through density functional theory calculations and experiments. The experimental results show that the doping of Al can increase the Curie temperature of the alloy, broaden the full width at half maximum (FWHM) and improve the mechanical properties of the alloy. The density functional theory describes the magnetic transition and mechanical behavior of the alloy, which is consistent with the experimental results. Therefore, the appropriate doping of Al in La(FeSi)13 alloy can obtain good integrated refrigeration capacity, which is helpful to realize multi-stage refrigeration application in a wide temperature range.

This paper focuses on the magnetocaloric effect (MCE) of Gd20Tb20Er20Al20M20 (M = Fe, Co) high-entropy metallic glasses (HE-MGs). XRD and TEM results indicate that both HE-MGs are amorphous. Magnetic studies show that both HE-MGs display spin-glass behavior, undergo a second-order phase transition from ferromagnetic to paramagnetic, and exhibit soft magnetic properties at the Curie temperature (T-C). Notable large and broad table-like magnetic entropy change characteristics of Gd20Tb20Er20Al20Fe20 (Gd20Tb20Er20Al20Co20) appear near a T-C of 92 (51) K. Hence, under 7 T magnetic field, |-triangle S-M(max)|, triangle T-FWHM, and RCP are 7.83 (10.10) Jkg(-1)K-1, 120.07 (71.88) K, and 1008.26 (805.70) Jkg(-1), respectively. Furthermore, the modulation of the magnetic and magnetocaloric properties of the samples after substitution of Fe for Co was revealed by the intricate 3d-3d and 3d-4f exchange interactions within the system. The magnetic phase transition critical behaviors in both HE-MGs were analyzed using the scaling law to clarify the deviation of amorphous materials from the mean-field theory. Thus, this study not only highlights the potential of this material for low-temperature magnetic refrigeration applications, but also expands our understanding of its physical properties.

In this study, La0.75Sr0.25Mn1−xCoxO3 (x = 0, 0.1, 0.2) samples were synthesized using a high-pressure heat treatment method, and their magnetic properties and critical phase transition behaviors were systematically investigated. The prepared samples exhibited excellent single-phase characteristics with space group R 3¯ c. As the Co content increased, TC decreased from 325 to 211 K. In a 7 T magnetic field, the RCP values of the samples increased from 364.52 to 384.66 J·kg−1, significantly enhancing the cooling efficiency of the samples. The three samples exhibited a second-order phase transition, indicating a relatively small hysteresis in the system. The critical exponents were obtained by MAPs and K-F method. These results indicate that with an increase in Co doping, the β values also increase, suggesting that Co doping facilitates the establishment of long-range ferromagnetic order in the three samples.

High entropy amorphous alloys (HE AMs) have attracted extensive interest lately due to their superior magnetocaloric properties. However, the critical behavior and mechanical properties have received less research, which restricts their applications. This work presented a comprehensive investigation of the magnetocaloric effect (MCE), critical behavior, and mechanical performance of quinary Gd20Dy20Er20Al20M20 (M = Fe, Co, Ni) HE AMs. All samples exhibited distinct spin glass-like behavior below TC and competitive MCE around hydrogen liquefaction temperature range. Excellent MCE was achieved by the HE AMs through a second-order phase transition from paramagnetic state to ferromagnetic state at 79 K for Fe, 41 K for Co, and 36 K for Ni. Among them, the maximum magnetic entropy change (-ΔSM)max of Gd20Dy20Er20Al20Co20 amorphous alloys was 9.59 J kg−1 K−1 under 0–5 T. Furthermore, RC and RCP of Gd20Dy20Er20Al20Fe20 amorphous alloys were respectively 519 J kg−1 and 613 J kg−1, larger than that of most RE-based amorphous alloys. For all samples, the critical behavior of the phase transition approached the mean field model, and this responded to the long-range ordering of the magnetic interaction. The bending plasticity of Gd20Dy20Er20Al20M20 (M = Fe, Co, Ni) HE AMs were 0.78, 1.03, 0.89, respectively. The adjustable Tc, large (-ΔSM), high RCP, and outstanding mechanical properties suggested Gd20Dy20Er20Al20M20 (M = Fe, Co, Ni) HE AMs may find utility as magnetic refrigerants in low-temperature applications.

LaFe 11.8 Si 1.2 /10 wt%Ce 60 Co 40 composites were prepared by spark plasma sintering and subsequent diffusion annealing. A novel core-shell structure is observed with the LaFe 11.8 Si 1.2 particles as the core and the (La,Ce) 2 (Fe,Co,Si) 17 (2:17) phase as the shell. As diffusion annealing time ( t a ) increases, this core-shell structure is replaced by the formation of the (La,Ce) 1 (Fe,Co,Si) 13 phase. Annealing at 1323 K for 12 h results in samples with (- D S M ) max of 9.30 J/(kg center dot K) ( D m 0 H = 2 T), good mechanical properties (( s bc ) max = 402 MPa, epsilon = 4.21%) and thermal conductivity of 8.7 W/(m center dot K). Thus, bulk composites with excellent comprehensive properties for magnetic refrigeration are obtained in this work. (c) 2023 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.