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Pyrochlore oxides, specifically G d 2 Z r 2 O 7 , have been a subject of interest due to their unique structural, physical, and magnetic properties. These properties make pyrochlore oxides potential candidates for various technological applications, including magnetocaloric refrigeration. Magnetocaloric refrigeration is a promising alternative to conventional refrigeration methods, as it is more energy-efficient and environmentally friendly. By studying the magnetocaloric effect of pyrochlore oxides like G d 2 Z r 2 O 7 , researchers can gain a deeper understanding of the underlying mechanisms and potential applications of these materials in magnetocaloric refrigeration systems. By employing advanced computational methods such as Monte Carlo simulations and first-principles calculations based on the full-potential linearized augmented plane wave (FP-LAPW) a technique is employed to examine the magnetic structure, researchers can investigate the magnetocaloric effect of pyrochlore oxides with high accuracy and precision. This information has the potential to aid in the advancement of more effective magnetocaloric systems materials and ultimately lead to the design and optimization of advanced magnetocaloric refrigeration systems. [ABSTRACT FROM AUTHOR]

The magnetization processes and magnetocaloric effect (MCE) of molecular magnets are studied using the quantum Heisenberg model with the goal of finding magnetic structures with optimal magnetocaloric properties. To fulfill this goal, we examine the influence of various factors such as quantum fluctuations, the magnitude and distribution of spins, the cluster size and its geometry on the conventional (cooling) and inverse (heating) MCE. We find, surprisingly, that the best cooling and heating effects are observed in the Ising limit on the smallest possible molecular clusters represented by dimers and trimers. The increasing Heisenberg interaction suppresses both the cooling as well as heating effects, but while the heating is reduced very strongly, for relatively small values of the anisotropic Heisenberg constant, the cooling effects are reduced only weakly. Since the heating effect is undesired in low-temperature refrigeration, the Heisenberg limit is also interesting from a practical point of view. Moreover, we find that spin distributions also have a significant influence on the magnetocaloric properties of molecular magnets. Specifically, configurations with large spins on the edges of the finite chain significantly enhance the cooling effect. [ABSTRACT FROM AUTHOR]

The magnetic properties of Ho6MnBi2 and Ho6FeBi2 crystals are investigated by means of density functional theory. These materials are currently an active subject of research in the context of magnetic refrigeration applications since they exhibit a remarkable magnetocaloric effect. In this work, the equation of state, density of states and magnetic moments are calculated and compared with previous experimental results for these materials. Also, the Curie temperatures for the paramagnetic to ferromagnetic phase transition observed in these systems are calculated from first principles. All the calculated quantities are in reasonable agreement with experimental data, which suggests that density functional theory could provide a reliable framework to theoretically investigate the magnetic properties of intermetallic ternary compounds. [ABSTRACT FROM AUTHOR]

Within Monte Carlo simulation in conjunction with the Metropolis method was used to investigate the magnetocaloric effect in the promising a two-layer system made up of spin S a and spin S b and having an AABB structure was characterized. The behavior of the isothermal magnetic entropy, the adiabatic temperature change is obtained, the relative cooling power was determined for the two-layer systems consisting of spins evaluated by S a and S b in each layer taking values in the rang (3/2,2,5/2,3,7/2). In recent years, the experimental behavior of double peaks for bilayer systems theoretically has been established, and an explanation is provided. Aside from that, the conditions that led to the change in behavior from double peak to single peak were gathered and examined. The relationship between spin value and isothermal magnetic entropy also the magnitude of the exchange contact between two layers was discovered. This article provides an updated view. [ABSTRACT FROM AUTHOR]

Two binuclear Gadolinium(III) (Gd) complex [Gd2(L1)2(H2L3)2(NO3)2] (1) and [Gd2(L2)2(H2L3)2(NO3)2] (2) were obtained by using 2‐hydroxybenzaldehyde or 2‐hydroxy‐1‐naphthaldehyde, 2‐aminophenol, pyridin‐2‐ylmethanamine and Gd(NO3)3 ⋅ 6H2O in CH3CN (H2L1=(E)‐2‐((2‐hydroxybenzylidene)amino)phenol, H2L2=(E)‐1‐(((2‐hydroxyphenyl)imino)methyl)naphthalen‐2‐ol, H2L3=pyridin‐2‐ylmethanamine). Structural analysis suggests that all the ligands as protective units protect the central Gd(III) ions at the periphery. Magnetization studies exhibited magnetocaloric effect of 14.45 J ⋅ kg−1 ⋅ K−1 at 4 K under ΔH=7 T for complex 1 and 12.69 J ⋅ kg−1 ⋅ K−1 at 2 K under ΔH=7 T for complex 2. In complexes 1 and 2, although the coordination configurations are the same, the significant difference in MCE may be due to the adjustments of the peripheral ligands leading to changes in the coordination field strength. The electron affinity of the ligands can impact the interaction between the ligands and Gd(III) ions. [ABSTRACT FROM AUTHOR]

Three novel polymeric Mn(II) acetate derivatives, identified as {[Mn2.5(OH)(CH3COO)4] ⋅ 0.5CH3OH ⋅ 0.5CH3CN}n (1), {[Mn3(CH3CO O)6] ⋅ 0.5CH3CN}n (2) and {Mn1.5K(CH3COO)4}n (3), have been successfully prepared by systematically adjusting the ratio of reactants and using the 2‐mercapto‐5‐methyl‐1,3,4‐thiadiazole (Hmmt) as the template agent. These three complexes can be regarded as the different crystalline forms of Mn(CH3COO)2 under different reaction conditions. Single‐crystal X‐ray diffraction analyses revealed that 1 and 2 feature the unique three‐dimensional (3D) framework. For 3, it displays a 2D structure, which is further assembled to form a 3D extended network via the weak hydrogen bond interactions. Magnetic studies confirmed that 1 and 2 show antiferromagnetic interactions, and 1 displays a long‐range ordering phase below the critical temperature (Tc) of 7.8 K. In addition, magnetisation data collected for 1–2 yield low magnetic entropy changes, which can be attributed to the strong antiferromagnetic interactions among the Mn(II) centres. [ABSTRACT FROM AUTHOR]

This work aims to investigate the structural stability, magnetic and electronic properties of M3AlC antiperovskites using density functional theory (DFT) and Monte Carlo simulation. The obtained ground state results reveal that the antiperovskites M3AlC are stable in the ferromagnetic (FM) state with a metallic character. The calculated total magnetic moments are 5.21 μ B and 3.34 μ B for Mn3AlC and Fe3AlC, respectively, with the total moments mainly from the M atom. The ferromagnetic behavior is confirmed by computing the density of state at Fermi level and verified the Stoner criterion. The magnetic and magnetocaloric behavior of M3AlC is investigated using Monte Carlo simulation and the obtained results demonstrate that the transition from ferromagnetic to paramagnetic state occurs at T C = 3 0 0 K and T C = 2 3 0 K for Mn3AlC and Fe3AlC, respectively. These values of T C are in good agreement with the experimental results. The magnetocaloric effect and critical behavior are studied and the obtained values of magnetic entropy change | Δ S mag | at 4.5 T is about 4.242 J/kg.K and 3.666 J/kg.K and the relative cooling power (RCP) are 342.434 J/kg.K and 325.26 J/kg.K for Mn3AlC and Fe3AlC at 4.5T, indicating that these compounds are more appropriate for magnetic refrigeration. Finally, the critical exponents (β , γ , δ) are calculated and the obtained values are close to the values of mean-field model. [ABSTRACT FROM AUTHOR]

Many exciting effects resulting from the coupling of magnetic sublattice with a magnetic field, may be exposed by changing the field. One such phenomenon is the magnetocaloric effect, which is characterized by the absorption or emission of heat in response to changes in the external magnetic field. Magnetic refrigeration based on the magnetocaloric effect has emerged as an attractive alternative to conventional cooling technology that relies on gas compression and expansion. It is not only more efficient and environmentally friendly, but it can also be implemented across a broad temperature range, from ultra-low to a few hundred Kelvin temperatures. One of the areas where magnetic cooling can have a significant impact is hydrogen liquefaction. Hydrogen is one of the most promising candidates for clean energy sources, but it must be liquefied to facilitate storage and transportation, which requires cooling it down to ∼20 K. The ideal magnetic refrigerant should exhibit consistent magnetocaloric properties across the entire operating temperature range of a cooler. This paper presents novel three-layer composite magnetic refrigerants that provide a uniform magnetocaloric response over a 30 K temperature range. The selected initial HoNi 2 , DyNi 2 , and TbNi 2 magnetic intermetallic compounds with a Laves phase structure exhibit large magnetocaloric properties in the temperature range of 13–37 K. The composite composition of 23.56 wt% HoNi 2 + 18.21 wt% DyNi 2 + 58.23 wt% TbNi 2 optimized for 2 T magnetic field change, was determined through numerical approach. The composites are manufactured using spark plasma sintering (SPS) and innovative high-isostatic-pressure (HIP) synthesis. The results of isothermal entropy change derived from magnetization data for a 2 T magnetic field change indicated 4.7 J/kgK (47.2 mJ/cm3K) and 4.4 J/kgK (44.2 mJ/cm3K) in the temperature range of approx. 13–42 K for composites after SPS and SPS + HIP processes, respectively. Despite the sample subjected to HIP showing slightly lower results, the entropy change is nearly uniform over the 30 K temperature range due to enhanced atomic diffusion between neighboring compounds, as confirmed by microscopic studies. Such a uniform magnetocaloric response in ∼30-K temperature range has never been observed before in layered refrigerants. By utilizing the innovative high-isostatic-pressure synthesis technique, we have paved the way to high-performing magnetic composite materials that can be used in cryogenic magnetic coolers operating over a broad temperature span, expanding the possibilities of what can be achieved and laying the foundation for cost-effective, clean hydrogen energy. [Display omitted] • Layered HoNi2 + DyNi2 + TbNi2 composites are investigated. • Spark plasma sintering (SPS) and high-isostatic-pressure (HIP) synthesis are used. • Both SPS and SPS + HIP samples provide similar magnetic entropy changes over a 30 K. • HIP improves uniformity of magnetic entropy changes. [ABSTRACT FROM AUTHOR]

Current inspection strives to perform a detailed elaboration of the Tsallis entropy‐based magnetocaloric effect (MCE) of GaAs quantum dot (QD) doped with Gaussian impurity and under applied Gaussian white noise. Noise takes additive and multiplicative pathways for its entry to the doped QD. MCE has been found to decrease following the enhancement of temperature. The enquiry manifests magnetic field‐induced confinement and consequent decline in the disorder of the system during the gradual variation of several physical parameters. However, harnessing the extent of above confinement involves extremely sensitive and delicate control over the resultant influence of the particular physical parameter undergoing change, its range of magnitude, application of noise and its mode of inclusion. Importantly, MCE has been found to maximize only during the change in the strength of the dopant potential under multiplicative noise. And, on most occasions, multiplicative noise profoundly raises the MCE over its value under the state devoid of noise and under additive noise. [ABSTRACT FROM AUTHOR]

We study the structural, magnetic, and magneto-thermal properties of the GdRhIn compound. The room-temperature X-ray diffraction measurements show a hexagonal crystal structure. Temperature and field dependence of magnetization suggest two magnetic transitions—antiferromagnetic to ferromagnetic at 16 K and ferromagnetic to paramagnetic at 34 K. The heat capacity measurements confirm both the magnetic transitions in GdRhIn. The magnetization data were used to calculate isothermal magnetic entropy change and refrigerant capacity in GdRhIn, which was found to be 10.3 J/Kg-K for the field change of 70 kOe and 282 J/Kg for the field change of 50 kOe, respectively. The large magnetocaloric effect in GdRhIn suggests that the material could be used for magnetic refrigeration at low temperatures. [ABSTRACT FROM AUTHOR]

The critical behavior and the magnetocaloric effect have been researched in rare-earth perovskite EuTiO 3 . Using classical Monte Carlo method, we simulate the phase transition behavior of EuTiO 3 on the Heisenberg model with uniaxial anisotropy and obtain the phase transition temperature T n = 5.4 K, which is almost consistent with the experimental results. The entropy change under isothermal Δ S and temperature change under adiabatic Δ T ad are calculated for different external magnetic fields. The results of the relative cooling power (RCP) are linear with the magnetic field. The critical exponents β =0.269, γ =1.250, and δ =5.602 are obtained by the power laws. These results are almost identical to those calculated using the MCE scaling law. [ABSTRACT FROM AUTHOR]

By simulating the thermomagnetization of Ba(Fe1-xScx)12O19 from approximately 100 to 750 K, the magnetocaloric effect (MCE) in Ba(Fe1-xScx)12O19 samples is approximated. Intriguingly, the thermomagnetic property of the undoped sample BaFe12O19 is described as a conventional MCE for high temperatures. However, at doping levels x of 0.128, 0.153, and 0.189, respectively, the thermomagnetic property of Sc-doped samples is defined as an inverse MCE below temperatures of 163, 239, and 318 K. In contrast, thermomagnetic property of Ba(Fe1-xScx)12O19 is described as conventional MCE above those temperatures. Additionally, Sc doping makes it possible for MCE in Ba(Fe1-xScx)12O19 to be strongly tailored. This is helpful for operating a magnetic refrigerator (MR) which occurs in various temperature ranges and results in a higher working temperature range. A promising function for Ba(Fe1-xScx)12O19 samples in MR at high-temperature applications in the automotive and food industries or aerospace. [ABSTRACT FROM AUTHOR]

Magnetic refrigeration based on magnetocaloric effect (MCE) has become a promising cooling technology to replace the traditional vapor compression refrigeration. However, traditional methods for searching MCE materials require producing many different compositions, causing unbearable workload and long experimental periods. Here, 3D printed La0.7Ce0.3Fe11.65Si1.35–Fe compositionally gradient alloys (CGAs) are successfully prepared using laser powder bed fusion equipped with a powder hopper with dual‐bin structure. This CGAs accelerate the high‐throughput screening for the best composition of La(Fe, Si)13/Fe with both high MCE and mechanical properties. The good interfacial compatibility between brittle 1:13 phase and reinforcing α‐Fe improves the mechanical properties significantly. Even after hydrogenation, the compressive strength and ultimate strain of the La(Fe, Si)13/Fe hydrides are ≈220% and ≈150% higher than those of stoichiometric La(Fe, Si)13. Meanwhile, the hydrogenated composite exhibits a large MCE under low magnetic field, e.g., the magnetic entropy change |ΔSM|max of 7.6 J kg−1 K−1 under 2 T is 52% higher than that of the benchmark Gd (5.0 J kg−1 K−1). Furthermore, this La(Fe, Si)13/Fe is 3D printed into various complex shapes suitable for heat exchangers. This study provides an innovative strategy for high‐throughput screening of new materials. [ABSTRACT FROM AUTHOR]

The critical behavior and the magnetocaloric effect have been researched in rare-earth perovskite EuTiO 3 . Using classical Monte Carlo method, we simulate the phase transition behavior of EuTiO 3 on the Heisenberg model with uniaxial anisotropy and obtain the phase transition temperature T n = 5.4 K, which is almost consistent with the experimental results. The entropy change under isothermal Δ S and temperature change under adiabatic Δ T ad are calculated for different external magnetic fields. The results of the relative cooling power (RCP) are linear with the magnetic field. The critical exponents β =0.269, γ =1.250, and δ =5.602 are obtained by the power laws. These results are almost identical to those calculated using the MCE scaling law. [ABSTRACT FROM AUTHOR]

By simulating the thermomagnetization of Ba(Fe1-xScx)12O19 from approximately 100 to 750 K, the magnetocaloric effect (MCE) in Ba(Fe1-xScx)12O19 samples is approximated. Intriguingly, the thermomagnetic property of the undoped sample BaFe12O19 is described as a conventional MCE for high temperatures. However, at doping levels x of 0.128, 0.153, and 0.189, respectively, the thermomagnetic property of Sc-doped samples is defined as an inverse MCE below temperatures of 163, 239, and 318 K. In contrast, thermomagnetic property of Ba(Fe1-xScx)12O19 is described as conventional MCE above those temperatures. Additionally, Sc doping makes it possible for MCE in Ba(Fe1-xScx)12O19 to be strongly tailored. This is helpful for operating a magnetic refrigerator (MR) which occurs in various temperature ranges and results in a higher working temperature range. A promising function for Ba(Fe1-xScx)12O19 samples in MR at high-temperature applications in the automotive and food industries or aerospace. [ABSTRACT FROM AUTHOR]

In this study, La0.63Sr0.2Nd0.17MnO3 was synthesized by the sol-gel method, and its structural, morphological, magnetic, and magnetocaloric effects were investigated. The structural properties were analyzed by x-ray diffraction (XRD), and scanning electron microscopy (SEM) was used to characterize the morphology. An integrated magnetic measurement system was used to determine the magnetic properties. La0.63Sr0.2Nd0.17MnO3 crystallized in a hexagonal crystal system with space group R-3c. This was also confirmed by Rietveld refinement of the x-ray data from La0.63Sr0.2Nd0.17MnO3. With the doping of Nd3+, the cell volume decreases, which can be explained by the angles and bond lengths of the bonds between the Mn and O ions and the distortion of the lattice. Near the Curie temperature, La0.63Sr0.2Nd0.17MnO3 exhibits significant magnetocaloric effects. The magnetic study of La0.63Sr0.2Nd0.17MnO3 suggests that the transition from the paramagnetic to ferromagnetic phase can occur near the Curie temperature. The maximum magnetic entropy change and relative cooling power (RCP) of La0.63Sr0.2Nd0.17MnO3 (298 K, 3 T) are 2.70 J/(kg K) and 135 (J/kg), respectively. The effect of f-orbitals on the magnetic properties of La0.8Sr0.2MnO3 was investigated by first-principles calculations in density functional theory. Thus, it can be concluded that the magnetocaloric effects of the material after doping with f-orbital ions (Nd3+) is enhanced compared to La0.8Sr0.2MnO3. [ABSTRACT FROM AUTHOR]

This study investigates the critical behavior analysis and predicting magnetocaloric properties of La0.6-xGdxSr0.4MnO3 manganites, focusing on the impact of varying gadolinium (Gd) doping levels (x = 0, 0.0125, 0.05, and 0.10). Using modified Arrott plots (MAPs) and the Kouvel–Fisher method, the critical exponents γ and β were determined, yielding values that indicate how Gd content influences magnetic phase transitions. Additionally, the magnetocaloric effect (MCE) was analyzed to assess the magnetic entropy change − Δ S M (T) and the Temperature-Averaged Entropy Change (TEC) across different magnetic field changes. The results show that increasing Gd doping enhances the magnetocaloric response, suggesting potential applications in magnetic refrigeration. Overall, the study provides insights into optimizing these manganites for applications in high-temperature sensors, spintronics, and magnetic cooling. Highlights: Using modified Arrott plots (MAPs) and the Kouvel–Fisher method, the critical exponents γ and β of La0.6-xGdxSr0.4MnO3 (x = 0, 0.0125, 0.05, and 0.10) manganites were derived. The magnetocaloric effect (MCE) was analyzed to assess the magnetic entropy change − Δ S M (T) and the Temperature-Averaged Entropy Change (TEC) across different magnetic field changes. [ABSTRACT FROM AUTHOR]

Rare earth elements possessing a diverse range of optical, electrical, and magnetic properties has attracted more attention. In the present work, GdClWO 4 compound with monoclinic structure was prepared, the structure, magnetism and magnetocaloric effect (MCE) were investigated. The magnetic phase transition temperature (T N), magnetic ground state and maximum magnetic entropy change ( − Δ S M max) were derived from magnetization measurements. Both first principles calculation and experimental results suggest that the compound displays antiferromagnetic (AFM) interactions, with a magnetic transition occurring at 0.6 K, shifting from a paramagnetic (PM) state to an AFM state. The − Δ S M max is up to 35.2 J kg−1 K−1 (205.9 mJ cm−3 K−1) for GdClWO 4 at T = 1.3 K under a magnetic field change of 0–50 kOe. In particular, the volumetric magnetic entropy change still remains 83.1 mJ cm−3 K−1 at 0.5 K and μ 0 Δ H = 20 kOe, which is almost twice as much as that of commercial refrigerant Gd 3 Ga 5 O 12 (GGG) under μ 0 Δ H = 20 kOe, establishing GdClWO 4 compound as a potential candidate for cryogenic refrigeration applications. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect has been extensively investigated in various types of magnetic solids to not only develop practical magnetic cooling applications but also deepen the understanding of these materials' underlying inherent properties. Through experimental determination and theoretical calculation, we conducted a systematic investigation of Gd 4 Ga 2 O 9 oxide in terms of its structural, magnetic, and magnetocaloric properties and found it to crystallize in a monoclinic structure belonging to the space group P 2 1 / c and to possess an antiferromagnetic semiconducting ground state. The consistent elements were uniformly distributed up to the nanoscale and presented as Gd3+, Ga3+, and O 2 states, respectively. The magnetocaloric performances of Gd 4 Ga 2 O 9 oxide were checked according to the parameters of maximum magnetic entropy change, refrigerant capacity, and temperature-averaged entropy changes (lift of 5 K), which were determined to be 25.77 J/kgK, 218.27 J/kg, and 23.43 J/kgK under 0–7 T magnetic field change. These parameters of Gd 4 Ga 2 O 9 oxide are comparable to those of some recently reported materials with prominent performances, which means that it can be considered for cryogenic magnetic cooling applications. [ABSTRACT FROM AUTHOR]

The concept of high-entropy oxides/alloys was introduced into the rare-earth orthoferrite (R FeO 3 , R represents a rare-earth ion) system. Doping five different rare-earth ions with equal molar ratios at the R -site, a single crystal of high-entropy orthoferrite (Y 0.2 Sm 0.2 Eu 0.2 Gd 0.2 Er 0.2)FeO 3 (HERFO) was synthesized using optical floating zone method. At high temperatures, the weak ferromagnetic (wFM) moments induced by the distortion of the Fe sublattices align along the c axis, with a spin configuration of Γ 4. As the temperature decreases, a spin reorientation transition (SRT) occurs from Γ 4 to Γ 2 due to the Fe3+- R 3+ super-exchange interactions, with an immediate state Γ 24. The wFM moments gradually rotate from the c axis to the a axis within the ac plane. In the zero-field-cooling (ZFC) mode, both the type-I and type-II spin switching (SSW) are observable along the a axis. Under low magnetic fields, the type-II SSW is magnetically controlled. The trigger temperature and variation in net moment of the type-II SSW exhibit systematic changes concerning the applied magnetic field. The rich magnetic phase transitions in HERFO make it a promising candidate for spintronic applications aimed at spin manipulation. Additionally, HERFO single crystal exhibits a large magnetocaloric effect (MCE) and magnetic entropy anisotropy, with the negative magnetic entropy change (‐ Δ S m) along the c axis (14.45 J/(kg·K)) being greater than that along the a and b axes (9.57 J/(kg·K) and 10.32 J/(kg·K)). Consequently, HERFO holds great promise as a novel material for magnetic refrigeration applications aimed at achieving rotational magnetic cooling. [ABSTRACT FROM AUTHOR]

This article summarizes the impact of the Ti ion at the Mn site of polycrystalline Sm0.5Sr0.4Nd0.1MnO3 samples, exploring the correlation between the structural, microstructural, magnetic, and magnetocaloric properties through the solid‐state route. The Rietveld refinement pattern divulges that all samples are crystallized predominantly in the orthorhombic phase with the Pnma space group. Temperature‐dependent magnetic studies of Sm0.5Sr0.4Nd0.1Mn1‐xTixO3 (x=0, 0.1, 0.2) expose phase separation phenomena in the field cooling curve, where the first peak at 42 K corresponds to the antiferromagnetic charge ordering or spin orientation of spontaneous magnetization, and the second peak at 87 K, 75.91 K, and 74.28 K corresponds to the paramagnetic to ferromagnetic transition. The maximum magnetic entropy changes (ΔSM) at T=110 K are discerned to be 2.5 J Kg−1 K−1, 1.65 J Kg−1 K−1, and 1.31 J Kg−1 K−1, respectively. Normalization of ΔS values in Sm0.5Sr0.4Nd0.1Mn1‐xTixO3 (x=0, 0.1, 0.2) does not overlap the universal behavior at magnetic fields (1T ‐ 7T), confirming the existence of field‐induced second‐order magnetic transitions. The relative cooling power (RCP) values are found to be 777.96 J Kg−1, 255.28 J Kg−1, and 190.58 J Kg−1 respectively. Further, the enhancement of the working span temperature and the broadening of specific heat capacity peaks in Sm0.5Sr0.4Nd0.1Mn1‐xTixO3 (x=0.1, 0.2) samples make these materials a promising candidate to serve as operating substances in magnetic refrigeration. [ABSTRACT FROM AUTHOR]

Advancements and utilization of magnetic refrigeration technology hinge on the ongoing enhancement and optimization of magnetic refrigeration material properties. Nevertheless, the intricacy of the magnetocaloric effect (MCE) mechanism has emerged as a bottleneck, constraining the progress and refinement of magnetic refrigeration materials. In this study, a classic magnetic system is chosen to investigate the mechanism of MCE across four different scales–macroscopic magnetism, micrometer‐scale magnetic domains, atomic magnetic moments, and electronic structure. It simultaneously exhibits two inverse MCEs and one direct MCE, with a working temperature span as wide as 125 K (most are <50 K) for the direct MCE. The measurements of the vibrating sample magnetometer, in situ Lorentz electron microscopy and variable‐temperature neutron powder diffraction directly reveal that the complex magnetic entropy changes arise from the magnetic domain wall pinning, the instability of Ho magnetic moments, and the spin rotation. First‐principles calculations elucidate the crucial role of strong hybridization between localized Ho and itinerant Co electrons in the spin reorientation of HoCo4Al. This study contributes significantly to comprehending the induction mechanism of the MCE and holds vital reference value for exploring new magnetic refrigeration materials and enhancing MCE performance. [ABSTRACT FROM AUTHOR]

In order to improve the magnetocaloric properties of MnNiSi-based alloys, a new type of high-entropy magnetocaloric alloy was constructed. In this work, Mn0.6Ni1−xSi0.62Fe0.4CoxGe0.38 (x = 0.4, 0.45, and 0.5) are found to exhibit magnetostructural first-order phase transitions from high-temperature Ni2In-type phases to low-temperature TiNiSi-type phases so that the alloys can achieve giant magnetocaloric effects. We investigate why chexagonal/ahexagonal (chexa/ahexa) gradually increases upon Co substitution, while phase transition temperature (Ttr) and isothermal magnetic entropy change (ΔSM) tend to gradually decrease. In particular, the x = 0.4 alloy with remarkable magnetocaloric properties is obtained by tuning Co/Ni, which shows a giant entropy change of 48.5 J∙kg−1K−1 at 309 K for 5 T and an adiabatic temperature change (ΔTad) of 8.6 K at 306.5 K. Moreover, the x = 0.55 HEA shows great hardness and compressive strength with values of 552 HV2 and 267 MPa, respectively, indicating that the mechanical properties undergo an effective enhancement. The large ΔSM and ΔTad may enable the MnNiSi-based HEAs to become a potential commercialized magnetocaloric material. [ABSTRACT FROM AUTHOR]

This study presents a new single-step synthesis of Fe 2 AlB 2 at 1150°C for 4 hours using hot isostatic pressing (HIPing). X-ray diffraction confirmed the material as single-phase, while metallographic etching revealed predominant equiaxial Fe 2 AlB 2 grains (∼25 μm) and minor unreacted boron particles and Al-rich zones at grain boundaries. Magnetocaloric investigations demonstrated an impressive isothermal entropy change of 2.9 J/kg.K at 2 T and 6.8 J/kg.K at 5 T, with corresponding adiabatic temperature changes of 1.1 K and 2.8 K at 2 and 5 T, respectively. The HIPed Fe 2 AlB 2 performance matches that of studies without post-treatments or doping. Fe 2 AlB 2 , composed of light and earth-abundant elements, can be synthesized in a single step using HIPing, making it an attractive option for magnetic refrigeration with improved energy efficiency and simplified manufacturing. • Successful synthesis of Fe2AlB2 through a single-step reactive hot isostatic pressing (HIPing) process. • Utilization of a 0.005 M NaOH + 0.01 M NaOCl solution for metallographic etching to reveal grain boundaries. • Equiaxial Fe2AlB2 grains (∼ 25 μm) in with Al enrichment at grain boundaries and a modest presence of unreacted B particles. • Magnetocaloric Effect (MCE) measurements show a -ΔSM of 2.9 and 6.8 J/kg·K at 2 and 5 T, respectively. • Determination of the relative cooling power (RCP) values of 39 J/kg and 142 J/kg at 2 and 5 T, respectively. [ABSTRACT FROM AUTHOR]

This study presents the modelling of magnetocaloric effect of Pr0.67Sr0.33MnO3 nanoparticles by using the mean-field theory (MFT). Theoretical calculations were used around the Curie temperature (TC) to simulate the temperature dependence of magnetic entropy change under several applied magnetic fields. The obtained results were compared with experimental data computed using the Maxwell relation. Discrepancy between the two methods confirm the invalidity of MFT for modelling the magnetocaloric properties of Pr0.67Sr0.33MnO3 nanoparticles. This invalidity suggests the presence of critical fluctuations near the TC, which can be attributed to the presence of disordered surface and/or magnetic frustration, and highlights the limitation of the used model. [ABSTRACT FROM AUTHOR]

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.

Most of the ferromagnetic shape memory (FSM) Heusler alloys, which are primarily studied in bulk form in the literature, exhibit p-d type hybridization. This study conducts a thorough multidirectional investigation of a strongly d-d hybridized quinary melt-spun annealed ribbon having the composition Ni35Mn34.5Co14Fe1Ti15.5 (NMCFT-1). This off-stoichiometric, polycrystalline FSM, fabricated using the melt-spin technique, exhibits a highly textured microstructure, double magnetic transitions and super-mechanical features mitigating brittleness. It crystallizes in a perfectly B2-type disorder austenite (Pm-3m, space group number 221) phase at room temperature. It has been hypothesized that geometric frustration is the causative factor for this disorder. Curie temperature of austenite phase ( T C A ) between paramagnetic → ferromagnetic state is found to be ∼364.57 K, whereas martensite transformation temperature from weak magnetic martensite state to ferromagnetic austenite state is ∼174.74 K. Calculated moments (effective moment, μ eff = 5.12 μ B ; low-temperature saturation moment, μ S (or M S (0) ) = 5.08 μ B ) yield a Rhodes–Wohlfarth ratio of ∼1, indicating the existence of the non-itinerant nature of 3d electrons, whereas the ferromagnetism and the linear or non-linear dependency of M s 2 (T ) on T 2 around T C A indicates the presence of long-range Rudermann–Kittel–Kasuya–Yosida-type interaction. More importantly, the maximum magnetic entropy change ( Δ S m ) obtained across the first-order magneto-structural transition and second-order magnetic transition are +18.2 J·kg−1K−1 at 6 T and −8.8 J·kg−1K−1 at 2 T, respectively, while a very high working temperature span (Δ T FWHM) of 28.561 K and 6.922 K are found for the same condition. The sample exhibits a significant relative cooling power of 402.98 J·kg−1 at a magnetic field of 6 T across the FOMT and 60.19 J·kg−1 at a 2 T field across the SOMT, respectively, along with excellent mechanical features such as a Vickers hardness (HV) of 411.80 HV (∼4.04 GPa). Meanwhile, Chen's super hard model fails to predict the ribbon's HV value, but Miao's hard model does, indicating that the ribbon is hard but not super hard. It also paves the way for additional investigation into innovative FSMs like this. [ABSTRACT FROM AUTHOR]

Most of the ferromagnetic shape memory (FSM) Heusler alloys, which are primarily studied in bulk form in the literature, exhibit p-d type hybridization. This study conducts a thorough multidirectional investigation of a strongly d-d hybridized quinary melt-spun annealed ribbon having the composition Ni35Mn34.5Co14Fe1Ti15.5 (NMCFT-1). This off-stoichiometric, polycrystalline FSM, fabricated using the melt-spin technique, exhibits a highly textured microstructure, double magnetic transitions and super-mechanical features mitigating brittleness. It crystallizes in a perfectly B2-type disorder austenite (Pm-3m, space group number 221) phase at room temperature. It has been hypothesized that geometric frustration is the causative factor for this disorder. Curie temperature of austenite phase ( T C A ) between paramagnetic → ferromagnetic state is found to be ∼364.57 K, whereas martensite transformation temperature from weak magnetic martensite state to ferromagnetic austenite state is ∼174.74 K. Calculated moments (effective moment, μ eff = 5.12 μ B ; low-temperature saturation moment, μ S (or M S (0) ) = 5.08 μ B ) yield a Rhodes–Wohlfarth ratio of ∼1, indicating the existence of the non-itinerant nature of 3d electrons, whereas the ferromagnetism and the linear or non-linear dependency of M s 2 (T ) on T 2 around T C A indicates the presence of long-range Rudermann–Kittel–Kasuya–Yosida-type interaction. More importantly, the maximum magnetic entropy change ( Δ S m ) obtained across the first-order magneto-structural transition and second-order magnetic transition are +18.2 J·kg−1K−1 at 6 T and −8.8 J·kg−1K−1 at 2 T, respectively, while a very high working temperature span (Δ T FWHM) of 28.561 K and 6.922 K are found for the same condition. The sample exhibits a significant relative cooling power of 402.98 J·kg−1 at a magnetic field of 6 T across the FOMT and 60.19 J·kg−1 at a 2 T field across the SOMT, respectively, along with excellent mechanical features such as a Vickers hardness (HV) of 411.80 HV (∼4.04 GPa). Meanwhile, Chen's super hard model fails to predict the ribbon's HV value, but Miao's hard model does, indicating that the ribbon is hard but not super hard. It also paves the way for additional investigation into innovative FSMs like this. [ABSTRACT FROM AUTHOR]

Abstract This study investigates the utilization of Al2O3 nanofluids in an Active Magnetic Regenerative (AMR) system, focusing on varying nanoparticle concentrations from 0.01 to 1.0%. Numerical modelling is used to analyze the effects of nanoparticle incorporation on system efficiency and cooling performance. Al2O3 nanoparticles are found to significantly increase the thermal conductivity, density, and viscosity of the base fluid while reducing specific heat capacity. Comparative analysis reveals that Al2O3 nanofluids outperform pure water in terms of cooling performance, achieving a lower final temperature and a higher temperature span after 60 min of operation. Moreover, the study highlights that cooling capacity and pumping work increase with higher nanoparticle concentrations, with a notable improvement of 64.95% in cooling capacity and 39.31% in pumping work for the 1.0% Al2O3 nanofluid compared to water. The Coefficient of Performance (COP) of the AMR system peaks at an optimal nanoparticle concentration of 0.2%, reaching 3.88, before declining due to increased pumping power requirements.

This study investigates the utilization of Al2O3 nanofluids in an Active Magnetic Regenerative (AMR) system, focusing on varying nanoparticle concentrations from 0.01 to 1.0%. Numerical modelling is used to analyze the effects of nanoparticle incorporation on system efficiency and cooling performance. Al2O3 nanoparticles are found to significantly increase the thermal conductivity, density, and viscosity of the base fluid while reducing specific heat capacity. Comparative analysis reveals that Al2O3 nanofluids outperform pure water in terms of cooling performance, achieving a lower final temperature and a higher temperature span after 60 min of operation. Moreover, the study highlights that cooling capacity and pumping work increase with higher nanoparticle concentrations, with a notable improvement of 64.95% in cooling capacity and 39.31% in pumping work for the 1.0% Al2O3 nanofluid compared to water. The Coefficient of Performance (COP) of the AMR system peaks at an optimal nanoparticle concentration of 0.2%, reaching 3.88, before declining due to increased pumping power requirements. [ABSTRACT FROM AUTHOR]

The ternary transition metal boride Fe2AlB2 is a unique ferromagnetic "MAB" phase that demonstrates a sizable magnetocaloric effect near room temperature—a feature that renders this material suitable for magnetic heat pump devices (MHP), a promising alternative to conventional vapor compression technology. Here, we provide a comprehensive review of the material properties of Fe2AlB2 (magnetofunctional response, transport properties, and mechanical stability) and discuss alloy synthesis from the perspective of shaping these materials as porous active magnetic regenerators in MHPs. Salient aspects of the coupled magnetic and structural phase transitions are critically assessed to elucidate the fundamental origin of the functional response. The goal is to provide insight into strategies to tune the magnetofunctional response via elemental substitution and microstructure optimization. Finally, outstanding challenges that reduce the commercial viability of Fe2AlB2 are discussed, and opportunities for further developments in this field are identified. [ABSTRACT FROM AUTHOR]

We herein fabricated two gadolinium-transition metal-based high entropy (HE) oxides of Gd(Mn 0.25 Fe 0.25 Al 0.25 Cr 0.25)O 3 [denoted as Gd(4 TM 0.25)O 3 ] and Gd(Mn 0.2 Fe 0.2 Al 0.2 Co 0.2 Ni 0.2)O 3 [denoted as Gd(5 TM 0.2)O 3 ] and determined their structural, magnetic, and magnetocaloric properties. Both of present HE oxides are found to crystallize in the single-phase perovskite-type orthorhombic structure with a homogeneous microstructure and exhibit prominent cryogenic magnetocaloric performances. The values of magnetic entropy change, refrigerant capacity, and temperature-averaged entropy change (6K-lift) under the magnetic field change of 0–7 T are estimated to be 20.34 J/kgK, 295.4 J/kg, and 19.56 J/kgK for Gd(4 TM 0.25)O 3 , and to be 22.45 J/kgK, 258.2 J/kg, and 20.79 J/kgK for Gd(5 TM 0.2)O 3 , respectively, which are comparable with recently reported candidate materials for practical magnetic cooling. These findings not only indicate potential applications of present perovskite-type Gd(4 TM 0.25)O 3 and Gd(5 TM 0.2)O 3 HE oxides, but also provide meaningful clues for exploring HE oxides with prominent cryogenic magnetocaloric performances. [ABSTRACT FROM AUTHOR]

In the era of energy transition and climate change, environmentally safe refrigeration technologies are of utmost importance. Magnetocaloric refrigeration (MCR) is one of the most promising alternatives to the existing vapor-compression systems. Overcoming the primary challenges of the low heat dissipation and elevated device production costs is imperative for MCR development. This work provides the first demonstration of an MCR prototype that combines the magnetocaloric material (MCM) gadolinium with a ferrofluidic thermal switch (TS). The performance was assessed using dispersions of MnFe 2 O 4 /Ethylene Glycol:Water and Fe 3 O 4 /paraffin oil. For the first time, a strategic asymmetry was introduced into MCR cycles. The inclusion of the TS did not uncover any advantages in the Gd-alone system by using symmetrical cycles. However, by applying/removing the magnetic field asymmetrically, a remarkable temperature span of up to 0.6 °C was achieved within the TS+MCM prototype. This represents a substantial improvement, reaching up to 60% compared to the Gd-alone configuration. The prototype ensures that a single magnetic field, responsible for driving the magnetocaloric effect, also activates the TS, thereby streamlining system operability and improving performance. To validate our findings, we developed a 1D numerical model, which consistently confirmed that system optimization can be achieved through the exclusive use of asymmetric cycles. Consequently, the application of magnetically-activated fluidic TSs and asymmetric cycles emerge as important strategies for enhancing MCR across a diverse range of systems. • First experimental verification of a magnetocaloric refrigeration cycle coupled with a fluidic thermal switch. • The presence of ferrofluid significantly improves the rate of heat exchange when compared to gadolinium in isolation. • Asymmetric cycles promote a temperature span increase up to ∼ 60%. • Numerical calculations provide confirmation that employing asymmetric cycles is an effective means to optimize refrigeration efficiency. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect (MCE) of Ni48Mn39.5Sn9.5Al3 ribbon is simulated using a phenomenological model with possible uses in magnetic refrigeration (MR). In this work, both conventional and inverse MCEs associated with magnetic (ferromagnet-antiferromagnet) and structural (austenite–martensite) phase transitions are theoretically investigated. The results show that three associated peaks of the inverse and conventional MCEs are observed. It is recommended that magnets with triple peak MCE behaviour, such as Ni48Mn39.5Sn9.5Al3 ribbons, may offer an intriguing MR with a larger temperature-range than conventional refrigerant compounds, particularly Ni48Mn39.5Sn9.5Al3 ribbons, which are cheap to use in MR. Furthermore, the MCE values of Ni48Mn39.5Sn9.5Al3 ribbons are significantly higher than those of some magnetocaloric materials from previous studies. Consequently, Ni48Mn39.5Sn9.5Al3 ribbons are appropriate magnetocaloric magnets for wide temperature range, covering cryogenic and room-temperatures. [ABSTRACT FROM AUTHOR]

Magnetic phase transition and magnetocaloric effect in the amorphous Gd52Fe28B20 alloy are exhaustively explored. The melt spinning technique was employed to produce the amorphous alloy. Considering the Landau theory and Banerjee criterion, the nature of the magnetic phase transition (MPT) follows a second order MPT at the Curie temperature (TC) from ferromagnetic to paramagnetic states. The Maxwell thermodynamic relation was used to calculate the maximum isothermal entropy change (− ∆SM). This alloy exhibits wide peaks in entropy versus temperature curves, which is advantageous for enhancing the relative cooling power (RCP). The RCP of Gd52Fe28B20 was found to be ~ 190 J kg−1 (at TC = 260 K, µ0H = 2 T), the value similar to that obtained in pure Gd (at TC = 293 K, µ0H = 2 T). Additionally, we provide a phenomenological model related to the theoretical assessment of the magnetocaloric effect. The dependence of theoretical parameters on temperature and magnetic field was established through rigorous analysis. The accuracy of these theoretical predictions was assessed by comparing them to experimental results. Consequently, this alloy is appropriate for use near the ordering temperature of 260 K, which bodes well for the development of novel magnetic refrigerants for active cooling applications. [ABSTRACT FROM AUTHOR]

Two series of 3d‐Gd mixed‐metal phosphonate complexes with either only two gadolinium centers such as {Gd2}, {Ni2Gd2}, {Co4Gd2}, {Co8Gd2}, {Fe6Gd2}, and {Fe17Gd2} or more than two gadoliniums such as {Co8Gd4}, {Mn8Gd4}, {Co4Gd6}, {Mn4Gd6}, {Co6Gd8}, {Ni5Gd8}, {Ni6Gd6}, {Co8Gd8}, and {Mn9Gd9} have been solvothermally prepared and magnetothermally studied. The nearly identical environments of the Gd(III) dimer in the first series allow us to qualitatively analyze the effect of magnetic exchange coupling on the magnetocaloric effect (MCE). By doubling, tripling, or quadrupling of the Gd(III) centers, the second series of 3d‐Gd mixed‐metal complexes was built to further test the other effects of exchange couplings on MCE in more complicated circumstances. For the antiferromagnetic coupling cases, the results are nearly identical but diversify when topological spin frustrations are created, whose massive low‐lying excited spin states help enhance MCE. For presumably ferromagnetically coupled ones, albeit are rare in phosphonate complexes, they do exhibit excellent MCE. Meanwhile, the complexes with weakly coupled metal centers serve as excellent examples for studying the effect of molecular mass on MCE when its magnitude is expressed in the unit of Joule per kilogram, from which we can see the values are directly proportional to the percentage of the Gd(III) ions in molecular weight. [ABSTRACT FROM AUTHOR]

The magnetic properties, band structure results, and magnetocaloric effect of GdCo1.8M0.2 with M = Fe, Mn, Cu, and Al are reported. The band structure calculations demonstrate that all the samples have a ferrimagnetically ordered ground state, in perfect agreement with the magnetic measurements. Calculated magnetic moments and variation with the alloy composition are strongly influenced by hybridisation mechanisms as sustained by an analysis of the orbital projected local density of states. The XPS measurements reveal no significant shift in the binding energy of the investigated Co core levels with a change in the dopant element. The Co 3s core-level spectra gave us direct evidence of the local magnetic moments on Co sites and an average magnetic moment of 1.3 µB/atom was found, being in good agreement with the theoretical estimation and magnetic measurements. From the Mn 3s core-level spectra, a value of 2.1 µB/Mn was obtained. The symmetric shapes of magnetic entropy changes, the Arrott plots, and the temperature dependence of Landau coefficients clearly indicate a second-order phase transition. The relative cooling power, RCP(S), normalized relative cooling power, RCP(∆S)/∆B, and temperature-averaged entropy change values indicate that these compounds could be promising candidates for applications in magnetic refrigeration devices. [ABSTRACT FROM AUTHOR]

At present, one of the main challenges that industry faces is its impact on global warming, linked to the greenhouse effect and ozone hole problems. These two environmental issues have not yet been solved completely and, concerning the industrial cold sector, countries are making various decisions on refrigerants. Magnetic refrigeration potentially represents a less impactful refrigeration technology. In this review, the physical basis of magnetic refrigeration is analysed, in order to propose this technology for industrial use. [ABSTRACT FROM AUTHOR]

The spin-1/2 Ising-Heisenberg branched chain, inspired by the magnetic structure of three isostructural polymeric coordination compounds [(Tp)2Fe2(CN)6X (bdmap)Cu2(H2O)] ⋅ H2O to be further denoted as Fe2Cu2 (Tp = tris(pyrazolyl)hydroborate, bdmapH = 1,3-bis(dimethylamino)-2-propanol, HX = acetic acid, propionic acid or trifluoroacetic acid), is rigorously studied using the transfer-matrix method. The overall ground-state phase diagram reveals three distinct phases: a quantum antiferromagnetic phase, a quantum ferrimagnetic phase and a classical ferromagnetic phase. In the zero-temperature magnetization curve, two quantum ground states are manifested as intermediate plateaus at zero and half of the saturation magnetization, while the magnetization reaches its saturated value within the classical ferromagnetic phase. The bipartite entanglement between nearest-neighbor Heisenberg spins is more pronounced in the quantum ferrimagnetic phase compared to the quantum antiferromagnetic phase due to a fully polarized nature of the Ising spins. A reasonable agreement between theoretical predictions for the spin-1/ 2 Ising-Heisenberg branched chain and experimental data measured for a temperature dependence of the magnetic susceptibility and a low-temperature magnetization curve suggests strong antiferromagnetic coupling between nearest-neighbor Cu2+-Cu2+ magnetic ions and moderately strong ferromagnetic coupling between nearest-neighbor Cu2+-Fe3+ magnetic ions in the polymeric compounds Fe2Cu2. A thermal entanglement between nearestneighbor Cu2+-Cu2+ magnetic ions persists up to a relatively high threshold temperature T ≈ 224 K and undergoes a transient magnetic-field-driven strengthening. [ABSTRACT FROM AUTHOR]

The investigation of the nonmagnetic W-substitution effect on the structure and magnetocaloric properties of the MnCoGe alloy was conducted. The analysis of phase composition revealed the coexistence of a hexagonal Ni2In-type phase and an orthorhombic TiNiSi-type phase. A detailed analysis of XRD patterns supported by Rietveld analysis showed changes in the lattice constants and the content of recognized phases, which depended on the W content in the alloy. A monotonic decrease in the Curie temperature with an increase in W content in the alloy composition was noticed. The values of ΔSM measured for the variation of the external magnetic field ~5T were equal to 5.30, 4.16, 2.32, and 3.01 for Mn0.97W0.03 CoGe, Mn0.95 W0.05 CoGe, Mn0.93W0.07 CoGe, and Mn0.9W0.1 CoGe alloy, respectively. The analysis of n vs T curves recovered for the tested alloys was characteristic of second-order phase transition. [ABSTRACT FROM AUTHOR]

The path dependence of the magnetocaloric effect (MCE) in CoS 1.76 Se 0.24 has been studied. A field-induced paramagnetic (PM)-ferromagnetic (FM) transition results in 4.6 J/kg-K peak value of isothermal entropy change (Δ S th ) for 90 kOe field change. Above 10 K, the temperature dependence of Δ S th calculated from the forward curve (0 kOe–90 kOe) and that calculated from the reverse curve (90 kOe–0 kOe) are found to be similar, whereas at lower temperature, contrasting behaviour is observed due to the kinetic arrest of first-order magnetic transition. [ABSTRACT FROM AUTHOR]

Multicomponent rare earth intermetallic compounds Tb0.33Ho0.33Er0.33Ni and Dy0.33Ho0.33Er0.33Ni crystallize in orthorhombic FeB-type structure (Space group Pnma, No. 62, oP8) and order ferromagnetically at 59 K and 40 K (TC) respectively. Hydrides of these samples show a presence of ~ 10-nm size nanoparticles with unit cell volume expansion. Magnetization measurements reveal that hydrides Tb0.33Ho0.33Er0.33NiH1.9 and Dy0.33Ho0.33Er0.33NiH1.9 remain paramagnetic from 300 K down to 5 K. Magnetization value at 5 K in 70 kOe field is ~ 5.1 µB/f.u. and 5.5 µB/f.u., respectively, for Tb0.33Ho0.33Er0.33NiH1.9 and Dy0.33Ho0.33Er0.33NiH1.9 samples. Despite the lack of ferromagnetic order, hydrides exhibit large low-temperature magnetocaloric effect with maximum isothermal magnetic entropy change values of about − 11.6 Jkg−1 K−1 at 14 K and – 12.9 Jkg−1 K−1 at 8 K respectively for 50 kOe magnetic field change. [ABSTRACT FROM AUTHOR]

In view of tuning different transitions, Co and V are substituted in Mn-rich Ni-Mn-Ga alloy. Ni41Co9Mn30V2Ga18 sample undergoes a coupled magnetostructural transition above room temperature with a low thermal and magnetic hysteresis and high sensitivity of martensite transition temperature (8 K/T) with the field. ∆SM is found to be a maximum of −2.33 J/kg-K for 3 T field change with a large RCP of 158 J/kg. The presence of intermartensite transition along with the magnetostructural transition widens the range of working temperature. [ABSTRACT FROM AUTHOR]

The Ho-Co-In alloy was thoroughly studied for its magnetic and magnetocaloric properties, revealing a dual-phase structure comprising cubic HoCo2 and an unidentifiable phase, with stoichiometry HoCo1.5In0.33. At distinct temperatures, T1 = 123 K and T2 = 34 K, the alloy showcased ferromagnetic behavior, while transitioning to antiferromagnetic ordering at T3 = 7 K. The ferromagnetic shifts were determined to be of second-order nature, displaying minimal magnetic hysteresis. The magnetocaloric effect (MCE) was computed using Maxwell's equations based on isothermal magnetization data. Because of multi-phase nature, the alloy's multiple magnetic transitions gave rise to twin peaks in the MCE graph, reaching relative cooling power (RCP) value of 595 J/kg for an applied magnetic field change of 0–9 T. Furthermore, the alloy showcased a notable maximum magnetoresistance, registering at -15% around 123 K. These findings shows the alloy's intricate magnetic behavior and its potential for diverse applications owing to its distinct magnetocaloric and magnetoresistive properties. [ABSTRACT FROM AUTHOR]

Mn5Ge3 compound is a well-established rare-earth-free magnetocaloric material with a near-room temperature magnetocaloric effect. Chemical modification could increase its relative cooling power and to achieve that we have substituted copper and synthesized Mn4.8Cu0.2Ge3 polycrystalline compound through arc-melting process. Mn4.8Cu0.2Ge3 is an itinerant ferromagnet with a second-order magnetic transition in the vicinity of room temperature. In comparison with the pure Mn5Ge3 compound, the temperature span of the magnetocaloric effect has widened, which is a favorable requirement in practical devices. The magnetization critical exponents were estimated through the modified Arrott plot and Kouvel-Fischer methods. An unconventional critical behavior was noticed in this compound, in which the critical exponents β and γ fall close to the standard 3D-XY and 3D-Ising models, respectively. On the other hand, the pure Mn5Ge3 single crystal shows 3D-Ising critical behavior, and the deviation from the standard universality class in Mn4.8Cu0.2Ge3 could be attributed to the modification in Mn–Mn distance induced by the copper. On analyzing the magnetic properties of Mn5-xCuxGe3 (x = 0.1, 0.2, and 0.3) series, we speculate that x = 0.2 compound breaks the series monotonicity due to the unique influence of Cu substitution on Mn–Mn interactions. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect (MKE) in cylindrical ferromagnetic nanowires (FN), the magnetic structure of which is characterized by a local spacing region with a Neel's type of transformation of magnetization vector M--a cross domain wall (DW), is reviewed. For nickel and iron nanowires, it is shown that the influence of the thermal motion of DW in a weak magnetic field smaller significantly than 2nM causes a negative MKE. In the absence of DW, there is a positive MKE in wires. Estimates show that it is possible by means of a negative MKE to reduce (or to increase with the reverse change of the magnetic field) the temperature of a compact comprised of 10³-104 nickel (iron) nanowires by 1 K. The results presented in review are of practical importance in the context of the development of state-of-the-art technologies, which are based on the magnetocaloric properties of cylindrical FN with а cross DW. [ABSTRACT FROM AUTHOR]

Rare-earth-based oxides are gradually becoming a new research hotspot in cryogenic magnetic refrigeration due to their advantages in bulk preparation and application. Magnetic transition from AFM to FM in EuTiO 3 provides an effective strategy for modulating magnetism and enhancing magnetocaloric effect (MCE) in this magnetic system. Herein the structure, magnetism, and MCE of a series of Ta-doped EuTiO 3 perovskites were investigated in detail. A significant lattice expansion was achieved by partially substituting Ta for B-site Ti without altering the crystal configuration, which tailors the cryogenic magnetism and MCEs of these compounds. Lattice expansion enhances ferromagnetic coupling, weakens antiferromagnetic super-exchange, and promotes the AFM-FM transition in EuTiO 3 , which enhances the low-field MCEs. The phase transition temperature of the compound increases from 5.5 K to about 9.5 K with increasing Ta doping. The values of − Δ S M max and RC of EuTi 0.9375 Ta 0.0625 O 3 are 15.9 J kg−1 K−1and 67.8 J kg−1 under magnetic field change of 0–1 T, which are enhanced by 44.5% and 105.5% over EuTiO 3 , respectively. Although a decrease in the magnetic entropy change occurs with increasing Ta doping, the refrigerating capacity is improved due to the broadened temperature range. This work not only provides a strategy for tailoring magnetic phase transition and MCE of magnetocaloric materials, but also offers effective candidates for magnetic refrigeration over a wide temperature range. [ABSTRACT FROM AUTHOR]

• A magnetic refrigerant prototype with two magnetic poles was designed. • The system has a high magnetic field utilization rate. • The cooling performance and power consumption were studied. • The maximum temperature span of this system is 17.5 K. • The COP of AMR were calculated and analyzed. Room temperature magnetic refrigeration technology is a potentially efficient and environmentally friendly refrigeration technology. A magnetic refrigeration prototype with two high/low magnetic field regions was designed and built. The device consists of eight beds, using gadolinium particles as the magnetocaloric material, with a total filling mass of 1.35 kg. The hydraulic system consists mainly of a magnetic centrifugal pump, solenoid valves, and check valves. The flow of the heat transfer fluid through the regenerators is controlled by controlling the opening and closing of the solenoid valves. The no-load temperature span, cooling capacity, power consumption, and COP of the regenerators were investigated separately. The maximum no-load temperature span of 17.5 K was obtained at an AMR frequency of 0.5 Hz and flow rate of 1.15 L/min. The total power consumption and the magnetic power and pumping power were analyzed for different operating conditions. [ABSTRACT FROM AUTHOR]

We have systematically investigated the critical behavior around paramagnetic-ferromagnetic (PM-FM) phase transition temperature, TC, and attempted to determine the Curie temperatures and critical exponents β, γ and δ of perovskite manganites La0.67Ba0.33–xSrxMnO3 (x = 0.1, 0.2 and 0.25).The TC determined from M(T) is observed to increase from 336.7 to 368.4 K, with Sr doping at Ba. The critical exponents β, γ and δ are determined from the magnetization, M(T,H), using Modified Arrott Plots for theoretically predicted models and critical M(H) isotherms at T = TC. From the critical exponents we have inferred that La0.67Ba0.33–xSrxMnO3 behave as a three-dimensional (3D) isotropic nearest heighbor Heisenberg ferromagnet in the critical region. We have further verified that the behavior of 3D isotropic nearest neighbor Heisenberg is in agreement with the values of exponent 'n' determined based on the relation between field dependent change in magnetic entropy at the Curie temperature, T = TC. Sr doping at Ba site in La0.67Ba0.33–xSrxMnO3 does not lead to any crossover in the type of magnetic interactions present in the materials, indicating a stable behavior of 3D isotropic nearest neighbor Heisenberg ferromagnet in the critical region. The differences in the values of parameters may be attributed to the complex nature of interactions present in these materials. [ABSTRACT FROM AUTHOR]