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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]

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]

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]

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]

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.

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.

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]

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]

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]

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]

A solid-state refrigerator device has the potential to overcome the use of greenhouse effect-related gases or hazardous chemicals. Most of these devices work on the basis of magnetocaloric effect (MCE). Ce(Fe0.975Cr0.025)2 is an engrossing material to study MCE originating from paramagnetic (PM)–ferromagnetic (FM; second-order) transition and FM–antiferromagnetic (first-order) transition. In the present work, the MCE of Ce(Fe0.975Cr0.025)2 compound, prepared in Arc melting in an argon atmosphere, has been studied. Magnetic entropy change (∆SM) and the relative cooling power have been calculated from the M–H curves to characterize the MCE. Direct and inverse MCE are found to be linked with two different magnetic transitions in this compound. [ABSTRACT FROM AUTHOR]

Determining the magnetocaloric effect (MCE) in dense nanoparticle systems (DNSs) poses a challenge due to the increased complexity of matter at the nanoscale. Given the interparticle magnetic interactions, diverse particle size and shape distributions, and the presence of inhomogeneous magnetic phases, selecting a suitable phenomenological model is essential to describe the temperature dependence of magnetic behavior in DNSs. Herein, we chose a cost‐effective Ni100‐xCrx DNS with adjustable magnetic transitions to showcase the resilience of the MCE across a broad temperature range (147–614 K). While the hyperbolic tangent model appears more fitting for materials with a single Curie temperature (TC), such as its parent bulk alloys, in the presence of a TC distribution a Gaussian distribution model proves to be better suited for DNSs. The latter model yields a magnetic entropy change, ΔSmax = 0.09–0.15 J kg‐K−1 in the DNS at a tiny field of 0.1T. The correlations between the broadening of the MCE peak and TC distribution are attributed to the particle size distribution and chemical inhomogeneity present in the DNS, paving the way for fine‐tuning MCE‐related properties such as the relative cooling power (13.17–33.45 J kg−1) and adiabatic temperature change (0.03–0.17 K). Our methodology not only enhances the potential for designing innovative MCE materials with broader operating ranges but also validates the universality of our phenomenological model for other families of nanocrystalline/nanogranular oxides/alloys thin films. [ABSTRACT FROM AUTHOR]

The present work aims to make an estimate of the adiabatic temperature change ( Δ T add ) parameter due to the magnetocaloric effect (MCE), for the rare-earth (RE)-based double perovskite La 2 NiMnO 6 system. Isothermal magnetization ( M versus H ) measurements are carried out on the La 2 NiMnO 6 sample, at temperatures around the ferromagnetic phase transition temperature ( T C ). The experimental magnetization data of La 2 NiMnO 6 are analyzed by using the Weiss mean-field model theory (MFT) and Landau theory of phase transitions. The magnetocaloric properties such as the isothermal magnetic entropy change ( Δ S M ), refrigerant capacity (RC) and the adiabatic temperature change ( Δ T add ) are evaluated using the experimental and numerically computed/simulated data. For the estimation of the adiabatic temperature change, the heat capacity data of La 2 NiMnO 6 system are generated using the mean-field model data and the reported Debye temperature ( Θ D ) value of La 2 NiMnO 6 . Additionally, Monte Carlo simulations are performed for the La 2 NiMnO 6 system, using Ising model Hamiltonian. The magnetocaloric properties are also extracted from the Monte Carlo simulations data. The La 2 NiMnO 6 shows a maximum adiabatic temperature change of around 2.3 K for the magnetic field change from zero to 70 kOe. [ABSTRACT FROM AUTHOR]

In this work, we report the effect of Zn concentration on structural, magnetic and magnetocaloric properties of (0.75)La 0.62 Nd 0.05 Ba 0·33 MnO 3 /(0.25)Ni 1- x Zn x Fe 2 O 4 (x = 0.5, 0.6 and 0.7) nanocomposites. The samples with different compositions were synthesized by co-precipitation process. The XRD analysis confirms the presence of both phases namely perovskite La 0.62 Nd 0.05 Ba 0·33 MnO 3 and spinel NiZnFe 2 O 4 and further proved by TEM analysis. Room Mössbauer measurements get insights information about the effect of Zn content in the hyperfine parameters and magnetic transition. Magnetic measurements M(T) reveal the presence of a magnetic transition from paramagnetic (PM) to ferromagnetic (FM) phase in the vicinity of Curie temperature. With decreasing Zn concentration, the Curie temperature increases as well as the maximum entropy change. [ABSTRACT FROM AUTHOR]

In this work, we will study magnetism and the magnetocaloric effect in amorphous ferromagnets formed by the series G d 100 - x N i x , where x = 29 , 32, 35 and 37. To calculate the magnetocaloric potential and magnetizations as a function of temperature and applied magnetic field, we will use the mean-field theory with the Handrich approximation to deal with the lack of structural order in amorphous systems. We seek to understand how the replacement of Gd by Ni influences the magnetocaloric properties of the binary alloys formed. The present study is important for the possible practical applications of the magnetocaloric effect and for understanding the microscopic mechanisms involved in the magnetic phase transitions of amorphous systems. [ABSTRACT FROM AUTHOR]

In this work, we will study magnetism and the magnetocaloric effect in amorphous ferromagnets formed by the series G d 100 - x N i x , where x = 29 , 32, 35 and 37. To calculate the magnetocaloric potential and magnetizations as a function of temperature and applied magnetic field, we will use the mean-field theory with the Handrich approximation to deal with the lack of structural order in amorphous systems. We seek to understand how the replacement of Gd by Ni influences the magnetocaloric properties of the binary alloys formed. The present study is important for the possible practical applications of the magnetocaloric effect and for understanding the microscopic mechanisms involved in the magnetic phase transitions of amorphous systems. [ABSTRACT FROM AUTHOR]

In this work, we fabricated a polycrystalline Tb2FeCrO6 double perovskite (DP) oxide by a solid-state reaction method and determined its structural, magnetic, and magnetocaloric (MC) properties. The Tb2FeCrO6 DP oxide was found to crystallize in a DP-type structure with the Pbnm space group and to undergo a paramagnetic-to-antiferromagnetic transition at a temperature of ~ 8.5 K. A large low-temperature MC effect was observed in the Tb2FeCrO6 DP oxide. The MC parameters in terms of maximum magnetic entropy changes, temperature-averaged entropy change (5 K), and relative cooling power for Tb2FeCrO6 DP oxide under a magnetic field change of 0–7 T were 12.9 J/kg K, 12.7 J/kg K, and 341.4 J/kg, respectively. These parameters were consistent with similarly high levels in recently updated MC materials, making the material a suitable candidate for low-temperature magnetic cooling applications. [ABSTRACT FROM AUTHOR]

The crystal structure, magnetic phase transitions and magnetocaloric effect of DyCo2−xGex (x = 0.0–0.2) compounds were studied. X-ray diffraction coupled with Rietveld analysis shows that all DyCo2−xGex samples maintain the cubic Laves structure (MgCu2-type, Fd-3 m space group), and the lattice parameter increases as x increases. Under an applied field change of 0–5 T, the maximum magnetic entropy change of DyCo2−xGex (x = 0.0, 0.05, 0.15 and 0.2) compounds are 10.4, 10.3, 7.3 and 6.3 J/kg K, and the values of relative cooling power are 290.6, 309.6, 290.4 and 271.8 J/kg, respectively. According to Arrott plots and the Inoue-Shimizu model, DyCo2 and DyCo1.95Ge0.05 compounds still maintain the first-order magnetic phase transition. But when the Ge content exceeds 0.05, a magnetic phase transition from first-order to second-order occurs. Magnetic measurement reveals that the Ge content increases the Curie temperature from 151 (for x = 0.0) to 179 K (for x = 0.2). This suggests that the DyCo2−xGex compounds are candidate materials for cryogenic magnetic cooling, which can be used in natural gas liquefaction, biological organ storage in medicine and quantum computer heat dissipation. [ABSTRACT FROM AUTHOR]

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The authors study magnetic properties of Heusler alloys with composition Ni54.4Mn17.6Ga26.2Si1.8 subjected to multiple isothermal forging. It is found that multiple isothermal forging shifts the temperatures of structural and magnetic phase transitions toward low values. Magnetization and the magnetocaloric effect are reduced slightly, and there is a qualitative change in the structure of the magnetic domain. [ABSTRACT FROM AUTHOR]

One important issue associated to magnetocaloric materials that hinders its technological application is the poor processability and structural integrity of those with the highest performance, usually intermetallics undergoing first‐order magnetic phase transitions. Additionally, the performance of these magnetocaloric materials highly depends on the structural stability of the magnetocaloric phase, which is, in many cases, very sensitive to temperature and mechanical processes. Additive manufacturing via the extrusion of polymer‐based composites is regarded as a promising way to overcome these issues. A recently presented manufacturing method of encapsulating functional fillers into polymer capsules has been used to produce a composite filament with a large load of magnetocaloric off‐stoichiometric Ni2MnGa Heusler alloy fillers with a uniform distribution throughout the polymer matrix as demonstrated by x‐ray tomography characterization. The incorporation of these metallic particles causes changes in the thermal behavior of the polymer as well as an increase in the flowability of the composite with respect to the polymer at the same temperature. The increased flowability of the composites found during manufacturing can be compensated by lowering the extrusion temperatures, making this technique even more convenient for preserving the filler properties, which is an important concern when additive manufacturing magnetocaloric materials. This is confirmed by the magnetic and magnetocaloric behavior of the composites, with responses proportional to the fraction of fillers. Highlights: Ultrasonic‐atomization produces highly spherical Ni‐Mn‐Ga Heusler alloy particles.Ni‐Mn‐Ga filled polymer capsules allow a direct extrusion of composites for AM.X‐ray tomography shows uniform volumetric filler distribution within the filaments.Decreased viscosity of the matrix favors the lowering of the processing temperature.The low processing temperatures avoid altering the MCE of the alloy fillers. [ABSTRACT FROM AUTHOR]

The development of magnetocaloric materials with a significantly enhanced volumetric cooling capability is highly desirable for the application of adiabatic demagnetization refrigerators in confined spatial environments. Here, the thermodynamic characteristics of a magnetically frustrated spin‐7/2 Gd9.33[SiO4]6O2 is presented, which exhibits strongly correlated spin disorder below ≈1.5 K. A quantitative model is proposed to describe the magnetization results by incorporating nearest‐neighbor Heisenberg antiferromagnetic and dipolar interactions. Remarkably, the recorded magnetocaloric responses are unprecedentedly large and applicable below 1.0 K. It is proposed that the S = 7/2 spin liquids serve as versatile platforms for investigating high‐performance magnetocaloric materials in the sub‐kelvin regime, particularly those exhibiting a superior cooling power per unit volume. [ABSTRACT FROM AUTHOR]

In this research, we have tried to investigate the effect of the cationic disorder on charge ordering and magnetic phase separation in La 0.5-x Eu x Ca 0.5-y Ba y MnO 3 (x = 0, 0.05, and 0.1) compounds synthesized by using the sol-gel method. All the samples possess the same average ionic radius at A site and the same Mn3+/Mn4+ ratio. Our analysis confirmed the chemical composition by energy dispersive X-ray spectroscopy and verified the structural integrity and purity of the phase by X-ray diffraction, revealing an orthorhombic structure with Pnma space group, which is in agreement with the tolerance factor. The important mismatch effect observed in the substituted specimens induces drastic effects on the structural and microstructural properties. Magnetic measurements indicate a great reduction of Curie temperature for substituted samples (from 250 K for x = 0 to 90 K for x = 0.05 and 85 K for x = 0.1), which indicates a weakening of ferromagnetic double exchange interactions induced by cationic disorder. The Arrott plots and the magnetocaloric study of the Eu−based samples indicate the persistence of the antiferromagnetic charge-ordered state characterizing the pristine compound (x = 0) as well as the presence of a first-ordered metamagnetic transition for all the studied samples, which is ascribed to the presence of antiferromagnetic domains. Such transition induced the appearance of a shoulder peak near 100 K in the magnetic entropy change curves for high magnetic field values, resulting in an extra cooling efficiency. [ABSTRACT FROM AUTHOR]

In this paper, the magnetocaloric properties and magnetic phase transition of the (La–Ca) MnO3 system after secondary doping with the large magnetic moment rare earth element Gd are investigated. Analysis reveals that the polycrystalline material La0.65Ca0.3Gd0.05MnO3 exhibits a magnetocaloric effect superior to both the un-secondary doped and similar types of materials at the critical point of the ferromagnetic–paramagnetic phase transition (TC = 173 K). Under 7 T magnetic field, the maximum magnetic entropy change |∆SMmax|, refrigerant capacity RC, and relative cooling capacity RCP are 8.10 J kg−1 K−1, 350.54 J kg−1, and 422.17 J kg−1, respectively. The high overlap between TEC (4 K) and |∆SMmax| at the same magnetic field indicates its good utility. Landau theory yields a negative slope of the Arrott plot at TC, and the fit of Landau coefficients b (TC) obtains negative values verifying the ferromagnetic–paramagnetic first-order phase transition. Further calculation of the n value and the universal curve plot using the magnetocaloric effect confirmed this type of magnetic phase transition and revealed the origin of the large magnetocaloric effect. The material provides new ideas for applications in cryogenic magnetic refrigeration. [ABSTRACT FROM AUTHOR]

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, Na RE O 2 (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 NaHoO 2 or NaErO 2 compound exhibits an antiferromagnetic ordering of RE 3+ 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 Δ S M at 2 K of 12 J/kg·K for the rhombohedral NaErO 2 and a relative cooling power (RCP) of 79.7 J/kg for the cubic NaHoO 2. [ABSTRACT FROM AUTHOR]

Minimizing the sintering time while ensuring high performances is an important optimization step for the preparation of magnetocaloric or thermomagnetic materials produced by powder metallurgy. Here, we study the influence of sintering time on the properties of a Mn0.95Fe1P0.56Si0.39B0.05 compound. In contrast to former reports investigating different annealing temperatures during heat treatments of several hours or days, we pay special attention to the earliest stages of sintering. After ball-milling and powder compaction, 2 min sintering at 1100 °C is found sufficient to form the desired Fe2P-type phase. Increasing the sintering time leads to a sharper first-order magnetic transition, a stronger latent heat, and usually to a larger isothermal entropy change, though not in all cases. As demonstrated by DSC or magnetization measurements, these parameters present dissimilar time evolutions, highlighting the existence of various underlying mechanisms. Chemical inhomogeneities are likely responsible for broadened transitions for the shortest sinterings. The development of strong latent heat requires longer sinterings than those for sharpening the magnetic transition. The microstructure may play a role as the average grain size progressively increases with the sintering time from 3.5 μm (2 min) to 30.1 μm (100 h). This systematic study has practical consequences for optimizing the preparation of MnFe(P,Si,B) compounds, but also raises intriguing questions on the influence of the microstructure and of the chemical homogeneity on magnetocaloric or thermomagnetic performances. [ABSTRACT FROM AUTHOR]

Abstract—Multicomponent polycrystalline TbInxCo2 – x (with х = 0–0.2) solid solutions are prepared for the first time, and their crystal structure and magnetic, magnetocaloric, and magnetostrictive properties are studied. X-ray diffraction patterns taken at room temperature demonstrate mainly the presence of the cubic C15 Laves phase in all samples. As the indium content increases to x = 0.1, the lattice parameter is found to increase; the further increase in the indium content to х = 0.2 leads to a decrease in the lattice parameter. In this case, the Curie temperature TC monotonically increases to 245 K. The isotheral magnetic entropy change ΔSmag is calculated in accordance with magnetic measurements using the thermodynamic Maxwell's relation. At a magnetic field change from 0 to 1.8 T, the maximum entropy change monotonically decreases and, for composition with x = 0.2, is 1.8 J/(kg К). As the indium content increases to x = 0.05, the volume magnetostriction increases. The further increase in the indium concentration leads to the decrease in the peak values and their shift to high temperatures. [ABSTRACT FROM AUTHOR]

Rare-earth orthoferrite REFeO3 (where RE is a rare-earth ion) is gaining interest. We created a high-entropy orthoferrite (Tm0.2Nd0.2Dy0.2Y0.2Yb0.2) FeO3 (HEOR) by doping five RE ions in equimolar ratios and grew the single crystal by optical floating zone method. It strongly tends to form a single-phase structure stabilized by high configurational entropy. In the low-temperature region (11.6–14.4 K), the spin reorientation transition (SRT) of Γ2 (Fx, Cy, Gz)–Γ24–Γ4 (Gx, Ay, Fz) occurs. The weak ferromagnetic (FM) moment, which comes from the Fe sublattices distortion, rotates from the a- to c-axis. The two-step dynamic processes (Γ2–Γ24–r4) are identified by AC susceptibility measurements. SRT in HEOR can be tuned in the range of 50–60000 Oe, which is an order of magnitude larger than that of orthoferrites in the peer system, making it a candidate for high-field spin sensing. Typical spin-switching (SSW) and continuous spin-switching (CSSW) effects occur under low magnetic fields due to the strong interactions between RE–Fe sublattices. The CSSW effect is tunable between 20–50 Oe, and hence, HEOR potentially can be applied to spin modulation devices. Furthermore, because of the strong anisotropy of magnetic entropy change (−ΔSm) and refrigeration capacity (RC) based on its high configurational entropy, HEOR is expected to provide a novel approach for refrigeration by altering the orientations of the crystallographic axes (anisotropic configurational entropy). [ABSTRACT FROM AUTHOR]