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This study investigates the compound system Mn5−xZnxGe3 (x = 0.1, 0.2, and 0.3) through experimental investigations and theoretical calculations. Zn doping lowers the Curie temperature and magnetic entropy change of Mn5−xZnxGe3 alloys. Analysis of phenomenological curves, including Landau theories, normalized curves, and Arrott curves during the study of isothermal magnetization curves, reveals a second-order phase transition in this system. Through an extensive investigation of critical behavior using critical isotherm curves and the Kouvel–Fisher (KF) method, the consistency and reliability of these critical indices are validated by the prediction of the scaling theory in the critical region. By scaling the dependence of |ΔSM| on M and applying crucial exponen21t values, an efficient new approach is utilized to calculate the spontaneous magnetization that agrees well with the values deduced from the KF method. Additionally, first-principles calculations reveal that the Mn atoms' 3d orbitals are more significantly close to the Fermi energy level, with Zn doping generally reducing both the electronic density of states and the total magnetic moment of the Mn 3d orbitals. Consequently, the introduction of Zn leads to a decrease in the Mn–Mn atom exchange coupling, resulting in a deterioration of the total exchange interaction. This phenomenon also explains the decrease in the Curie temperature TC due to Zn doping, aligning with experimental observations. [ABSTRACT FROM AUTHOR]

This study examines the application of machine learning algorithms, specifically the Random Forest regression model, to optimize the magnetocaloric effect in all- d -metal Heusler alloys. The model was trained using descriptors related to the mean properties of individual atoms, the properties of simple compounds in their ground state, and measures of chemical disorder. It demonstrated high accuracy in predicting structural properties, while exhibiting moderate accuracy in predicting magnetic properties. To identify optimal alloy compositions, a genetic algorithm was used to find those with the greatest differences in magnetization during martensitic transitions. Using this combined approach, the Ni–Co–Mn–Ti alloy system was thoroughly explored, resulting in the discovery of an alloy with a maximum magnetization difference. These results are consistent with previous research based on density functional theory and highlight the effectiveness of integrating machine learning with genetic algorithms for the discovery of new materials with outstanding magnetocaloric properties. The study emphasizes the need for further refinement of models capable of accurately predicting complex magnetic interactions, which is essential for fully leveraging the potential of all- d -metal Heusler alloys in practical applications. [ABSTRACT FROM AUTHOR]

Magnetic refrigeration working based on the magnetocaloric effect can be the perfect replacement of the conventional gas compression-based refrigeration technology and reduces its harmful effects on the environment. The boundary between a first-order and a second-order phase transition would be where the perfect magnetocaloric material would be found. Therefore, establishing the sequence of phase transitions clearly is essential for the characterization of other phase change materials and for applied magnetocaloric research. A quantitative fingerprint of second-order thermomagnetic phase transitions is reported here in Si-substituted high content Mn-based inverse Heusler alloy systems, which are found to be crystallized in cubic structures. The second-order nature of the phase transition has been confirmed from the Arrott plot analysis and a correlation between magnetocaloric effect and local exponent is established. Using the Arrott plot, the critical exponents are evaluated employing different techniques such as modified Arrott plot, Kouvel–Fisher method, and critical isotherm. Their values are found to be in great agreement with each other and follow the mean-field model signifying the presence of long-range ordering in the materials. The high value of isothermal magnetic entropy change and the reversibility justifies the suitability of the reported materials in the practical application as magnetic refrigerants. [ABSTRACT FROM AUTHOR]

The possibility observation of the electric field controlled multicaloric response through quasi-isostatic compression as a result of the converse piezoelectric effect was demonstrated on the cylindrical type magnetoelectric composite MnAs/PZT. It was shown that an electric voltage of 100 V corresponding to an electric field of E ∼0.3 kV/mm applied to the walls of the piezoelectric component PZT of the MnAs/PZT composite contributes to an increase in the maximum adiabatic temperature change by 0.2 K in the temperature range of the magnetostructural phase transition of MnAs ∼317 K at a magnetic field change of 1.8 T. Numerical analysis using the finite element method has shown that an electric field voltage of 100 V is capable of creating a quasi-isostatic mechanical stress in the region inside a cylindrical PZT tube of ∼3 MPa. Moreover, in the region of weak pressures up to 10 MPa, the contribution to the total adiabatic temperature change from piezo-mechanical compression linearly depends on the electrical voltage that can be used for control by magnetic and caloric properties of multicaloric materials. [ABSTRACT FROM AUTHOR]

Magnetic characteristics, magnetocaloric effect, and critical behavior of Nd1−xSrxMnO3 compounds by Sr doping (x = 0.2, 0.3, 0.4, 0.5) were studied. All samples maintained orthorhombic structures, but the space group changed from Pnma (No. 62) for x = 0.2, 0.3 to Imma (No. 74) for x = 0.4, 0.5. As Sr doping increased, the Curie temperature (TC), Curie–Weiss temperature (TCW), and magnetization increased, attributed to the double exchange (DE) interaction. A discrepancy between TCW and TC was observed due to the competition between polarons and DE interaction. The critical behavior was investigated systematically using the self-consistent (modified Arrott plots, MAP) method and the Kouvel–Fisher (KF) relation. The KF relation was suitable for the samples with x = 0.2 and 0.5, while the MAP method was suitable for the samples with x = 0.3 and 0.4. Among the Ising, XY, Heisenberg, and mean-field models, the samples with x = 0.2, 0.3, and 0.4 aligned more closely with the mean-field model, except for the x = 0.5 sample. Entropy change (−ΔSM) of Nd1−xSrxMnO3 (0.2 ≤ x ≤ 0.5) increased with the applied field, with the maximum value observed around TC. For the sample with x = 0.3, (−ΔSM) reached 4.315 J/kg K at μ0ΔH = 50 kOe, corresponding to a relative cooling power (RCP) of 280.48 J/kg. Remarkably, the x = 0.4 sample displayed (−ΔSM) of 3.298 J/kg K at μ0ΔH = 50 kOe near room temperature, with the RCP of 283.64 J/kg. These findings underscore the role of Sr doping in tuning the magnetic properties, critical behavior, and magnetocaloric effect of NdMnO3. [ABSTRACT FROM AUTHOR]

The effects of sintering temperature (Ts) and chemical substitution on the structural and magnetic properties of manganite compounds L a 1 − x S r x M n 1 − y F e y O 3 (0.025 ≤ x ≤ 0.7 ; y = 0.01 , 0.15) are explored in a search to optimize their magnetocaloric properties around room temperature. A ferromagnetic (FM) to paramagnetic (PM) phase transition is observed at a Curie temperature Tc that can be controlled to approach room temperature by Sr and Fe substitution, but also by adjusting the sintering temperature Ts. Accordingly, the magnetic entropy change (− Δ S M ) quantifying the magnetocaloric effect (MCE) presents a peak at or close to Tc that shifts and broadens with both Sr and Fe doping and is further tuned with sintering temperature. Altogether, we show that it is possible to adjust the strength and dominance of the ferromagnetic coupling in these ceramics, but also using disorder as a tool to broaden and adjust the temperature range with a significant magnetic entropy change. [ABSTRACT FROM AUTHOR]

The effects of sintering temperature (Ts) and chemical substitution on the structural and magnetic properties of manganite compounds L a 1 − x S r x M n 1 − y F e y O 3 (0.025 ≤ x ≤ 0.7 ; y = 0.01 , 0.15) are explored in a search to optimize their magnetocaloric properties around room temperature. A ferromagnetic (FM) to paramagnetic (PM) phase transition is observed at a Curie temperature Tc that can be controlled to approach room temperature by Sr and Fe substitution, but also by adjusting the sintering temperature Ts. Accordingly, the magnetic entropy change (− Δ S M ) quantifying the magnetocaloric effect (MCE) presents a peak at or close to Tc that shifts and broadens with both Sr and Fe doping and is further tuned with sintering temperature. Altogether, we show that it is possible to adjust the strength and dominance of the ferromagnetic coupling in these ceramics, but also using disorder as a tool to broaden and adjust the temperature range with a significant magnetic entropy change. [ABSTRACT FROM AUTHOR]

Using commercially available components, a compact laboratory-type prototype has been developed and assembled to demonstrate single and multicaloric effects arising from single and cyclic applications of magnetic fields and uniaxial mechanical loads. Using the example of the LaFe11.4Mn0.3Si1.3H1.6 alloy with a first-order phase transition near room temperature, the possibility of observing magnetocaloric, elastocaloric, and multicaloric effects is demonstrated. It is shown that by selecting protocols for applying combined external influences: magnetic field and mechanical load, it is possible to observe a synergistic effect for adiabatic temperature change, which amounts to 1.17 K (0.31 T and 19 MPa) at a temperature of 291.5 K for the multicaloric effect, which exceeds the corresponding value of |ΔT| = 0.75 K (0.31 T) at a temperature of 291.65 K for the magnetocaloric effect. The proposed approaches and obtained results can be used for the development of new prototypes of multicaloric cooling systems and the optimization of current ones. [ABSTRACT FROM AUTHOR]

We synthesized the Lu 2 CoCrO 6 compound, multiferroic member of double perovskite system, by sol–gel method and then investigated the crystal structure, magnetization, magnetocaloric effect (MCE), and electrical polarization study. The analysis of powder x-ray diffraction pattern confirms that the monoclinic crystal structure with P2 1 /n space group is better fitting for the Lu 2 CoCrO 6 compound. Distribution between Co and Cr ions at the B-site is not perfectly ordered. Partial ordering between these B-site cations leads to a certain degree of disorder due to the presence of antisite defects and antiphase boundaries. These anti-site disorders (in the B-site) generate various fascinating magnetic phenomena. Although the temperature dependent inverse susceptibility plot shows predominant antiferromagnetic ground state in this system, simultaneously, a second order magnetic phase transition was observed from the Arrott plot. Moreover, the isothermal magnetization study confirms the coexistence of antiferromagnetic (AFM) and ferromagnetic (FM) phases below the transition temperature. The investigation of the magnetocaloric effect shows that the AFM phase of the system converts into the FM phases above critical field values. However, the breakdown of universal behavior of MCE in the paramagnetic region confirms the coexistence of the AFM phase as a secondary phase within the FM matrix. In addition, at lower temperatures, we observe a clear and well-defined ferroelectric hysteresis loop, suggesting ferroelectricity in the material. From these results, we conclude that Lu 2 CoCrO 6 is a multiferroic material in which the coexisting magnetic and multiferroic phases appear to be correlated and weak magneto-electric coupling was also observed. Furthermore, our experimental results help to encourage basic fundamental as well as applied research on rare-earth and transition metal based double perovskite systems due to their complex exchange interaction and multiferroic behavior. [ABSTRACT FROM AUTHOR]

Magnetocaloric materials, which exploit reversible temperature changes induced by magnetic field variations, are promising for advancing energy-efficient cooling technologies. The potential integration of two-dimensional materials into magnetocaloric systems represents an emerging opportunity to enhance the magnetocaloric cooling efficiency. In this study, we use atomistic spin dynamics simulations based on first-principles parameters to systematically evaluate how magnetocaloric properties transition from three-dimensional (3D) to two-dimensional (2D) ferromagnetic materials. We find that 2D features such as reduced Curie temperature, sharper magnetic transition, and higher magnetic susceptibility are beneficial for magnetocaloric applications, while the relatively higher lattice heat capacity in 2D can compromise achievable adiabatic temperature changes. We further propose GdSi 2 as a promising 2D magnetocaloric material. Our calculation predicts that GdSi 2 exhibits an isothermal entropy change Δ S M of 22.5 J kg − 1 K − 1 and an adiabatic temperature change Δ T a d of 6.2 K, near the hydrogen liquefaction temperature (T C ≈ 25 K). Our analysis offers valuable theoretical insights into the magnetocaloric effect in 2D ferromagnets and demonstrates that 2D ferromagnets hold promise for cooling and thermal management applications in compact and miniaturized nanodevices. [ABSTRACT FROM AUTHOR]

A magnetocaloric effect (MCE) due to adiabatic change of temperature was directly measured in an Fe47.1Mn26.1Ga26.8 alloy undergoing martensitic transformation. Its values in the high-temperature region were positive, while in the temperature range below temperatures of martensitic transformation, the adiabatic change of temperature in the magnetic field was negative. The x-ray diffraction analysis revealed the presence of a Heusler L21 (B2) phase and a γ-phase in the Fe47.1Mn26.1Ga26.8 alloy above temperature of martensitic transformation. The features of field-dependent magnetization and temperature variation in MCE indicate the occurrence of ferromagnetic-to-antiferromagnetic transition in the γ-phase, which is responsible for the observed inverse magnetocaloric effect. [ABSTRACT FROM AUTHOR]

Magnetic refrigeration is an active research area considering its potential to replace gas-based refrigeration systems, which are detrimental to the environment owing to chlorofluorocarbon emissions. Heusler alloys such as Ni2MnGa are known for their magnetocaloric effect, and addition of elements like Cu has increased the refrigeration capacity of the system. Magnetocaloric properties are a strict function of composition, and few alloy compositions in Mn–Ni–Cu–Ga can exhibit enhanced magnetocaloric properties. Most of the previous works have focused on Mn–Ni–Cu–Ga, and the enhancement of magnetocaloric properties is attributed to adding Cu. However, no magnetocaloric material has been reported in the Mn–Ni–Cu system, which could potentially show benefit from Cu addition. Hence, in the present study, thermodynamic optimization of the Mn–Ni–Cu-based ternary system and its three sub-binaries, Mn–Cu, Mn–Ni, and Ni–Cu, are performed using the CALculation of PHAse Diagram approach. In order to capture the liquidus in the Mn–Ni system and congruent transformation, a few alloy compositions were prepared and analyzed using differential thermal analysis. Using the current optimized database, temperatures are calculated as a function of Mn, Ni, and Cu compositions to ascertain the phase transition between the austenite and martensite phases, which occur around room temperature. [ABSTRACT FROM AUTHOR]

In this article, a comprehensive study of the effect of calcium substitution on structural magnetic, magnetocaloric properties, and role of Griffiths phase on magnetocaloric properties of half-doped manganites L a 0.5 S r 0.5 − x C a x Mn O 3 (x = 0 , 0.25 , 0.5) ] have been presented. A structural phase transition I4/mcm − Pbnm is observed in the whole series. The system exhibits two magnetic transitions for Ca-00 and Ca-25, whereas only one phase transition is observed for Ca-50. Paramagnetic (PM)–ferromagnetic (FM) transition is observed in the whole series and ferromagnetic (FM) - antiferromagnetic (AFM) phase transition is only observed in Ca-25. Interestingly, short range FM clusters exist in the PM matrix of Ca-50, which is a signature of Griffiths phase (GP). The confirmation of GP has been carried out by performing iso-field magnetization measurements at 200 Oe, 500 Oe, and 1 kOe, respectively. Further magnetocaloric properties have been discussed on the basis of isothermal magnetization curves recorded at certain temperature intervals. Calcium substitution favors the enhancement of magnetic entropy change in the series, especially for Ca-50, a magnetic entropy change of 4.5 J/(kg K) with relative cooling power of 180 J/kg under 5 T magnetic field was observed. Iso-field magnetization and magnetocaloric effect along with critical behavior analysis have been carried out to probe the GP and other inhomogeneities present in the respective series. [ABSTRACT FROM AUTHOR]

In this study, phase transitions (structural and magnetic) and associated magnetocaloric properties of stoichiometric MnCoGe have been investigated as a function of annealing pressure. Metastable phases were generated by annealing at 800 ° C followed by rapid cooling under pressures up to 6.0 GPa. The x-ray diffraction results reveal that the crystal cell volume of the metastable phases continuously decreases with increasing thermal processing pressure, leading to a decrease in the structural transition temperature. The magnetic and structural transitions merge and form a first-order magnetostructural transition between the ferromagnetic orthorhombic and paramagnetic hexagonal phases over a broad temperature range (>80 K) spanning room temperature, yielding considerable magnetic entropy changes. These findings demonstrate the utility of thermal processing under high pressure, i.e., high-pressure annealing, to control the magnetostructural transitions and associated magnetocaloric properties of MnCoGe without altering its chemical composition. [ABSTRACT FROM AUTHOR]

In this work, we studied the nature and dilemma of the inverse magnetocaloric effect using Ni50Mn36In14 magnetic shape memory alloy. In this context, the inverse magnetocaloric effects of Ni50Mn36In14 magnetic shape memory alloy polycrystalline samples were investigated as a function of annealing heat treatments by the thermo-magnetometry method. Two forms of Ni49TiMn36In14 magnetic shape memory alloy were studied: one that predominantly undergoes a magnetic phase transition and the other that exhibits both a magnetic and martensitic phase transition. The magnetic behaviors and magnetocaloric properties of these alloys were analyzed to investigate the competition between magnetic and lattice contributions to the total entropy change. Finally, the mutually contradictory role of magnetic and lattice contributions was demonstrated. [ABSTRACT FROM AUTHOR]

This paper reports on the application of a near-infrared (NIR) imaging system for visualizing heat transfer dynamics from a bulk gadolinium (Gd) sample to the surrounding water during the magnetization/demagnetization process of the magnetocaloric effect (MCE). The suggested approach relied on the spectral variation in water absorption band at 1150 nm wavelength within the NIR spectrum. An experimental setup integrated a telecentric uniform-illumination system, a halogen lamp, and an NIR camera to enable real-time monitoring of a single magnetization and demagnetization cycle induced by an external magnetic field, which was generated by a permanent-magnet-based magnetic circuit. Two-dimensional absorbance images captured during this cycle clearly depicted the thermal energy generated by the MCE in water. Furthermore, an analysis of the thermal boundary layer and the quantification of heat transfer from Gd to water provided insights into the dynamics over time. These results indicated the potential of our NIR imaging techniques in optimizing thermal–fluid interactions within MCE systems, thereby improving the design and efficiency of magnetic refrigeration systems. [ABSTRACT FROM AUTHOR]

We demonstrate magnetocaloric entropy change and compensation temperatures in ferrimagnetic Gdx(Fe10Co90)100−x amorphous thin films with transition metal-rich and rare earth-rich configurations. Thin films are sputtered with same Gd/FeCo elemental ratio at different thicknesses and of various Gd/FeCo ratios at a constant thickness to understand the effect of these two parameters on an antiferromagnetically coupled magnetic sub-lattice system. Temperature- and field-dependent magnetic measurements [M(H,T)] and magnetocaloric studies are performed over a broad range of temperature (70–600 K) by applying a magnetic field of ±15 kOe on sputter deposited 90 nm thin films of Gdx(Fe10Co90)1−x(x = 30,40,50,55,70). The compensation temperature is found to increase with increasing Gd concentration for thin films of the same thickness. A high magnetocaloric entropy change around 0.97 J/kg K (ΔH = ± 15 kOe) is observed for thin films having the same Gd/FeCo elemental ratio. Furthermore, we observed a "table-like" magnetocaloric entropy change in GdFeCo thin film stacks with a high operational window (60 K) at a low applied field for an Ericsson magnetic regenerator around room temperature. The studies will provide important insight into magnetocaloric studies for Ericsson-cycle refrigeration in thin films having antiferromagnetically coupled sublattices. [ABSTRACT FROM AUTHOR]

The article presents the study of the magnetocaloric effect (MCE) for the rhombohedral Laves phase of Pr 2 Rh 3 Ge, which shows a magnetic order below T C = 8.5 K. We have established that the compound exhibits a continuous second-order type of transition which was demonstrated and confirmed by several different techniques, mainly by analyzing universal curves of normalized entropy change as a function of scaled temperature. The observed MCE, in our opinion, is a consequence of an indirect exchange coupling between the magnetic sublattices of the rare earth ions, which, however, does not exclude the potential contribution of sublattice-containing transition metals. In this paper, the procedure to evaluate the MCE from magnetization and specific heat data is described. As a result, important parameters such as the isothermal magnetic entropy change (Δ S M), adiabatic temperature change (Δ T a d ), relative cooling power (RCP), and the temperature averaged entropy change (TEC) were determined. The highest values of − Δ S M , Δ T a d , and RCP for a field change (Δ μ 0 H) of 5 T at T C are 5.96 J/kg K, 3.87 K, and 72.62 J/kg, respectively. These results obtained for Pr 2 Rh 3 Ge seem to be, however, low compared to the values obtained for the rhombohedral Laves phases, belonging to the group of ternary germanides RE 2 Rh 3 Ge containing heavy rare earth metals (RE = Gd, Tb, Ho, and Er). Nevertheless, we believe that the results presented in this work extend and complement the current knowledge on the magnetocaloric properties of this family of materials. [ABSTRACT FROM AUTHOR]

The advancement of magnetic materials with coupled magneto-structural phase transition (MST) to fulfill the ultimate objectives of practical solid-state cooling applications requires a better understanding of the hysteresis phenomenon linked across the phase transition region along with the large magnetocaloric parameters. For the present sample Mn0.65Ni0.65Fe0.70Si, the MST is associated with a sharp jump in magnetization along with a small thermal hysteresis of ∼13 K. A giant isothermal magnetic entropy change (| Δ S M max |) of ∼37.6 J kg−1 K−1 at 299 K and effective refrigerant capacity (R C effe ) of ∼214.3 J kg−1 under ΔH = 30 kOe is obtained with excellent compatibility between the martensite and austenite phases. The geometrical compatibility condition, i.e., very small (∼0.55%) deviation of the middle eigenvalue (λ 2) from unity justifies the observation of small hysteresis in the present material. The investigation of hysteresis behavior under different extents of the driving forces (temperature or magnetic field) reveals that both the driving forces trigger equally the phase transition and are responsible equivalently for the hysteresis phenomenon. The present study provides a pathway to understand the complexity of the hysteresis behavior, its impact on the reversibility of magnetocaloric effect, and its minimization by optimizing the geometrical compatibility condition between the austenite and martensite phases. [ABSTRACT FROM AUTHOR]

Magnetic refrigeration technology is regarded as one of the ideal solutions for cryogenic refrigeration, while magnetocaloric materials are the crucial ones. A series of polycrystalline RE2Ti2O7 (RE = Gd, Tb, and Ho) compounds were prepared by a simple one-step solid-phase reaction method in the atmosphere. The crystal structure, magnetic properties, and magnetocaloric effect (MCE) of these compounds were systematically investigated. Crystallographic research indicates that these compounds crystallized in a pyrochlore structure. Meanwhile, magnetic measurements illustrate that this class of pyrochlore oxides is highly frustrated magnetic materials and exhibits complex magnetic behavior. In addition, under the field change of 0–1 T, the values of the maximum magnetic entropy change (− Δ S M max ) and the refrigeration capacity are calculated to be 0.9 and 5.8 J/kg for Gd2Ti2O7, 9.0 and 32.9 J/kg for Tb2Ti2O7, 9.9 and 29.9 J/kg for Ho2Ti2O7, respectively. Therefore, RE2Ti2O7 (RE = Tb and Ho) pyrochlores exhibit excellent MCEs under low magnetic fields, providing candidate materials for the application of cryogenic magnetic refrigeration technology. [ABSTRACT FROM AUTHOR]

In this work, the magnetocaloric effect in Ni50Mn36In5Sb9 alloy was increased by more than 50% through directional solidification, and the magnetic entropy change increased to 36.2 J kg−1 K−1 under the field of 5 T. The calculated results of differential scanning calorimetry curves confirmed the enhanced entropy change, which also increased from 29.7 to 40.7 J kg−1 K−1. Moreover, first-principles calculations show that the surface formation energy along the L21 (220) plane is the lowest at room temperature, and it is easy to form and undergo martensitic transformation from the (220) crystal plane. Directional solidification causes the alloy to grow basically toward the (220) crystal plane, improve atomic ordering, reduce grain boundaries, and increase grain size. Thereby, the magnetic entropy change is enhanced. [ABSTRACT FROM AUTHOR]

Ferroelectric (FE) electrocaloric materials research has been blossoming worldwide for solid-state refrigeration and potential cooling systems replacing thermoelectric Peltier coolers in microelectronics. In this work, we report the outcomes from a systematic study of combined phase transition (thermodynamics) based on the phenomenological Landau theory and distributed electric field (electrostatics of thin film interfaces) in FE bilayer films. Specifically, the compositional variation of ferroelectric bilayers results in broken spatial inversion symmetry leading to asymmetric thermodynamic potentials due to a combination of normal (first- and second-order phase transition) and relaxor (dispersive dielectric constant) ferroelectric behaviors devised for efficient electrocaloric cooling effects. Extensive theoretical analyses conducted for bilayers consisting of insulating materials highlight modified phase transition temperature behavior and self-poling by effective electric field amplification arising due to bilayers' electrostatic coupling yielding significant changes in isothermal entropy (ΔS) and adiabatic temperature (ΔT). The theoretical calculation insights supported with experimental results signify, through case studies for a combination of materials experimental parameters, that amplification of the local electric field and materials engineering maximize the number of coexisting phases at or away from the morphotropic phase boundary of constituent layers in bilayer thin film architectures, which can be applicable toward other classes of materials and multilayer systems. These are effective ways for efficient cooling, in general, and for microelectronics thermal management either directly or by developing a thermal switch with phase change materials integrated with thermoelectric coolers for residual heat dissipation, both at the system and on-chip levels. [ABSTRACT FROM AUTHOR]

Ferromagnetic single crystalline MnNiSi samples were first fabricated through a Sn-flux growth technique, followed by measurements of their structural characteristics and intrinsic magnetic properties. Additionally, the critical behavior for second-order ferromagnetic to paramagnetic phase transition was investigated through utilization of techniques such as the modified Arrott plot, the Kouvel–Fisher method, and the magnetocaloric effect scaling law method. Through different methods of analysis, reliable critical exponents were obtained. Renormalization of interactions around the Curie temperature indicates the reliability of the obtained exponents. The obtained critical exponents are close to those theoretically predicted for a three-dimensional isotropic short-range Heisenberg ferromagnet but shift toward the long-range mean-field estimates. This may arise from the coupling of short- and long-range interactions as well as the competition between localized Mn–Mn magnetic interactions and the hybridization between p- and d-type orbitals. [ABSTRACT FROM AUTHOR]

In this study, we investigate the magnetocaloric effects (MCE) and critical behavior of Gd-doped La 0. 6 5 Ca 0. 3 5 − x GdxMnO3 (x = 0 , 0. 1 0 , 0. 1 5) polycrystalline materials. Our results reveal excellent MCE in the Gd-doped samples. Under a magnetic field of 7 T, the full-width at half maximum (Δ T FWHM ) increases from 41 K (x = 0. 0 0) to 121 K (x = 0. 1 0) and 112 K (x = 0. 1 5). Additionally, the refrigerant capacity (RC) is enhanced by 149% and 145% at x = 0. 1 0 and x = 0. 1 5 , respectively, compared to the parent phase. We propose that these improvements can be attributed to the introduction of Gd 3 + ions, which possess smaller ionic radii. This reduction in the average A-site ionic radius weakens the double exchange (DE) interactions, resulting in a more continuous phase transition within the system. Supporting this view, we observe a decrease in magnetization strength after doping, a reduction in Curie temperature ( T C) from 250 K (x = 0. 0 0) to 134 K (x = 0. 1 0) and 130 K (x = 0. 1 5) and a transformation from a first-order to a second-order phase transition in the doped samples. To characterize the critical behavior of the phase transition in the doped samples, we employ the K-F method. The obtained critical exponents for x = 0. 1 0 and x = 0. 1 5 are β = 0. 3 8 0 ± 0. 0 0 6 , γ = 1. 3 2 3 ± 0. 0 0 3 , δ = 4. 4 8 2 ± 0. 0 0 5 and β = 0. 4 7 7 ± 0. 0 0 8 , γ = 1. 0 8 3 ± 0. 0 0 4 , δ = 3. 2 7 0 ± 0. 0 0 2 , respectively. Furthermore, the calculation of the n values suggests a transition of the phase transition in the doped samples from short-range ordering to long-range ordering. [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]

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]

The structural, magnetic and magnetocaloric properties of perovskite manganites La0.67Sr0.28Pr0.05Mn1− x Co x O3 (x = 0.05, 0.075 and 0.10) (LSPMCO) are investigated. LSPMCO crystallizes as a rhombohedral structure with R -3 c space group. As the Co content increases, the cell volume expands, the Mn–O–Mn bond angle reduces and the length of the Mn–O bond increases. The samples show irregular submicron particles under a Zeiss scanning electron microscopy. The particle size becomes larger with increasing doping. The chemical composition of the samples is confirmed by x-ray photoelectron spectroscopy (XPS). The ferromagnetic (FM) to paramagnetic (PM) phase transition occurs near the Curie temperature (T C), and all transitions are second-order phase transitions (SMOPT) characterized by minimal thermal and magnetic hystereses. Critical behavior analysis indicates that the critical parameters of LSPMCO closely align with those predicted by the mean-field model. The T C declines with Co doping and reaches near room temperature (302 K) at x = 0.075. The maximum magnetic entropy change ( − Δ S M max ) at x = 0.05 is 4.27 J/kg⋅K, and the relative cooling power (RCP) peaks at 310.81 J/K. Therefore, the system holds significant potential for development as a magnetic refrigeration material, meriting further professional and objective evaluation. [ABSTRACT FROM AUTHOR]

Holmium orthophosphate (HoPO4) was prepared using the solid-state method. The XRD pattern analyses have proved that HoPO4 crystallises in the tetragonal structure (I41 / amd). The maximum magnetic entropy change (− Δ S M max) and the relative cooling power (RCP) reach 34.5 J / kg·K and 414.84 J kg−1 at 2.4 K under a magnetic field of 50 kOe, respectively. The lowest transition temperature and the large magnetocaloric effect (MCE) showed that HoPO4 is a potential candidate for superfluid helium magnetic refrigeration applications. [ABSTRACT FROM AUTHOR]

This research paper investigates new and first insights into the magnetic and magnetocaloric properties of one-dimensional (1D) cobalt ferrite CoFe2O4 (CFO) nanofibers (NFs) fabricated using a sol–gel-based electrospinning technique, focusing in particular on their behavior at low temperatures for specific applications. The microstructural, structural, magnetic, and magnetocaloric properties of the calcined CFO NFs were explored. The microstructure of the NFs, with an average diameter of 210 nm, was examined by scanning and transmission electron microscopy (SEM, TEM). The x-ray diffraction (XRD) of the CFO NFs showed a pure cubic close-packed (ccp) spinel crystalline structure with the Fd 3 ¯ m space group. The Raman spectroscopic studies further confirm the cubic inverse spinel phase. The magnetic properties were explored as a function of temperature, ranging from 10 K to 300 K, and ferromagnetic behavior was observed with the highest saturation magnetization of 75.87 emu/g and coercivity of 723 Oe at room temperature. The variation of the magnetic entropy was measured indirectly using the Maxwell approach with an increasing magnetic field. A maximum of Δ S = 1.71 J/K was reached around 32 K. At 180 K, the associated adiabatic temperature change, ΔTmax, was 0.93 K, with a large RCP value of 7.58 J/kg, which is reasonably high for the corresponding nanoparticles (NPs). This work suggests that 1D CFO NFs offer a promising route for the production of nanostructured magnetic materials, potentially impacting various electronic and electromagnetic device applications at low temperatures. [ABSTRACT FROM AUTHOR]

We have investigated the effect of potassium (K) doping at Sr-sites on the structural, magnetic, magnetocaloric, and critical behaviors of La0.65Sr0.35−xKxMnO3(x = 0.075 and 0.15) perovskite manganite. These samples were successfully prepared using the sol–gel method. X-ray powder diffraction (XRD) showed that our samples crystallize in the rhombohedral structure within space group R 3 ¯ c (No.167). As the temperature increases, the synthesized compounds undergo a phase transition from ferromagnetic (FM) to paramagnetic (PM) material. The magnetocaloric effect has been evaluated by assessing the isothermal magnetization curve at different temperatures close to the Curie temperature (TC), employing the Maxwell relationship. At an applied field with a magnitude of 5 T, the maximum magnetic entropy change ( - Δ S M max) and relative cooling power (RCP) are 4.25 J/kg K and 288 J/kg for x = 0.075 and 3.67 J/kg K and 267 J/kg for x = 0.15, respectively. The important magnetic entropy change, along with the adaptable Curie temperature and high relative cooling power (CP), renders these oxides beneficial for magnetic refrigeration across extensive temperature ranges, including near-room temperatures. Critical phenomena have been studied using different theoretical models: modified Arrott plots (MAP), Kouvel–Fisher (KF) method and critical isotherm (CI) analysis. The obtained critical exponents (β, γ and δ) revealed that the simple x = 0.075 is consistent with the 3D Ising model, whereas the critical exponents determined for x = 0.15 were close to the 3D Heisenberg model. The obtained values of the critical exponents were verified by the Widom relationship and scaling hypothesis, which confirmed the associated models. [ABSTRACT FROM AUTHOR]

Holmium orthophosphate (HoPO4) was prepared using the solid-state method. The XRD pattern analyses have proved that HoPO4 crystallises in the tetragonal structure (I41 / amd). The maximum magnetic entropy change (− Δ S M max) and the relative cooling power (RCP) reach 34.5 J / kg·K and 414.84 J kg−1 at 2.4 K under a magnetic field of 50 kOe, respectively. The lowest transition temperature and the large magnetocaloric effect (MCE) showed that HoPO4 is a potential candidate for superfluid helium magnetic refrigeration applications. [ABSTRACT FROM AUTHOR]

Zero thermal expansion (ZTE) alloys are critically needed in sophisticated modern industries, including telescope manufacturing, satellite technology, and semiconductor production, owing to their exceptional dimensional stability. In this study, high‐performance ZTE with a negligible coefficient of thermal expansion αv = 2.7 ppm K−1 over a broad temperature range of 10–220 K is discovered in ErCo2.8Fe0.2 magnet. Owing to an unconventional sublattice‐magnetovolume effect in the Er atoms, the negative thermal expansion in Fe‐substituted ErCo3−xFex magnets can be easily tuned to high‐performance ZTE. Moreover, the direct visualization of the magnetic transition in the predominant magnetization from the Er to the Co/Fe sublattices, as observed by the Lorentz transmission electron microscopy, further elucidates the manipulation mechanism behind the high‐performance ZTE. This study reports a convenient and effective strategy to optimize the thermal expansion characteristics of Er‐Co‐Fe magnets, which can guide future research that broadens the application scope of magnetic materials by leveraging the significant correlation between the magnetic properties and crystal structure of such systems. [ABSTRACT FROM AUTHOR]

Shape‐morphing of thermosets is challenging due to their permanently cross‐linked polymer network structure. Here, a magnetothermal shape‐morphing strategy is proposed for complex thermoset structures via reshaping, assembly, and shape memory. The thermoset composite is fabricated by adding magnetic nanoparticles into dynamically cross‐linked thermoset resin, which imparts magnetothermal effect and reprocessability under an alternating magnetic field. Epoxy composites are prepared with various weight fractions of Fe3O4 nanoparticles, and their magnetothermal and thermomechanical properties are studied. For a composite with 15 wt% Fe3O4 nanoparticles, the glass transition temperature Tg is 62 °C, and the topology freezing transition temperature Tv is 175 °C. An alternating magnetic field with a working power of 2000 W can generate a temperature of 156 °C, enabling bond exchange reactions and stress relaxation in the dynamically cross‐linked epoxy resin. Magnetothermal reshaping and bonding facilitate the assembly of complex‐shaped structures from simple units, while magnetothermal shape memory provides rapid actuation deformation responses within 60 s. Various examples of magnetothermal shape‐morphing of complex thermoset structures, including grasper, origami, and octopus‐inspired functional structures, are demonstrated. The results indicate that the present shape‐morphing strategy provides advantages such as remote control, high efficiency, flexible design, and straightforward structural fabrication. [ABSTRACT FROM AUTHOR]

In this manuscript, the magnetic and magnetocaloric properties of the Ga2$_{2}$MnNi compound are investigated using Monte Carlo simulations and first‐principles calculations. Initially, the electronic, structural, and magnetic characteristics of the alloy are explored. The findings indicate that the ferromagnetic state in the F4¯3$\bar{4} 3$m (No. 216) structure, with an optimal lattice parameter of 5.88 Å, was the most stable state compared to nonmagnetic (NM) and antiferromagnetic (AFM) states. Phonon dispersion studies confirm the alloy's dynamic stability, while the density of states reveal metallic behavior at the Fermi level. The total magnetic moment is calculated to be 3.48  μB$\left(\mu\right)_{\text{B}}$. Additionally, exchange interactions are computed for Monte Carlo simulations, predicting a Curie temperature (Tc$_{\text{c}}$) of 331 K, consistent with experimental measurements (Tc$_{\text{c}}$ = 330 K). Furthermore, the alloy exhibited a relative cooling power (RCP) of 1133.16 J kg−1 and a magnetocaloric effect of 19.65 J kg−1 K−1 at an applied magnetic field of 5 T. These results indicate that the Ga2$_{2}$MnNi full‐Heusler alloy is a potential option for use in magnetic refrigeration applications. [ABSTRACT FROM AUTHOR]

This paper investigated the impact of Co ions doping on the structure, magnetic properties, and magnetocaloric effect for La 0.8 Sr 0.2 Mn 1- x Co x O 3 ceramics (LSMCO) by sol-gel method and first-principles calculations The use of first-principles calculations was provided for subsequent experiments. The sol-gel preparation of LSMCO ceramics and sintered at 950 °C for 10 h. It was shown that the samples' cell volume and lattice constants changed slightly with increasing Co2+ doping but remained a rhombohedral structure (No.167, R-3c space group) by statistics of TEM and XRD. The average particle size for the LSMCO ceramics ranged from 130 nm to 170 nm. LSMCO's chemical composition was verified by EDS and XPS and it was demonstrated that Co2+ was successfully doped. The oxidation state of La was found to be +3, Mn is a mixture of Mn3+ and Mn4+ valence states, and Co is a mixture of Co3+ and Co2+ valence states using XPS. In the vicinity of Tc, all samples presented the second-order magnetic phase transition from ferromagnetic to paramagnetic resorting to normalization and the Banerjee criterion. The Tc dropped from 292 K to 237 K with increasing Co2+ doping. The blocking temperature and the saturation magnetization were suppressed by the Co2+ substitution while the maximum magnetic entropy change of the LSMCO ceramics was observed to reduce as Co2+ increased. When the external magnetic field is 5 T, the La 0.8 Sr 0.2 Mn 0.95 Co 0.05 O 3 ceramics has a Tc of 292 K and a maximum magnetic entropy change value of 3.47 J/(kg K). [ABSTRACT FROM AUTHOR]

The reaction of MnCl2·4H2O with HL ((1-methyl-1H-imidazol-2-yl)methanol) and pdH2 (1, 3 propanediol) in a basic MeCN solution results in the formation of a mixed-valence [Mn20] cationic cluster and two [MnIICl4] counter anions. The metallic skeleton of the cluster describes two geometrically equivalent mixed-valent, linked [MnIII6MnII4] supertetrahedra in which nearest-neighbor metal ions have a different oxidation state. Magnetic susceptibility, magnetization data and heat capacity measurements support evidence of predominant ferromagnetic correlations, leading to a s = 22 spin ground state for the [MnIII6MnII4] supertetrahedra, which are pair-linked by a weak antiferromagnetic coupling. The properties are discussed in the context of the magnetocaloric effect and the potential application of this compound in cryogenic refrigeration. [ABSTRACT FROM AUTHOR]

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 double perovskite oxide RE2FeCrO6 (RE = GD, Tb, Dy, Er) were systematically studied, and the Griffiths phase evolution was observed. In Tb2FeCrO6, Dy2FeCrO6, and Er2FeCrO6, there are antiferromagnetic (AFM)‐ferromagnetic (FM) first‐order phase transition and the Griffiths phase with coexistence of FM and paramagnetic (PM) was observed by the EPR spectra. Gd2FeCrO6 has an AFM–PM second‐order phase transition, and there is no first‐order phase transition in the range of ∆H = 0–50 kOe. As the temperature decreases, all four sets of samples present χ−1 (T) deviates downwards from the Curie–Weiss linear behavior from 0.2 to 5 kOe, corresponding to the typical characteristics of Griffiths phase evolution. In addition, all four sets of samples have excellent magnetocaloric performance. Especially, the Gd2FeCrO6 oxide has giant magnetic entropy change and relative cooling power (−∆SMmax = 30.31 J/kg K and RCP = 312.8 J/kg when ∆H = 50 kOe). From the perspective of low‐temperature magnetic refrigeration application, the present work provides important candidate references for magnetic component researchers. [ABSTRACT FROM AUTHOR]

Compared with traditional techniques, solid‐state magnetocaloric phase transition materials (MPTMs), based on the giant magnetocaloric effect (GMCE), can achieve a higher energy conversion efficiency for caloric applications. As one of the most promising MPTMs, the hexagonal (Mn,Fe)2(P,Si)‐based compounds host some advantages, but the existing hysteresis and relatively unstable GMCE properties need to be properly tackled. In this study, it is found that substitutions with Ni, Pd, and Pt can maintain and even enhance the GMCE (≈8.7% maximum improvement of |Δsm|). For a magnetic field change of Δμ0H = 2 T, all samples obtain a |Δsm| in the range of 20–25 J kg−1 K−1 with a low thermal hysteresis ΔThys (≤5.6 K). The performance surpasses almost all other (Mn,Fe)2(P,Si)‐based materials with ΔThys (<10 K) reported until now. The occupancy of substitutional Ni/Pd/Pt atoms is determined by X‐ray diffraction, neutron diffraction, and density functional theory calculations. The difference in GMCE properties upon doping is understood from the competition between a weakening of the magnetic exchange interactions and the different degrees of orbital hybridization among 3d‐4d‐5d elements. The studies elaborate on the responsible mechanism and provide a general strategy through d‐block doping to further optimize the GMCE of this materials family. [ABSTRACT FROM AUTHOR]

This study explores the critical behavior and magnetocaloric properties of La0.5Sm0.2Sr0.3Mn1-xCrxO3 manganites, with a focus on the novel effect of Cr doping (x = 0, 0.1, 0.15, and 0.2) on magnetic phase transitions and magnetocaloric response. Unlike previous works, this study provides new insights by revealing how chromium substitution alters the critical exponents γ and β, using modified Arrott plots (MAPs) and the Kouvel–Fisher method, resulting in a deviation from mean-field theory and suggesting a shift in the universality class. These findings underscore the novel impact of Cr on magnetic ion interactions and lattice structure. Furthermore, this research uniquely examines the effect of Cr doping on the magnetocaloric effect (MCE), showing that increasing Cr content tailors the magnetic entropy change − ∆SM(T) and the Temperature-Averaged Entropy Change (TEC), enhancing the potential of these materials for magnetic refrigeration. This work significantly contributes to the optimization of manganites for applications in magnetic cooling, spintronics, and temperature-sensitive sensors. [ABSTRACT FROM AUTHOR]

In this research work, samples of Pr0.8Sr0.2MnO3 were prepared using two methods: the conventional high-temperature ceramic method (sample R1) and the sol–gel method (sample R2) in order to form a composite. The Curie temperatures were found to be 161 K and 210 K for R1 and R2, respectively. We conducted a theoretical investigation of the magnetic and magnetocaloric (MC) properties of a composite constructed from R1 and R2 compounds to enhance the MC effect.The results suggest that our composite, with a Curie temperature evaluated at 190 K, could be a potential candidate for magnetic refrigeration. Refined values of the critical exponents β, γ, and δ, determined from the modified Arrott plots and the Kouvel–Fisher method, indicate that the behavior of the composite compound is consistent with the 3D Heisenberg model for T ≤ TC and with the mean-field model for T > TC. [ABSTRACT FROM AUTHOR]

Rare earth‐based perovskites have become an attractive research interest in the field of cryogenic magnetic refrigerants due to their unique advantages in practical applications. The remarkable magnetocaloric effect (MCE) renders EuTiO3 a potential magnetic refrigerant in the liquid helium temperature range. More impressively, the tunability between antiferromagnetism (AFM) and ferromagnetism (FM) provides the feasibility of tailoring the magnetism and enhancing the magnetocaloric performance. In this study, the magnetism of EuTi0.75Al0.125Zr0.125O3 is investigated in depth through first‐principles calculations and experimental methods. Both theoretical calculations and experimental results reveal that it exhibits significant ferromagnetism due to the AFM‐FM magnetic transition promoted by the co‐substitution of Al and Zr. Lattice expansion and altered electronic interactions are responsible for the FM behavior, which leads to a significant enhancement of the MCE. With the field change of 0−1 T, the peak values of magnetic entropy change (−ΔSM), refrigerating capacity (RC), and adiabatic temperature change (ΔTad) reach 18.9 J kg−1 K−1, 77.7 J kg−1, and 7.4 K, respectively. More surprisingly, the values of maximum magnetic entropy change (−ΔSMmax$ - {{\Delta}}S_{\mathrm{M}}^{{\mathrm{max}}}$) and maximum adiabatic temperature change ΔTadmax${{\Delta}}T_{{\mathrm{ad}}}^{{\mathrm{max}}}$ for EuTi0.75Al0.125Zr0.125O3 reach 11.4 J kg−1 K−1 and 3.7 K under the field change of 0−0.5 T, respectively. The remarkable magnetocaloric performance proves it to be a brilliant magnetic refrigerant operating near liquid helium temperature. [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]

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]

An off-stoichiometric Fe 2 MnSn alloy was prepared by vacuum arc melting and homogenized by vacuum annealing. The structural analysis indicated that the alloy exhibits a D0 19 hexagonal structure. Isothermal magnetization analysis at room temperature showed soft ferromagnetic behavior and exchange magnetic anisotropy. Furthermore, the isofield magnetization study revealed a Curie temperature ( T c ) of 455 K with a second-order magnetic phase transition. A similar trace of the transition point was observed in the differential scanning calorimetric analysis. We estimated a magnetic entropy change ( Δ S M = − 4 J kg - 1 K - 1 ) and refrigerant capacity (RC = 116 J kg - 1 ) from M-T measurements, highlighting its potential for thermomagnetic generators and magnetic refrigerator applications. [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]