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In this work, we study the magnetocaloric effect (MCE) in a working substance corresponding to a square lattice of spins with Q possible orientations, known as the "Q-state clock model". When the Q-state clock model has Q ≥ 5 possible configurations, it presents the famous Berezinskii–Kosterlitz–Thouless (BKT) phase associated with vortex states. We calculate the thermodynamic quantities using Monte Carlo simulations for even Q numbers, ranging from Q = 2 to Q = 8 spin orientations per site in a lattice. We use lattices of different sizes with N = L × L = 8 2 , 16 2 , 32 2 , 64 2 , and 128 2 sites, considering free boundary conditions and an external magnetic field varying between B = 0 and B = 1.0 in natural units of the system. By obtaining the entropy, it is possible to quantify the MCE through an isothermal process in which the external magnetic field on the spin system is varied. In particular, we find the values of Q that maximize the MCE depending on the lattice size and the magnetic phase transitions linked with the process. Given the broader relevance of the Q-state clock model in areas such as percolation theory, neural networks, and biological systems, where multi-state interactions are essential, our study provides a robust framework in applied quantum mechanics, statistical physics, and related fields. [ABSTRACT FROM AUTHOR]

The La0.9·0.1MnO2.9 compound were prepared by sol–gel method with the aim of obtaining a material with interesting magnetocaloric and thermoelectric properties. The prepared material crystallized in rhombohedric system with R-3c space group. In the magnetization vs. temperature graph, it is observed a paramagnetic (PM)-ferromagnetic (FM) transition with a Curie temperature TC of 209 K. From the fit of hysteresis cycle at 5 K, it is observed that the dominant contribution is ferromagnetic. A magnetic entropy change, calculated from the isothermal magnetization curves, was observed for the sample with a peak centered on TC. The total electronic density states (TDOS) show the coexistence of metallic behavior for spin-up states and semiconductor characteristic, with a Eg = 1.3 eV, for spin-down states. Thermoelectric properties analysis revealed promising behavior with ZT that assesses the efficacy of a compound in a thermoelectric field, reaching 1.1 at 420 K. [ABSTRACT FROM AUTHOR]

The preparation of materials with enhanced magnetocaloric properties is crucial for magnetic refrigeration. In this study, Nd-doped Gd5Si4 microparticles and nanomaterials were synthesized using the reduction–diffusion method. The impact of Nd doping with varying compositions on the structure and entropy change properties of the materials was investigated. The Curie temperatures of both the micron- and nano-sized materials ranged from 190 K to 210 K, which were lower than previously reported values. Micron-sized samples doped with 1% Nd exhibited superior magnetocaloric properties, demonstrating a maximum entropy change of 4.98 J⋅kg−1⋅K−1 at 5 T, with an entropy change exceeding 4 J⋅kg−1⋅K−1 over a wide temperature range of approximately 70 K. Conversely, the nanomaterials had broader entropy change peaks but lower values. All samples exhibited a second-order phase transition, as confirmed by the Arrott plots. [ABSTRACT FROM AUTHOR]

This perspective provides an overview of the state of research and innovation in the areas of magnetocaloric and pyromagnetic materials, and electrocaloric and pyroelectric materials, including the overlapping sub‐areas of multicaloric and multipyro materials that can operate simultaneously under the application of magnetic and electric fields. These materials are critically examined for their potential to revolutionize cooling, heating, and energy‐harvesting applications. This perspective first summarizes the state‐of‐the‐art advancements and highlights recent significant developments. Then, it is identified and discussed that the prevailing challenges hindering the widespread adoption of technologies based on these materials. In this context, after consulting with members of the caloric and pyro communities, a technology roadmap is outlined to guide research efforts in overcoming current barriers to applications, with the goal of achieving impactful results by 2040. This roadmap emphasizes the importance of focusing on under‐researched materials, novel devices, and application spaces, paving the way for interdisciplinary efforts that can lead to significant reductions in carbon dioxide emissions. [ABSTRACT FROM AUTHOR]

Abstract The NaZn13 type itinerant magnet LaFe13−xSix has seen considerable interest due to its unique combination of large magnetocaloric effect and low hysteresis. Here, this alloy with a combination of magnetometry, bespoke microcalorimetry, and inelastic neutron scattering is investigated. Inelastic neutron scattering reveals the presence of broad quasielastic scattering that persists across the magnetic transition, which is attributed to spin fluctuations. In addition, a quasielastic peak is observed at Q = 0.52 Å−1 for x = 1.2 that exists only in the paramagnetic state in proximity to the itinerant metamagnetic transition and argue that this indicates emergence of a hidden mag the netic phase that drives the first‐order phase transition in this system.

Abstract The application of external stimuli such as the magnetic and electric field in magnetocaloric and electrocaloric materials, and stress and pressure in elastocaloric and barocaloric materials give rise to a new generation of a refrigeration technology based on caloric materials which are considered an emerging alternative to classical refrigeration. Active caloric regenerator (ACR) made in parallel plates is studied under a large number of materials with Comsol multiphysics for a 2D numerical model. In this work, we compare various types of caloric materials, in terms of their thermodynamic properties, working mechanisms, and potential applications as solid refrigerant on caloric refrigeration devices. For this purpose, the energy equation, Navier-Stocks equation, and continuity equation are considered to study the heat transfer phenomena in refrigerator. The water was used as a carrier fluid to transport the thermal energy from the solid refrigerants to heat exchanger. This study is performed at velocity 0.06 m/s and the frequency 2 Hz at room temperature. Among them, Gadolinium show the best results in term temperature span, coefficient of performance, and the cooling power, higher than every other caloric materials, conferring to magnetocaloric cooling globally the most promising system. Our analysis provides insights into the selection and optimization of caloric materials for caloric refrigeration, which can contribute to the development of sustainable energy systems.

The study reports the influence of rare-earth ion doping on the structural, magnetic, and magnetocaloric properties of ferrimagnetic Gd3−xRExFe5O12 (RE = Y, Nd, Sm, and Dy, x = 0.0, 0.25, 0.50, and 0.75) garnet compound prepared via facile autocombustion method followed by annealing in air. X-Ray diffraction (XRD) data analysis confirmed the presence of a single-phase garnet. The compound’s lattice parameters and cell volume varied according to differences in ionic radii of the doped rare-earth ions. The RE3+ substitution changed the site-to-site bond lengths and bond angles, affecting the magnetic interaction between site ions. Magnetization measurements for all RE3+-doped samples demonstrated paramagnetic behavior at room temperature and soft-ferrimagnetic behavior at 5 K. The isothermal magnetic entropy changes (−ΔSM) were derived from the magnetic isotherm curves, M vs. T, in a field up to 3 T in the Gd3−xRExFe5O12 sample. The maximum magnetic entropy change (−∆SMmax) increased with Dy3+ and Sm3+substitution and decreased for Nd3+ and Y3+ substitution with x content. The Dy3+-doped Gd2.25Dy0.75Fe5O12 sample showed −∆SMmax~2.03 Jkg−1K−1, which is ~7% higher than that of Gd3Fe5O12 (1.91 Jkg−1K−1). A first-principal density function theory (DFT) technique was used to shed light on observed properties. The study shows that the magnetic moments of the doped rare-earths ions play a vital role in tuning the magnetocaloric properties of the garnet compound.

The study reports the influence of rare-earth ion doping on the structural, magnetic, and magnetocaloric properties of ferrimagnetic Gd3−xRExFe5O12 (RE = Y, Nd, Sm, and Dy, x = 0.0, 0.25, 0.50, and 0.75) garnet compound prepared via facile autocombustion method followed by annealing in air. X-Ray diffraction (XRD) data analysis confirmed the presence of a single-phase garnet. The compound's lattice parameters and cell volume varied according to differences in ionic radii of the doped rare-earth ions. The RE3+ substitution changed the site-to-site bond lengths and bond angles, affecting the magnetic interaction between site ions. Magnetization measurements for all RE3+-doped samples demonstrated paramagnetic behavior at room temperature and soft-ferrimagnetic behavior at 5 K. The isothermal magnetic entropy changes (−ΔSM) were derived from the magnetic isotherm curves, M vs. T, in a field up to 3 T in the Gd3−xRExFe5O12 sample. The maximum magnetic entropy change ( − ∆ S M m a x ) increased with Dy3+ and Sm3+substitution and decreased for Nd3+ and Y3+ substitution with x content. The Dy3+-doped Gd2.25Dy0.75Fe5O12 sample showed − ∆ S M m a x ~2.03 Jkg−1K−1, which is ~7% higher than that of Gd3Fe5O12 (1.91 Jkg−1K−1). A first-principal density function theory (DFT) technique was used to shed light on observed properties. The study shows that the magnetic moments of the doped rare-earths ions play a vital role in tuning the magnetocaloric properties of the garnet compound. [ABSTRACT FROM AUTHOR]

The effects of K+ doping on structure, magnetic characteristics, magnetocaloric properties, and critical behavior of La 0.7-x Nd 0.1 Sr 0.2 K x Mn 0.95 Ni 0.05 O 3 (LNSKMNO) ceramics (x = 0.00, 0.05, and 0.10) were investigated. The X-ray diffraction and refinement findings revealed that LNSKMNO exhibited a distinctive rhombohedral structure of the R-3c space group (No. 167). To validate the chemical composition of LNSKMNO ceramics, EDS spectroscopy and X-ray photoelectron spectroscopy (XPS) were utilized. The magnetization of LNSKMNO exhibited a temperature-dependent behavior, revealing a phase transition from the ferromagnetic (FM) phase to the paramagnetic (PM) phase at approximately the Curie temperature (Tc). By utilizing normalization and Banerjee's criterion, the magnetic phase transition of LNSKMNO was determined to be a second order magnetic phase transition. The maximal magnetic entropy (− Δ S M max) of LNSKMNO around Tc was 4.24, 4.53, and 4.07 J/(kg K) at the 5 T external magnetic field (H). The Kouvel-Fisher approach and modified Arrott plot were used for determining the values of the critical exponents of β , γ , and δ. The critical exponents for LNSKMNO ceramics generally conformed to those obtained based on the Mean-field model. [ABSTRACT FROM AUTHOR]

The application of external stimuli such as the magnetic and electric field in magnetocaloric and electrocaloric materials, and stress and pressure in elastocaloric and barocaloric materials give rise to a new generation of a refrigeration technology based on caloric materials which are considered an emerging alternative to classical refrigeration. Active caloric regenerator (ACR) made in parallel plates is studied under a large number of materials with Comsol multiphysics for a 2D numerical model. In this work, we compare various types of caloric materials, in terms of their thermodynamic properties, working mechanisms, and potential applications as solid refrigerant on caloric refrigeration devices. For this purpose, the energy equation, Navier-Stocks equation, and continuity equation are considered to study the heat transfer phenomena in refrigerator. The water was used as a carrier fluid to transport the thermal energy from the solid refrigerants to heat exchanger. This study is performed at velocity 0.06 m/s and the frequency 2 Hz at room temperature. Among them, Gadolinium show the best results in term temperature span, coefficient of performance, and the cooling power, higher than every other caloric materials, conferring to magnetocaloric cooling globally the most promising system. Our analysis provides insights into the selection and optimization of caloric materials for caloric refrigeration, which can contribute to the development of sustainable energy systems. [ABSTRACT FROM AUTHOR]

The influence of Ba substitution (5–15%) on magnetic and magnetocaloric properties of La0.5Sr0.5CoO3 ceramics has been investigated in this study. Hysteresis loops confirm the ferromagnetic nature of the Ba-substituted cobaltites. The magnetic entropy change peaks, - Δ S M max , in La0.5(Sr1–xBax)0.5CoO3 are observed at their respective TC values of 241, 239 and 237 K for x = 0.05, 0.1 and 0.15, respectively. However, the position of - Δ S M max shifts to a slightly higher temperature for an applied field above 1 T, which is accounted for by the short-range ferromagnetic correlations existing above TC. The values of - Δ S M max for x = 0.05, 0.1 and 0.15 corresponding to a field change of 5 T are recorded as 2.46, 2.51 and 2.42 J kg–1 K–1, respectively. A remarkable enhancement in relative cooling power is observed with Ba substitution becoming highest at 141.38 J kg–1 for x = 0.15. All these attributes of the studied materials suggest the feasibility to find applications as magnetic refrigerants. [ABSTRACT FROM AUTHOR]

Introduction: Magnetocaloric energy conversion represents an alternative to existing refrigeration, heat pump and energy harvesting technologies. A crucial part of a magnetocaloric device concerns the magnetic field source. It uses mainly rare-earth materials and consists of moving parts and a drive system while displaying a limited energy efficiency and unavailability of fast and variable control of the magnetic field. Recent advances in efficient heat transfer for high-frequency magnetic cooling call for new developments of magnetic field sources that can operate with high efficiency at high frequencies. Objectives: We report the concept of an electro-permanent magnetic (EPM) field source that efficiently recovers magnetic energy. In contrast to existing magnets, it allows very well-controlled operation without any moving parts. The main objective of this paper is to present a numerical and experimental study in which such an EPM was designed, built and tested. Methods: An extensive numerical investigation of the proposed design was carried out in terms of various geometrical and operating parameters. One of the design variations was built and experimentally evaluated for its energy efficiency and temperature increase at various operating frequencies. Results: We demonstrate an energy efficiency of these magnets of over 80% and operation with frequencies up to 50 Hz, which is crucial for future high-power-density and high-frequency magnetocaloric devices. Conclusions: Considering high energy efficiency at high operating frequencies, such EPMs would allow for miniaturization, making them a viable option for future compact magnetocaloric devices.

• Dead volumes adversely affect the performance of magnetic refrigerators. • A simulator has been set up to test the device under different working conditions. • Working parameters can be tuned to mitigate dead volume negative effects. • Device must be operated at lower frequencies and higher utilization factors. • A higher fluid mass flow rate is required, as well as increased torque. Regenerative magnetic refrigeration at room temperature has the potential to overcome various problems affecting vapor compression devices while providing competitive performance, but the effects of several loss mechanisms must be evaluated and accounted for. In actual devices, inactive sections in the regenerator originate dead volumes leading to possible non-optimal exploitation of the magnetocaloric material and the associated loss mechanism. While magnetic refrigeration gained attention, few studies have systematically investigated the effects of dead volume on system performance. In this work, a one-dimensional model valid for a generic magnetic refrigerator device (either linearly reciprocating or with continuous, or discontinuous, rotary motion) is used to study the effect of the dead volume. The device performance was assessed by comparing the characteristic curves (cooling power, and COP) of an ideal device (zero dead volume) to the corresponding characteristic curves for different dead volume ratios. The performance is negatively affected if the device is operated under the same working conditions and control parameter settings used in the ideal device. This effect is higher for higher temperature spans. Nevertheless, the device could approximate the ideal performance by adjusting its control parameters. The main measures to mitigate the negative effects of dead volumes can be summarized in the necessity to operate at lower frequencies, higher fluid mass flow rates, and higher torque. The results of this study prove that the proper control of such operative parameters is able to maximize the device performance and mitigate the performance losses due to the dead volume effects. [ABSTRACT FROM AUTHOR]

Effect of cadmium (Cd) substitution on magnetic and electrical properties of spinel Ni1−xCdxCr2O4 (x = 0–0.30) samples have been studied. Due to non-Jahn–Teller Cd ion substitution, a structural transition from the tetragonal ( I 4 1 / a m d ) to cubic ( F d 3 ¯ m ) phase is seen at room temperature. The long-range competitive ferrimagnetic and antiferromagnetic interactions in the x = 0.05 and 0.10 samples are responsible for the observed large value of coercive and exchange bias field. Cd substitution significantly enhances the antiferromagnetic component of canted spin structure of NiCr2O4 and leads to a cluster glass phase for x = 0.30 samples. Observed memory effect and relaxation of isothermal remanent magnetization confirms the metastability and nonequilibrium dynamics in the glassy phase. For x = 0.20 sample, we have observed reversible magnetocaloric behavior with a maximum negative entropy change of - Δ S M = - 1.031 3 × 10 - 4 cal / g K . Dielectric, impedance and ac conductivity data have been investigated in the temperature range of T = 27–300 K and frequency range of f = 20–105 Hz. Study of impedance spectra and ac conductivity indicates non Debye type of dielectric relaxation and correlated barrier hopping (CBH) of charge carriers is controlling the conduction mechanism in these samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electro permanent magnet is proposed for magnetocaloric refrigeration. • Electro permanent magnet is numerically and experimentally evaluated. • Its energy efficiency above 80% is reached with magnetic energy recovery. • Magnetic field can be switched between min and max up to 50 times per second. • Fast switching of magnetic field can be used with thermal switches. Magnetocaloric energy conversion represents an alternative to existing refrigeration, heat pump and energy harvesting technologies. A crucial part of a magnetocaloric device concerns the magnetic field source. It uses mainly rare-earth materials and consists of moving parts and a drive system while displaying a limited energy efficiency and unavailability of fast and variable control of the magnetic field. Recent advances in efficient heat transfer for high-frequency magnetic cooling call for new developments of magnetic field sources that can operate with high efficiency at high frequencies. We report the concept of an electro-permanent magnetic (EPM) field source that efficiently recovers magnetic energy. In contrast to existing magnets, it allows very well-controlled operation without any moving parts. The main objective of this paper is to present a numerical and experimental study in which such an EPM was designed, built and tested. An extensive numerical investigation of the proposed design was carried out in terms of various geometrical and operating parameters. One of the design variations was built and experimentally evaluated for its energy efficiency and temperature increase at various operating frequencies. We demonstrate an energy efficiency of these magnets of over 80% and operation with frequencies up to 50 Hz, which is crucial for future high-power-density and high-frequency magnetocaloric devices. Considering high energy efficiency at high operating frequencies, such EPMs would allow for miniaturization, making them a viable option for future compact magnetocaloric devices. [ABSTRACT FROM AUTHOR]

A significant barrier to the commercialization of magnetic heat pumping is the lack of scalable, low-cost manufacturing techniques that enable shaping brittle magnetocaloric materials into heat exchange structures with porous geometries, controlled chemical gradients, and advantageous anisotropic microstructures. Though direct ink writing additive manufacturing has the potential to expand into a viable net-shaping technology for functional magnetic alloys, it is typically challenging to fabricate dense parts—an observation ascribed to the constraint on powder particle size that inevitably impacts both green density of 3D printed parts and shrinkage during sintering. To this end, we report a comprehensive study on the influence of precursor powder characteristics on the magnetic and structural properties of 3D printed test coupons produced using La _0.67 Ca _0.33 MnO _3 magnetocaloric particles. Ink formulations comprising powders with nano-scaled, micron-scaled, and bimodal size distributions were printed and sintered. The impact of particle size on part quality and magnetofunctional response was examined, and it was found that test coupon fabricated using nano-scaled powders (∼100–200 nm) demonstrated the lowest part porosity (∼17%) and the highest magnetocaloric response (8 J kg ^−1 ·K ^−1 at μ _0 H = 5T). The results presented in this work address critical technical questions about the process feasibility of making magnetic heat pumps with additive manufacturing schemes.

We present an efficient computational approach to evaluate field-dependent entropy of magnetocaloric materials from ab-initio methods. The temperature dependence is reported for the entropy change, specific heat and magnetization for hcp Gd. To obtain optimal accuracy in the calculations, a mixed-scheme for magnetic Monte Carlo simulations is proposed and found to be superior to using pure quantum or classic statistics. It is demonstrated that lattice and magnetic contributions play a role in the entropy change and that the dominating contribution comes from the magnetic contribution. The total calculated entropy change agrees with measurements at room temperature.

The magnetic behaviors and magnetocaloric effect (MCE) of Pr0.7Sr0.3MnO3 (PSMO-7) film grown on a (001) SrTiO3 single-crystal substrate by a pulsed laser deposition (PLD) were studied in this paper. X-ray diffraction with a high resolution (HRXRD) measurement shows that PSMO-7 film is grown with a (001) single orientation. The magnetic properties and the MCE related to the ferromagnetic (FM) phase transition of the PSMO-7 film are investigated using the temperature dependence of magnetization M(T) and the magnetic field dependence of magnetization M(H). The M(T) data suggest that with decreasing temperatures, the PSMO-7 film goes through the transition from the paramagnetic (PM) state to the FM state at around the Curie temperature (TC). The TC (about 193 K) can be obtained by the linear fit of the Curie law. Magnetic hysteresis loop measurements show that the PSMO-7 film exhibits the FM feature at temperatures of 10, 100, and 150 K (low magnetic hysteresis can be found), while the film reveals the PM feature with the temperature increased up to 200 and/or 300 K. The research results of M(H) data are consistent with the M(T) data. Furthermore, the magnetic entropy change ( − Δ S M ) of the PSMO-7 film was studied. It was found that the maximum value of ( − Δ S M ) near TC reaches about 4.7 J/kg·K under the applied field change of 20 kOe, which is comparable to that of metal Gd ( − Δ S M of 2.8 J/kg K under 10 kOe), indicating the potential applications of PSMO-7 film in the field of magnetic refrigeration. [ABSTRACT FROM AUTHOR]

The study reports the synthesis and characterization of the magnetic and magnetocaloric effects of metal-oxide (MO) modified La0.7Ca0.3MnO3 perovskites manganite. The powder composite samples, with a nominal composition of (1 − x)La0.7Ca0.3MnO3-xMO (Wt.% x = 0.0, 2.5, 5.0), were prepared using the facile autocombustion method, followed by an annealing process. The phase purity and structure were confirmed by X-ray diffraction. Temperature and field-dependent magnetization measurements and Arrott analysis revealed mixed first- and second-order phase transition (ferromagnetic to paramagnetic) in composite samples. The phase transition temperature shifted to lower temperatures with the addition of MO in the composite. A large magnetic entropy change (4.75 JKg−1K−1 at 1T and 8.77 JKg−1K−1 at 5T) was observed in the La0.7Ca0.3MnO3 (LCMO) sample and was suppressed, due to the presence of the MO phase in the composite samples. On the other hand, the addition of MO as a secondary phase in the LCMO samples enhanced their relative cooling power (RCP). The RCP of all composite samples increased with respect to the pristine LCMO, except for LCMO–5%NiO. The highest RCP value of 267 JKg−1 was observed in LCMO–5%CuO samples, which was 23.4% higher than the 213 JKg−1 observed for the pure LCMO at a magnetic field of 5T. The enhanced RCP of these composites makes them attractive for potential refrigeration applications. [ABSTRACT FROM AUTHOR]

Materials with both high thermoelectric (TE) performance and excellent magnetocaloric (MC) properties near room temperature are of great importance for all-solid-state TE/MC hybrid refrigeration. A combination of such two critical characteristics, however, is hardly attainable in single phase compounds. Herein we report a composite material that comprises Bi-Sb-Te thermoelectric and Ni-Mn-In magnetocaloric components as an innovative thermoelectromagnetic material with dual functionalities. The diffusion mechanism between the two components during solidification is well studied by experimental electron probe microanalyzer tests and theoretical density functional theory calculations. By rationalizing the sintering parameters, the interdiffusion of the two components in the composite material is significantly mitigated. As a consequence, Bi 0.4 Sb 1.6 Te 3 /15 wt % Ni 50 Mn 35 In 15 composite material demonstrates a high thermoelectric figure of merit ( ZT = 0.66) together with a large magnetic entropy change (Δ S max = 3.08 J kg -1 K -1 under a magnetic field of 5 T), both achieved around 300 K. This study suggests that thermoelectromagnetic composite material holds a great promise for all-solid-state TE/MC hybrid cooling.

Doped lanthanum manganites La1−xCaxMnO3 with five different concentrations of Ca (x = 0.1, 0.2, 0.3, 0.4 and 0.5) were synthesized by high-temperature solid-state reaction method and characterized. The prepared samples were experimentally analyzed by X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-Vis), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and vibrating sample magnetometer (VSM) measurements. Orthorhombic structure is confirmed for this compound from powder X-ray diffraction data. The XRD data confirm the shrinkage in the unit cell of synthesized samples for increasing calcium concentration. The UV–Visible analysis for the estimation of optical band gap (Eg) reveals that the band gap decreases with the incorporation of Ca. The synthesized samples were investigated for charge density distribution using maximum entropy method, utilizing the XRD data sets. From the charge density analysis, it is found that the bond lengths for La–O and Mn–O bonds decrease with the addition of Ca. The ionic nature between La and O atoms and covalent nature between Mn and O atoms are enhanced for 40% of calcium-doping. For 50% of Ca-doped sample, ionic nature between La and O atoms and covalent nature between Mn and O atoms decrease. All the prepared samples exhibit ferromagnetism at 20 K and paramagnetism at 300 K. [ABSTRACT FROM AUTHOR]

Multiferroic oxide materials have attracted much intention in recent years due to their application in different fields such as magnetic refrigeration, spintronic devices. The existence of the magnetocaloric or magnetoelectric coupling or both of them in same rare earth manganites RMnO3, where R = Y, Eu, Tb...., are considered as promising compounds for both fundamental and applied research. In this framework, the orthorhombic YMnO3 appears as one of these materials. In this work, we perform a first-principles study of the electronic, magnetic and electric property of the mutliferroic YMnO3 using the density functional theory (DFT) within the generalized gradient approximation (GGA) with non-collinear magnetic structure calculations. In purpose to study deeply the different properties of this material physical model will be purposed, the magnetic anisotropy and magnetocaloric properties will be evaluated. Monte Carlo simulation (MCS) using Heisenberg model was employed. Semiconductor behavior was observed for antiferromagnetic type E for this compound, and the strong hybridation p-d related to the super-exchange interaction between Mn–O-Mn bond angle that contributes to the appearance of the electric polarization, weak polarization along the z axis was observed; however, there is high contribution along y axis Py ∼ −40 (μ C / cm 2) . Regarding the magnetic properties, the exchange couplings J1 and J2 were computed, magnetic anisotropy shows that the easy axis is along x axis, and finally we obtain the magnetic critical temperature around 46 K using MCS method. The isothermal magnetic entropy change, the adiabatic temperature change and the relative cooling power (RCP) were calculated for O-YMnO3 under different magnetic fields. The highest obtained isothermal entropy change is found to be 18.31 J/kg K for H = 10 T. The RCP maximum value is found to be 101.46 J/kg and the adiabatic temperature change reaches a maximum value close to 4.11 K in the field change of H = 10 T. [ABSTRACT FROM AUTHOR]

The thermal and magnetic cycling of a magnetocaloric material degrades its mechanical properties and device performance. We used ab initio tensile and shear simulations to investigate the mechanical properties such as ideal strength, fracture toughness and deformation and failure mechanisms of Fe2AlB2 at finite strain. The weakest direction of Fe2AlB2 is [010], and the weakest slip system is (010)[100]. The ideal tensile strength (σm = 12.51 GPa) of Fe2AlB2 is less than its ideal shear strength (τm = 13.32 GPa). The strain energy difference (ΔE = −13 eV/f.u.) of Fe2AlB2 confirms cleavage fracture as its most plausible failure mode. The concomitant changes in the c‐lattice parameter and Al–Al bond along the c‐axis determine the ideal tensile strength of Fe2AlB2. Likewise, the subtle changes in the a‐lattice parameter and Al–Al bond along the a‐axis specify its ideal shear strength. The tensile strain induces a magnetic to nonmagnetic transition in Fe2AlB2 at the critical tensile strain (εc = 0.08). A similar transition occurs at the critical fracture strain (εcf = 0.48) due to shear deformation. The brittle nature of Fe2AlB2 is predicted by its anisotropic Poisson's ratios, strength ratio, and failure mode. The fracture toughness of Fe2AlB2 for mode I fracture is (KIc = 2.17 MPa m1/2), mode II fracture is (KIIc = 1.33 MPa m1/2), and mode III fracture is (KIIIc = 1.16 MPa m1/2). The failure mechanism of Fe2AlB2 due to the tensile deformation is marked by the sharp and appreciable changes in the lattice parameters, bonding characteristics, and magnetic moment of Fe at the critical fracture strain (εcf = 0.44). This study provides a fundamental understanding of the mechanical behavior of Fe2AlB2 at the finite strain relevant to the cycling stability of the magnetocaloric Fe2AlB2. [ABSTRACT FROM AUTHOR]

The thermal and magnetic cycling of a magnetocaloric material degrades its mechanical properties and device performance. We used ab initio tensile and shear simulations to investigate the mechanical properties such as ideal strength, fracture toughness and deformation and failure mechanisms of Fe2AlB2 at finite strain. The weakest direction of Fe2AlB2 is [010], and the weakest slip system is (010)[100]. The ideal tensile strength (σm = 12.51 GPa) of Fe2AlB2 is less than its ideal shear strength (τm = 13.32 GPa). The strain energy difference (ΔE = −13 eV/f.u.) of Fe2AlB2 confirms cleavage fracture as its most plausible failure mode. The concomitant changes in the c‐lattice parameter and Al–Al bond along the c‐axis determine the ideal tensile strength of Fe2AlB2. Likewise, the subtle changes in the a‐lattice parameter and Al–Al bond along the a‐axis specify its ideal shear strength. The tensile strain induces a magnetic to nonmagnetic transition in Fe2AlB2 at the critical tensile strain (εc = 0.08). A similar transition occurs at the critical fracture strain (εcf = 0.48) due to shear deformation. The brittle nature of Fe2AlB2 is predicted by its anisotropic Poisson's ratios, strength ratio, and failure mode. The fracture toughness of Fe2AlB2 for mode I fracture is (KIc = 2.17 MPa m1/2), mode II fracture is (KIIc = 1.33 MPa m1/2), and mode III fracture is (KIIIc = 1.16 MPa m1/2). The failure mechanism of Fe2AlB2 due to the tensile deformation is marked by the sharp and appreciable changes in the lattice parameters, bonding characteristics, and magnetic moment of Fe at the critical fracture strain (εcf = 0.44). This study provides a fundamental understanding of the mechanical behavior of Fe2AlB2 at the finite strain relevant to the cycling stability of the magnetocaloric Fe2AlB2. [ABSTRACT FROM AUTHOR]

Multiferroic oxide materials have attracted much intention in recent years due to their application in different fields such as magnetic refrigeration, spintronic devices. The existence of the magnetocaloric or magnetoelectric coupling or both of them in same rare earth manganites RMnO3, where R = Y, Eu, Tb...., are considered as promising compounds for both fundamental and applied research. In this framework, the orthorhombic YMnO3 appears as one of these materials. In this work, we perform a first-principles study of the electronic, magnetic and electric property of the mutliferroic YMnO3 using the density functional theory (DFT) within the generalized gradient approximation (GGA) with non-collinear magnetic structure calculations. In purpose to study deeply the different properties of this material physical model will be purposed, the magnetic anisotropy and magnetocaloric properties will be evaluated. Monte Carlo simulation (MCS) using Heisenberg model was employed. Semiconductor behavior was observed for antiferromagnetic type E for this compound, and the strong hybridation p-d related to the super-exchange interaction between Mn–O-Mn bond angle that contributes to the appearance of the electric polarization, weak polarization along the z axis was observed; however, there is high contribution along y axis Py ∼ −40 (μ C / cm 2) . Regarding the magnetic properties, the exchange couplings J1 and J2 were computed, magnetic anisotropy shows that the easy axis is along x axis, and finally we obtain the magnetic critical temperature around 46 K using MCS method. The isothermal magnetic entropy change, the adiabatic temperature change and the relative cooling power (RCP) were calculated for O-YMnO3 under different magnetic fields. The highest obtained isothermal entropy change is found to be 18.31 J/kg K for H = 10 T. The RCP maximum value is found to be 101.46 J/kg and the adiabatic temperature change reaches a maximum value close to 4.11 K in the field change of H = 10 T. [ABSTRACT FROM AUTHOR]

The widespread need to pump heat necessitates improvements that will increase energy efficiency and, more generally, reduce environmental impact. As discussed at the recent Calorics 2022 Conference, heat-pump devices based on caloric materials offer an intriguing alternative to gas combustion and vapor compression. [ABSTRACT FROM AUTHOR]

Due to the environmental protection and energy shortage, the electric vehicles (EV) is gradually replacing traditional fuel vehicles. EV generally use more energy for air conditioning system, especially EV have almost no waste heat from engine to be discharged to the passenger compartment to achieve thermal comfort in heating condition. The energy consumption of the heating system for EV will decrease the maximum mileage. Therefore, the energy saving technology for heating system is developing and applied for EV. The article introduced the advance of conventional and emerging heating system for the EV. The positive temperature coefficient (PTC) heater is a convenient heating method used in EV, but PTC heater has some defects such as low efficiency. The heat pump (HP) system is gradually replacing PTC. However, HP has various problems to be overcome, such as the heating capacity and efficiency in low temperature environment. In addition, other novel technologies are proposed to reduce the energy consumption. This article reviews the literature of novel heating methods for EV, introduces adsorption air conditioning systems (AAC), fuel combustion (FC), heat storage (HS), waste heat recovery (WHR), thermoelectric effect (TE) and magnetocaloric effect (ME).© 2017 Elsevier Inc. All rights reserved.

• Synthesis of La₁.₄Ca₁.₆Mn₂O₇ (A) and La₁.₃Ca₁.₆Eu₀.₁Mn₂O₇ (B) and their Mn₃O₄ composites via autocombustion technique. • A second-order magnetic phase transition was observed for all composites. • After adding Mn 3 O 4 to A and B compounds, the magnetic entropy of the composite was considerably enhanced. • An increase in relative cooling power (RCP) and temperature-averaged entropy change (TEC) were observed for the composites. • Mn₃O₄ adds magnetic interactions and alters the magnetic phase transition behavior of the composite material. The study reports the synthesis and magnetocaloric properties of the rare-earth element as Eu3+ doped La 1.4 Ca 1.6 Mn 2 O 7 -Mn 3 O 4 composites prepared by the one-pot autocombustion technique. Eu3+ co-doping enhanced the Curie temperatures from 181 K for La 1.4 Ca 1.6 Mn 2 O 7 (LCMO) to 186 K for La 1.3 Ca 1.6 Eu 0.1 Mn 2 O 7 perovskites, which consequently enhanced the relative cooling power value of the compound. Moreover, these composites were also prepared in the presence of 10 wt% of Mn 3 O 4 nanoparticles. The presence of Mn 3 O 4 at the intervening grain boundaries between La 1.4 Ca 1.6 Mn 2 O 7 (A) and La 1.3 Ca 1.6 Eu 0.1 Mn 2 O 7 (B) phases altered the double exchange interaction between Mn3+ and Mn4+ ions. The temperature-dependent field-cooled magnetization curves showed that these nanocomposites' interfacial magnetic interactions significantly expanded the second-order ferromagnetic-to-paramagnetic phase transition temperature. This further enhanced the magnetic entropy magnitudes |ΔS Max | up to 0.521 J kg−1 k−1 and the associated relative cooling power value to 43.67 J kg−1 under a 5T applied magnetic field. The temperature-averaged entropy change (TEC) values of composites outperformed the individual values of samples A and B between the temperature range of 80–240 K. The fundamental key of this work is to demonstrate the potentiality of enhancing the magnetic phase transition temperature and magnetocaloric effect in the framework of interfacial coupling between LCMO and the Mn 3 O 4 phases of the nanocomposites. [ABSTRACT FROM AUTHOR]

The RE 5 Pt 2 In 4 (RE = Gd-Tm) rare earth compounds have been investigated by means of X-ray diffraction (XRD) as well as by DC and AC magnetometric measurements. The compounds crystallize in an orthorhombic crystal structure of the Lu 5 Ni 2 In 4 -type (Pbam space group, No. 55). With decreasing temperature, the intermetallics undergo a transition from para- to ferro-/ferri- (RE = Gd, Tb, Ho, Er) or antiferromagnetic state (RE = Tm). In case of Dy 5 Pt 2 In 4 , the ferromagnetic state is reached through an intermediate antiferromagnetic order present in a limited temperature range. The critical temperatures of magnetic ordering range from 4.1 K (RE = Tm) up to 108 K (RE = Tb). For the majority of investigated compounds, a cascade of additional magnetic transitions is found below the respective critical temperatures of magnetic ordering. The magnetic moments are found solely on the rare earth atoms, while the moments of the remaining Pt and In atoms are absent or are too small to be detected while accompanied by the strong rare earth's moments. The magnetocaloric (MCE) performance of RE 5 T 2 In 4 (RE = Gd-Tm) is found quite good, especially while taking into account the compounds with RE = Ho and Er. Maximum magnetic entropy change (− Δ S M m a x ) reaches 11.8 (RE = Ho) or 11.4 J ⋅ kg−1 ⋅ K−1 (RE = Er) under magnetic flux density change of 0–9 T. Under the same conditions, the relative cooling power (RCP) and refrigerant capacity (RC) equal 607 and 495 J ⋅ kg−1 (RE = Ho) or 434 and 341 J ⋅ kg−1 (RE = Er). • RE 5 Pt 2 In 4 (RE = Gd-Tm) order magnetically at low temperatures. • Magnetic moments are found on the rare-earth atoms which occupy three Wyckoff sites. • The compounds show complex magnetic properties. • A cascade of temperature-induced magnetic transitions is detected. [ABSTRACT FROM AUTHOR]

We present an efficient computational approach to evaluate field-dependent entropy of magnetocaloric materials from ab-initio methods. The temperature dependence is reported for the entropy change, specific heat and magnetization for hcp Gd. To obtain optimal accuracy in the calculations, a mixed-scheme for magnetic Monte Carlo simulations is proposed and found to be superior to using pure quantum or classic statistics. It is demonstrated that lattice and magnetic contributions play a role in the entropy change and that the dominating contribution comes from the magnetic contribution. The total calculated entropy change agrees with measurements at room temperature. Demonstration of the accuracy of ab-initio theory, coupled to statistical methods, for accurate calculations of the total entropy variation associated with the magnetic transition of Gd. Reproduction of experimental data of entropy change. [ABSTRACT FROM AUTHOR]

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

A bulk gadolinium (Gd) single crystal exhibits virtually zero remnant magnetization, a common trait among soft uniaxial ferromagnets. This characteristic is reflected in our magnetometry data showing virtually hysteresis free isothermal magnetization loops with large saturation magnetization. The absence of hysteresis allows to model the measured easy axis magnetization as a function of temperature and applied magnetic field, rather than a relation, which permits the application of Maxwell relations from equilibrium thermodynamics. Demagnetization effects broaden the isothermal first-order transition from negative to positive magnetization. By analyzing magnetization data within the coexistence regime, we deduce the isothermal entropy change and the field-induced heat capacity change. Comparing the numerically inferred heat capacity with relaxation calorimetric data confirms the applicability of the Maxwell relation. Analysis of the entropy in the mixed phase region suggests the presence of hitherto unresolved nanoscale magnetic structures in the demagnetized state of Gd. To support this prediction, Monte Carlo simulations of a 3D Ising model with dipolar interactions are performed. Analyzing the cluster size statistics and magnetization from the model provides strong qualitative support of our analytic approach., (Creative Commons Attribution license.)

Among the magnetocaloric materials featuring first-order phase transitions (FOPT), FeRh is considered as a reference system to study the FOPT because it is a "simple" binary system with a CsCl structure exhibiting a large adiabatic temperature change. Recently, ab initio theory predicted that changes in the Fe/Rh stoichiometry in the vicinity of equiatomic composition strongly influence the FOPT characteristics. However, this theoretical prediction was not clearly verified experimentally. Here, we investigated the composition dependence of the transitional hysteresis in FeRh. It is shown that a Fe excess of only 1 at. % induces a ferromagnetic state in the whole temperature range (from 5 K up to T ) for a minor portion of the sample (≈10%), while 5 at. % is enough to completely eliminate the FOPT. Element-specific X-ray magnetic circular dichroism (XMCD) measurements suggest that this ferromagnetic contribution arises from residual FeRh ferromagnetic regions. We attribute the formation of such domains to Fe antisite defects, as Mössbauer spectroscopy demonstrates the presence of Fe atoms located at the 1b (Rh) sites in the CsCl-type structure. As a consequence, compared with the equiatomic composition, the slightly Fe-rich sample exhibits completely different FOPT properties, influencing the magnetocaloric performances. Thus, our study sheds light on the origin of the remarkable stoichiometric sensitivity of the FOPT behavior in FeRh. These insights have broader implications for understanding FOPT dynamics and the role of residual ferromagnetic domains.c ) for a minor portion of the sample (≈10%), while 5 at. % is enough to completely eliminate the FOPT. Element-specific X-ray magnetic circular dichroism (XMCD) measurements suggest that this ferromagnetic contribution arises from residual FeRh ferromagnetic regions. We attribute the formation of such domains to Fe antisite defects, as Mössbauer spectroscopy demonstrates the presence of Fe atoms located at the 1b (Rh) sites in the CsCl-type structure. As a consequence, compared with the equiatomic composition, the slightly Fe-rich sample exhibits completely different FOPT properties, influencing the magnetocaloric performances. Thus, our study sheds light on the origin of the remarkable stoichiometric sensitivity of the FOPT behavior in FeRh. These insights have broader implications for understanding FOPT dynamics and the role of residual ferromagnetic domains.

The influence of transition metal oxide (MO) on the structural, magnetic, and magnetocaloric properties for La0.45Nd0.25Sr0.3MnO3(LSMO)/ $x$ -wt.% MO (MO = CuO, CoO and NiO) nanocomposite samples has been investigated using X-ray powder diffraction (XRD) and magnetic measurements. Pure phase nanocomposites were prepared via the one-pot autocombustion method. The XRD patterns of the composite reveal the presence of a distinct pure phase of LSMO and MOs. Temperature-dependent field-cooled magnetization curve exhibits second-order phase transition near room temperature. The isothermal magnetic entropy change ($\Delta S_{M}$) is calculated from magnetic isotherms. LSMO—2.5 wt.% CuO composite—display $\Delta S_{M}\sim -3.95$ J/kg $\cdot \text{K}$ , highest among studied composites, which is 110% higher than LSMO. While the relative cooling power (RCP) values were observed to be maximum for 5 wt.% CoO composite. [ABSTRACT FROM AUTHOR]