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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]

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]

We have studied the impact of demagnetizing fields on the magnetocaloric effect of commercial-grade gadolinium plates. Adiabatic temperature changes (Δ T) were measured for magnetic fields applied along the parallel and perpendicular directions of the plates. The differences in the obtained Δ T values were accounted for by differences in the internal field due to demagnetizing effects. A combination of calorimetric measurements under a magnetic field and thermometric measurements has enabled us to obtain Brayton cycles for the two different magnetic field orientations. It has been found that the refrigerant capacity for a Brayton cycle working at 1.6 T around room temperature reduces from R C = 9.4 to R C = 5.5 J kg − 1 when the demagnetizing factor changes from N D = 0.035 to N D = 0.928 for the parallel and perpendicular configurations, respectively. It has been shown that it is possible to obtain significant demagnetizing field-induced magnetocaloric effects by rotating the sample in a region of a constant applied magnetic field. The refrigerant capacity of a Brayton cycle around room temperature for a 1.6 T constant applied magnetic field is R C = 0.6 J kg − 1 . The feasibility of these demagnetizing field-induced effects has been confirmed by direct thermometric measurements, which reveal adiabatic temperature changes of 1 K when the sample is rotated between the perpendicular and parallel configurations. [ABSTRACT FROM AUTHOR]

Magnetocaloric properties of TbCrO3 and TmCrO3 are reported and compared with those of the previously reported rare-earth chromites RCrO3 (R = Gd, Dy, Ho, and Er) and other perovskite-type oxides. The samples of TbCrO3 and TmCrO3 in this work were synthesized using a citrate gel combustion technique, and their magnetic properties were investigated and compared with those reported previously on RCrO3 (R = Gd, Dy, Ho, and Er). The Cr3+–Cr3+ ordering temperatures were found to strongly depend on the ionic radii of the rare-earth. By fitting the dc magnetization data with modified Curie–Weiss law including the Dzyaloshinsky–Moriya antisymmetric exchange interaction (D) and the symmetric exchange constant Je, spin canting angles (α) were obtained. In general, α was found to increase with the decreasing ionic radii of R3+ in RCrO3. The magnetocaloric properties investigated included the magnetic entropy change (−ΔS) for a given change in magnetic field (ΔH), the corresponding adiabatic temperature change (ΔTad), and their relative variations (ΔTad/ΔH) and (−ΔS/ΔH). It is observed that for RCrO3, (−ΔS) measured in the vicinity of the ordering temperature of R3+–R3+, varies almost as G2/3 where G is the de Gennes factor. Among RCrO3, GdCrO3 shows the largest value of (−ΔS/ΔH), because of its largest G factor and its magnitudes of (ΔTad/ΔH) and (−ΔS/ΔH) compare well with the reported values for the perovskites GdFeO3 and EuTiO3. These comparisons presented here provide useful information on the potential use of these materials in magneto-refrigeration technology. [ABSTRACT FROM AUTHOR]

Reactive single-step hot-pressing at 1473 K and 35 MPa for 4 h produces dense, bulk, near single-phase, low-cost, and low-criticality Fe2Al1.15B2 and Fe2Al1.1B2Ge0.05Ga0.05 MAB samples, showing second-order magnetic phase transition with favorable magnetocaloric properties around room temperature. The magnetic as well as the magnetocaloric properties can be tailored upon Ge and Ga doping, leading to an increase in the Curie temperature T C and the spontaneous magnetization m S. The maximum isothermal entropy change Δ s T , m a x of hot-pressed Fe2Al1.15B2 in magnetic field changes of 2 and 5 T amounts to 2.5 and 5 J(kgK)−1 at 287.5 K and increases by Ge and Ga addition to 3.1 and 6.2 J(kgK)−1 at 306.5 K, respectively. The directly measured maximum adiabatic temperature change Δ T a d , m a x is improved by composition modification from 0.9 to 1.1 K in magnetic field changes of 1.93 T. Overall, we demonstrate that hot-pressing provides a much faster, more scalable, and processing costs reducing alternative compared to conventional synthesis routes to produce heat exchangers for magnetic cooling devices. Therefore, our criticality assessment shows that hot-pressed Fe-based MAB phases provide a promising compromise of material and processing costs, criticality, and magnetocaloric performance, demonstrating the potential for low-cost and low-criticality magnetocaloric applications around room temperature. [ABSTRACT FROM AUTHOR]

The magnetic and magnetocaloric properties of a zigzag triangular nano-graphene with Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interactions in the mixed 1 and 3/2 spins are studied with the aid of the Monte Carlo investigations. The thermal magnetizations and the magnetic susceptibilities are considered. The phase diagram of the system and the variation of magnetizations with crystal field are established. The magnetic entropy for different external magnetic fields has been also sketched. The dependence of the field on the relative cooling power (RCP) of the system is found; the specific heat displacement of the system is displayed. Also, the adiabatic temperature of the system has been defined. Lastly, the magnetic hysteresis cycle with mixed spins S = 1 and σ = 3/2 for several different parameters is obtained. It can be observed that the values obtained for RCP rise with increasing external magnetic field and reduce with increasing N for constant parameters. The critical temperature values are also affected by the increasing number of non-magnetic layers. In addition, the effect of the RKKY interaction decreases as 1/N2. As a consequence, the system becomes rapidly out of order as the number of non-magnetic layers N is increased. [ABSTRACT FROM AUTHOR]

This paper investigates the full compressible magnetohydrodynamic system in three-dimensional exterior domains. For the initial-boundary-value problem of this system with slip boundary condition for the velocity, adiabatic one for the temperature, and perfect one for the magnetic field, we establish the global existence and uniqueness of strong solutions, under the condition that the initial data are of small energy but possibly large oscillations, where the initial density and temperature are both allowed to vanish. Moreover, the large-time behavior of the strong solutions is also shown. [ABSTRACT FROM AUTHOR]

The magnetostructural transition (MST) can be tuned close to room temperature for an isostructurally alloyed (MnNiGe)1−x(Fe2Ge)x (x = 0.1) compound by partially substituting a small amount of Si for Ge (7 at. %). In this study, the effect of hydrostatic pressure (p) on MST is investigated. In comparison to purely magnetically induced phase transition, pressure initiates structural transition more abruptly, which results in an increase in the isothermal entropy change by a factor of 2 from −Δs = 25.6 (p = 0) to 45.6 J/kg K (p = 190 MPa) for a magnetic field change of 2 T. Since the direct assessment of the adiabatic temperature change, ΔTad, is difficult due to the large volume change and subsequent structural breakdown at MST, an indirect method has been employed to estimate ΔTad. [ABSTRACT FROM AUTHOR]

Natural gases have played a significant role in different sectors of the global economy. Recent analyses have shown that the world's gas consumption doubled over the last three decades; further growth of the gas consumption is predicted, rising to be 23%–28% of the total primary energy demand by 2030. Therefore, liquefaction of natural gases rapidly gains global importance. In this context, magnetic refrigeration emerges as a modern energy-saving technique, which is an alternative to the traditional gas-compression refrigeration. This paper is devoted to the study of the magnetocaloric effect in magnetic fields up to 10 T on a representative of the Laves phase alloys, GdNi2, which is considered as a perspective material for liquefaction of natural gases. For a magnetic field change of 10 T, the magnetic entropy change ΔSm ≈ −17 J/kg K and the adiabatic temperature change ΔTad ≈ 6.8 K was attained around Curie temperature TC = 70 K. The maximal value of the adiabatic temperature change measured directly in pulsed magnetic fields up to 50 T is ΔTad ≈ 15 K. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect in the Fe49Rh51 alloy was systematically studied using three different approaches: in-field differential scanning calorimetry, standard direct measurement of the adiabatic temperature change, and a non-contact method based on a thermo-optical phenomenon, the mirage effect, which was able to directly test the magnetocaloric response induced by a fast magnetic field variation. The metamagnetic phase transition of Fe49Rh51 was studied in the temperature range of 290–330 K at magnetic fields up to 1.8 T through magnetic and calorimetric measurements. The estimated parameters of phase transition were comparable with the literature data. The values of adiabatic temperature change obtained with the three methods (calorimetry, standard direct measurement, and mirage-based technique), which explore three different time scales of the field variation (static field, 1 T s−1, 770 T s−1), were consistent, proving the absence of dynamic constraints in the first-order magnetostructural transition at the maximum field sweep rate. [ABSTRACT FROM AUTHOR]

The multicaloric effect is described by a temperature or entropy change of a material triggered by external stimuli applied or removed simultaneously or sequentially. The prerequisite for this is a material exhibiting multiple ferroic states. However, direct measurements of the effect are rarely reported. Now, for this reason, we built a measurement device allowing to determine the adiabatic temperature change in pulsed magnetic fields and, simultaneously, under the influence of a uniaxial load. We selected the all- d -metal Heusler alloy Ni–Mn–Ti–Co for our first test because of its enhanced mechanical properties and enormous magneto- and elastocaloric effects. Ni–Mn–Ti–Co was exposed to pulsed magnetic fields up to 10 T and uniaxial stresses up to 80 MPa, and the corresponding adiabatic temperature changes were measured. With our new experimental tool, we are able to better understand multicaloric materials and determine their cross-coupling responses to different stimuli. [ABSTRACT FROM AUTHOR]

The rotating magnetocaloric effect, which is an alternative way to cooldown or heat up magnetic materials, is characterized by the isothermal entropy change (Δ S i s o r o t ) and adiabatic temperature change (Δ T a d r o t ) in thermodynamic processes upon rotation of the magnetic field. In this paper, we make some comments on the determination of the rotating magnetocaloric quantity Δ S i s o r o t with an application in the real compounds PrSi and HoMn 2 O 5. [ABSTRACT FROM AUTHOR]

We describe magneto-, baro-, and elastocaloric effects (MCEs, BCEs, and eCEs) in materials, which possess both discontinuous (first-order) and continuous (second-order) magnetic phase transitions. Our ab initio theory of the interacting electrons of materials in terms of disordered local moments has produced explicit mechanisms for the drivers of these transitions, and here, we study associated caloric effects in three case studies where both types of transition are evident. Our earlier work had described FeRh's magnetic phase diagram and large MCE. Here, we present calculations of its substantial BCE and eCE. We describe the MCE of dysprosium and find very good agreement with experimental values for isothermal entropy (Δ S i s o ) and adiabatic temperature (Δ T a d ) changes over a large temperature span and different applied magnetic field values. We examine the conditions for optimal values of both Δ S i s o and Δ T a d that comply with a Clausius–Clapeyron analysis, which we use to propose a promising elastocaloric cooling cycle arising from the unusual dependence of the entropy on temperature and biaxial strain found in our third case study—the Mn 3 GaN antiperovskite. We explain how both Δ S i s o and Δ T a d can be kept large by exploiting the complex tensile strain–temperature magnetic phase diagram, which we had earlier predicted for this material and also propose that hysteresis effects will be absent from half of the caloric cycle. This rich and complex behavior stems from the frustrated nature of the interactions among the Mn local moments. [ABSTRACT FROM AUTHOR]

Oriented polycrystalline Nd1 − xTbxCo5 alloys are fabricated successfully by the magnetic field bonding technique, and magnetocrystalline anisotropy (MCA) and rotating magnetocaloric effect (RMCE) have been studied systematically. Two successive spin-reorientation transitions (SRTs), "easy-plane" to "easy-cone" transition at TSR1 followed by "easy-cone" to "easy-axis" transition at TSR2, are observed. The SRT temperatures shift toward room temperature due to the enhancement of MCA by substituting Nd with Tb of a higher MCA constant. In addition, two competing mechanisms on MCA might be induced by substituting Nd with Tb, which leads to the nonlinear variation of RMCE. The RMCE and the working temperature range increase largely by substituting Nd with a small amount of Tb, e.g., the maximum rotating adiabatic temperature change ΔTrot increases by ∼60% from x = 0 to 0.1. The relatively large RMCE over a wide working temperature range (from 240 K to 310 K) makes x = 0.1 compound attractive candidate for rotating magnetic refrigeration around room temperature. [ABSTRACT FROM AUTHOR]

Direct measurements of the adiabatic temperature change (Δ T ad) in cyclic magnetic fields with a frequency of up to 30 Hz in the La 0.9 Pr 0.1 Fe 11.2 Co 0.7 Si 1.1 alloy were carried out. For this alloy, the magnetocaloric effect (MCE) under magnetic field change of 1.8 T is 2.8 K and the temperature hysteresis does not exceed 0.5 K. Under magnetic field change of 0.62 T with frequencies of up to 20 Hz, the MCE shows a weak frequency dependence (less than 5%), while under magnetic field change of 1.2 T the frequency dependence is clear pronounced. Long-term exposure to a low frequency cyclic magnetic field does not result in a change in the MCE value, while at frequencies more than 10 Hz noticeable degradation of the MCE is observed. The results of the study show that the upper limit of the operation of magnetic refrigerators can reach several tens of Hz. [ABSTRACT FROM AUTHOR]

A specific heat of the magnetic solid exhibiting AFM–FM phase transition is computed using the Landau-type theory of phase transitions. The experimentally observed dependence of the specific heat value on the external magnetic field is modelled. It is shown, that this dependence has strong influence on the giant magnetocaloric effect (MCE), which is inherent to the solids exhibiting the phase transitions accompanied by the strong change of magnetization value: the disregard of this dependence leads to the noticeable overestimation of adiabatic temperature change, which is the practically important characteristic of MCE. The temperature change characterizing the giant MCE observed in Fe–Rh alloys is computed. The reasonable agreement between the available experimental data and obtained theoretical results is demonstrated. [ABSTRACT FROM AUTHOR]

Experimental studies of the magnetic and magnetocaloric properties of the Laves phase of GdNi2 have been carried out in external static up to 3 T and pulsed up to 50 T magnetic fields. It has been found that in a magnetic field of 3 T the change in the magnetic entropy of the alloy reaches its maximum value ΔSm = −8 J/(kg K) in the vicinity of the Curie temperature TC = 73.6 K. The corresponding adiabatic temperature change in this case, calculated by an indirect method, is ΔTad ≈ 3 K. The maximum value of the adiabatic temperature change measured by the direct method in a pulsed magnetic field of 50 T at T0 = 77 K, was equal to ΔTad = 15 K, which agrees well with theoretical predictions. [ABSTRACT FROM AUTHOR]

An inverse magnetocaloric effect is studied in Ni 2 Mn 1 + x X 1 − x -type Heusler alloys. Principally known for their shape-memory properties, these alloys also exhibit significant entropy and temperature changes (Δ S and Δ T A d , respectively) under adiabatic conditions when a modest magnetic field is applied. We investigated the impact on magnetocaloric properties of introducing substantial chemical disorder on the X -site (X = Si , Ga , In), of replacing Ni with nonmagnetic Ag, and of replacing a small amount of Mn with Gd. While a reduction in Δ S is observed in the first two cases, we observe a significant enhancement of Δ S when a small amount of Gd is substituted for Mn. A thermodynamic analysis was conducted using magnetization and heat capacity data to estimate adiabatic temperature changes in the range of Δ T A d ≃ − 1 to − 3 K for a 5 T magnetic field. Several alloys characterized in this study exhibit these respectable Δ T A d values near room temperature, making them potentially viable candidates for magnetic refrigeration applications. [ABSTRACT FROM AUTHOR]

• Multi-component compound Gd 0.2 Tb 0.2 Dy 0.2 Ho 0.2 Er 0.2 Ni has FeB-type orthorhombic structure. • The compound Gd 0.2 Tb 0.2 Dy 0.2 Ho 0.2 Er 0.2 Ni orders ferromagnetically at 66 K (T C). • The sample shows large magnetocaloric effect around T C. Magnetic and magnetocaloric properties of multi-component rare earth intermetallic compound Gd 0.2 Tb 0.2 Dy 0.2 Ho 0.2 Er 0.2 Ni has been studied in applied magnetic fields up to 70 kOe. Polycrystalline Gd 0.2 Tb 0.2 Dy 0.2 Ho 0.2 Er 0.2 Ni has orthorhombic FeB-type crystal structure at 300 K (space group Pnma , no. 62, oP 8) and orders ferromagnetically at ∼66 K (T C). Magnetization vs field isotherms have been measured around T C and also the temperature dependence of heat capacity in zero magnetic field. Using these data, isothermal magnetic entropy change (ΔS m) and adiabatic temperature change (ΔT ad) near the ferromagnetic transition are estimated. A normal magnetocaloric effect with a maximum ΔS m value of −16.4 J kg−1 K−1 and ΔT ad value of 6.2 K is obtained for 70 kOe field change at 62.5 K. Magnetocaloric effect is moderate when compared to that in the parent RNi (R = Gd, Tb, Dy, Ho and Er) compounds. A relative cooling power of ∼930 J/kg is obtained for 70 kOe field change for the Gd 0.2 Tb 0.2 Dy 0.2 Ho 0.2 Er 0.2 Ni sample. [ABSTRACT FROM AUTHOR]

[Display omitted] In the present article, Monte Carlo simulations were used to investigate the magnetic properties and magnetocaloric effetc of Polyphenylene Dendrimers bilayers under the Ruderman-Kittel-Kasuya-Yosida exchange interactions, considering mixed spins S = 5/2 and σ = 2. The phases of the ground state at zero temperature are explained in more detail. Additionally, we analyze the effects of varying the number of non-magnetic layers (NML), reduced exchange interactions between the two first nearest neighbors of spins S-S (R SS), between spins σ-σ (R σσ), and reduced crystal field (d) on the total magnetization and hysteresis loops. Besides, the parameters NML, R SS , R σσ , and d were varied to determine the reduced critical temperature. The impact of different reduced external magnetic fields (h/J Sσ) on specific heat, magnetic entropy changes, and adiabatic temperature changes was studied as functions of reduced temperature. Finally, we have examined the relative cooling power (RCP) for several parameters h/J Sσ. [ABSTRACT FROM AUTHOR]

In multiferroic materials, adiabatic temperature changes can be obtained by the combined application of electric, stress, and magnetic fields. These external stimuli provide additional channels of entropy variations resulting in a multi-caloric response. In ferroelectric (FE) materials, caloric responses can be obtained with the application of electric and mechanical fields. Here, we compute the intrinsic elastocaloric and stress-mediated electrocaloric behavior of prototypical FE materials using the Landau-Devonshire theory of phase transformations with appropriate electrical and electro-mechanical boundary conditions. We show that an elastocaloric adiabatic temperature variation of 12.7 °C can be obtained in PbTiO3 with the application of uniaxial tensile stress of 500MPa near its Curie point. This is 59% higher than its pure intrinsic electrocaloric response for an electric field difference of 100 kV/cm. Moreover, external stresses allow the maximum electro-elastocaloric response to be tuned towards room temperature. Our calculations show that relaxor FEs should exhibit large adiabatic temperature variations in relatively broad temperature ranges. These findings indicate that caloric responses in ferroic materials can be deterministically controlled and enhanced by utilizing a variety of external stimuli. [ABSTRACT FROM AUTHOR]

Achieving appreciable elastocaloric effect under low external field is critical for solid-state cooling technology. Here, a non-isothermal Phase-Field Model (PFM) coupling martensitic transformation with mechanics, heat transfer and magnetostrictive behavior is proposed to simulate Magneto-elastoCaloric Effect (M-eCE) that is induced by magnetic field in a multiferroic composite (e.g., Magnetostrictive-Shape Memory Alloys (MEA-SMA) composite). In the PFM, a nonlinear constitutive hyperbolic tangent model is utilized to model the macroscopic magnetostrictive behavior of MEA, and the heat transfer coupled with phase transformation is employed to calculate the adiabatic temperature change (Δ T ad ) during M-eC cooling cycles. The influences of magnetic field, geometrical dimension, and ambient temperature on Δ T ad are comprehensively investigated. Machine Learning (ML) is further conducted on the database from PFM simulations to accelerate the prediction and design of MEA-SMA composite with an improved Δ T ad . It is found that a large Δ T ad of 10–14 K and a wide working temperature window of 30 K can be achieved under ultra-low magnetic field of 0.15–0.38 T by optimizing the composite's geometrical dimension. The present work combining PFM and ML for evaluating M-eCE provides a theoretical framework for the optimization of M-eC cooling devices, and is also potentially extended to other multicaloric effects (e.g., electro-elastocaloric effect). [Display omitted] • A non-isothermal phase-field model is proposed for magneto-elastocaloric effect (M-eCE). • Effects of magnetic field, geometric dimension, and ambient temperature on M-eCE are revealed. • A large temperature change of 10–14 K is achieved by a low magnetic field (0.15–0.38 T). • Machine learning is used to accelerate the prediction and optimization of M-eCE. [ABSTRACT FROM AUTHOR]

Generation of low temperatures below 1 K has been required for applications and fundamental research, given this, development of new materials utilized for demagnetization cooling has extensively been performed in recent years. Here, we studied two polynuclear Gd3+-based molecular compounds of Gd0.33[Gd4(OH)4(OAc)3][Rh4Zn4(L-cys)12]·32H2O (1Gd) and Gd0.33[Gd4(OH)4(OAc)3][Ir4Zn4(L-cys)12]·28H2O (2Gd) (L-cys = L-cysteinate) which show paramagnetic even at low temperatures due to their frustrated arrangement of Gd3+ ions. We discuss the magnitude of the magnetocaloric effect (MCE) in them inferred from the isothermal magnetic entropy change (ΔSM\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${\Delta S}_{\text{M}}$$\end{document}) from isothermal magnetization data. The − ΔSMmax\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\Delta S_{{\text{M}}}^{{{\text{max}}}}$$\end{document} of 1Gd and 2Gd are 15.15 J kg−1 K−1 and 17.49 J kg−1 K−1 occur at 2.0 K under an applied field from 0 to 7 T, respectively. We also discussed the results of heat capacity measurement under magnetic fields to confirm the validity of the entropy change for 1Gd. Furthermore, with an aim of detecting their MCE directly, we have developed a new non-magnetic and metal-free magnetocaloric measurement cell. The adiabatic temperature change (ΔTad\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\Delta T_{{{\text{ad}}}}$$\end{document}) occurs in a small amount of sample on an order of 102-microgram with the application and removal of various magnitude magnetic fields starting from several initial temperatures were detected directly, to evaluate the potential of them to be a refrigerant for an adiabatic demagnetization refrigerator. The instrumental design for direct measurements of MCE is described along with the construction details. [ABSTRACT FROM AUTHOR]

Magnetocaloric materials change their temperature when a magnetic field is applied or removed, which allows building a magnetic cooling device. We derive an analytical expression for the maximum heat that such a material can transfer in one cooling cycle by investigating the operation of a simplified active magnetic regenerator (AMR). The model largely only depends on the adiabatic temperature change, the specific entropy change, and the temperature span between the hot and cold reservoirs. While this expression overestimates the performance of a real AMR due to its simplification, it can predict an upper limit of any AMRs' performance independent of the implementation details. Based on this, we calculate the upper limit of the cooling power of magnetic cooling devices at any temperature span, frequency, mass, and material. This upper limit is used to predict how the thermal span is scaling with the applied magnetic field, and it can be utilized for the optimization of the magnetic field source. Additionally, we confirm that the product of isothermal entropy and adiabatic temperature change, already used in the literature, is a suitable figure of merit for magnetocaloric materials. [ABSTRACT FROM AUTHOR]

We study the dependence of the magnetocaloric effect on the magnetic field-change-rate the first order magnetostructural transition in Mn3GaC by measuring the adiabatic temperature change ΔT at three different time scales: 11mTs-1, 700mTs-1, and ~1000T s-1. We find that the maximum adiabatic temperature-change of about 5K is reached in the 11mTs-1 and 700mTs-1 rates, whereas for the ~1000 T s-1-rate the transition lags the change in the magnetic field so that the maximum adiabatic temperature-change is not attained. [ABSTRACT FROM AUTHOR]

• Large magnetocaloric effect in gaudefroyite mineral. • The giant magnetic entropy |ΔS m |= 17 J kg−1 K−1 (H||c) at 18 K and |ΔS m |= 20 J kg−1 K−1 (H||ab) at 12 K at an applied magnetic field 10 T. • Promising rare-earth free natural materials for cryogenic cooling technologies. The magnetic and magnetocaloric properties of gaudefroyite minerals were studied. The magnetocaloric effect was investigated by direct and indirect methods in the temperature range 4.2–40 K and magnetic field up to 10 T. The magnetization was measured in a low magnetic field (200 Oe) with zero-field cooled and field cooling protocol and previous observation of typical spin glass behavior was confirmed. The giant magnetic entropy changes with anisotropic behavior and maximums |ΔS m |= 17 J kg−1 K−1 (H||c) at 18 K and |ΔS m |= 20 J kg−1 K−1 (H||ab) at 12 K at an applied magnetic field 10 T were observed. The direct measurements of the magnetocaloric effect demonstrated the maximum of adiabatic temperature changes of ΔT ad = 11 K at a magnetic field change of 10 T (H||ab) at 11.5 K. Obtained values of magnetocaloric parameters for the mineral of gaudefroyite are comparable to promising materials for magnetic crycooling technologies (for example, hydrogen (LH 2) liquefaction) and have an advantage for the absence of rare-earth elements in the gaudefroyite. [ABSTRACT FROM AUTHOR]

In this report, we present results of the direct measurements of the adiabatic temperature change in MnAs1−xPx compounds (x = 0, 0.02, 0.025, and 0.03) in cyclic magnetic fields up to 8 T. The substitution of As by P results in a slight shift of the Curie temperature and more notable change in the magnetocaloric effect (MCE) value. Estimations of the lattice and magnetic contributions show that in the MnAs compound, the lattice contribution dominates (about 70% of the total MCE). Substitution of As with phosphorus leads to a decrease in the total value of the MCE, which is caused by a decrease in the lattice contribution, and the magnetic contribution almost does not change in the absolute value. A reversible degradation of the magnetocaloric effect in cyclic magnetic fields is found, which restricts the application of this material to the magnetic cooling technology. [ABSTRACT FROM AUTHOR]

The world's growing hunger for artificial cold, on the one hand, and the ever more stringent climate targets, on the other, pose an enormous challenge to mankind. Novel, efficient, and environmentally friendly refrigeration technologies based on solid-state refrigerants can offer a way out of the problems arising from climate-damaging substances used in conventional vapor-compressors. Multicaloric materials stand out because of their large temperature changes, which can be induced by the application of different external stimuli such as a magnetic, electric, or a mechanical field. Despite the high potential for applications and the interesting physics of this group of materials, few studies focus on their investigation by direct methods. In this paper, we report on the advanced characterization of all relevant physical quantities that determine the multicaloric effect of a Ni-Mn-In Heusler compound. We have used a purpose-designed calorimeter to determine the isothermal entropy and adiabatic temperature changes resulting from the combined action of magnetic field and uniaxial stress on this metamagnetic shape-memory alloy. From these results, we can conclude that the multicaloric response of this alloy by appropriate changes of uniaxial stress and magnetic field largely outperforms the caloric response of the alloy when subjected to only a single stimulus. We anticipate that our findings can be applied to other multicaloric materials, thus inspiring the development of refrigeration devices based on the multicaloric effect. [ABSTRACT FROM AUTHOR]

A new concept named "rotating magnetocaloric effect (RMCE)" has been proposed and attracted more attention recently. Unlike the traditional MCE that is achieved by moving the magnetic refrigerant in and out of magnetic field, RMCE can be realized by rotating the anisotropic material within the static field, thus implying the possible higher efficiency and simpler device. However, most studies on RMCE are concentrated on single crystals, which are generally more expensive and difficult to prepare in comparison with polycrystals. Therefore, it is highly desirable to search polycrystalline materials with high RMCE. Here, the textured HoNiSi polycrystal is reported to show a giant RMCE, e.g., the rotating magnetic entropy change (−Δ S R) are 18.5 and 26.7 J/kg K and rotating adiabatic temperature change (Δ T R) are 7.0 and 13.4 K under 2 and 5 T, respectively. This giant RMCE over a wide temperature range especially under low field suggests textured HoNiSi as promising material for practical application of rotary magnetic refrigeration. Moreover, the large magnetic anisotropy of HoNiSi is explained by the single-ion magnetic anisotropy theory, and the coherent orientation of crystallographic texture and rare-earth ion moments leads to the large RMCE in the textured HoNiSi polycrystal. This work reveals that the strongly coherent orientation of crystallographic texture and rare-earth ion moments is a key to realize large RMCE in polycrystalline materials. Image, graphical abstract [ABSTRACT FROM AUTHOR]

We report upon the specific heat and magnetocaloric properties of Cu2MnBO5 over a temperature range of 60–350 K and in magnetic fields up to 18 kOe. It is found that at temperatures below the Curie temperature (TC ∼ 92 K), CP(T)/T possesses a linear temperature-dependent behavior, which is associated with the predominance of two-dimensional antiferromagnetic interactions of magnons. The temperature independence of CP/T = f(T) is observed in the temperature range of 95–160 K, which can be attributed to the excitation of the Wigner glass phase. The magnetocaloric effect [i.e., the adiabatic temperature change, ΔTad (T,H)] is assessed through a direct measurement or an indirect method using the CP(T,H) data. Owing to its strong magnetocrystalline anisotropy, an anisotropic magnetocaloric effect (MCE) or the rotating MCE [ΔTadrot (T)] is observed in Cu2MnBO5. A deep minimum in the ΔTadrot (T) near the TC is observed and ascribed to the anisotropy of the paramagnetic susceptibility. [ABSTRACT FROM AUTHOR]

Direct measurements of the adiabatic temperature change (ΔTad) in Gd and Mn1.15Fe0.8P0.5Si0.5C0.05 are made using a homemade adiabatic magnetocalorimeter at 260–360 K and 0–7 T. The system uses a servo motor to drive the samples into and out of the magnetic field under a vacuum environment provided by the Physical Property Measurement System (PPMS). The peak values of ΔTad for Gd and Mn1.15Fe0.8P0.5Si0.5C0.05 at 7 T are 8.71 K and 6.41 K at ambient temperatures of 303 K and 317 K, respectively. Based on the theory model, it is found that ΔTad of Gd depends on the 2/3 exponential function of magnetic field H (ΔTad ∝ H2/3), whereas the Mn1.15Fe0.8P0.5Si0.5C0.05 compound follows the power law of ΔTad ∝ H0.66–1.04 due to the first order magnetic transitions. Furthermore, using the constructed experimental instrument, the adiabatic temperature change in different magnetic materials, including materials with first/second order magnetic transition and blocks, flakes, or powders, can be directly measured under large magnetic fields and wide temperature spans. [ABSTRACT FROM AUTHOR]

In this study, magnetic and magnetocaloric properties of (La0.8Pr0.2)0.67Ba0.33MnO3 manganite synthesized by sol-gel method were investigated. Under low magnetic field, temperature-dependent zero-field-cooled, field-cooled, and field-heated measurements were performed and the magnetic phase transition temperature corresponding to the sudden drop in magnetization was determined as 200 K. The magnetic entropy change value of the sample is determined as 2.2 J/kgK in 4.8 T magnetic field from isothermal magnetization curves. The adiabatic temperature change (ΔTad) of the sample was measured directly using an adiabatic calorimeter and measured as 0.72 K with a field change of 3 T. As a result of cyclic measurement of ΔTad, it is observed that the material has a reversible magnetocaloric effect (MCE) during the application and removal of the field 5 times. This reversible MCE property of the material is important in that it is the most desirable property of potential materials to be used in magnetic cooling systems. [ABSTRACT FROM AUTHOR]

The heavy rare-earth-based Laves phases are well-studied intermetallic materials that stand out for their remarkably high magnetocaloric effects, particularly at cryogenic temperatures. In this study, we present the findings of our comprehensive investigation of cobalt Laves phases R Co 2 with R standing for erbium, holmium, dysprosium, and terbium. This includes the determination of the magnetocaloric effect by indirect methods using calorimetric and magnetization data. Furthermore, for the first time in these materials, we directly measured the adiabatic temperature change at high magnetic fields up to 20 T. The largest Δ T ad value of 17 K, we obtained for ErCo 2. Because the order of the transition significantly impacts the efficiency of thermodynamic cycles, we have also focused on determining the transition order in these materials. This was done through the application of established methods and a recently proposed quantitative criterion including the value of the local exponent n. Further, we compare our results with other materials using a straightforward material-based figure of merit - the temperature-averaged entropy change (TEC). Our results demonstrate the great potential of these materials for applications such as for magnetic hydrogen liquefaction. • A comprehensive experimental study was conducted on the magnetocaloric effect in Laves phases RCo2 (R=Er, Ho, Dy, Tb). • Directly obtained adiabatic temperature changes in RCo2 at high magnetic fields up to 20 T are provided for the first time. • Calorimetric, magnetization, and directly obtained data are in good agreement between each other. • The study highlights the potential of these materials in applications such as magnetic hydrogen liquefaction. [ABSTRACT FROM AUTHOR]

Solid-state cooling technology has attracted great attention to replace traditional vapor-compression cooling technology due to its advantages of environmentally friendly, energy conservation, and high efficiency. However, the cooling performance of a single field (magnetic, stress or electric field) induced caloric effect is still insufficient. Recently, a larger multicaloric effect is expected to be achieved by the synergistic regulation of multiple fields. In this study, we choose all- d -metal Ni 37 Co 13 Mn 35 Ti 15 alloy with magnetostructural phase transition and systematically study the multicaloric effect through the synergistic regulation of external stress and magnetic fields based on our homemade multicaloric effect testing device. The magnetic field and stress field play opposite effects on the phase transition, thus contributing contradictory caloric effect to multicaloric effect. By loading stress without magnetic field while unloading stress under magnetic field of 1.1 T, the stress hysteresis and energy hysteresis loss can be reduced by up to 45.2% and 54.8% in comparison with those obtained from a non-ideal regulation protocol. Moreover, the maximum adiabatic temperature change |Δ T ad | during unloading increases by 24% from 6.3 K to 7.8 K with the application of magnetic field (1.1 T), suggesting a larger multicaloric effect than that of a single elastocaloric effect. These results prove that multi-field synergistic regulation is an effective means to enhance the multicaloric effect and reduce the hysteresis and energy loss of materials with the magnetostructural transition. • The multicaloric effect of alloys is directly measured by a homemade device. • The caloric effects are compared under different protocols of regulation. • The adiabatic temperature change of multicaloric effect increases by 24%. • The energy loss and stress hysteresis of multicaloric effect are reduced. [ABSTRACT FROM AUTHOR]

In the present work the influence of Ge doping on crystal structure, microstructure, martensitic transformation (MT) and magnetocaloric effect (MCE) of Heusler-type Ni 45 Co 5 Mn 36.7 In 13.3- x Ge x (x = 0, 2, and 3 at. %) metamagnetic shape memory alloys (MetaMSMAs) have been studied. Melt-spinning was used to prepare ribbons of these alloys since the ribbon shape ensures a high surface-to-volume ratio favoring a high heat exchange rate in a solid-state refrigeration. Furthermore, melt-spinning can induce a specific microstructure and stabilize metastable phases at room temperature. The ribbons were examined by X-ray diffraction at different temperatures, scanning electron microscopy, calorimetry, thermomagnetization, and magnetic field induced adiabatic temperature change measurements carried out across MT. It was found that Ge doping gave rise to enhanced antiferromagnetic interactions, stabilized martensitic phase, increased the MT temperature, causing larger magnetization jumps at MT and making narrower MT hysteresis. The x = 3 ribbon exhibited an inverse MCE at 303 K characterized by the isothermal magnetic entropy change value of |26.9|J/kgK at μ 0 H = 5 T and an adiabatic temperature change of ǀ1.5ǀ K at μ 0 H = 1.96 T. These values are comparable with the previously reported data on the Ni–Mn-based metamagnetic shape memory alloys in a bulk form. Transformation behavior and inverse magnetocaloric effect in Ni 45 Co 5 Mn 36.7 In 10.3 Ge 3 metamagnetic shape memory melt-spun ribbons. The inset depicts SEM micrographs of the free side of the ribbon in the austenitic (323 K) and martensitic (233 K) phases. [Display omitted] • Ni 45 Co 5 Mn 36.7 In 13.3- x Ge x (x = 0, 2, and 3) metamagnetic shape memory alloys successfully prepared by melt-spinning to maximize the surface-to-volume ratio. • The Ge-doping shifts the martensitic transformation temperature, increase magnetization saturation across MT, and reduce the thermal hysteresis. • The x = 3 sample indicated a value of.|26.9|J/kgK at μ 0 H = 5 T and ǀ1.5ǀ K at μ 0 H = 1.96 T for inverse MCE at 303 K. [ABSTRACT FROM AUTHOR]

We have studied the magnetic and magnetocaloric response of MnFe 4 Si 3 to pulsed and static magnetic fields up to 50 T. We determine the adiabatic temperature change ΔT ad directly in pulsed fields and compare to the results of magnetization and specific heat measurements in static magnetic fields. The high ability of cycling even in fields μ 0 H = 50 T confirms the high structural stability of MnFe 4 Si 3 against field changes, an important property for applications. The magnetic response to magnetic fields up to μ 0 H = 35 T shows that the anisotropy can be overcome by fields of approx. 4 T. • Magnetic and magnetocaloric properties of single crystalline MnFe 4 Si 3 have been studied in pulsed and static fields. The adiabatic temperature change ∆T ad determined directly in pulsed fields is in good agreement to the results of magnetization and specific heat measurements in static magnetic fields. • Direct measurement of the adiabatic temperature change using pulsed magnetic fields is an excellent technique for the evaluation of the magnetocaloric effect, as it provides nearly adiabatic conditions and an experimental situation that is close to the one present in real applications. • The compound MnFe 4 Si 3 shows high cyclability even in very high fields which confirms its high structural stability against field changes, an important property for applications. [ABSTRACT FROM AUTHOR]

Magnetic shape memory alloys (MSMAs) have attracted great interests due to their multifunctional properties associated with external-field-induced martensitic transition, such as magnetostrain, magnetoresistance, magnetocaloric effect and elastocaloric effect. Search for MSMAs displaying a unique combination of strong metamagnetic transition and stable, large caloric effect is nowadays very active. Here we report the simultaneous achievement of a strong metamagnetic transition as well as a large magnetic-field-induced entropy change of 17.4 J kg−1 K−1 under 2 T and a stable, large elastocaloric effect with adiabatic temperature change of ∼5.0 K during more than 2100 mechanical cycles, in a Ni-Fe-Co-Mn-Sn MSMA. Such combination in a single material has never been reported in the literature. Furthermore, we demonstrate that fully reversible metamagnetic transition and consequently large, reversible multicaloric effect can be achieved by increasing magnetic field from 0 T to 2 T at zero stress and decreasing field from 2 T to 0 T at a uniaxial stress of 23.5 MPa. This dual-stimulus magnetic-mechanical multicaloric cooling cycle also provides an opportunity for achieving reversible magnetoresistance and magnetostrain under the coupling of a low magnetic field and small stress, which is beneficial for practical applications. The high cyclic stability of large caloric effects is ascribed to the good geometric compatibility at the interface between austenite and martensite as revealed by employing multiscale characterization approaches, including in-situ synchrotron high-energy X-ray diffraction and transmission electron microscopy. This study has great implications on developing high-performance multifunctional alloys with magnetostructural transition for actuation, magnetic recording and solid-state refrigeration applications. Image 1 [ABSTRACT FROM AUTHOR]

The magnetocaloric effect (MCE) in single crystals of MnAs compound was studied both experimentally and theoretically. Direct measurement of MCE showed that the adiabatic temperature change (ΔT ad) in a magnetic field of 10 T was 15 K. But direct measurement of the quasi-adiabatic heat transfer (ΔQ) of the sample yielded a value of 9500 J/kg in a magnetic field of 10 T. To date, it is the highest experimentally recorded value for ΔQ by direct measurement. Phenomenological considerations that take into account the interaction of magnetic and structural order parameters explain a number of anomalies in the magnetic and magnetocaloric properties of MnAs that were observed during the experiments. Image 1 • The MCE of MnAs single crystal by a direct method is investigated. • Adiabatic temperature change is 15 K in 10 T at temperature of 311 K. • Isothermal heat transfer is 9300 J/kg in10 T at temperature of 318 K. • Phenomenological model explain a number of anomalies in the magnetic properties. • The jumps in magnetization change decrease the MnAs magnetocaloric characteristics. [ABSTRACT FROM AUTHOR]

• An operation mode for caloric refrigeration, "cooling by sweeping", is presented. • Device heat flow is established by exploiting applied field dynamics. • A simple magnetic refrigerator geometry is considered for validation. • Using this method, no fluids or thermally switchable components are required. So far, all ferroic-based refrigerator prototypes have relied either in fluids or thermally switchable components as main heat exchangers, which brings some issues in terms of their applicability, such as the use of pumps for moving the fluid and the availability of thermally switchable components. We show that such heat exchangers are not necessary if field dynamics are explored. By using the example of magnetocaloric refrigeration, we show numerically that the operation of a simple apparatus constituted only by a magnetocaloric material and a magnet sweeping at a given frequency results in refrigeration. With the optimization of the type of motion, resting times after the complete application and removal of the magnetic field and frequency, a temperature span of 0.87 K is reached, which represents ∼ 20% of the maximum adiabatic temperature span of the material used in modeling, gadolinium. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The adiabatic temperature change Δ T ad of a Mn 1.3 Fe 0.7 P 0.5 Si 0.55 Fe 2 P-type alloy was measured under different magnetic field-sweep rates from 0.93 Ts−1 to 2870 Ts−1. We find a field-sweep-rate independent magnetocaloric effect due to a partial alignment of magnetic moments in the paramagnetic region overlapping with the magnetocaloric effect of the first-order phase transition. Additionally, the first-order phase transition is not completed even in fields up to 20 T leading to a non-saturating behavior of Δ T ad . Measurements in different pulsed fields reveal that the first-order phase transition cannot follow the fast field changes as previously assumed, resulting in a distinct field-dependent hysteresis in Δ T ad . [ABSTRACT FROM AUTHOR]

The adiabatic temperature change (ATad) in Ni45 Mn43CoSn11 has been measured by a direct method in magnetic field changes up to 14 T. Large reversible magnetocaloric effects resulting in ΔTad of about = -11 and 5 K have been observed for magnetic field changes of 14 T at the magnetostructural (TA ~ 260 K) and magnetic transitions (TC ~ 320 K), respectively. The impact of the thermomagnetic history on ΔTad at high magnetic fields has been reported. The significant observed changes in the relaxation time of ΔTad, depending on the type of the phase transitions, magnetization, and demagnetization cycle are discussed. [ABSTRACT FROM AUTHOR]

This study presents the results of direct measurements of the adiabatic temperature change (∆T ad) in Ni 50 Mn 28 Ga 22−x (Cu, Zn)x (x = 0; 1,5) alloys in cyclic magnetic fields of 0.62 and 1.2 T at frequencies f= 1, 5, 10, and 20 Hz. The substitution of zinc and copper for the initial composition resulted in a decrease in ∆T ad and a stronger frequency dependence. The strong frequency dependence of ∆T ad near T C in the Ni 50 Mn 28 Ga 22−x (Cu, Zn)x system is due to the inhomogeneous microstructure and the coexistence of martensite-austenite phases, which give rise to two simultaneously acting mechanisms. Firstly, the addition of Zn and Cu increases the coercive force H C , resulting in an increase in the viscosity coefficient. Secondly, an increase in the frequency of the cyclic magnetic field (i.e., an increase in the field sweep rate) leads to the same effect, increasing the viscosity coefficient. Which, in our opinion, is the reason for the frequency dependences of ∆T ad near T C. The study found that the specific cooling power (SCP) for the Ni 50 Mn 28 Ga 22 sample in a cyclic magnetic field of 1.2 T increased with frequency, reaching 4.75 W/g at 20 Hz, which is 14.1 times greater than at 1 Hz. This suggests that, under conditions of sufficient heat exchange, the cooling efficiency of a magnetic refrigerator can be greatly improved by increasing the operating frequency. • Direct measurements of the ∆T ad in Ni 50 Mn 28 Ga 22−x (Cu, Zn)x (x = 0; 1,5) alloys in cyclic magnetic fields of 0.62 and 1.2 T. • The substitution of Zn and Cu for the initial composition resulted in a decrease in ∆T ad and a stronger frequency dependence. • Specific cooling power for the Ni 50 Mn 28 Ga 22 sample in a cyclic magnetic field of 1.2 T increases with frequency. • The addition of Zn and Cu increases the coercive force H C , resulting in an increase in the viscosity coefficient. [ABSTRACT FROM AUTHOR]

The paper presents the results of a study of magnetization, specific heat (C P), thermal diffusivity (η), thermal conductivity (κ) and direct measurements magnetocaloric effect of polycrystalline samples Pr 0.7 Sr 0.3−x Ba x MnO 3 (x = 0–0.3). An increase in the Ba concentration leads to a decrease in the Curie temperature (T C), an increase in the disorder parameter (σ 2) and a noticeable increase in thermal conductivity of the ferromagnetic phase (FM). The κ(Т) data near Т С revealed small minima and a sharp jump-like change in thermal conductivity upon transition to the FM phase. These results suggest that the anomalies in the temperature dependences of η(Т) and κ(Т) are associated with the scattering of thermal phonons both from distortions of the crystal lattice and from spin fluctuations. The giant change of η (Δη/η ∼ 67%) and κ (Δκ/κ ∼ 33%) was found in a magnetic field of 1.8 T for the x = 0 (Pr 0.7 Sr 0.3 MnO 3) sample. The maximum values of ∆T, ∆S and relative cooling power (RCP), observed for this sample in a field of 1.8 T, are equal to 1.81 K, 3.38 J/kg K and 74.02 J/kg, respectively. In the studied Pr 0.7 Sr 0.3−x Ba x MnO 3 samples, the specific cooling power value at f = 0.2 Hz is 0.35, 0.29, 0.21, and 0.11 W/g for x = 0, 0.1, 0.2, and 0.3 sample, respectively. • Specific heat, thermal diffusivity, and thermal conductivity of polycrystalline samples Pr 0.7 Sr 0.3-x Ba x MnO 3. • An increase in Ba concentration leads to a decrease in T C , an increase in disorder parameter. • Magneto-thermal diffusivity (Δη/η) and magneto-thermal conductivity (Δκ/κ) in a 1.8 T magnetic field for Pr 0.7 Sr 0.3-x Ba x MnO 3 was study. • Gigantic values of changes Δη/η ∼ 67% and Δκ/κ ∼ 33% were found in a magnetic field of 1.8 T for a sample with x = 0. • Direct measurements of adiabatic temperature change in a cyclic magnetic field 1.8 T. [ABSTRACT FROM AUTHOR]

The use of multi-stimuli materials is a promising approach for increasing the cooling capacity of magnetic refrigerators. The working body undergoes both a magnetic field and an external compressive pressure during cooling. The proposed material must have outstanding magnetocaloric and mechanical properties. The magnetocaloric properties should provide a high adiabatic temperature change value in a limited field range. Mechanical stability at high pressures and adequate geometry are required to ensure high heat transfer values. The compounds La(Fe,Si) 13 and their hydrides are the most suitable for the manufacture of such devices. They are able to work at both room and cryogenic temperatures. In the article, we present the results of direct measurements of the magnetocaloric effect and mechanical compression tests of the cast and hydrogenated La(Fe,Si) 13 H δ rods. The samples were reinforced with a secondary alpha-iron phase, which ensured their mechanical integrity during hydrogenation and cycle performance. The addition of a secondary alpha-iron phase leads to a decrease in the magnetocaloric effect value. Therefore, we determine the optimal content of the secondary phase, which provides a balance between the caloric and mechanical alloy properties. • An optimization of La(Fe,Si) 13 alloys and their hydrides for multi-stimuli cooling cycle applications has been carried out. • A bundle of 100–300 µm- diameter rods was proposed as the most adequate in the operating frequency range above 3 Hz. • The 15 vol% of α-Fe in the La(Fe,Si) 13 alloys provides a balance between the caloric and mechanical alloy properties. [ABSTRACT FROM AUTHOR]

TmB4 is an anisotropic magnetic system with geometrical frustration of Shastry-Sutherland type. Experimentally, it was the rotating magnetocaloric effect (R-MCE) of TmB4 evaluated from measurements of temperature dependences of heat capacity in various magnetic fields and crystallographic orientations. R-MCE in this system shows a complex behavior of the adiabatic temperature change (AdT) -- cooling above TN and two heating regions in ordered phase [1]. In this contribution, a theoretical model with spin-electron Hamiltonian was suggested to explain the complex AdT behavior. The model is based on the idea of two interacting subsystems: the localized spins of rare earth ions, and the itinerant electrons in conduction band. The received results from Monte Carlo approach successfully reproduce the observed heating and cooling regions. Thus, our study shows that measurements of R-MCE can be an effective tool for investigation of the microscopic properties of magnetization processes. [ABSTRACT FROM AUTHOR]

Owing to a high degree of geometrical frustration an Ising antiferromagnet on a kagome lattice is known to exhibit no long-range ordering at any temperature, including the ground state. Nevertheless, at low temperatures it shows a strongly correlated, highly fluctuating regime known as a cooperative paramagnet or classical spin liquid. In the ground state it is characterized by a macroscopic degeneracy which translates to a relatively large value of the residual entropy. It has been shown that the presence of a macroscopic degeneracy associated with geometrical frustration below the saturation field can facilitate an enhanced magnetocaloric effect, which can exceed that of an ideal paramagnet with equivalent spin by more than an order of magnitude. In the present study we investigate magnetic and magnetocaloric properties of the Ising antiferromagnet on a kagome lattice by Monte Carlo simulation. In particular, we calculate the entropy of the system using the thermodynamic integration method and evaluate quantities which characterize magnetocaloric effect, such as the isothermal entropy and adiabatic temperature changes in a varying magnetic field. It is found that the Ising antiferromagnet on a kagome lattice shows the most interesting magnetocaloric properties at low temperatures and moderate magnetic fields, suggesting that its potential can be used in technological applications for low-temperature magnetic refrigeration. [ABSTRACT FROM AUTHOR]

TmB4 is an anisotropic magnetic system with geometrical frustration of Shastry-Sutherland type. Experimentally, it was the rotating magnetocaloric effect (R-MCE) of TmB4 evaluated from measurements of temperature dependences of heat capacity in various magnetic fields and crystallographic orientations. R-MCE in this system shows a complex behavior of the adiabatic temperature change (AdT) -- cooling above TN and two heating regions in ordered phase [1]. In this contribution, a theoretical model with spin-electron Hamiltonian was suggested to explain the complex AdT behavior. The model is based on the idea of two interacting subsystems: the localized spins of rare earth ions, and the itinerant electrons in conduction band. The received results from Monte Carlo approach successfully reproduce the observed heating and cooling regions. Thus, our study shows that measurements of R-MCE can be an effective tool for investigation of the microscopic properties of magnetization processes. [ABSTRACT FROM AUTHOR]

Graphical abstract Temperature dependence of the magnetic entropy change for α-Dy 2 S 3 single crystals in magnetic field change within 5 T H ‖ b (a) and H ⊥ b (b). Highlights • Specific heat measurements in the wide temperature/magnetic field range for α- R 2 S 3 (R = Tb, Dy) single crystals. • Effect of magnetic field on the specific heat near the successive AFM ordering temperatures. • Estimation of magnetic entropy change and adiabatic temperature change from specific heat in magnetic field. • Influence of magnitude and orientation of magnetic field on the magnetocaloric effect. Abstract The magnetocaloric effects (MCE) of α-Tb 2 S 3 and α-Dy 2 S 3 single crystals exhibiting successive antiferromagnetic (AFM) transitions have been investigated by analyzing specific heat measured in magnetic field. The temperature dependence of specific heat in the vicinity of the successive transitions shows obvious distinction depending on the orientations of the applied magnetic field for both α-Tb 2 S 3 and α-Dy 2 S 3 that having orthorhombic crystal structures. When the magnetic field is increased, the specific heat is as follows: For α-Tb 2 S 3 in H ‖ b , the peak around T N2 shifts to lower temperature but the other one peak around T N1 barely moves; In H ⊥ b , the peak around T N2 has no shift almost within 3 T but suddenly moves to lower temperature in 4 T and the other one peak around T N1 shifts to lower temperature in specific heat versus temperature. In the case of α-Dy 2 S 3 , the two peaks around T N2 and T N1 shift to lower temperatures in H ‖ b but move to higher temperatures when the magnetic field is increased up to 5 T by H ⊥ b in spite of antiferromagnetic transitions. Therefore, the maximum value and corresponding temperature of both isothermal magnetic entropy change (Δ S m) and adiabatic temperature change (Δ T ad) in the magnetic field H ⊥ b are extremely different in low temperature range from that in the field of H ‖ b . The results propone that the MCE of α-Tb 2 S 3 and α-Dy 2 S 3 could be controlled at low temperature by the magnitude and orientation of magnetic field. It also indicates that the refrigerating capacity and thermal absorption capacity will be controlled by changing magnitude and orientation of magnetic field on the α-Tb 2 S 3 and α-Dy 2 S 3 single crystals. [ABSTRACT FROM AUTHOR]