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

Solid‐state caloric effects as intrinsic thermal responses to different physical external stimuli (magnetic‐, uniaxial stress‐, pressure‐, and electric‐fields) can achieve a higher energy efficiency compared with traditional gas compression techniques. Among these effects, magnetocaloric energy conversion is regarded as the best available alternative and has been exploited extensively for promising application scenarios in the last decades. This review systematically introduces the magnetocaloric effect and its applications, and summarizes the corresponding representative magnetocaloric materials, as well as important progress in recent years. Specifically, the review focuses on some key understandings of the magnetocaloric effect by utilizing state‐of‐the‐art technical tools such as synchrotron X‐ray, neutron scattering, muon spin spectroscopy, positron annihilation spectroscopy, high magnetic fields, etc., and highlights their importance toward advanced materials design and development. An overview of the basic principles and applications of these advanced techniques on magnetocaloric materials is provided. Finally, the challenges and perspectives on further developments in this field are discussed. Further in‐depth understanding and manufacturing technology advancement combined with fast‐developed artificial intelligence and machine learning are expected to advance the magnetocaloric energy conversion technology closer to real applications. [ABSTRACT FROM AUTHOR]

This article presents the results of a novel concept of heat and cold decoupling from magnetocaloric materials (MCM) by unidirectional fluid flow. An experimental setup was developed to analyse the heat/cold decoupling and determine the optimal process parameters. Three different kinds of magnetocaloric material samples were analysed by using this setup. Comparing the measuring results to those of existing active magnetic regenerator (AMR) systems shows a very good performance and indicates a higher achievable thermal power output when using a unidirectional fluid flow. [ABSTRACT FROM AUTHOR]

Owing to low ductility of magnetocaloric material (MCM)s, the plastic deformation process is quite challenging, and information available on the deformation process of MCMs is limited. In this study, the cold rolling and wire drawing processes of Gd wire including heat treatment were conducted. Uniaxial compression test of as-cast and heat treated Gd rod was conducted to evaluate the material property. The magnetocaloric effect (MCE) of drawn Gd wire was indirectly measured using a vibrating sample magnetometer (VSM). Pass schedule of cold rolling and wire drawing process for the Gd wire of Ø1.0 was designed. Finite element (FE) simulation of drawing process was conducted to investigate the drawing force for each drawing pass and strain distribution. Friction coefficient between the drawing die and Gd wire was evaluated via FE simulation and drawing experiments using a lubricant. Magnetic properties of the deformed and annealed Gd wire were evaluated and compared. The evaluated magnetic properties have shown that the presented process schedule is reasonable for manufacturing magnetocaloric wire without diminishing the magnetocaloric effect.

In this work, a Ni-doped MnCoGe alloy has been synthesized by doping 4 wt% of Ni in place of Ge. The room temperature XRD pattern shows that the alloy has crystallized in two phases: hexagonal-MnCoGe and cubic-Co2MnGe and in addition, there are vacancies at Co and Ge sites. Around room temperature, MnCoGe phase has hexagonal structure and as the temperature is lowered, the structural transition takes place to orthorhombic-MnCoGe phase. When external magnetic field is low, orthorhombic phase is antiferromagnetic, but as field strength is increased, the ferromagnetic ground state is established. This alloy undergoes a second-order ferromagnetic transition followed by a first-order structural transition in a narrow temperature width. These have synergistically resulted in a single, reversible - Δ S (T) curve across a very wide temperature span. The magnitude of entropy change has to be, however, improved by Ni–Ge tuning to enhance the relative cooling power. Regardless, a modest magnetocaloric effect with negligible hysteresis has been attained near room temperature via Ni-doping in MnCoGe alloy. [ABSTRACT FROM AUTHOR]

Magnetocaloric heat pumping (MCHP) promises to be more efficient than traditional vapor compression while also eliminating the deleterious effects of gaseous refrigerants. While MCHP devices have shown the temperature spans and efficiencies needed for different heating and cooling applications, they struggle to become commercially viable due to their large size and mass, and resultant high cost. This paper evaluates a baseline MCHP device and explores methods to boost its system power density (SPD). The key components of the baseline system are the gadolinium packed-particle bed active magnetic regenerator (AMR) and a magnetic source composed of permanent magnets and high permeability magnetic steel. To enhance the SPD, the paper evaluates maximizing the AMR volume, opting for first-order magnetocaloric materials, optimizing the magnet and AMR geometry, and reducing the size of magnets and magnetic steel parts. At larger thermal powers, increasing the AMR diameter and the number of magnetic poles were evaluated. Using finite element models, solid models, and estimates of magnetocaloric material performance, thermal powers ranging from 37 W to 44 kW at a nominal 10 K temperature span were projected, and SPD was estimated to improve from 6 W/kg to 81 W/kg. Neglecting end effects, an upper limit of 114 W/g is estimated. Compared to SPD of off-the-shelf compressors with similar environment temperatures, MCHP power density using gadolinium is competitive up to roughly 200 W of cooling power. This is extended to 1 kW when using LaFeSi alloys and up to 3 kW in the limiting case. These results indicate that the performance and mass of MCHP can match that of compressors, which is a critical step toward cost-competitive magnetocaloric technology. • Performance estimates cover a 37 W to 43.5 kW range of magnetocaloric heat pumps. • Modifications increase the projected system power density by a factor of three. • Estimates show a maximum 114 W/kg power density for similar magnetocaloric devices. • Power density of low-power magnetocaloric heat pumps match existing compressors. [ABSTRACT FROM AUTHOR]

Magnetic refrigeration (MR) based on the magnetocaloric effect (MCE) has been recognized as an environmentally benign and energy-efficient cooling technology. Exploring suitable magnetocaloric materials is a crucial prerequisite for practical MR applications. We have herein provided a systematic investigation of the crystal structure, microstructure, electronic structure, magnetic phase transition, critical behavior, and MCE of the GdCoC compound featuring excellent cryogenic magnetocaloric performance by means of experimental determination and theoretical calculation. The GdCoC compound is crystallized in a simple layered tetragonal crystal structure with a P 4 2 / mmc space group and undergoes two successive ferromagnetic (FM) transitions along with a low-temperature weak antiferromagnetic (AFM) transition under low magnetic fields. Density functional theory calculations confirms the FM coupling of the Gd and Co intra-sublattice interactions, whereas AFM coupling for their inter-sublattice interaction. The magnetic transitions are merged in to one under high magnetic fields which has been confirmed to be second-order type and its critical behavior can be understood in the framework of tri-critical mean-field model, whereas the low-temperature weak AFM transition is belonging to the first-order type. The excellent magnetocaloric performance of the GdCoC compound was identified by the parameters of magnetic entropy change, adiabatic temperature change, temperature-averaged entropy change, relative cooling power, and refrigerant capacity, which are superior to most of the well-known magnetocaloric materials with similar working temperatures, making it attractive for practical cryogenic MR applications. [Display omitted] [ABSTRACT FROM AUTHOR]

The doping of Ho into Gd can not only adjust the Curie temperature of Gd1-xHox alloy but also enhance the maximal magnetic entropy change. In the present paper, the magnetocaloric characteristics of Gd1-xHox alloys were calculated by means of the de Gennes model, and the isothermal magnetic entropy change of Gd1-xHox (x = 0, 0.05, 0.10, 0.15, 0.20) alloys versus temperature curves generally exhibit a caret-like shape. Furthermore, the composite material composed of Gd and Gd0.80Ho0.20 is introduced in order to obtain a gentler entropy change curve over a large temperature span. Consequently, it is found under magnetic field change from 0 to 2 T that the composite composed of Gd and Gd0.80Ho0.20 with 67% mass ratio of Gd possesses a maximal full width at half maxima δTFWHM of the isothermal magnetic entropy change curve which is 87.3 K, with temperature 217.9 K of the cold end at half-width and temperature 305.2 K of the hot end at half-width. In such a case, the maximal magnetic entropy change is 4.17 J/(kgK), relative cooling power (RCP) is about 360 J/kg, and refrigeration capacity (RC) achieves 280.6 J/kg. The results show that the composite magnetocaloric material can largely enhance the material performance for magnetic refrigeration application. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect (MCE) is an important phenomenon occurring in cryogenic cooling. Herein, a promising MCE material, GdVO4 nanopowder, was synthesized using a microwave-assisted hydrothermal method. The magnetic properties of the produced GdVO4 nanopowder were measured to investigate its MCE efficiency. The as-prepared GdVO4 nanopowder exhibited an antiferromagnetic–paramagnetic transition at 2.20 K, lower than that of bulk GdVO4 (2.50 K). The nanocrystalline GdVO4 showed weak antiferromagnetism due to size effects, where the broken symmetry of the surfaces resulted in a low crystalline anisotropy. However, the GdVO4 nanopowder after annealing at 900 °C showed an increased TN of 2.50 K due to aggregation and the resulting suppression of the size effects. Based on the Maxwell relation, the magnetic entropy change was obtained and compared with that of bulk GdVO4. Although the change in the maximum magnetic entropy was reduced for the nanocrystalline GdVO4 compared to that of bulk GdVO4, the absence of hysteresis loss in the nanocrystalline GdVO4 is important for high-efficiency magnetocaloric materials to be used in hydrogen liquefaction applications. [ABSTRACT FROM AUTHOR]

The microstructure, phase constitution and corrosion behavior of non-stoichiometric La x Fe 11 Co 0. 8 Si 1.2 (x = 1.0, 1.2, 1.4, 1.6) magnetocaloric alloys were investigated. Annealed La x Fe 11 Co 0. 8 Si 1.2 compounds, containing the desired NaZn 13 -type matrix phase (1:13 phase), as well as a small α-Fe and La-rich phase content, exhibited high micro-galvanic corrosion in deionized water. The size of the La-rich phase in the La x Fe 11 Co 0. 8 Si 1.2 alloys varied with the La content. The refined La-rich phase in the La 1. 4 Fe 11 Co 0. 8 Si 1.2 alloy led to reduced galvanic corrosion and a more protective corrosion layer. Due to the internal stress of the corrosion product, the corrosion product of the coarse La-rich phase in the La 1. 6 Fe 11 Co 0. 8 Si 1.2 alloy easily cracked, leading to higher corrosion. Among these alloys, the La 1. 4 Fe 11 Co 0. 8 Si 1.2 alloy with a high content of the 1:13 phase and a small finer La-rich phase content, exhibited strong corrosion resistance. • Corrosion behavior of magnetocaloric La x Fe 11 Co 0·8 Si 1.2 (x = 1.0, 1.2, 1.4, 1.6) alloys was investigated. • A uniform distribution of fine La-rich and α-Fe phases can improve the corrosion resistance. • With excessive corrosion products, cracks appear on the corrosion layer due to internal stress. • The La 1·4 Fe 11 Co 0·8 Si 1.2 alloy exhibited the best corrosion resistance in the La x Fe 11 Co 0·8 Si 1.2 (x = 1.0, 1.2, 1.4, 1.6) alloy series. [ABSTRACT FROM AUTHOR]

• Magnetocaloric effect of single crystal GdTiO 3 was studied. • GdTiO 3 had a 2nd order transition from paramagnetic to ferrimagnetic state at 33 K. • A small anisotropy was found in the magnetization and specific heat. • The magnetization showed no hysteresis. • Entropy-temperature diagram of the single crystal GdTiO 3 was obtained. • GdTiO 3 has the potential as a magnetic refrigerant for hydrogen liquefaction. We studied the magnetocaloric effect in a single crystal GdTiO 3. Single crystal GdTiO 3 had a second order phase transition from a paramagnetic to ferrimagnetic state at 33 K. The maximum entropy change of - Δ S = 0.10 J/cm3 K was observed in a 5 T field at the transition temperature. A small anisotropy was found in the magnetization and specific heat in low magnetic fields. The magnetization showed no hysteresis. Temperature dependencies of entropy, which are important for analyzing the refrigeration cycle, were calculated from the magnetization and specific heat measurements. These results indicate that GdTiO 3 has the potential for applications as a magnetic refrigerant for hydrogen liquefaction. [ABSTRACT FROM AUTHOR]

This work employs a thermal analysis experimental procedure that contributes for understanding of the MnAs compound thermal hysteresis associated with its magnetic transition near room temperature. The study was performed using a differential scanning calorimeter and different heating rates in a temperature interval around the magnetic transition temperature. The experiment consisted in two procedures, the first one analyzed the onset and peak temperatures of the thermal event associated with the magnetic transition at different heating rates. The second procedure consisted in the analysis of the formation and decomposition of the phase associated with the magnetic transition by means of the thermal event enthalpy as a function of the temperature. The results show that the onset temperatures during cooling increase almost linearly with cooling rate and the onset temperatures during heating are almost constant. Also, the transition enthalpy changes with heating rate and with reaction progress, exhibiting different behaviors during heating and cooling, thus suggesting two different mechanisms for the phase transition. Image 1073 • Thermal hysteresis is independent of the formed phase fraction. • Specifying T, P and M is not enough to specify its state. • This additional condition can be the volume of the material. • Thermal hysteresis may be correlated with the internal pressure. [ABSTRACT FROM AUTHOR]

Rare earth elements (REEs) are the core of many future-sustainable technologies. One example is magnetocaloric refrigeration, an emerging field essential for the efficient use of energy. Future adoption of this technology will require adequate processing of end-of-life units and production residues. Currently, REEs have very high supply risk, and their recovery rates are below 1%. So far, their recovery from magnetocaloric materials has not been addressed. This work reports on a leaching and solvent extraction process to recover REEs from genuine magnetocaloric materials comprising cerium, iron, lanthanum, manganese and silicon. Leaching was studied using nitric, hydrochloric and sulfuric acid solutions, with optimizations in terms of temperature, acid concentration and solid-to-liquid ratio. Recovery of REEs from nitric, hydrochloric, and sulfuric acid leachates was investigated with three types of solvating extractants: tributyl phosphate (TBP), trioctylphosphine oxides (Cyanex 923) and tetraoctyl digylcol amide (TODGA). Extraction was most effective from nitric acid media. Very good extraction selectivity between REEs and non-REEs was achieved with TODGA. Cyanex 923 showed better extraction efficiency than TBP, and performed best in aliphatic diluents. A separation factor of 3.3 between cerium and lanthanum was achieved with 1 mol/L Cyanex 923 in Isopar L. [ABSTRACT FROM AUTHOR]

First-order phase transition magnetocaloric materials in multi-stage regenerators are attractive for magnetocaloric refrigeration because of their relatively high available power and the potential for the use of low-cost elements such as iron in their production. In this work a model is used to represent the thermodynamic properties of magnetocaloric materials allowing the magnetocaloric materials to be fully parameterized for the first time. A numerical model is used to carry out a large study including the material parameters and the parameters that describe magnetocaloric machines and their operation. A unique method of evaluating material refrigeration capacity is introduced and used to normalize material inputs. The results are analyzed both in terms of the direct impact of the material parameters and the interactions between machine and material parameters on performance. It was found that machine cooling power was maximized for the cases with the largest adiabatic temperature changes. It was also found that many machine parameters and material parameters interact when determining the performance of a machine. This suggests that materials and machine research would benefit from a closer collaboration. [ABSTRACT FROM AUTHOR]

Hypothermia is an effective neuroprotective strategy for acute stroke. However, in clinical practice, the induction of hypothermia is achieved through the systemic reduction of body temperature (using thermal covers or endovascular cooling devices) which results in a complex system associated in many cases to side effects. Therefore, the aim of this study was to test the magnetocaloric effect as a potential new therapeutic strategy for stroke by means of an adiabatic magnetic refrigerator device. As a first approach, we have developed a simple device to evaluate in vitro the thermodynamic behavior of different concentrations of commercial gadolinium powder as a reference magnetocaloric material. The samples, properly thermally insulated, were cyclically magnetized and demagnetized at room temperature by 1 T permanent magnets in order to induce an adiabatic magnetic effect. Under the experimental conditions tested, results showed a maximun non-accumulative temperature variation of 0.2 °C, insufficient to carry out an effective hypothermia. This study allowed us to discuss about the use of new materials and strategies for further in vivo experiments. [ABSTRACT FROM AUTHOR]

Composites consisted of MnCoGe magnetocaloric alloy and BiSbTe thermoelectric alloy were prepared to explore their potential use in all-solid-state cooling. It was found that in the composites the phase transition of MnCoGe from orthorhombic to hexagonal phase causes a large drop of magnetostructural transition temperature from room temperature to 270 K. The diffusion of Mn into BiSbTe leads to the formation of interfacial phase Mn(Bi,Sb) 2 Te 4 and doping effect that depresses the thermoelectric performance. By adopting a low-temperature sintering strategy, the phase transition was restricted and the doping effect due to Mn diffusion was alleviated. As a result, the magnetostructural transition temperature around 300 K is maintained and the room-temperature magnetocaloric and thermoelectric properties are simultaneously optimized. The maximum magnetic entropy change of 4.3 × 10−3 J kg−1 K−1 at 2.0 T and maximum ZT value of 0.81 at 384 K have been obtained on the composite incorporated with 1 wt % MnCoGe. This work demonstrates that the control of phase transition and the doping effect of MnCoGe is crucial in optimizing the thermo-electro-magnetic properties of MnCoGe/BiSbTe composites. • The diffusion of Mn and formation of interfacial phase Mn(Bi,Sb) 2 Te 4 in MnCoGe/BiSbTe thermo-electro-magnetic composites were identified by the atomic-resolution STEM, which is crucial in affecting the thermoelectric and magnetocaloric performance. By regulating the magnetostructural transition and element diffusion, enhanced thermoelectric and magnetocaloric properties were realized in the composites. [ABSTRACT FROM AUTHOR]

We present magnetocaloric effect measurements of the ferromagnetic semiconductor EuS in the vicinity of its ordering temperature. Single phase EuS powder was synthesized by CS 2 gas sulfurization of Eu 2 O 3 . A sintered compact with relative density over 95% was prepared by pulsed electric current sintering of the powder. Temperature and magnetic field dependence of the magnetization and specific heat were characteristic of a paramagnetic to ferromagnetic second order phase transition. The entropy change induced by an external magnetic field and the specific heat were both close to those of a single crystal. We obtained an entropy-temperature ( S – T ) diagram of the EuS sintered compact. Carnot cycle liquefaction of hydrogen using EuS was compared with several other materials, with results indicating that sintered EuS is an excellent magnetic refrigerant for hydrogen liquefaction. [ABSTRACT FROM AUTHOR]

A hybrid numerical model of the magnetic refrigerator with multi-material microchannel regenerator has been developed. The magnetocaloric effect was implemented using instantaneous temperature rise/drop (discrete method). Two pipe-in-pipe heat exchangers at two ends of the regenerator were treated using ε-NTU method. The commercially available compounds of LaFe 13-x-y Co x Si y as well as hypothetical compounds of Gadolinium were considered as the magnetocaloric materials (MCMs) with different Curie temperatures. The predicted results of the present work for parallel-plate regenerators employing different compounds of LaFe 13-x-y Co x Si y were broadly in good agreement with the available experimental data. The cooling capacity increases as the number of MCMs increase. However, for a given length of regenerator, an optimum number of MCMs was seen yielding the maximum performance of the refrigerator. For a given number of MCMs, a smaller Curie temperature difference Δ T Cu between the MCMs was found to give higher performance. [ABSTRACT FROM AUTHOR]

Shape memory Heusler alloy Ni 50 Mn 35 In 12 Si 3 is investigated with electron spin resonance (ESR) technique in a temperature range of 200–300 K. ESR is a dynamic probe allowing us to separate the responses from various magnetic phases, thus to study the complex phase transitions. The sample shows three transition temperatures: T c A (271 K), T M (247 K) and T c M (212 K), where T c A is the Curie temperature of austenitic phase, T M and T c M are the temperatures of magnetostructural martensitic transition and the Curie temperature of martensitic phase, respectively. Furthermore, ESR data reveals the coexistence of two magnetic modes in whole temperature range of 200–300 K. Particularly in martensitic phase, two magnetic modes are attributed to two different kinds of lattice deformation, the slip and twinning deformations. [ABSTRACT FROM AUTHOR]

Mössbauer spectroscopy in the ferromagnetic AlFe B reveals T=299 K and shows good agreement with magnetic measurements. The crystals are plate-shaped. The flakes are found from X-ray diffraction to be in the crystallographic ac-plane in the orthorhombic system. The axes of the principle electric field gradient tensor are, by symmetry, colinear with the crystal a-, b- and c-axes. By using information about the quadrupole splitting and line asymmetry in the paramagnetic regime together with the quadrupole shift of the resonance lines in the ferromagnetic regime the magnetic hyperfine field direction is found to be in the ab-plane having an angle =40 to the b-axis. [ABSTRACT FROM AUTHOR]

Due to the large innovative applications involving magnetocaloric materials, such as magnetic cooling devices and thermomagnetic engines, the number of studies on their characterization have been increasing over the past two decades. Although indispensable, magnetic measurements are considerably time-consuming, which sometimes hinder depth studies on the subject. We propose a method that uses artificial neural networks to predict magnetic measurements of magnetocaloric materials with first- and second-order phase transitions, aiming to reduce the required number of measured field dependent magnetization curves M (H) in standard studies. We validate the method for magnetic measurements of the first- and second-order phase transition materials Gd 5 Ge 4 and Gd 5 Si 2. 4 Ge 1. 6 , respectively. The application of the proposed method results in very high accuracies, with r 2 > 0. 98 , when comparing the prediction to measured M (H) curves. The entropy change vs temperature curves upon the application of 5 T magnetic fields are also predicted. • Development of an AI method that predicts magnetic measurements. • Method validated for first- and second-order magnetocaloric materials. • The application of the method reduces the measuring times by approximately 70%. [ABSTRACT FROM AUTHOR]

This review outlines recent advances in the design of 3d-, 4f-, and 3d–4f type magnetic molecules for use as excellent cryogenic magnetic coolants based on the magnetocaloric effect (MCE), and the structure-magnetocaloric correlations of reported molecular coolants. Further improvements in the MCE values of molecular magnetic materials are also proposed based on assembly strategies from molecular chemistry and crystal engineering. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect is the thermal response of a material to an external magnetic field. This manuscript focuses on the physics and the properties of materials which are commonly used for magnetic refrigeration at cryogenic temperatures. After a brief overview of the magnetocaloric effect and associated thermodynamics, typical requirements on refrigerants are discussed from a standpoint of cooling power density optimization. Finally, a compilation of the most important properties of several common magnetocaloric materials is presented. [ABSTRACT FROM AUTHOR]

Abstract: Based on the experimental isothermal entropy change of the magnetic materials Gd x Dy1−x , the thermodynamic performance of a regeneration Ericsson refrigeration cycle is evaluated and analyzed. The effects of non-perfect regeneration on the cyclic performance are highlighted. For a room temperature hot reservoir, the cooling quantity, non-perfect regeneration heat quantity, and net cooling quantity of the established regeneration Ericsson refrigeration cycle are calculated as a function of the cold reservoir temperature. Furthermore, for several typical compositions x of the Gd x Dy1−x alloys, the values of the cooling quantity, non-perfect regeneration heat quantity, work input, net cooling quantity, and coefficient of performance (COP) are listed for given temperatures of the cold reservoir. The cyclic performance of the Gd x Dy1−x alloys with different composition x is compared and some significant analyses are provided. [Copyright &y& Elsevier]

Abstract: Astronautics has constructed a large-scale rotary magnetic refrigerator which was designed to provide 2 kW of cooling power over a temperature span of 12 K with Electrical Coefficient Of Performance (COPe) > 2. The system uses a NdFeB magnet assembly with peak field of 1.44 T which rotates over twelve beds arranged circumferentially. Each bed was packed with six layers of LaFeSiH of different Curie temperatures, chosen to optimize system performance over the desired span. We report here on the performance of this system at flow rates ranging from 12.5 to 21.2 L min−1. At the largest flow rate, the system produced 3042 W of cooling power at zero span and peak performance of 2502 W over a span of 11 K. To our knowledge, this represents the largest cooling power yet observed for a magnetic refrigeration system. We show that the measured performance is in good agreement with theoretical prediction. [Copyright &y& Elsevier]

Abstract: Ensure wellbeing for each of us is a first necessity for peace and development of society while preserving the environmental balance of the blue planet. Today's society is faced with major challenges such as the supply of energy, water, food, etc. Refrigeration is an important factor in the modern world. It is vital before life (sperm banks), for life (conversation food, medicine, …), and after life (preservation of human organs and tissues). However the negative impact of refrigeration on the environment is visible and, consequently, refrigeration systems are subject to prescriptive regulation. This regulation provides a great opportunity for the emergence of new refrigeration technologies and new product markets. In recent years, magnetic refrigeration is considered as a serious alternative for conventional systems. Today proof of the concept is established. Therefore what remains is to provide systems for the society. [Copyright &y& Elsevier]

Abstract: The thermodynamic cycle performance of Gadolinium (Gd) and Gd0.87Dy0.13 used as the working substance in regeneration magnetic Brayton and Ericsson refrigeration cycles are investigated under different external magnetic field conditions. Based on the experimental iso-field heat capacities of Gd with different magnetic fields, the effects of magnetic field change on thermodynamic performances including the magnetic entropy change, cooling quantity, non-perfect regeneration, net cooling quantity, and coefficient of performance (COP) are analyzed and discussed. The present work shows the possibility of reducing the regenerative losses and thereby improving the net cooling quantity for a given field change by selecting optimal initial and final magnetic field values. The similar analysis and calculation of the related thermodynamic performances are further applied to the magnetic material Gd0.87Dy0.13 which exhibits better net cooling quantities when compared to Gd at low temperature. [Copyright &y& Elsevier]

Abstract: We report on the magnetic and structural properties of Mn0.66Fe1.29P1−x Si x melt-spun ribbons with 0.34≤x≤0.42 that are promising candidates for high-temperature magnetocaloric applications. A magnetic moment of up to 4.57μB/f.u. for x=0.34 indicates high magnetic density in the system, which is certainly advantageous for the magnetocaloric effects. Introducing site disorder at the 3g site by replacing 1/3 of Fe with Mn appears to enhance the magnetic interaction, while the strong magnetoelastic coupling is maintained. This site disorder also shows a stabilizing effect on the hexagonal crystal structure, which is maintained to a high Si content. The moment alignment within the crystallographic unit cell is also affected when the Si content is increased from x=0.34 to 0.42 in the Mn0.66Fe1.29P1−x Si x compounds as the canting angle with respect to the c-direction increases. [Copyright &y& Elsevier]

Abstract: We present a comprehensive study of the magnetocaloric materials series La(Fe1−x Co x )11.9Si1.1 with . The ferromagnetic samples were manufactured using a novel powder metallurgy process by which industrial scale production is feasible. This new production method makes the materials more attractive as magnetic refrigerants for room temperature magnetic refrigeration. The Curie temperature of the compounds can be easily tuned by altering the Co content and all samples have little magnetic anisotropy and present a second-order magnetic transition so that thermal and magnetic hysteresis is absent. For all seven samples, we have calculated the magnetic entropy change, , from initial curve measurements and measured the adiabatic temperature change, , directly. In addition, for two of the samples, we determined the heat capacity as a function of applied magnetic field and the thermal conductivity. Where relevant, the results are compared with those of Gd, the benchmark material for room temperature magnetic refrigeration. [ABSTRACT FROM AUTHOR]

Abstract: A first part of the article contains a thermodynamic theory describing the temperature distribution in a Curie wheel. The occurring nonlinear ordinary differential equation has an analytical solution. If a Curie wheel is stabilized by levitation, it is named Palmy wheel. These wheels show a full structure, and because of this reason, their uptake of heat from a flame (Curie wheel) or by (solar) light absorption (Palmy wheel) only on the periphery of a cylinder is very limited. To improve the method, a modification of the principle by introducing a convective heat transport into a porous wheel is discussed. By this the power conversion rate from a heat flux to mechanical and electric power is very much increased. The second part of the article presents results of a theoretical/numerical study on the efficiencies of magnetic power conversion plants operating with porous wheels. Furthermore, these efficiencies—which are promising—are compared with those of existing power conversion plants, as e.g. geothermal binary cycle power plants. [Copyright &y& Elsevier]

• We synthesized single phase Mn 1.15 Fe 0.85 P 0.55 Si 0.45-x Al x polycrystalline bulk sample using conventional solid state reaction. • The curie temperature can be systematically tuned by substitution of Al at Si-site due to the lattice engineering effect. • We found the inverse relationship between the curie temperature and the lattice constant ratio (a / c). [Display omitted] Bulk polycrystalline samples of hexagonal Fe 2 P-type Al-added Mn 1.15 Fe 0.85 P 0.55 Si 0.45 were prepared via a solid-state reaction under controlled heat treatment, and their magnetocaloric properties, including magnetization and entropy change, were investigated. Notably, the Curie temperature, which is directly related to the operating temperature of magnetocaloric materials, could be systematically tuned through Al substitution at Si sites owing to the lattice engineering effect. We found an inverse relationship between the Curie temperature and the ratio of the c -axis lattice constant to a -axis lattice constant, which enables the design of magnetocaloric materials for high-performance magnetic cooling systems. [ABSTRACT FROM AUTHOR]

• DyVO 4 nanoparticles were synthesized by a microwave-assisted hydrothermal method. • Weak antiferromagnetic DyVO 4 exhibits low temperature magnetocaloric properties. • Low-temperature MCE effects can be applied for hydrogen liquefaction. This study verified the possibility of synthesizing DyVO 4 nanoparticles by a microwave-assisted hydrothermal method as a cryogenic magnetic cooling material. The synthesized DyVO 4 nanoparticles were approximately 10 nm in size with a typical tetragonal zircon-type phase. No antiferromagnetic-to-paramagnetic transition was observed in the temperature-dependent magnetization measurements within our measurement range due to the small particle size. The Curie–Weiss temperature (−2.65 K) obtained from Curie–Weiss fitting indicated weak antiferromagnetism, and an effective moment was calculated as 7.71 μ B. Based on isothermal magnetization measurements with an applied magnetic field, the DyVO 4 nanoparticles showed a different paramagnetic behavior with bulk antiferromagnetic DyVO 4 due to particle size effects, and a positive slope was found in the Arrott plots, indicating a second-order magnetic phase transition. Furthermore, a structural transition due to the Jahn–Teller effect was weakly observed at approximately 10 K. At Δ H = 50 k O e , the maximum change in magnetic entropy and relative cooling power were 10.32 J kg−1 K−1 and 175.44 J kg−1, respectively. [ABSTRACT FROM AUTHOR]

An overview of the magnetocaloric properties of the MnAs 1− x Sb x is presented. The temperature dependence of the isothermal magnetic entropy, Δ S mag , and the refrigerant capacity, RC, have been investigated theoretically and experimentally in a composite based on second order MnAs 1− x Sb x phases. This work demonstrates the outstanding agreement between the experimental results and the continuous curves predicted by numerical calculations, indicating that this approach can be used to design magnetic refrigerant materials with enhanced magnetocaloric response in magnetic refrigerator performing an Ericsson cycle near room temperature. [ABSTRACT FROM AUTHOR]

We detected a crossover from negative to positive thermal expansion with increasing Mn in HoCo 2 Mn x below the Curie temperature through high quality neutron diffraction measurements from 5 K to 400 K. Almost isotropic zero thermal expansion with coefficient of thermal expansion α l = − 4.894 × 10−7/K was achieved over a large range of temperature from 5 K to T C = 225 K in the compound HoCo 2 Mn 0.5. While the addition of manganese was shown to change the temperature dependence of the lattice, it was also noted that the Curie temperature rose significantly from 88 K in HoCo 2 to 253 K in HoCo 2 Mn providing a hope for a room temperature transition in similar doping series materials. • The Mn doped samples HoCo 2 Mn x (x = 0–1.0) are still isostructure to the parent compound HoCo 2 with pure phase. • The introduction of Mn into HoCo 2 compounds led to an unusual thermal expansion transformation from strong negative to positive thermal expansion in HoCo 2 Mn x compounds. • Almost zero thermal expansion can be achieved over a wide temperature rang (around 200 K) in the compound HoCo 2 Mn 0.5. [ABSTRACT FROM AUTHOR]

• An irreversible regenerative ferromagnetic Brayton refrigeration cycle is set up. • Gd 0.95 Er 0.05 , Gd 0.95 Dy 0.05 , and Gd are, respectively, used as the working substance. • The cooling rate, COP, and thermoeconomical function are derived and optimized. • The effects of some important parameters on the systemic performance are discussed. • The optimal cyclic performances with three working substances are compared. An irreversible regenerative Brayton refrigerator cycle is established, in which the nonperfect regenerator, regenerative time, heat leak, and irreversible adiabatic processes are taken into account. The mathematical expressions of the refrigeration rate, coefficient of performance, and thermoeconomic function of the refrigeration cycle are derived and the thermoeconomic function is optimized. Moreover, choosing Gd, Gd 0.95 Dy 0.05 and Gd 0.95 Er 0.05 as the working substances respectively, we discussed in detail the influences of the thermoeconomic and thermodynamic parameters on the optimal thermoeconomic and thermodynamic performances. The results show that the thermoeconomic performance of the refrigeration cycle using Gd or Gd 0.95 Dy 0.05 as the working substance is better than that using Gd 0.95 Er 0.05 and the thermoeconomic performance of the refrigeration cycle using Gd 0.95 Dy 0.05 as the working substance is better than that using Gd in the situation with the lower adiabatic magnetization. [ABSTRACT FROM AUTHOR]

• Recently, there are surging demand of studying magnetocaloric materials in order to achieve environmentally friendly refrigeration techniques. • So far, a theoretical estimation of the magnetocaloric effect (MCE) has been based on the analysis of specific heat capacity and magnetization. • In the meantime, the direct observation of qausi-adiabatic MCE cannot be overlooked for deeper understanding. • In this manuscript, we introduce quasi-adiabatic and non-equilibrium perturbation terms to equilibrium equation of the MCE. The model well explains the reversible MCE from a paramagnetic material YbPt 2 Sn as well as the irreversible MCE from a complex-phase material Ce 1 - x La x B 6 . Magnetocaloric effect (MCE) has drawn much attention because its magnetic cooling property enables refrigeration without producing noxious gas or using rapidly depleting resources. However, applications for everyday life are yet distant. In addition, we need to understand more about the practical aspect of the MCE. Here, we introduce a phenomenological model to explain the quasi-adiabatic MCE. Correction factors to the equilibrium thermodynamic feature implied by the entropy landscape are devised in analytic forms. To demonstrate the validity of the model, the MCE from two different materials is investigated. The recently discovered metallic paramagnet, YbPt 2 Sn, shows a linear and reversible MCE which is typical of a paramagnetic system and suitable for cryogenics without 3He. On the other hand, a complex-phase material, Ce 0.5 La 0.5 B 6 , exhibits a pronounced irreversible MCE especially across a magnetic phase boundary. A term that describes the field induced heating near a phase transition turns out to be essential in resolving the irreversible, non-equilibrium MCE. [ABSTRACT FROM AUTHOR]