Magnetic Refrigeration Technology Research Articles

Modeling the magnetic cooling efficiency of spinel ferrite magnetocaloric compounds for magnetic refrigeration application using hybrid intelligent computational methods

Spinel ferrite exhibits large magnetocaloric effect that promotes its candidature for solid state magnetic refrigeration technology. This method of cooling is promising and can conveniently replace the gas-compression method of refrigeration due to its energy saving capacity and ecological cleanliness. Among the available magnetocaloric materials, spinel ferrite metal oxide enjoys low production cost, non-toxicity, ease of preparation and non-oxidative. However, effective utilization of this magnetocaloric material for cooling technology requires determination of its magnetic cooling efficiency which is subjected to time consuming, intensive and laborious experimental procedures. This work employs the applied magnetic field, ionic radii and the concentrations of spinel ferrite constituents to develop a genetically hybridized support vector regression model (G-SVR) and extreme learning machine (ELM) intelligent model for determining magnetic cooling efficiency of spinel ferrite compounds. The developed G-SVR model outperforms ELM model for the testing set of spinel ferrite samples with percentage improvement of 60.57%, 19.69% and 64.73% using root mean square error, correlation coefficient and mean absolute error respectively, as performance measuring parameters. Influence of metal ions such as zinc, nickel and cadmium on magnetic cooling efficiency of various kinds of spinel ferrite compounds was investigated using the developed models. The presented intelligent approaches for spinel ferrite magnetic cooling efficiency determination in this work, with characteristic lower cost, quickness, effectiveness and precision would definitely facilitate and strengthen practical implementation of magnetic refrigeration technology for energy conservation and environmental friendliness.

Excellent magnetocaloric performance in the carbide compounds RE2Cr2C3 (RE = Er, Ho, and Dy) and their composites

The rare earth (RE) based alloys or compounds with excellent cryogenic magnetocaloric performance have received much research interest recently due to their potential applications of environmental friend magnetic refrigeration (MR) technology. Herein, three ternary RE-based carbide compounds RE2Cr2C3 (RE = Er, Ho, and Dy) were synthesized, an investigation of combined experimental and theoretical has been performed with regard to crystal structure, magnetic properties, magnetic phase transition as well as the magnetocaloric effect (MCE) and magnetocaloric performance. All the RE2Cr2C3 carbide compounds are crystallized in the orthorhombic type crystal structure (C12/m1 space group). The magnetic ground state was confirmed to be ferromagnetic (FM) for Er2Cr2C3, whereas antiferromagnetic (AFM) for Ho2Cr2C3 and Dy2Cr2C3 compounds by density functional theory calculation in addition to experimental observation. Large cryogenic MCE has been observed with the maximum isothermal magnetic entropy change (-ΔSMmax) of 15.20, 13.98 and 9.04 J/kgK for Er2Cr2C, Ho2Cr2C3 and Dy2Cr2C3 under the magnetic field change (ΔH) of 0–5 T, respectively. Additionally, low field table-like MCE has been achieved in the Er2Cr2C3/Ho2Cr2C3 composites, which is benefit for active applications. These results assess and highlight the potential applicative interest of RE2Cr2C3 carbide compounds in the field of cryogenic MR.

Probing the effect of Pr doping on the magnetic and magnetocaloric properties of [formula omitted] double perovskites

We report the possible variations in the magnetocaloric properties of Ba2−xPrxFeMoO6 (0.0 ≤ x ≤ 0.4) induced by the controlled substitution of rare earth element Praseodymium (Pr) at the Barium-site in the lattice. Pellets of the double perovskite samples prepared via the conventional solid state reaction method were thoroughly investigated using X-ray diffraction followed by Rietveld analyses that established a cubic crystal structure (Fm-3m) in these samples. The magnetization of the samples was measured as a function of temperature that indicated a single ferromagnetic to paramagnetic phase transition in these materials as the temperature was increased. The Pr doping did not change the crystalline structure but resulted in non-monotonic evolution of the Curie temperature (TC) and decreased magnetization. A second order of magnetic phase transition in these materials was confirmed by the Arrott plots analyses as well as the ‘universal master curve method’ which indicated the reversible nature of magnetization plus lower hysteresis associated with these materials. Though the Pr doping did not enhance the magnetic entropy change and the relative cooling power yet the near room temperature TC, chemically stable structure, moderate magnetization and tunable magnetocaloric properties of these materials make them attractive for exploration in numerous applications in spintronics and magnetic refrigeration technology.

Improved magnetocaloric effects in AlFe2B2 intermetallics through the enhancement of magnetoelastic coupling

The development of high-performance magnetocaloric material is one of the keys to actualize the room-temperature magnetic refrigeration technology. Here the effects and mechanisms of solidification behaviors and microstructures on the magnetocaloric effect (MCE) of AlFe2B2 intermetallics are investigated. The solidification behaviors of AlxFe2B2 (x = 1.0, 1.2, 1.4, 1.6, and 1.8) were regulated via controlling the content of Al element, that is, peritectic reaction for x < 1.4 and direct crystallization for x ≥ 1.4. The magnetic entropy changes under an applied magnetic field of 5 T of AlFe2B2 intermetallics prepared by peritectic reaction can reach 7.2 J kg−1K−1 near room-temperature, which is much larger than that of direct crystallization samples (~5 J kg−1K−1). The reason is attributed to the abrupt change of crystal cells and its effect on the magnetoelastic coupling. The present work provides a new perspective to accurately control the MCE of AlFe2B2 phase, which is beneficial for its further practical application.

Electronic structure, magnetic properties and magnetocaloric performance in rare earths (RE) based RE2BaZnO5 (RE = Gd, Dy, Ho, and Er) compounds

Nowadays, the rare earths (RE) based magnetic materials with various promising functional characterizations are playing particularly important roles in present modern society and daily life. The magnetocaloric (MC) effect which is the basis of solid state magnetic refrigeration (MR) technology has been extensively investigated in various magnetic materials. In this work, a series of high quality RE-based RE2BaZnO5 (RE = Gd, Dy, Ho, and Er) compounds have been fabricated and a combination of theoretical and experimental investigation has been performed in terms of the crystal structure, electronic structure, magnetic properties and magnetic phase transition (MPT) as well as the MC effects and MC performance. All the RE2BaZnO5 compounds are confirmed to crystallize in the orthorhombic structure belonging to Pnma space group and with a typical semi-conductor characteristic. Based on the magnetization measurements and the first principle calculations, all the RE2BaZnO5 compounds are ordering magnetically below 3 K and the ground state is of a ferromagnetic (FM) ordering for RE = Dy or Ho, whereas is of an antiferromagnetic (AFM) ordering for RE = Gd or Er, respectively. Additionally, considerable MC effects have been observed for all the RE2BaZnO5 compounds which are related to the first ordered MPT for RE = Gd or Er, whereas related to the second order MPT for RE = Dy or Ho, respectively. Moreover, considerable MC effects and promising MC performance have been realized in the present RE2BaZnO5 compounds, especially for the Dy2BaZnO5 and Ho2BaZnO5, making them considerable for cryogenic MR applications.

Structural, magnetic, and magnetocaloric properties of La0.7Sr0.2Nd0.1Mn1-xNixO3 (x= 0.05, 0.10, and 0.15): B-site doping

In this study, La0.7Sr0.2Nd0.1Mn1-xNixO3 (x = 0.05, 0.10, 0.15) systems were synthesized following the sol-gel (SG) approach and their structural, magnetic, and magnetocaloric characteristics were determined. The X-ray Diffraction (XRD) patterns revealed that all samples were in the R-3c space group. Magnetic studies revealed that an increase in the Ni2+ dopant resulted in a ferromagnetic (FM) to paramagnetic (PM) transition near the Curie temperature (Tc), when Tc decreased from 280 K to 220 K. The maximum change in magnetic entropy (−ΔSMMax) gradually decreased while the relative cooling power (RCP) gradually increased. The −ΔSMMax and RCP values for La0.7Sr0.2Nd0.1Mn0.95Ni0.05O3 were 4.28 J/(kg·K) and 267.67 (J/kg), respectively at 280 K when the external magnetic field variation was 5 T. This material can potentially be one of the candidates for developing the magnetic refrigeration technology.

Machine learning assisted development of Fe2P-type magnetocaloric compounds for cryogenic applications

Fe2P-type compounds exhibit a giant magnetocaloric effect (MCE) and are extensively studied for room temperature applications. The reduction of their transition temperature below 77 K can pave the way for the potential application of these materials for hydrogen liquefaction using cryogenic magnetic refrigeration. Most of the known magnetocaloric materials with a giant MCE below 77 K are rare-earth-based compounds. In order to explore the possibility of developing rare-earth-free compounds with cryogenic MCE, we collected a dataset by conducting data mining on published experimental results on Fe2P-type magnetocaloric compounds and used machine learning for composition optimization aiming at lowering the transition temperature below 77 K. Guided by the predictions of an artificial neural network, we found a promising composition of Mn1.70Fe0.30P0.63Si0.37 with a transition temperature of 97 K at 1 T magnetic field which was lowered to 73 K by the minor substitution of Fe with Co. The developed rare-earth-free compounds exhibit a large magnetocaloric performance in isothermal magnetic entropy change (∆SM) of 7.5–11.5 J/kgK at the temperatures below 100 K. This study demonstrates that data-driven development of magnetocaloric materials can efficiently boost the optimization of their properties, thus aiding the practical applicability of magnetic refrigeration technology.

Magnetocaloric effect in manganites in alternating magnetic fields

Direct measurements of the magnetocaloric effect in La0.7Ca0.3MnO3, La1−xAgyMnO3, and Sm1−xSrxMnO3 manganites in alternating magnetic fields at frequencies up to 20 Hz and an amplitude of 6.2 kOe are carried out. A decrease of the MCE with the field frequency reaching 20%, 55% and 70% in La0.7Ca0.3MnO3, Sm1−xSrxMnO3 and La1−xAgyMnO3 is discovered in all studied manganites. The value estimates of the cooling power depending on the frequency of the alternating magnetic field are carried out. The largest value among the studied materials is achieved for La0.7Ca0.3MnO3 manganite, which is the most promising to be used in magnetic refrigeration technology. The data are compared with those for Gd in the same conditions.

Tuning of the Magnetocaloric Properties of Mn5Ge3 Compound by Chemical Modification

The rare earth-free Mn5Ge3 compound shows magnetocaloric properties similar to those of pure Gd; therefore, it is a good candidate for magnetic refrigeration technology. In this work, we investigate the influence of chemical substitution on the crystal structure and the magnetic, thermodynamic, and magnetocaloric properties of a polycrystalline Mn5Ge3 compound prepared by induction melting. For this purpose, we replaced 5% of the Mn with Cr or Co and 5% of the Ge with B or Al. The additional chemical elements were shown not to change the crystal structure of the parent compound (space group P63/mcm, No. 193). In the case of the magnetic properties, all samples remained ferromagnetic with the ordering temperature (TC) lower than for the original compound (TC = 295(1) K). The exception was the sample with B, where we observed an increase in TC by 3 K. The maximum value of the magnetic entropy change, |∆Sm|MAX (for a magnetic field change of 5 T), decreased from 7.1(1) for Mn5Ge3 to 6.2(1), 6.8(1), 4.8(1), and 5.8(1) J kg−1 K−1 for the alloys with B, Al, Cr, and Co, respectively. The adiabatic temperature change (∆Tad) (for a magnetic field change of 1 T) was determined from the specific heat measurements and was equal to 1.1(1), 1.2(1), 1.2(1), 0.8(1), and 0.8(1) K for Mn5Ge3, Mn5Ge2.85B0.15, Mn5Ge2.85Al0.15, Mn4.75Cr0.25Ge3, and Mn4.75Co0.25Ge3, respectively. The obtained data were compared with those from the literature. It was found that the substitution allowed for tuning of the ordering temperature in a wide temperature range. At the same time, the reduction in the magnetocaloric parameters’ values was relatively small. Therefore, the produced Mn5Ge3-based alloys allow for the expansion of the operation temperature range of the parent compound as a magnetocaloric material.

Magnetic properties, magnetic transition and large magneto-caloric effect in the Ho0.2Er0.2Tm0.2Ni0.2Cu0.2 amorphous ribbon

The magneto-caloric (MC) effect in rare earths (RE) based magnetic materials have been extensively investigated in recent years not only due to the potential applications in the field of cryogenic magnetic refrigeration (MR) technology but also for better understanding the magnetic properties and magnetic transition of these materials. In this work, we reported a systematical investigation of the cryogenic magnetic and MC properties in the RE-based equi-atomic Ho0.2Er0.2Tm0.2Ni0.2Cu0.2 amorphous ribbon. The Ho0.2Er0.2Tm0.2Ni0.2Cu0.2 amorphous ribbon reveals a second order magnetic transition (SOMT) at ∼11.5 K from paramagnetic to ferromagnetic states. Large reversible MC effect and promising MC performances were found in the Ho0.2Er0.2Tm0.2Ni0.2Cu0.2 amorphous ribbon, and the MC parameters of the maximum isothermal magnetic entropy changes (-ΔSMmax) as well as the refrigerant capacity/relative cooling power (RC/RCP) under the magnetic field change of 0–50 kOe are evaluated to be 15.44 J/kgK and 317.4/397.2 J/kg, respectively.

Theoretical study of the magnetic properties and the magnetocaloric effect in lanthanum manganite lacunar compounds

Based on the Monte Carlo method and using the Ising model, the magnetic as well as the magnetocaloric properties of lacunar compounds La1-xxMnO3 (x = 0.1 and 0.2) were investigated. Free boundary conditions for our system were applied to simulate the 3D-Ising Hamiltonian of these systems. Cubic magnetic sublattices of size L3, with L = 20, 24 and 28, were investigated in this study to compute the magnetization and the magnetic susceptibility as a function of temperature (T) at various applied fields. In order to calculate the variation of the magnetic entropy versus the applied magnetic field, we have examined an isothermal process by considering a term of magneto-crystalline anisotropy. In order to validate the results, many parameters were calculated. The results obtained are in good agreement with the experimental ones. The high relative cooling power values of our compounds leads to promising material for magnetic refrigeration technology. This material could be considered as a good candidate for applications requiring high values of TC.

Magnetic properties and promising magnetocaloric performances in the antiferromagnetic GdFe2Si2 compound

The magnetocaloric (MC) effect-based solid-state magnetic refrigeration (MR) technology has been recognized as an alternative novel method to the presently commercialized gas compression technology. Searching for suitable candidates with promising MC performances is one of the most urgent tasks. Herein, combined experimental and theoretical investigations on the magnetic properties, magnetic phase transition, and cryogenic MC performances of GdFe2Si2 have been performed. An unstable antiferromagnetic (AFM) interaction in the ground state has been confirmed in GdFe2Si2. Moreover, a huge reversible cryogenic MC effect and promising MC performances in GdFe2Si2 have been observed. The maximum isothermal magnetic entropy change, temperature-averaged entropy change with 2 K lift, and refrigerant capacity for GdFe2Si2 were 30.01 J kg−1 K−1, 29.37 J kg−1 K−1, and 328.45 J kg−1 at around 8.6 K with the magnetic change of 0–7 T, respectively. Evidently, the values of these MC parameters for the present AFM compound GdFe2Si2 are superior to those of most recently reported rare-earth-based MC materials, suggesting the potential application for active cryogenic MR.

Magnetic properties and giant cryogenic magnetocaloric effect in B-site ordered antiferromagnetic Gd2MgTiO6 double perovskite oxide

The magnetic refrigeration (MR) technology by utilizing the magnetocaloric (MC) effects of magnetic solids have been realized to be a promising energy efficiency and environmentally friendly technology. Developing or discovering proper magnetic solids with promising MC performances is one of the most important tasks at present stage since a huge gap still exists between the requirement of practical MR application and the MC performances of the magnetic solids. Herein, we reported a combined theoretical and experimental investigation of the crystal structure together with the magnetic properties, magnetic phase transition (MPT) and MC performances in Gd2MgTiO6 oxide. The Gd2MgTiO6 is confirmed to crystalize in a B-site ordered monoclinic double perovskite (DP) crystal structure. A rather unstable antiferromagnetic (AFM) interaction with large magnetic moment and semi-conductor characteristic with the band gap of 2.977 eV have been confirmed in Gd2TiMgO6 DP oxide at ground state. Giant reversible cryogenic MC effect together with excellent MC performances have been confirmed by a series of the figure of merits including the values of maximum magnetic entropy change (-ΔSM) and refrigerant capacity (RC), which are evaluated to be 46.21 J/kgK and 300.27 J/kg around 3.3 K with the magnetic change of 0–7 T, these values are much better than most of the recently reported famous cryogenic MC materials and the commercialized magnetic refrigerants gadolinium gallium garnet (GGG) as well. The observed excellent MC performances suggest that Gd2TiMgO6 DP oxide is a promising candidate material for cryogenic MR applications.

Study of the doping of Sr by Ag in manganites La0.57Nd0.1Sr0.33-xAgxMnO3 (0.00–0.15) on assessment structural, magneticand Magnetocaloric at room temperature

We describe in this manuscript the effect of the substitution of a divalent element such as strontium Sr2+ by a monovalent element such as silver Ag+ on the variation of the Mn-Mn distance between two adjacent MnO6 octahedra and also on the evolution of Mn -O -Mn and also on the overlap of manganese d orbitals and oxygen 2p orbitals. then in this study, we synthesized by the solid-solid method the polycrystalline oxides La0.57Nd0.1Sr0.33-xAgxMnO3 (x = 0 and 0.15) LNSAMO.X-ray diffraction study shows that these compounds crystallize in the rhombohedral structure of space group R-3C and exhibit a second Mn3O4 phase of space group I 41 / amd. All the magnetization curves show a high temperature transition from a ferromagnetic state to a paramagnetic state near the Curie temperature (TC) and a second transition associated with the secondary phase Mn3O4. The Curie temperature decreases from 321 K to 307 K as the disorder increases. However, we have noticed that the substitution of strontium which is a magnetic element by non-magnetic silver causes the increase of the magnetization as well as the decrease of the temperature of Curie TC. When an external magnetic field μ0H = 5 T, we find that the values ofmagnetic entropy (ΔSMmax) are equal to 2.68, 4.55 and 5.08 J Kg 1 K 1, respectively, for x = 0.0, 0.1 and 0.15 samples. The relative cooling power (RCP) is around 80.10 J/kg, 137 J/kg,146.74 J/kg of X = 0, X = 0.1 f, X = 0.15 compounds for the 5T magnetic field. By basing the results of this work, we achieve that the controlled Ag doping adapts perfectly to the magnetic and Magnetocaloric characteristic of LNSMO Which perform a significant function in the realization of much potential applying of the compound in the field of approximately-room temperature magnetic refrigeration technology.

Magnetic and anisotropic magnetocaloric effects of HoCoSi fast quenching ribbons

The performance of magnetocaloric effect materials is one of the key factors restricting the development of magnetic refrigeration technology. Materials with anisotropic magnetocaloric effect can be used in the rotary magnetic refrigeration technology, which is beneficial to the simplification of refrigeration devices. In this work, the magnetic properties, magnetocaloric effects, and magnetic anisotropies of rapidly quenched HoCoSi compounds are investigated. At low temperatures below &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;t&lt;/sub&gt; = 5.7 K, the HoCoSi ferromagnetism and helical magnetism coexist. With the increase of temperature, the HoCoSi undergoes a second-order phase transition from ferromagnetic (FM) to paramagnetic (PM) phase at &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;C&lt;/sub&gt; = 13.7 K. Both XRD and SEM show that the HoCoSi has a preferred orientation. In order to obtain a large magnetocaloric effect and to determine the effect of preferred orientation on magnetism and magnetocaloric effect, the isothermal magnetization curves of the 10 m/s–HoCoSi fast quenched belt in the directions of &lt;i&gt;H&lt;/i&gt; parallel and perpendicular to texture around the Curie temperature are analyzed. The corresponding magnetic entropy change (–Δ&lt;i&gt;S&lt;/i&gt;&lt;sub&gt;M&lt;/sub&gt;) and magnetic refrigeration capacity (RC) are calculated. Under the magnetic field changing from 0 to 5 T, the value of –Δ&lt;i&gt;S&lt;/i&gt;&lt;sub&gt;M&lt;/sub&gt; is 22 J/(kg·K) in the direction of &lt;i&gt;H&lt;/i&gt; parallel to the texture and 12 J/(kg·K) in the direction of &lt;i&gt;H&lt;/i&gt; perpendicular to texture , and their corresponding values of RC(RCP)are 360 (393.8) J·kg&lt;sup&gt;–1&lt;/sup&gt; and 160 (254.4) J/kg. The value of –Δ&lt;i&gt;S&lt;/i&gt;&lt;sub&gt;M&lt;/sub&gt; reaches 12.5 J/(kg·K)even at &lt;i&gt;μ&lt;/i&gt;&lt;sub&gt;0&lt;/sub&gt;&lt;i&gt;H&lt;/i&gt; = 0–2 T in the direction of H parallel to the texture. It is obvious that the 10-m/s-HoCoSi fast quenching belt shows a large low-field magnetocaloric effect and obvious magnetic anisotropy, which is expected to be used to realize the magnetic refrigeration technology of rotating samples.

Influence of Ni content on structural, magnetocaloric and electrical properties in manganite La0.6Ba0.2Sr0.2Mn1-x Ni x O3 (0 ≤ x ≤ 0.1) type perovskites.

We present a detailed study on the physical properties of La0.6Ba0.2Sr0.2Mn1−xNixO3 samples (x = 0.00, 0.05 and 0.1). The ceramics were fabricated using the sol–gel route. Structural refinement, employing the Rietveld method, disclosed a rhombohedral R3̄c phase. The magnetization vs. temperature plots show a paramagnetic–ferromagnetic (PM–FM) transition phase at the TC (Curie temperature), which decreases from 354 K to 301 K. From the Arrott diagrams M2vs. μ0H/M, we can conclude the phase transition is of the second order. Based on measurements of the isothermal magnetization around TC, the magnetocaloric effects (MCEs) have been calculated. The entropy maximum change (−ΔSM) values are 7.40 J kg−1 K−1, 5.6 J kg−1 K−1 and 4.48 J kg−1 K−1, whereas the relative cooling power (RCP) values are 232 J kg−1, 230 J kg−1 and 156 J kg−1 for x = 0.00, 0.05 and 0.10, respectively, under an external field (μ0H) of 5 T. Through these results, the La0.6Ba0.2Sr0.2Mn1−xNixO3 (0 ≤ x ≤ 0.1) samples can be suggested for use in magnetic refrigeration technology above room temperature. The electrical resistivity (ρ) vs. temperature plots exhibit a transition from metallic behavior to semiconductor behavior in the vicinity of TM–SC. The adiabatic small polaron hopping (ASPH) model is applied in the PM-semiconducting part (T > TMS). Throughout the temperature range, ρ is adjusted by the percolation model. This model is based on the phase segregation of FM-metal clusters and PM-insulating regions.

Research Progress of Doped Manganite Materials in Magnetic Refrigeration

Magnetic refrigeration technology is a new, green, high-efficiency approach. It has attracted increasing attention from researchers and has a strong competitiveness over traditional refrigeration methods. With the continuous development of social lives, magnetic refrigeration technology must have important application prospects. This article briefly describes the basic principles. The focus is on the introduction and summary of research on perovskite manganite doping in magnetic refrigeration. Finally, the outlook and summary of magnetic refrigeration technology are presented.

Review of the influence of copper and chromium substitution on crystal structure, magnetic properties and magnetocaloric effect of GdFe2−x(Cu, Cr)x (x = 0, 0.1, 0.15 and 0.2) intermetallic compounds

The iron-based compounds GdFe2−x(Cu,Cr)x (x = 0, 0.1, 0.15 and 0.2) were synthesized successfully by means of arc-melting and annealing at 800 °C for one week. The structural, magnetic and magnetocaloric properties of these intermetallic compounds were investigated systematically in detail using X-ray powder diffraction (XRD) analysis, Scanning electron microscopy (SEM) equipped with Energy dispersive X-ray spectroscopy (EDS), and magnetic measurements. The Rietveld analysis of X-ray diffraction patterns proves that GdFe2−x(Cu,Cr)x (x = 0, 0.1, 0.15 and 0.2) compounds crystallize in the cubic laves phase MgCu2-type structure with the Fd3̄m space group. Gadolinium and iron atoms statistically occupy the 8a and 16d sites respectively. Moreover, copper and chromium atoms substitute the iron atoms at site 8a in the MgCu2-type structure. The temperature dependence of magnetization studied in a broad temperature range reveals that all compounds exhibit a ferromagnetic-paramagnetic transition at Curie temperature (TC). We find that the substitution of iron by copper and chromium leads to a decrease in the magnetic ordering transition temperature. The Arrott plots of all our samples show the occurrence of a second-order phase transition. Besides, the performance of magnetocaloric effect (MCE) for GdFe2−x(Cu,Cr)x (x = 0, 0.1, 0.15 and 0.2) compounds was evaluated by the magnetic entropy change (ΔSM) and the related Relative Cooling Power (RCP). In the vicinity of TC, the ΔSM reached a maximum value of 0.79 J/kg.K, 1.2 J/kg.K, 1.4 J/kg.K and 2.5 J/kg.K, while the RCP was found to be 13.2 J/kg, 21.6 J/kg, 31.7 J/kg and 44.3 J/kg, respectively for GdFe2−xCux (x = 0, 0.1, 0.15 and 0.2) compounds. Furthermore, the GdFe2−xCrx (x = 0.1, 0.15 and 2) compounds show ΔSM values of about 0.9 J/kg.K, 1.3 J/kg.K and 1.8 J/kg.K, and RCP values of 14.8 J/kg, 25.4 J/kg and 36.8 J/kg respectively, under a field change of 1.56 T. Through these results, the GdFe2−x(Cu,Cr)x (x = 0, 0.1, 0.15 and 0.2) compounds can be an attractive materials for use in magnetic refrigeration and heat pumping technology above room temperature.

Development of magnetic refrigeration materials andtechnology

Magnetic refrigeration technology based on magnetic phase transition has great application potential in solid refrigeration due to its advantages of energy saving, high efficiency, environmental protection, stability and reliability. It has great significance for realizing the transformation and upgrading of refrigeration industry. Magnetic refrigeration technology has gotten certain achievements in materials and systems after decades of research and accumulation. Many magnetic refrigeration materials with practical value have been developed, and a variety of high-efficiency refrigeration system structures have been designed, which promoting the application process of magnetic refrigeration technology. This paper introduces the thermodynamic principle of magnetic refrigeration, the research progress of magnetic refrigeration materials and technology. Several kinds of magnetocaloric materials with promising application prospects were emphatically introduced. Room temperature magnetic refrigeration materials mainly include Gd-based, La-Fe-Si and Mn-based materials etc., among which La-Fe-Si series of materials with independent intellectual property rights in China is considered to be one of the most promising magnetic refrigerant materials. Afterwards low temperature magnetic refrigeration materials mainly include binary, ternary, quaternary rare earth intermetallic compounds and rare earth metal oxides. It describs the magnetic refrigeration technology and its research progress of room temperature and low temperature and analyzes the structures and characteristics of different types of magnetic refrigeration systems. The development trend of magnetic refrigeration materials and technology future is also prospected at the end of this paper.

Magnetism and magnetocaloric effect of rare earth &amp;lt;italic&amp;gt;RET&amp;lt;/italic&amp;gt;&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;&amp;lt;italic&amp;gt;X&amp;lt;/italic&amp;gt;&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; compounds

Magnetic refrigeration (MR) technology is considered to be an energy-saving alternative to the commonly used gas compression/expressing refrigeration technology. Currently, searching or designing magnetic solids with an excellent magnetocaloric effect (MCE) that works at different temperature regions is one of the most important targets. Therefore, the investigation of magnetism and MCE of rare-earth-based compounds is a prominent topic in the field of refrigeration. Among them, the ternary rare-earth compounds of RET 2 X 2 ( T = 3d, 4d, or 5d transition elements; X = B, P, Si, and Ge) with a ThCr2Si2-type crystal structure have attracted considerable attention owing to their unique physical and chemical properties. In this study, the crystal structure, magnetism, and MCE of RE Mn2(Si, Ge)2, RE Ru2(Si, Ge)2, RE Co2B2 and related compounds are briefly reviewed. Some of these compounds show excellent magnetocaloric properties with potential application in the field of active cryogenic MR.