Magnetic Refrigeration Technology Research Articles

Time dependent model to analyze the magnetic refrigeration performance of gadolinium near the room temperature

Abstract A practical time-dependent model has been constructed to forecast the effectiveness and productivity of a magnetic regenerative refrigerator, as well as to assess its cycle efficiency. The model incorporates many irreversible factors, including the cycle frequency, heat transfer efficiency, and heat leak. Furthermore, it is utilized to scrutinize a magnetic refrigerator that employs spherical Gd particles as the magnetic substance and water as the heat transfer medium. The different cycle steps of the magnetic refrigerator are examined, while the cooling capacity and temperature differential between the two heat exchangers are appraised. The results also show that the magnetic refrigerator can obtain a temperature span of 5 K under 0.8 T magnetic field after 30 cycles in a particular situation. The findings provide valuable information for the future planning and advancement of magnetic refrigeration technology at room temperature.

Unusual Magnetocaloric Effect Triggered by Spin Reorientation

AbstractAdvancements and utilization of magnetic refrigeration technology hinge on the ongoing enhancement and optimization of magnetic refrigeration material properties. Nevertheless, the intricacy of the magnetocaloric effect (MCE) mechanism has emerged as a bottleneck, constraining the progress and refinement of magnetic refrigeration materials. In this study, a classic magnetic system is chosen to investigate the mechanism of MCE across four different scales–macroscopic magnetism, micrometer‐scale magnetic domains, atomic magnetic moments, and electronic structure. It simultaneously exhibits two inverse MCEs and one direct MCE, with a working temperature span as wide as 125 K (most are <50 K) for the direct MCE. The measurements of the vibrating sample magnetometer, in situ Lorentz electron microscopy and variable‐temperature neutron powder diffraction directly reveal that the complex magnetic entropy changes arise from the magnetic domain wall pinning, the instability of Ho magnetic moments, and the spin rotation. First‐principles calculations elucidate the crucial role of strong hybridization between localized Ho and itinerant Co electrons in the spin reorientation of HoCo4Al. This study contributes significantly to comprehending the induction mechanism of the MCE and holds vital reference value for exploring new magnetic refrigeration materials and enhancing MCE performance.

Simulation study of heat transfer enhancement for all-solid-state room temperature magnetic refrigeration system

To address issues relating to large thermal resistance and low heat transfer efficiency between and inside magnetocaloric materials (MCM) in all-solid-state room-temperature magnetic refrigeration technology, this study adopted the method of inserting high thermal conductivity materials (HTCM) into MCM and coupling Peltier elements between MCMs to enhance the heat transfer inside MCM and between microcells, thereby improving the refrigeration performance of the system. In doing so, a two-dimensional simulation model was developed using COMSOL Multiphysics software. The cooling performance enhancement effect of the system resulting from heat transfer improvement within MCM and between MCMs was investigated separately. Furthermore, the impacts of various system operating parameters (such as the number of micro-cell divisions, initial operating temperature, heat transfer time, magnetic field strength, Peltier input voltage), different HTCMs and insertion volume ratios on the system’s cooling performance were explored. The simulation results reveal that, in comparison with the original magnetic refrigeration system, the optimized heat transfer time of the system following enhanced heat transfer within the MCM is reduced from 180s to 8s, accompanied by a 115% increase in the maximum temperature span. Furthermore, coupling the Peltier elements elevates the maximum temperature span by 274%.

Three-dimensional critical behavior in Mn1.5Cr1.5O4: A material for magnetocaloric energy conversion

The multifunctional and tunable properties of spinel oxides bring their applicability in various sustainable applications. In this line, the current work systematically examines the magnetic and magnetocaloric properties of Mn1.5Cr1.5O4. The presence of Mn2+ ions in the tetragonal site leads to complex magnetic interactions. It undergoes a ferrimagnetic to paramagnetic transition at 58 K. The critical exponents obtained from the modified Arrot plot, β = 0.346 and γ = 1.051, suggests that the system does not fall into any of the universal class. The exchange interaction strength reveals the coexistence of short- and long-range ordering. Mn1.5Cr1.5O4 displays a magnetic entropy change of -4.11 J kg−1K−1 and a relative cooling power of 70.68 J kg−1 at 58 K for a field change of 70 kOe. Thus, the major results of the study recommend the applicability of Mn1.5Cr1.5O4 towards gas (fuel, H2) liquefaction based on solid-state active magnetic refrigeration technology.

Large magnetocaloric effect and giant magnetoresistance in rare earth based intermetallic compound ErAl3: construction of magnetic phase diagram

This study explores the magnetic and magnetotransport behavior of polycrystalline ErAl3 compound. The polycrystalline compound adopts HoAl3-type structures with the R-3m space group, No. 166-2 and hR60 configurations. Multiple magnetic orderings and two field-induced metamagnetic transitions are observed. ErAl3 exhibits a significant magnetocaloric effect (MCE), −ΔSM = 15.25 J kg−1 K−1 and high relative cooling power of 383 J kg−1 with applied magnetic field change (ΔH) of 70 kOe near the paramagnetic to ferromagnetic transition, showcasing its potential for magnetic refrigeration technology. The compound also demonstrates metallic behavior, with a notable magnetoresistance of 48.5 % at 2 K due to the suppression of antiferromagnetism. The magnetic phase diagram reveals four distinct phases influenced by temperature and magnetic field, identified through the study of the MCE.

Magnetic properties and cryogenic magnetocaloric effect in α-Gd2(MoO4)3 compound

Magnetic refrigeration technology has received extensive attention due to its application prospects in various fields. The research of magnetocaloric materials is the basis for the development of magnetic refrigeration technology. In this study, the α-Gd2(MoO4)3 was prepared by the high temperature solid state reaction. By X-ray diffraction characterization, α-Gd2(MoO4)3 crystallizes in monoclinic structure (space group C12/c1). Furthermore, its magnetism and magnetocaloric effect are investigated. The magnetic ordering temperature of α-Gd2(MoO4)3 is less than 1.8 K and there is a second-order phase transition. The maximum magnetic entropy changes are 20.8 and 32.7 J kg−1 K−1 under the field changes of 0–2 T and 0–5 T, respectively. Besides, the refrigeration capacity and relative cooling power are 142.0 and 190 J kg−1 under field change of 0–5 T. These properties indicate that α-Gd2(MoO4)3 is an excellent candidate for low temperature magnetic refrigeration.

Design of Excellent Mechanical Performances and Magnetic Refrigeration via In Situ Forming Dual-Phase Alloys.

Magnetic refrigeration technology can achieve higher energy efficiency based on the magnetocaloric effect (MCE). However, the practical application of MCE materials is hindered by their poor mechanical properties, making them challenging to process into devices. Conventional strengthening strategies usually lead to a trade-off with refrigeration capacity reduction. Here, a novel design is presented to overcome this dilemma by forming dual-phase alloys through in situ precipitation of a tough magnetic refrigeration phase within an intermetallic compound with excellent MCE. In the alloy 87.5Gd-12.5Co, incorporating the interconnected tough phase Gd contributes to enhanced strength (≈505MPa) with good ductility (≈9.2%). The strengthening phase Gd simultaneously exhibits excellent MCE, enabling the alloy to achieve a peak refrigeration capacity of 720 J kg-1. Moreover, the alloy shows low thermal expansion induced by the synergistic effect of the two phases. It is beneficial for maintaining structural stability during heat exchange in magnetic refrigeration. The coupling interaction between the two magnetic phases can broaden the refrigeration temperature range and reduce hysteresis. This study guides the development of new high-performance materials with an excellent combination of mechanical and magnetic refrigeration properties as needed for gas liquefaction and refrigerators.

High-performance magnetic refrigeration materials: Prediction and realization

Magnetic refrigeration technology based on the magnetocaloric effect provides an optimal replacement for conventional refrigeration technology. However, an efficient approach to developing superior magnetic refrigeration materials to satisfy practical requirements is still lacking. Here, a feasible approach to develop magnetic refrigeration materials with a superior magnetocaloric effect is designed. Based on this screening rule, the 23 rare-earth-based compounds with inverse perovskite structures were revealed in space group Pm3̅m (No. 221). The First principle calculations are used to predict the magnetism, and electronic structure of candidate compounds, and there are 13 rare earth-based compounds in the candidate materials that have a ferromagnetic magnetic ground state. The Er3SnC, Ho3SnC, Gd3SnC, and Gd3AlC compounds were realized, and the magnetism, magnetocaloric effects were investigated. The experimental results demonstrate that the magnetic ground states of the prepared compounds are in agreement with theoretical predictions. The Er3SnC, Ho3SnC and Gd3SnC compounds with ferromagnetic states exhibit superior magnetocaloric effects.

Structural, magnetic and magnetocaloric properties of Li-substituted La0.8K0.2-xLixMnO3 perovskite manganites

In this study we report the effect of lithium substitution on the structural, magnetic and magnetocaloric properties of La0.8K0.2-xLixMnO3 (0 ≤ x ≤ 0.075) samples synthesized by the sol–gel technique at low temperature. The investigated compounds crystallize in a rhombohedral system with R3¯c space group. The thermal variation of the magnetization under an applied magnetic field of 0.05 T showed that all our compounds exhibited a paramagnetic to ferromagnetic transition with decreasing temperature. With increasing lithium content, the Curie temperature TC, decreases from 287.4 K for x = 0 to 172.6 K for x = 0.075. The maximum of the magnetic entropy change, -ΔSMMax, is found to be 3.19, 3.51, 2.39 and 2.24 J kg−1 K−1 in a magnetic field change of 5 T for x = 0, 0.025, 0.05 and 0.075 respectively. The La0.8K0.175Li0.025MnO3 sample displays a higher maximum relative cooling power value of 320.5 J kg−1, equal to 78 % of that of gadolinium. Technically, this large value associated to a TC of 270 K makes the present sample very promising for magnetic refrigeration technology below room temperature.

A Monte Carlo investigation of the magnetic behaviors and magnetocaloric effect of the nanoporous graphenes of a mixed spin ferrimagnetic (2, 3/2)

Based on the Monte Carlo calculation, we have investigated the magnetic behavior and the magnetocaloric effect of the nanoporous graphenes of a mixed spin ferrimagnetic (2, 3/2). We start by discussing the ground state phase diagrams corresponding to several physical parameters at the temperature T=0 K. In addition, the reduced critical and compensation temperatures have been found with distinct values of the number of lattice sites (L). The influence of the parameter L, reduced exchange couplings Rσσ, Rsσ, and the reduced crystal field on the total magnetic and hysteresis cycles has also been studied. We begin by exploring the impact of the reduced external magnetic field on the specific heat (Cp), magnetic entropy change (-∆Sm), adiabatic temperature change (ΔTa), and relative cooling power (RCP). These results indicate that the nanoporous graphene compound could be a promising candidate for magnetic refrigeration technology.

Development and experimental analysis of a multi-bed active magnetic regenerator

Room temperature magnetic refrigeration technology is a potentially efficient and environmentally friendly refrigeration technology. A magnetic refrigeration prototype with two high/low magnetic field regions was designed and built. The device consists of eight beds, using gadolinium particles as the magnetocaloric material, with a total filling mass of 1.35 kg. The hydraulic system consists mainly of a magnetic centrifugal pump, solenoid valves, and check valves. The flow of the heat transfer fluid through the regenerators is controlled by controlling the opening and closing of the solenoid valves. The no-load temperature span, cooling capacity, power consumption, and COP of the regenerators were investigated separately. The maximum no-load temperature span of 17.5 K was obtained at an AMR frequency of 0.5 Hz and flow rate of 1.15 L/min. The total power consumption and the magnetic power and pumping power were analyzed for different operating conditions.

Hysteresis-free reversible magnetocaloric effect and critical behavior of Ni39.56Fe7.27Co2.97Mn40.65Sn9.55 full heusler alloy

Utilizing the magnetocaloric effect (MCE), magnetic refrigeration technology offers an advantage over traditional gas-based refrigerators, which produce harmful gases. Herein, we study the MCE and critical magnetic behavior of Fe and Co substituted Ni39.56Fe7.27Co2.97Mn40.65Sn9.55 Heusler alloy near the paramagnetic (PM) to ferromagnetic (FM) transition temperature. With Fm3̅m space group, the present sample crystallizes in cubic L21 structure. Arrott plots and hysteresis-free continuous phase transition confirm a second-order transition from FM to PM. Again, this second-order transition is verified by collapsing scaled entropy curves for various fields into a single universal curve. The critical exponent values obtained using several analytical techniques, like the Kouvel-Fisher method, modified Arrott plot, and critical isotherm, correspond to the mean-field theory universality class having long-range ordering. The above findings suggest our sample to be a suitable magnetic refrigerant by overcoming the difficulty of obtaining a reversible and high value of magnetic entropy change along with substantial relative cooling power across the second-order phase transition.

Preparation and Performance of Micro-Arc Oxidation Coatings for Corrosion Protection of LaFe11.6Si1.4 Alloy.

The microstructure, corrosion resistance, and phase-transition process of micro-arc oxidation (MAO) coatings prepared on LaFe11.6Si1.4 alloy surfaces in different electrolyte systems were systematically investigated. Research has demonstrated that various electrolyte systems do not alter the main components of the coatings. However, the synergistic action of Na2CO3 and Na2B4O7 more effectively modulated the ionization and chemical reactions of the MAO process and accelerated the formation of α-Al2O3. Moreover, the addition of Na2CO3 and Na2B4O7 improved the micromorphology of the coating, resulting in a uniform coating thickness and good bonding with the LaFe11.6Si1.4 substrate. The dynamic potential polarization analysis was performed in a three-electrode system consisting of a LaFe11.6Si1.4 working electrode, a saturated calomel reference electrode, and a platinum auxiliary electrode. The results showed that the self-corrosion potential of the LaFe11.6Si1.4 alloy without surface treatment was -0.68 V, with a current density of 8.96 × 10-6 A/cm2. In contrast, the presence of a micro-arc electrolytic oxidation coating significantly improved the corrosion resistance of the LaFe11.6Si1.4 substrate, where the minimum corrosion current density was 1.32 × 10-7 A/cm2 and the corrosion potential was -0.50 V. Similarly, after optimizing the MAO electrolyte with Na2CO3 and Na2B4O7, the corrosion resistance of the material further improved. Simultaneously, the effect of the coatings on the order of the phase transition, latent heat, and temperature is negligible. Therefore, micro-arc oxidation technology based on the in situ growth coating of the material surface effectively improves the working life and stability of La(Fe, Si)13 materials in the refrigeration cycle, which is an excellent alternative as a protection technology to promote the practical process of magnetic refrigeration technology.

Large low-field magnetocaloric performances of the ErCu1.95T0.05Si2 (T = Mn, Fe, Co and Ni) compounds

Magnetocaloric materials are at the heart of magnetic refrigeration (MR) technology. However, there is a scarcity of materials with a large magnetocaloric effect (MCE) at magnetic fields below 2 T. To address this limitation, we investigate the effect of doping in the ErCu2Si2 compound with relatively inexpensive neighboring atoms of Mn, Fe, Co, and Ni in the Cu position, respectively. The results show a significant enhancement in the MCE at low fields. Under the magnetic field change of 0–2 T, the values of maximum magnetic entropy change (−ΔSMmax) for the ErCu1.95T0.05Si2 (T = Mn, Fe, Co and Ni) compounds are 16.4 J/kg·K, 17.5 J/kg·K, 17.8 J/kg·K, and 18.6 J/kg·K, respectively. Compared to those of the parent compound ErCu2Si2, the −ΔSMmax of the ErCu1.95T0.05Si2 (T = Mn, Fe, Co and Ni) compounds exhibit enhancements of 3%, 11%, 13%, and 17%, respectively. Additionally, the magnetic transition temperatures of these doped compounds are lower than that of the parent compound ErCu2Si2, occurring below 2 K. Therefore, ErCu1.95T0.05Si2 (T = Mn, Fe, Co and Ni) compounds with large low-field MCE and negligible loss of hysteresis have the potential to serve as candidate materials for cryogenic magnetic refrigeration.

Gadolinium: A DFT exploration of structural, electronic, and magnetic features in bulk and film configurations for enhanced magnetocaloric understanding

Gadolinium stands as the favored choice among magnetic refrigerant materials for numerous active magnetic regenerator (AMR) prototypes due to its remarkable ability to exhibit a substantial change in magnetic entropy. This unique characteristic arises from its status as one of the elemental ferromagnets with a high Curie temperature, closely aligning with room temperature conditions, and undergoing a second-order magnetic phase transition. In this comprehensive study, we employ density functional theory (DFT) calculations to explore the structural, electronic, and magnetic properties of both Gadolinium bulk and film configurations. Our primary objective is to gain a deeper understanding of the intricate physics underlying the intriguing magnetocaloric features observed in Gadolinium. This investigation provides valuable insights into the potential applications and the broader implications of Gadolinium in the realm of magnetic refrigeration technology.

Magnetic properties and cryogenic magnetocaloric effect of pyrochlore structure RE2Ti2O7 (RE = Gd, Tb, and Ho) compounds

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

Magnetocaloric effect modeling of dysprosium-transition metal based intermetallic alloys for magnetic refrigeration application using hybrid genetic algorithm based support vector regression intelligent method.

Intermetallic alloy containing rare earth dysprosium ions with the associated unfilled 4f shell electrons and sub-lattice of 3d-transition metal, results into fascinating magnetic properties which are useful for green refrigeration technological application. Magnetocaloric effect remains the fundamental principle upon which magnetic refrigeration technology is based while this cooling technology has advantages of cost effectiveness, high efficiency and environmental friendliness as compared with the existing conventional gas compression systems. Maximum magnetic entropy change (which controls the hugeness of magnetocaloric effect) of intermetallic alloy Dy-T-X (where T = transition metal and X = any other metal or nonmetal) is modeled in this work using hybrid genetic algorithm based support vector regression (GSVR) computational intelligent method with applied magnetic field, ionic concentration and ionic radii descriptors. The developed GSVR-G model with kernel Gaussian function outperforms GSVR-P model with polynomial function with improvement of 85.23%, 78.82% and 78.67% on the basis of the computed correlation coefficient (CC), mean absolute error (MAE) and root mean square error (RMSE) on testing sample, respectively. The developed model further investigates the influence of applied external magnetic field on magnetocaloric effect of DyCuAl intermetallic alloy. The developed models in this work circumvent experimental challenges of magnetocaloric effect determination while the recorded precision of the developed model further opens doors for possible exploration of these intermetallic compounds for addressing environmental challenges associated with the present system of cooling.

Giant low-field magnetocaloric effect in unstable antiferromagnetic Tm1–xErxNi2Si2 (x = 0.2, 0.4) compounds

Magnetic refrigeration (MR) technology is regarded as an ideal solution for cryogenic applications, relying on magnetocaloric materials which provide necessary chilling effect. A series of polycrystalline Tm1–xErxNi2Si2 (x = 0.2, 0.4) compounds was synthesized, and their magnetic properties, magnetic phase transition together with magnetocaloric effect (MCE) were studied. The Tm1–xErxNi2Si2 (x = 0.2, 0.4) compounds display a field-induced metamagnetic transition from antiferromagnetic (AFM) to ferromagnetism (FM) in excess of 0.2 T, respectively. Meanwhile, the AFM ground state is unstable. Under the field change of 0–2 T, the values of maximal magnetic entropy change (−ΔSMmax) and refrigerant capacity (RC) for Tm0.8Er0.2Ni2Si2 compound are 17.9 J/(kg·K) and 83.5 J/kg, respectively. The large reversible MCE under low magnetic fields (≤2 T) indicates that Tm0.8Er0.2Ni2Si2 compound can serve as potential candidate materials for cryogenic magnetic refrigeration.

Structure and cryogenic magnetocaloric effects of NaREO2 (RE = Er, Ho) compounds

Rare-earth (RE) based oxides have presented great application prospects in low-temperature magnetic refrigeration technology. Thus far, studies on magnetic and especially magnetocaloric properties of alkali-metal RE oxides are limited, largely due to the difficulty in synthesizing these oxides. In this work, NaREO2 (RE = Er, Ho) compounds with both the rhombohedral (R3‾m space group) and cubic (Fm3‾m space group) structures were prepared by a facile ball-milling-aided sintering approach. The cubic structural compounds exhibit a spherical microstructure composed of vertically-grown irregular hexahedra, which sharply contrast with a loose lamellar microstructure of the rhombohedral structural compound. The as-prepared NaHoO2 or NaErO2 compound exhibits an antiferromagnetic ordering of RE3+ moments at a temperature of 2.4 K or lower than 2 K respectively. An excellent comprehensive magnetic refrigeration performance at cryogenic temperatures in a low magnetic field change of 0–20 kOe was obtained in these compounds, including a complete reversibility of the magnetocaloric effect, a maximal magnetic-entropy change ΔSM at 2 K of 12 J/kg·K for the rhombohedral NaErO2 and a relative cooling power (RCP) of 79.7 J/kg for the cubic NaHoO2.

Effect of Cr substitution on structural, magnetic, magnetocaloric and critical behaviors of La0.7Y0.05Ba0.25MnO3 perovskite manganite

A thorough investigation was conducted into the structural, magnetic, and critical properties of La0.7Y0.05Ba0.25Mn1-xCrxO3 (x = 0 and 0.15) perovskite manganite synthesized using the sol-gel method. The samples possess an orthorhombic structure with the Pnma space group according to X-ray diffraction (XRD) patterns. The average ion radii of the B-site cation (<rB>), the unit cell volume (V), and <θMn,Cr–O–Mn,Cr > bond angle decreased with Cr substitution. While the average bond distance, <dMn,Cr–O>, and Goldschmidt tolerance factor (tG) increased. The samples present a magnetic transition from a paramagnetic (PM) phase to a ferromagnetic (FM) phase at Curie temperature (TC). Addition of Cr to La0.7Y0.05Ba0.25MnO3 decreased the TC value from 310 K (for x = 0 sample) to 258 K (for x = 0.15 sample). Using Banerjee's criteria, second-order phase transitions were determined for the samples. Both samples showed significant maximum entropy change |ΔSMmax| and relative cooling power (RCP) whose values decreased from (6.40 J Kg−1 K−1 and 231 J Kg−1 for x = 0) to (4.45 J Kg−1 K−1 and 185 J Kg−1 for x = 0.15), respectively. These values indicate that the La0.7Y0.05Ba0.25Mn1-xCrxO3 manganites exhibit favourable magnetocaloric effect (MCE) and demonstrate promising potential for application as materials in magnetic refrigeration technology. The estimated critical exponents (β, γ, and δ) for the x = 0 sample align with the 3D-Ising model, while for x = 0.15, they closely resemble the 3D-Heisenberg model. This shift in the universality class can be attributed to the interplay between competing ferromagnetic double-exchange and antiferromagnetic super-exchange interactions that exist within the prepared samples.