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Magnetic refrigeration is a fascinating superior choice technology as compared with traditional refrigeration that relies on a unique property of particular materials, known as the magnetocaloric effect (MCE). This paper provides a thorough understanding of different magnetic refrigeration technologies using a variety of models to evaluate the coefficient of performance (COP) and specific cooling capacity outputs. Accordingly, magnetic refrigeration models are divided into four categories: rotating, reciprocating, C-shaped magnetic refrigeration, and active magnetic regenerator. The working principles of these models were described, and their outputs were extracted and compared. Furthermore, the influence of the magnetocaloric effect, the magnetization area, and the thermodynamic processes and cycles on the efficiency of magnetic refrigeration was investigated and discussed to achieve a maximum cooling capacity. The classes of magnetocaloric magnetic materials were summarized from previous studies and their potential magnetic characteristics are emphasized. The essential characteristics of magnetic refrigeration systems are highlighted to determine the significant advantages, difficulties, drawbacks, and feasibility analyses of these systems. Moreover, a cost analysis was provided in order to judge the feasibility of these systems for commercial use.

The present paper provides a short review of the magnetocaloric effect and selected magnetocaloric materials, such as Gd-based alloys, MnCoGe alloys, and La(Fe, Si)13-type alloys. The magnetocaloric effect is a fundamental environmentally friendly technique for lowering temperature, which is nowadays highly developed due to its potential application in domestic refrigerators or heat pumps. This article delivers information on the theory of the magnetocaloric effect. Moreover, it reviews the structure and thermomagnetic properties of selected materials suitable for active magnetic regenerators working at close to room temperature.

The chemical stability effect was investigated using two perovskite compositions, La0.7Nd0.1Sr0.2MnO3 and La0.7Nd0.1Sr0.2Mn0.96In0.04O3. Synthesis of these perovskites was carried out by the sol–gel method. X-ray powder diffraction study, coupled with Rietveld refinement, revealed a rhombohedral structure with the R3¯c space group. The magnetic investigation showed that both compositions exhibit a second-order phase transition. La0.7Nd0.1Sr0.2MnO3 has a Curie temperature TC of 290 K and maximum magnetic entropy change value of 4.79 J kg−1 K−1, while La0.7Nd0.1Sr0.2Mn0.96In0.04O3 has a Curie temperature TC of 277 K and maximum magnetic entropy change value of 6.2 J kg−1 K−1. The critical properties of these compositions were analyzed and found to obey the mean-field model for La0.7Nd0.1Sr0.2 Mn0.96In0.04O3 and the Heisenberg model for La0.7Nd0.1Sr0.2MnO3.

The multiferroic spinel crystalline A Cr 2 O 4 ( A  = Co, Ni) were synthesized via a traditional sol-gel reaction and characterized with respect to the structural, magnetic properties and magnetocaloric performances. The A Cr 2 O 4 oxides are confirmed to crystallize in cubic Al 2 MgO 4 -type structure with space group Fd 3 ¯ m and tetragonal CdMn 2 O 4 -type structure with I41/amdz space group for A  = Co, Ni, respectively. Both A Cr 2 O 4 compounds reveal a typical second-ordered magnetic transition (SOMT) form paramagnetic to ferromagnetic (PM-FM) around its own Curie temperature T C and followed by a low temperature anomalous which is probably due to the spin glass (SG) transition behavior. The calculated peak values of magnetic entropy change (−  ∆S M max ) around its own T C under the external magnetic field changes Δ H  = 7 T are 1.54 and 1.19 J·kg −1  K −1 for A  = Co, Ni, respectively, and the corresponding relative cooling power (RCP) is 22.2 and 22.33 J·kg −1 .

The La0.8Na0.2Mn1-xCoxO3 (0 ≤ x ≤ 0.06) manganite are prepared by the sol gel–based Pechini route. The effect of substitution in Mn site with Co upon the structural, magnetic, and magnetocaloric properties has been analyzed by means X-ray diffraction and linear extracting magnetometer. These nanoparticles crystallize in a rhombohedral symmetry with R3-c space group without any detectable impurity phase. All prepared sample show a paramagnetic (PM) ferromagnetic (FM) phase transition near the critical temperature Tc. In fact, the experimental results confirm that Mn site substitution with Co decreases the Curie temperature Tc. Magnetocaloric results revealed large relative cooling power RCP values making our samples potential candidate for magnetic refrigeration applications. Referring to the universal data, we revealed a second-order nature of magnetic phase transition for all samples following the mean field approximation.

We present a mean field study on the R 6 Fe 23 system, where R = Dy, Ho, Er, and Tm, to calculate the magnetization, magnetic heat capacity, and the magnetocaloric effect (MCE) (isothermal entropy change (ΔS m ) and the adiabatic temperature change (ΔT ad )) for different field changes up to 5 T and at temperatures ranging from 0 to 600 K. The maximum ΔS m , using the trapezoidal method, for the R 6 Fe 23 system is in the range 4.9–9.8 J/K mol, and the maximum ΔT ad is in the range 9.56–15.17 K for a field change Δ H  = 5 T. The largest ΔS m and largest ΔT ad are found for Tm 6 Fe 23 to be 9.8 J/K mol and 15.17 K at Curie temperature T c  = 489 K, for Δ H  = 5 T. The relative cooling power RCP(S) is in the range 148–560 J/mol for Δ H  = 5 T, which is comparable to that of bench-mark materials, e.g., Gd. Also, the RCP based on the adiabatic temperature change, RCP(T) is in the range 449–1092 K 2 for Δ H  = 5 T, which is comparable also to that of bench-mark materials, e.g., Gd. We investigated the type of phase transition in the light of universal curves, Arrott plots, and the behavior of the magnetic moment, magnetic heat capacity, and MCE (ΔS m , ΔT ad ), which confirm that the type of phase transition at T c of this system is second-order phase transition (SOPT). A calculation of some critical exponents adds more evidence that the MFT is fairly suitable to handle the aforementioned properties in the studied systems.

This study systematically investigates the impact of Cu2+ doping on the structural, magnetic, and magnetocaloric properties of CuxCo1−xCr2O4 nanoparticles synthesized via a solution combustion method. Cu incorporation up to x = 20% induces a progressive structural transformation from a cubic spinel to a trigonal corundum phase, as confirmed by X-ray diffraction and Raman spectroscopy. The doping process also leads to increased particle size, improved crystallinity, and reduced agglomeration. Magnetic measurements reveal a transition from hard to soft ferrimagnetic behavior with increasing Cu content, accompanied by a notable rise in the Curie temperature from 97.7 K (x = 0) to 140.2 K (x = 20%). The magnetocaloric effect (MCE) is significantly enhanced at higher doping levels, with the 20% Cu-doped sample exhibiting a maximum magnetic entropy change (−ΔSM) of 2.015 J/kg-K and a relative cooling power (RCP) of 58.87 J/kg under a 60 kOe field. Arrott plot analysis confirms that the magnetic phase transitions remain second-order in nature across all compositions. These results demonstrate that Cu doping is an effective strategy for tuning the magnetostructural response of CoCr2O4 nanoparticles, making them promising candidates for low-temperature magnetic refrigeration applications.

We investigated the magnetic and magnetocaloric properties of Gd100-xCox ( x = 40 to 56) thin films fabricated by the sputtering technique. Under an applied field change Δ H = 20 kOe , the magnetic entropy change ( Δ S m ) decreases from 2.64 Jkg−1K−1 for x = 44 to about 1.27 Jkg−1K−1 for x = 56. Increasing the Co concentration from x = 40 to 56 shifts the Curie temperature of Gd100-xCox ( x = 40 to 56) thin films from 180 K toward 337 K. Moreover, we extracted the values of critical parameters Tc, β, γ, and δ by using the modified Arrott plot methods. The results indicate the presence of a long-range ferromagnetic order. More importantly, we showed that the relative cooling power (RCP), which is a key parameter in magnetic refrigeration applications, is strongly enhanced by changing the Co concentration in the Gd100-xCox thin films. Our findings help pave the way toward the enhancement of the magnetocaloric effect in magnetic thin films.

Magnetic refrigeration is based on the magnetocaloric effect, which refers to the ability of some materials to heat up when magnetized and cool down when demagnetized. An active magnetic regenerative (AMR) refrigeration apparatus using twin beds and a permanent magnet array was constructed for an experimental study. The twin AMR beds were filled with gadolinium spheres. They were magnetized and demagnetized in turn using a permanent magnet array and exchanged heat by means of water flowing back and forth between the hot and cold sides. The temperatures of various locations within the AMR beds were measured in real time. Herein, the experimental results using the apparatus are discussed.

The adiabatic temperature change (ΔT ad ) during the magnetization process of polycrystalline gadolinium and Ni 51 Mn 33.4 In 15.6 Heusler alloy is directly measured near the Curie temperature. The cooling factor (CF) is introduced as the area under the curve of adiabatic temperature change versus ambient temperature. The CF provides more representative measure of cooling performance in the operational temperature range. Selecting different temperature abscissas qualitatively changes the interpretation of the cooling performance of a magnetocaloric material. In particular, plotting ΔT ad versus initial temperature gives a measurably different CF compared to that given by plotting ΔT ad versus average temperature.