•The magnetic refrigerator operating between 77 K and 20 K is fabricated and tested.•The AMR reached the lowest temperature of 25 K and the temperature span is 52 K.•The numerical estimation of the ...performance is compared with the experimental result.
The experimental investigation of an active magnetic regenerative refrigerator (AMRR) operating between 77 K and 20 K is discussed in this paper, with detailed energy transfer analysis. A multi-layered active magnetic regenerator (AMR) is used, which consists of four different rare earth intermetallic compounds in the form of irregular powder. Numerical simulation confirms that the AMR can attain its target operating temperature range. Magnetic field alternation throughout the AMR is generated by a high temperature superconducting (HTS) magnet. The HTS magnet is cooled by a two stage Gifford-McMahon (GM) cryocooler. Helium gas was employed as a working fluid and its oscillating flow in the AMR is controlled in accordance with the magnetic field variation. The AMR is divided into two stages and each stage has a different mass flow rate as needed to achieve the desired cooling performance. The temperature variation of the AMR during the experiment is monitored by temperature sensors installed inside the AMR. The experimental results show that the AMRR is capable of achieving no-load temperature of 25.4 K while the warm end temperature is 77 K. The performance of the AMRR is analyzed by observing internal temperature variations at cyclic steady state. Furthermore, numerical estimation of the cooling capacity and the temperature variation of the AMR are examined and compared with the experimental results.
The crystal structure, magnetic properties and magnetocaloric effect (MCE) of HoCoC2 and ErCoC2 have been investigated. They both crystallize in orthorhombic CeNiC2-type structure with Amm2 space ...group and a second-order paramagnetic to ferromagnetic phase transition around the Curie temperature TC ∼11 K and ∼14 K occurred in them. Under the magnetic field change (ΔH) of 0–5 T, the maximal values of magnetic entropy change, refrigerant capacity and relative cooling power are 15.6 J/kg K, 183 J/kg, 242 J/kg for HoCoC2 and 17.2 J/kg K, 243 J/kg, 375 J/kg for ErCoC2, respectively.
•RECoC2 (RE = Ho and Er) were synthesized by arc melting method.•Magnetism and MCE in RECoC2 (RE = Ho and Er) were studied.•Large reversible MCE was observed for both compounds.•RECoC2 (RE = Ho and Er) are good candidates for magnetic refrigeration.
The thermodynamic characterisation of magnetocaloric materials is an essential task when evaluating the performance of a cooling process based on the magnetocaloric effect and its application in a ...magnetic refrigeration cycle. Several methods for the characterisation of magnetocaloric materials and their thermodynamic properties are available in the literature. These can be generally divided into theoretical and experimental methods. The experimental methods can be further divided into direct and indirect methods. In this paper, a new procedure based on an artificial neural network to predict the thermodynamic properties of magnetocaloric materials is reported. The results show that the procedure provides highly accurate predictions of both the isothermal entropy and the adiabatic temperature change for two different groups of magnetocaloric materials that were used to validate the procedure. In comparison with the commonly used techniques, such as the mean field theory or the interpolation of experimental data, this procedure provides highly accurate, time-effective predictions with the input of a small amount of experimental data. Furthermore, this procedure opens up the possibility to speed up the characterisation of new magnetocaloric materials by reducing the time required for experiments.
We present a comprehensive study of the magnetocaloric materials series La(Fe
1−
x
Co
x
)
11.9Si
1.1 with
0.055
<
x
<
0.122
. 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,
Δ
S
M
, from initial curve measurements and measured the adiabatic temperature change,
Δ
T
ad
, 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.
► The Ho4Co3-type hexagonal phase was obtained for fully crystallized ribbons. ► B substitution leads to almost no change in the MCE behavior of crystalline alloys. ► The (−ΔSM) for amorphous alloys ...increases with increasing B content. ► (Gd4Co3)100−xBx amorphous alloys are good candidates working near 200K.
Crystallized Gd4Co3 alloy has shown promising magnetocaloric properties resulting from two successive magnetic-entropy changes of the hexagonal phase. In this work, magnetic (Gd4Co3)100−xBx (x=0, 5, 10 and 15) amorphous ribbons were prepared by melt spinning. The onset crystallization temperatures Tx for the alloys with x=0, 5, 10 and 15 were found to be about 560, 565, 575 and 585K, respectively. The Ho4Co3-type hexagonal phase was obtained for crystallized ribbons after annealing. All the amorphous and crystalline alloys order ferromagnetically and undergo the second-order transition at their Curie temperatures. Under an applied field change from 0 to 5T, the maximum value of (−ΔSM) for (Gd4Co3)100−xBx amorphous alloys increased from 6.7 to 7.8Jkg−1K−1 with increasing B content. Large values of the refrigerant capacity (RC) were also obtained. For the crystallized alloys, the maximum value of (−ΔSM) decreased to 6.2–6.4Jkg−1K−1. Large magnetic entropy change and RC value, negligible coercive force and hysteresis, as well as high stability enable the (Gd4Co3)100−xBx amorphous alloys competitive candidates for the magnetic refrigeration materials working in the vicinity of 200K.
► The magnetic and magnetocaloric properties of La0.4Ca0.6MnO3+δ nanoparticles. ► Increasing particle size improves crystallinity and long range ferromagnetic order. ► Increasing particle size ...increases magnetocaloric effect and refrigerant capacity.
We report a systematic study of the effects of size reduction on the magnetic and magnetocaloric properties of amorphous and crystalline La0.4Ca0.6MnO3+δ nanoparticles. The materials were synthesized using a modified wet chemical Pechini route, starting with nitrate precursors to produce the perovskite structure. Phase purity, structure, size, and crystallinity were investigated using XRD and TEM. Thermal treatments resulted in nanocrystals with average diameters of 25nm, 50nm, and 130nm, as well as amorphous particles ∼10nm in diameter. Magnetic measurements revealed broad, second order ferromagnetic transitions in the nanocrystals. As particle size increased from 10nm to 130nm, the Curie temperature shifted from 40K to 255K. Magnetization, magnetic entropy change (ΔSM), and refrigerant capacity (RC) also increased with size in the nanocrystalline samples. For a field change of 5T, the 130nm particles exhibit a magnetic entropy change of 2.8J/kgK and a large refrigerant capacity of ∼240J/kg at 250K. Interestingly, the 10nm amorphous particles undergo the sharpest magnetic transition, leading to a larger value of ΔSM than in the 25nm or 50nm crystalline particles. These results reveal that size reduction has a significant impact on the magnetic and magnetocaloric properties of La0.4Ca0.6MnO3+δ.
The magnetic properties and magnetocaloric effects (MCEs) in La0.8R0.2(Fe0.919Co0.081)11.7Al1.3 (R=Pr, Nd) compounds have been investigated. When Pr and Nd substitute for La, the Curie temperature of ...compounds decreases. The values of the MCEs are enhanced significantly by a partial substitution of Nd for La. Under the field change of 2 and 5 T, the maximum magnetic entropy changes for La0.8Nd0.2(Fe0.919Co0.081)11.7Al1.3 compound are -4.56 and -9.46 J/Kg K, respectively. It can be exploited for room temperature magnetic refrigeration material.
A systematic study of the size effect on the magnetic and structural properties of a Ni 51 Mn 33.4 In 15.6 Heusler alloy converted to nanoparticles has been performed. We present new data to explain ...the enhanced magnetic properties of the nanostructured Heusler alloy synthesized through a high-energy ball-milling technique. The properties of the particles were characterized by X-ray diffraction, electron microscopy, and magnetometer techniques. Isothermal magnetic field variation of magnetization exhibits field hysteresis in bulk Ni 51 Mn 33.4 In 15.6 alloy across the martensitic transition. As the size of the nanoparticles is reduced, there is an increase in the magnetization per unit of applied magnetic field, and a decrease in the coercivity as well as a substantial reduction in hysteresis.
In the present investigation, the effect of iron addition on the structural, magnetic and magnetocaloric properties of Gd5Si1.7Ge2.3-xFex alloys with x = 0–0.4 has been carried out. Structural ...analysis reveal that Gd5Si1.7Ge2.3-xFex compounds crystallize in a combination of monoclinic and orthorhombic structures at room temperature. With increase in Fe substitution up to x ≤ 0.3, the compounds stabilize in orthorhombic structure with Pbnm space group. First-order and second-order transitions are observed for low Fe concentrations. For x = 0.4, only a second-order transition is evident which is due to the stabilization of the orthorhombic structure. At lower fields, the presence of short-range ferromagnetic correlations indicate competing intra-layer and inter-layer magnetic interactions. The Curie temperature increases from 243 K to 287 K with increase in Fe concentration. The entropy change (-ΔSM) is found to be 10.1 J/kg K at 247 K, 11.3 J/kg K at 253 K, 7.9 J/kg K at 273 K and 7 J/kg K at 287 K for x = 0.1, 0.2, 0.3 and 0.4 respectively, for a field change of 50 kOe. Universal curve analysis corroborates the transition from first-order to second-order as evidenced by magnetization measurements. Tuning the transition temperature to near room temperature through the proper substitution of transition elements paves an interesting route towards the development of materials for room temperature refrigeration applications.
•Gd5Si1.7Ge2.3-xFexcompounds with x = 0, 0.1, 0.2, 0.3 and 0.4 has been synthesised.•Rietveld refinement reveal a combination of Gd5Si2Ge2 and Gd5Si4 phases.•An enhancement in Curie temperature has been observed from 240 K to 287 K in x=0.4.•Curie temperature tailored to near room temperature without compromising MCE values i.e. for Fe0.4 TC is 287 K with an MCE value of 7 J/kg K at 50 kOe.
The present study investigates the effects of the substitution of potassium K the A-site on the magnetic and magnetocaloric properties of the brownmillerite compounds La
1−
x
K
x
SrMn
2
O
5+
δ
(0.1 ≤ ...
x
≤ 0.3). Our samples were synthesized using the conventional solid-state reaction at high temperature. The findings from structure studies revealed that all the samples crystallized in the orthorhombic system with a Pnma space group. The properties of magnetic refrigerants may also be affected. Magnetic measurements and Arrott's analysis were used to detect a second-order ferromagnetic phase change in each sample. The Curie temperature
T
C
decreased with more substitution of potassium content. Arrott plots showed that all samples exhibited a second-order magnetic phase transition. Magnetocaloric effect was calculated in terms of isothermal magnetic entropy change. Additionally, it leads to a decrease in magnetic entropy Δ
S
M
, as calculated from isothermal magnetization data. For
x
= 0.1, 0.2, and 0.3, the maximum magnetic entropy change |Δ
S
M
| around
T
C
’s calculated to be 1.2 J kg
−1
K
−1
, 1.08 J kg
−1
K
−1
and 0.8 J kg
−1
K
−1
correspondingly.
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