Magnetic Refrigerant Materials Research Articles

Influence of Zn on magnetocaloric effect in (0.95)La0.7Sr0.3MnO3/Ni1−xZnxFe2O4 ceramic composites

We report the magnetic and magnetocaloric properties of (0.95)La0.7Sr0.3MnO3/(0.05)Ni1−xZnxFe2O4 (x=0.0, 0.1, 0.3, and 0.5) ceramic composites. The composite samples with nominal compositions were prepared using the conventional solid-state reaction method. The phase purity and structure were confirmed by using X-ray diffraction. Temperature dependent magnetization measurements and Arrott analysis reveal second order of magnetic phase transition in the composite samples. A maximum in magnetic entropy change of ∼0.75J/kgK at 1T has been observed in (0.95)La0.7Sr0.3MnO3/(0.05)NiFe2O4 sample. The values of magnetic entropy change of these composites make them attractive for potential applications. These composite samples may consider as potential material for magnetic refrigeration near room temperature.

Low field induced giant anisotropic magnetocaloric effect in DyFeO3 single crystal**Project supported by the National Basic Research Program of China (Grant Nos. 2010CB934202, 2011CB921801, and 2012CB933102) and the National Natural Science Foundation of China (Grant Nos. 11174351, 11274360, and 11034004).

We have investigated the anisotropic magnetocaloric effect and the rotating field magnetic entropy in DyFeO3 single crystal. A giant rotating field entropy change of was achieved from b axis to c axis in bc plane at 5 K for a low field change of 20 kOe. The large anisotropic magnetic entropy change is mainly accounted for the 4f electron of rare-earth Dy3 + ion. The large value of rotating field entropy change, together with large refrigeration capacity and negligible hysteresis, suggests that the multiferroic ferrite DyFeO3 singlecrystal could be a potential material for anisotropic magnetic refrigeration at low field, which can be realized in the practical application around liquid helium temperature region.

Magnetic properties and magnetocaloric effects in HoPd intermetallic**Project supported by the National Natural Science Foundation of China (Grant Nos. 51322605, 11104337, 51271192, and 11274357) and the Knowledge Innovation Project of the Chinese Academy of Sciences.

A large reversible magnetocaloric effect accompanied by a second order magnetic phase transition from PM to FM is observed in the HoPd compound. Under the magnetic field change of and the refrigerant capacity RC for the compound are evaluated to be 20 J/(kg · K) and 342 J/kg, respectively. In particular, large (11.3 J/(kg · K)) and RC (142 J/kg) are achieved under a low magnetic field change of 0–2 T with no thermal hysteresis and magnetic hysteresis loss. The large reversible magnetocaloric effect (both the large -ΔSM and the high RC) indicates that HoPd is a promising material for magnetic refrigeration at low temperature.

The effect of Co doping on the magnetic and magnetocaloric properties of Pr0.7Ca0.3Mn1−xCoxO3 manganites

In this work, we report the effect of low amount of cobalt doping at the Mn-site on the magnetic and magnetocaloric properties of Pr0.7Ca0.3Mn1−xCoxO3 (0≤x≤0.1) powder samples. Our samples, elaborated using the solid–solid reaction method at high temperature, are single phase and crystallize in the orthorhombic system with Pnma space group. While the parent compound Pr0.7Ca0.3MnO3 exhibits a charge order state at low temperature, the substituted samples with low amount of cobalt exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. The Curie temperature TC increases with Co content from 105K for x=0 to 116K for x=0.1. The maximum values of the magnetic entropy change |ΔSMmax| are found to be 0.8J/kgK, 2.2J/kgK, 3.1J/kgK and 3.2J/kgK in a magnetic field change of 5T for x=0, 0.02, 0.05 and 0.1 respectively. The maximum value of the relative cooling power RCP is found to be 378.2J/kg in the Pr0.7Ca0.3Mn0.95Co0.05O3 at 5T. This value of RCP is about 92% of that obtained in gadolinium metal, known as one of the most important materials for magnetic refrigeration, at the same magnetic field change of 5T.

Mechanical properties and magnetocaloric effects in La(Fe, Si)13 hydrides bonded with different epoxy resins

The mechanical properties and magnetocaloric effect (MCE) of bonded La(Fe, Si)13 hydrides have been studied in detail. The mechanical strength increases with increasing the grade of epoxy resin from E-20 to E-51. This occurs because more pores and boundaries are filled with high grade resin since high epoxide content increases the degree of crosslinking and reduces the viscosity and shrinkage of resin. The compressive strength reaches 162 MPa for the bonded LaFe11.7Si1.3C0.2H1.8 with 3 wt. % E-51, which is 35% higher than that of bulk LaFe11.7Si1.3C0.2 compound (120 MPa). The mass ΔSM values remain almost same in bonded hydrides and are in a good agreement with the theoretical value. The maximum volumetric ΔSM values are 61.8, 58.0, and 54.7 mJ/cm3 K for bonded hydrides with epoxy resins E-20, E-44, and E-51, respectively, much higher than those of some magnetocaloric materials in same temperature range. The improved mechanical properties and large MCE indicate that bonded LaFe11.7Si1.3C0.2H1.8 is a promising material for room temperature magnetic refrigeration.

The effect of Al doping on the crystal structure and magnetocaloric behavior of Mn1.2Fe0.8P1−xGex compounds

We studied the influence of Al doping on the crystal structure and magnetocaloric properties of Mn1.2Fe0.8P1−xGexAly compounds prepared by spark plasma sintering, with x=0.24, 0.25, 0.26 and y=0, 0.004, 0.008, 0.010 or 0.12. These compounds have the same Fe2P-type structure (space group P6¯2m) as the undoped system, and we found that the addition of Al had significant effects on the hexagonal unit cell of the compound and its physical properties. As y increased, the lattice parameter a and cell volume increased, the lattice parameter c decreased, the thermal hysteresis (ΔThys) decreased, and the Curie temperature (Tc) became significantly higher than at y=0. The variations of Tc and ΔThys correlated almost linearly with variation in the c/a ratio, indicating that Tc can be increased with Al doping. In addition, Al doping did not have any adverse effects on other magnetocaloric properties, such as the entropy change, adiabatic temperature change, and the temperature range of the coexistence of the paramagnetic and ferromagnetic phases. We also found that the magnetocaloric properties of Mn1.2Fe0.8P1−xGexAly compounds could be improved by homogenous annealing. The particular composition Mn1.2Fe0.8P0.74Ge0.26Al0.010 exhibited a Tc close to room temperature (292.2K) with a hysteresis of ΔThys 2.1K, making it a very promising material for magnetic refrigeration around room temperature.

The Magnetic and Magnetocaloric Properties of Pr1−x Bi x MnO3 (x = 0.2 and 0.4) Manganites

The magnetic and magnetocaloric properties of Pr1−x Bi x MnO3 (x = 0.2 and 0.4) nanocrystalline manganites have been studied systematically. Samples were prepared using the Pechini sol–gel method. The variation of the magnetization as a function of temperature and applied magnetic field were carried out. Magnetic measurements show that all the materials exhibit a paramagnetic–ferromagnetic transition when the temperature decreases. Magnetocaloric effect has been calculated in terms of isothermal magnetic entropy change. A large magnetocaloric effect has been observed, the maximum entropy change, ${\Delta S}_{\mathrm {M}}^{\text {max}}$ ¦reaches 0.7 and 2.1 J kg−1 K−1 under a magnetic applied field of 5 T with an RCP values of 183 J kg−1 for Pr0.8Bi0.2MnO3 sample. These perovskites have the large magnetic entropy changes induced by low magnetic field change, which is beneficial for the household application of active magnetic refrigerant (AMR) materials.

Magnetization and Magnetocaloric Effect in Sol-Gel Derived Nanocrystalline Copper-Zinc Ferrite.

We report the sol-gel synthesis and magnetocaloric effect in nanocrystalline copper-zinc ferrite (Cu0.5Zn0.5Fe2O4). The synthesized powder was characterized by using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and magnetization measurements. The XRD results confirm the formation of single phase spinel structure. The average particle size was found to be ~58 nm. FE-SEM results suggested that the nanoparticles are agglomerated and spherical in shape. Magnetization measurement reveals that Cu0.5Zn0.5Fe2O4 nanoparticles exhibit transition temperature (Tc) above room temperature. The maximum magnetic entropy change (ΔSM)max shows interesting behaviour and was found to vary with the applied magnetic field. This nanopowder can be considered as potential material for magnetic refrigeration above room temperature.

Strain modulated large magnetocaloric effect in Sm0.55Sr0.45MnO3 epitaxial films

Epitaxial Sm0.55Sr0.45MnO3 thin films were deposited on LAO (001), LSAT (001), and STO (001) single crystalline substrates by pulsed laser deposition technique to investigate the correlation between the substrate induced film lattice strain and magnetocaloric effect (MCE). The film on LAO substrate (S_LAO), which is under compressive strain, undergoes ferromagnetic → paramagnetic transition at TC ∼ 165 K. The films on STO (S_STO) and LSAT (S_LSAT) substrates are under tensile strain and have TC ∼ 120 K and 130 K, respectively. At T < TC, the zero field cooled and field cooled magnetization curves of all the films show huge bifurcation. In case of S_STO and S_LSAT films, hysteresis is also observed between field cooled cooling and warming cycle in magnetization versus temperature measurement at low magnetic field similar to first order-like magnetic phase transition. No signature of first order magnetic phase transition has been observed in the case of S_LAO film. Most interestingly, both normal (i.e., negative ΔSM) and inverse (i.e., positive ΔSM) MCE around TC and above Tp, respectively, for S_STO and S_LSAT films have been observed with maximum value of MCE ∼ 10 J kg−1 K−1. The S_STO film also exhibits a large relative cooling power of 142 J/kg for a magnetic field change of 1 T. Our findings of substrate-induced strain modulated large MCE in epitaxial Sm0.55Sr0.45MnO3 films have been well explained through the substrate induced film lattice strain, and it may be useful for active magnetic refrigerant materials.

Numerical simulation of a hybrid magnetic refrigeration combined with high pressure Stirling regenerative refrigeration effect

Magnetic refrigeration is a cooling method based on the magnetocaloric effect, which uses solid magnetocaloric materials as refrigerant, and helium, water or other fluid as heat transfer fluids. Stirling refrigeration is a kind of mature gas regenerative cooling method, using helium gas as the refrigerant. These refrigerations have similar cycling characteristics, and are both safe, environmantal-friendly and high efficient cooling methods. Therefore, a hybrid magnetic refrigerator combined with Stirling gas refrigeration effect is proposed and designed. In our previous works for hybrid magnetic refrigeration, numerical simulation and experimental performance of the low-pressure hybrid magnetic refrigerator was carried out, and the cycling mechanism of hybrid magnetic refrigeration was also figured out. In this study, a numerical model for the high-pressure hybrid magnetic refrigeration cycle is established. The magnetic refrigeration materials are utilized as the regenerator matrix for both gas Stirling and active magnetic regenerative refrigeration in this model. Effects of gas Stirling and active magnetic regenerative refrigeration are combined to build a kind of high efficient refrigeration cycle. Ansys Fluent software is applied in this paper. Based on the physical model of hybrid refrigerator and the theories of magnetocaloric effect and numerical calculation of regenerator, computational fluid dynamics (CFD) model of high-pressure hybrid magnetic refrigerator is established. This paper describes the internal heat transfer mechanism of Stirling and magnetic refrigeration effect in an active regenerator. Some parameters of the model such as working frequency and utilization are analyzed and the best phase angle is figured out in order to couple these two cooling effects positively. Simulation results show that Stirling and magnetic cooling effects can be coupled positively at phase angle of 60o. Results also show that with increasing system pressure, which means to increase the utilization of the system, the system frequency can enhance the cooling performance of the system as well as improve the coefficient of performance (COP) of it. The results and analysis of the numerical model will be helpful for the construction of experimental prototype in our future work.

Large reversible magnetocaloric effect in antiferromagnetic HoNiSi compound

Magnetic properties and magnetocaloric effect (MCE) of intermetallic HoNiSi compound have been investigated systematically. It is found that HoNiSi exhibits antiferromagnetic (AFM) state below the Néel temperature TN of 3.8 K, which is quite close to the liquid helium temperature (4 K). A giant MCE without hysteresis loss is observed in HoNiSi, which is related to the field-induced first-order metamagnetic transition from AFM to ferromagnetic states. For a magnetic field change of 2 T, the maximum values of magnetic entropy change (−ΔSM) and adiabatic temperature change (ΔTad) are 17.5 J/kg K and 4.5 K, respectively. In addition, HoNiSi presents both large values of positive and negative ΔSM for the low field changes, i.e., the maximum −ΔSM values are 9.2 J/kg K around TN and −7.2 J/kg K below TN for the field changes of 1 and 0.5 T, respectively. A universal curve of ΔSM is successfully constructed by using phenomenological procedure, proving the applicability of universal ΔSM curve for AFM materials. The giant reversible MCE for relatively low magnetic field change makes HoNiSi attractive candidate for magnetic refrigerant materials around liquid helium temperature.

Structural, magnetic, and magnetocaloric studies of La0.67Ba0.22Sr0.11Mn1−x Co x O3 manganites

In this work, we report the effect of Co doping on the structural and magnetic properties of La0.67Ba0.22Sr0.11Mn1−x Co x O3 (x = 0.0, 0.1, 0.2, 0.3 and 1) nanopowder samples synthesized by sol–gel method. All the samples crystallized in the orthorhombic system with Pnma space group, and the unit cell volume decreased significantly for x = 0.1, and then increased with increasing Co concentration up to x = 0.3. The stoichiometry and grain morphology of all samples were investigated by energy dispersive X-ray analysis and scanning electron microscopy. The magnetization measurements indicated that all samples exhibited a paramagnetic–ferromagnetic transition, and the transition temperature decreased with the increasing Co concentration. The magnetocaloric measurements on this series gave a significant magnetic entropy change (−ΔS M) near Curie temperature. The undoped sample gave a maximum magnetic entropy change of 2.75 J/kg K in a field change of 5 T, with a relative cooling power (RCP) of 290 J/kg. Intermediate level of substitution of Co for Mn (x = 0.2) was found to result in a decrease of the maximum magnetic entropy change, and to induce significant broadening of the peak, resulting in a relatively high RCP value of 270 J/kg. The observed maximum entropy change was found to be slightly lower than that calculated using the Landau model, and more significant deviations from the calculated values were observed at low temperatures. Our results on the magnetocaloric properties suggest that the parent compound La0.67Ba0.22Sr0.11MnO3 is attractive as a possible material for magnetic refrigeration around ambient temperature, whereas Co-doped samples are more efficient at lower temperatures.

Magnetic property and magnetocaloric effect in TmCoAl compound

A large reversible magnetocaloric effect accompanied by a second order magnetic phase transition from paramagnetic (PM) to ferromagnetic (FM) has been observed in TmCoAl intermetallic compound. For the magnetic field change of 5 T, the maximum value of magnetic entropy change (−ΔSMmax) and the value of refrigerant capacity (RC) are evaluated to be 18.2 J/kg K and 211 J/kg, respectively. In particular, a large −ΔSMmax (10.2 J/kg K) is achieved at 7.5 K under a low magnetic field change from 0 to 2 T with no thermal hysteresis and magnetic hysteresis loss. The large reversible magnetocaloric effect (both the large −ΔSM and the high RC) indicates that TmCoAl is one of a promising material for magnetic refrigeration in low temperature.

Investigations in MnAs1−xSbx: Experimental validation of a new magnetocaloric composite

Abstract 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.

Magnetic phase transitions and magnetocaloric effect of MnCoGe1−xSix

Here a cheaper alternative magnetic refrigeration material using MnCoGe1−xSix (x=0, 0.1, 0.3, and 0.5) alloys were investigated. The polycrystalline MnCoGe1−xSix alloys were prepared by arc-melting followed by annealing at 1123K for 72h. At a 0.5at% Si substitution, the Curie temperatures increased by 10% to 374K, the magnetic entropy change (|ΔSM|) values decreased by 32% to 2.1Jkg−1K−1 in an applied field from 0 to 2T and by 24% to 4.4Jkg−1K−1 in an applied field from 0 to 5T. However, the refrigeration capacity (RCFWHM) of this MnCoGe0.5Si0.5 alloy improved by 27% to 282Jkg−1 and the operation temperature range (δTFWHM) improved by 92% to 96K in an applied field at 5T. The MnCoGe0.5Si0.5 alloy can compete with some of the MCE properties of the MnCo0.95Ni0.05Ge, LaFe11Al2C0.5, (Fe85Co5Cr10)91Zr7B2, and even the Gd5Si2Ge2 alloys. The broad operation temperature range (96K) at a higher Curie temperature (374K) suggests that the MnCoGe0.5Si0.5 alloy can become a cheaper alternative MCE material (costing 70% less than a MnCoGe alloy).

The Influence of Vanadium on Magnetism and Magnetocaloric Properties of Fe 8 0 − x V x B12Si8 (x = 8, 10, and 13.7) Amorphous Alloys

Amorphous soft magnetic Fe80−x VxB12Si8 ribbons (0 ≤ x ≤ 14) have been fabricated by melt spinning technique, and their magnetic and magnetocaloric properties have been studied. The value of magnetocaloric effect has been determined from the measurements of magnetization as a function of temperature and an external magnetic field. The addition of vanadium to the ternary Fe80B12Si8 alloy results in a decrease of the Curie temperature of amorphous alloys, TC, from 473.5 to 335 K. With an increasing V content, the average magnetic moment of Fe atom and the magnetic entropy change also decrease. Fe66.3V13.7B12Si8 alloy exhibits the highest refrigeration capacity of 93.7 J kg−1 and moderate peak magnetic entropy of 1.034 J kg−1 K−1 (TC = 335 K) under the maximum applied field of 2 T. The results from this work showed that V containing amorphous alloy 13.7 at. % is an interesting material and potential candidate for magnetic refrigerants working near room temperature. The observed −ΔSMmax values compare favorably with other amorphous Fe-based alloys.

Giant magnetic entropy change in manganese perovskite La0.67Sr0.16Ca0.17MnO3 near room temperature

Structural, magnetic and magnetocaloric properties of La0.67Sr0.16Ca0.17MnO3 perovskite have been studied. A solid state reaction method was used in the preparation phase. X-ray diffraction analysis using Rietveld refinement revealed that this sample crystallizes in the distorted rhombohedral system with R3‾c space group. The variation of magnetization (M) vs. temperature (T), under an applied magnetic field of 0.05T, revealed a transition from a ferromagnetic (FM) to paramagnetic (PM) phase at around Curie temperature (TC=336K). Using Arrott plots, it was found that the transition is of a second-order. Isothermal measurements of magnetization allow us, through thermodynamic Maxwell relations, to determine the magnetic entropy change (ΔSM). A large ΔSM deduced from isothermal magnetization curves, has been observed in our sample with a peak centered around its respective TC. The maximum of the magnetic entropy change ΔSMmax in a magnetic field change of 5T is found to be 5.51Jkg−1K−1 at 335K. In addition, the compound showed a large relative cooling power (RCP) value of about 234J/kg while the maximum refrigerant capacity of 174J/kg was attained at the applied field of 5T. As a result, the studied sample can be considered as a potential material for magnetic refrigeration.

Structural and magnetic phase transition in quinary Ni45Co5(Mn, In, Sn)50 Heusler alloy

The structure, magnetic phase transition and martensitic transformation of quinary Ni45Co5(Mn, In, Sn)50 Heusler alloy are investigated systematically. X-ray diffraction reveals that there are two kinds of typical structure in alloys, the martensite phase with tetragonal structure and the austenite with cubic structure. Furthermore, it is found that Mn content plays an important role in the evolution of the crystal structure of quinary alloys, making the structure of alloys transform the cubic phase to tetragonal with increasing Mn content, and the threshold of structure transformation is about the Mn content of 35%. The temperature dependence of magnetization indicates that the tetragonal phase usually exhibits a low magnetization, while the cubic corresponds to a high magnetization. Particularly, the strong coupling between magnetism and structure occurs in Ni45Co5Mn40InxSn10−x alloys, and the alloys exhibit a large magnetic entropy change of 22.5Jkg−1K−1 in martensitic transformation, making it a good candidate for magnetic refrigeration materials.

Structural and Magnetocaloric Properties of ErFe 2 . 4 Al 0 . 6 Compound

The structural and magnetic properties of the single-phase pseudobinary ErFe 2.4Al 0.6 compound, obtained under arc-melting conditions, have been investigated. Single crystal X-ray diffraction analysis revealed that this compound is stabilized with a hexagonal CeNi 3-type structure (space group P6 3 /mmc). The partial substitution of Fe by Al in this compound occurring at all the metallic sites is reflected in the decrease of the Curie temperature Tc. Magnetization curves (2–450 K; 0–5 T) indicate a ferrimagnetic ordering with four magnetic phases induced by competitional interactions between magnetic moments of both Er and Fe. The magnetocaloric effect has been estimated from the magnetic isotherms. The relative cooling power (RCP) value indicates relatively promising magnetic refrigerant material.

Influence of the demagnetizing factor on the magnetocaloric effect: Critical scaling and numerical simulations

In recent years, the magnetocaloric effect is studied not only for the search of potential magnetic refrigerant materials but also for the analysis of critical phenomena. In both cases, the demagnetizing field might have a notable influence on the results. In this work, we carry out a systematic study, based on theoretical simulations, of the influence of the demagnetizing factor on the magnetocaloric properties. On the one hand, we show that demagnetizing factor affects only slightly the magnetic entropy change (ΔSM), reducing its magnitude and shifting the peak to higher temperatures. On the other hand, it dramatically affects the exponent n of field dependence (ΔSM∝Hn) at temperatures below the peak. We demonstrate that scaling of the magnetocaloric curves can be used to remove the influence of the demagnetizing field and, to which extent, critical exponent determination can be affected. Results of numerical simulations are compared with experimental data from a ball milled powder alloy.