Room Temperature Magnetic Refrigeration Applications Research Articles

Combinatorial design of partial ordered Al–Cr–Mn–Co medium-entropy alloys for room temperature magnetic refrigeration applications

Multi-component alloys have received increasing interest for functional applications in recent years. Here, we explore the magnetocaloric response for Al–Cr–Mn–Co medium-entropy alloys by integrated theoretical and experimental methods. Under the guidance of thermodynamic and ab initio calculations, a dual-phase system with large magnetic moment, i.e., Al50Cr19Mn19Co12, is synthesized, and the structural and magnetocaloric properties are confirmed via characterization. The obtained results indicate that the selected alloy exhibits a co-continuous mixture of a disordered body-centered cubic and an ordered B2 phase. The ab initio and Monte Carlo calculations indicate that the presence of the ordered B2 phase is responsible for the substantial magnetocaloric effect. The magnetization measurements demonstrated that this alloy undergoes a second-order magnetic transition with the Curie temperature of ∼300 K. The magnetocaloric properties are examined using magnetic entropy change, refrigeration capacity, and adiabatic temperature change. The property-directed strategy explored here is intended to contribute to the study of potential multi-component alloys in magnetocaloric applications.

Synthesis, structure, morphology, magnetism, and magnetocaloric-effect studies of La0.7Sr0.3Mn1−xFexO3 perovskite nanoparticles

Single-phase La0.7Sr0.3Mn1−xFexO3 (x = 0.0, 0.04, 0.08, 0.12, 0.16, 0.20, 0.24, and 0.30) perovskites were synthesized by the sol-gel method followed by sintering at 800 °C for 5 h. The XRD showed the rhombohedral structure with the R-3c space group and there was a slight change in the lattice parameters as well as the unit cell volume of the compounds with Fe doping. The average particle size of the samples was in the range of 43–70 nm. All samples show a ferromagnetic to paramagnetic second-order magnetic phase transition at TC and TC decreases linearly from 370 K for x = 0 to 98 K for x = 0.3. From the XPS measurement, it was found that the oxidation state of Fe and La are + 3 and the Mn has a mixed valence state of Mn4+/Mn3+. The saturation magnetization and the blocking temperature were suppressed by the Fe substitution while (-ΔSM)max was found to decrease as Fe content increased. The sample with x = 0.08 has a Curie temperature of 297 K, the highest relative cooling power (RCP) of 153 J/kg, and (-ΔSM)max value of 1.46 J/kg.K at µoΔH = 2.8 T. The La0.7Sr0.3Mn1−xFexO3 iron-substituted manganites may be regarded as a prospective candidate for room-temperature magnetic refrigeration applications.

Room temperature magnetocaloric effect and electrical transport properties of Co50Fe7V25Ga18Heusler alloys undergoing martensitic transformation

The metamagnetic martensitic transformation from the ferromagnetic austenite phase to the paramagnetic martensite phase was excited in the Co50Fe7V25Ga18 Heusler alloy near room temperature. Accompanying the transformation, the alloy exhibits a good magnetocaloric effect near room temperature with a cooling capacity of 17.02 J/kg under 3 T magnetic field at 302 K and the cusp-type anomalous of the resistivity with the magnetoresistance effect of ∼ 2.27% under a 3 T magnetic field. The power law equations for the temperature dependence of resistivity indicates the actuality of half-metallic properties. Our experimental results indicate that Co50Fe7V25Ga18 Heusler alloy is likely to become a potential candidate for room-temperature magnetic refrigeration and magnetic sensors applications.

A Setup for Direct Measurement of the Adiabatic Temperature Change in Magnetocaloric Materials

In order to find a highly efficient, environment-friendly magnetic refrigerant, direct measurements of the adiabatic temperature change Δ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_adb</i> is required. Here, in this work a simple setup for the Δ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_adb</i> measurement is presented. Using a permanent magnet Halbach array with a maximum magnetic field of 1.8 T and a rate of magnetic field change of 5 T/s, accurate determination of Δ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_adb</i> is possible in this system. The operating temperature range of the system is from 100 K to 400 K, designed for the characterization of materials with potential for room temperature magnetic refrigeration applications. Using the setup, the Δ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_adb</i> of a first-order and two second-order compounds have been studied. Results from the direct measurement for the first-order compound have been compared with Δ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_adb</i> calculated from the temperature and magnetic field dependent specific heat data. By comparing results from direct and indirect measurements, it is concluded that for a reliable characterization of the magnetocaloric effect, direct measurement of Δ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_adb</i> should be adopted.

Microstructure and transition behavior of Fe&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;P-based first-order magnetic phase-transition alloys

<p indent="0mm">Fe₂P-based first-order magnetic phase-transition alloys have been considered as one of the best candidates for room-temperature magnetic refrigeration applications due to their low cost, tunable working temperature range and superior magnetocaloric performance. Previous studies mainly focused on optimizing the magnetocaloric properties as well as uncovering the spin-lattice-electronic multi-coupling in the Fe₂P-based alloys, while the structure and phase transition behavior at the micrometer scale have rarely been reported. In the present study, we performed intensive studies on the microstructure and phase transition behavior in the Fe₂P-based alloys by means of transmission electron microscopy and X-ray powder diffraction (XRD). SiO₂ and Fe₃Si-type secondary phases with micrometer or sub-micrometer sizes are distributed along the grain boundary. <italic>In-situ</italic> XRD measurements indicate that the paramagnetic-ferromagnetic (PM-FM) transition is accompanied with significant lattice distortion in the hexagonal structure. The hexagonal unit cell is expanded by approximately 0.8% along the <italic>a</italic> axis, while it is contracted by about 1.8% along the <italic>c</italic> axis. The serve lattice distortion will induce large elastic energy, raise the energy barrier and thus bring about thermal hysteresis for the first-order magnetic transition. The magnetic transition-induced lattice distortion is more easily accommodated in the regions close to secondary phases and grain boundaries, where the atomic arrangement is more disordered. As a result, the nucleation of the PM-FM transition is found to start from the defect areas. However, the secondary phases and grain boundaries pin the domain walls, which hinders the growth of the ferromagnetic phase. The pinning effect of the defects will increase the energy barrier, causing an increase in the thermal hysteresis and the critical driven field for the first-order PM-FM transition. As a consequence, in order to further optimize the magnetocaloric performance, more efforts should made on tailoring both the intrinsic (e.g., lattice discontinuity) and extrinsic (e.g., size and distribution of the secondary phases) factors dominating the first-order magnetic transition of Fe₂P-based alloys.

Scale-Up of Magnetocaloric NiCoMnIn Heuslers by Powder Metallurgy for Room Temperature Magnetic Refrigeration

We present a new approach for a large-scale production of the rare-earth free NiCoMnIn Heusler alloy for room temperature magnetic refrigeration applications. This class of compounds has recently attracted attention thanks to the large reversible isothermal entropy change (ΔSiso) and adiabatic temperature change (ΔTad) associated to a first order magneto structural phase transition. A large-scale production method, however, has not yet been proposed. For giant magnetocaloric materials and especially for Heusler compounds, the synthesis has a predominant role in tailoring the physical-chemical properties, due to the high sensitivity of the first order transition characteristics on chemical composition and microstructure. Up to 250 grams of the nominal composition Ni45.7 Co4.2Mn36.6In13.3 alloy were prepared in a unique sample starting from industrial grade powdered elements. The phase transition temperatures and magnetocaloric properties were investigated by magnetic and direct adiabatic temperature measurements and were found to be homogeneous in the whole sample. The mechanical stability of the produced alloy and its workability were investigated. A low-temperature thermal treatment was identified and showed promising results by reducing hysteresis and transition width.

Tailoring the magnetic entropy change towards room temperature in Sr-site deficient La0.6Dy0.07Sr0.33MnO3 manganite

The Sr-deficient compound could be a potential candidate for room temperature magnetic refrigeration applications.

Large magnetocaloric effect near to room temperature in Sr doped La0.7Ca0.3MnO3

The goal of this work is to demonstrate the positive effect of high energy ball milling on the magnetocaloric properties of materials based on strontium-calcium doped lanthanum manganite. We report a detailed study of crystal structure, magnetic behavior and magnetocaloric effect of La0.7Ca0.3−xSrxMnO3 (0 ≤ x ≤ 0.2, Δx = 0.05) powders, synthesized by assisted high-energy ball milling. The X-ray diffraction patterns disclose the complete formation of manganite with an orthorhombic structure for x ≤ 0.15, and rhombohedral structure for x = 0.2. Magnetic properties show a reduction of the magnetic saturation, and an increase in the Curie temperature with the strontium substitution, in all explored compositions (above room temperature). Arrot curves display that strontium doped manganites exhibit a second-order magnetic transition from ferrimagnetic to paramagnetic order. The magnetocaloric effect was calculated by measuring the isothermal magnetization around the Curie temperature, from 0 to 1.8 T, using Maxwell relations. All the synthesized manganites show magnetocaloric effect larger as compared to that of the parent compounds synthesized by other methods. The un-doped sample (x = 0) presents 7.43 J kg−1 K−1 and 93.29 J kg−1 of maximum magnetic entropy change (|ΔSM|) and the relative cooling power (RCP), respectively, under a low applied field (μoH) of 1.8 T. As it is expected, the introduction of strontium into the manganite, slightly reduces the magnetic entropy at 1.8 T, from 6.29 to 3.47 J kg−1 K−1 for x = 0.05 and x = 0.2, respectively. At the same time, the presence of strontium increases the working temperature above room temperature for strontium contents higer than 0.05, both attributed to the change in the crystal structure. These values are suitable for room-temperature magnetic refrigeration applications, using low magnetic fields (<1.8 T), increasing its potential application in the domestic refrigeration.

Analysis of the magnetic transition and magnetocaloric effect in Mn5Ge2.9Ag0.1 compound

Here we investigate analytical models to understand magnetic and magnetocaloric properties of Mn5Ge2.9Ag0.1 compound prepared by arc-melting method. The Mn5Ge2.9Ag0.1 alloy, undergoing a second-order transition, shows a maximum magnetic entropy change of about 6.86 J/kgK and the relative cooling power (RCP) value of 386 J/kg at 298 K under a field change of 5T. Based on a phenomenological model, the magnetocaloric properties obtained from temperature-dependent magnetization data are in good agreement with the experimental results. To give a better understanding of magnetic transition and the effective magnetic entropy change, we quantify the coupling of lattice energy and electronic energy contribution to the effective magnetic entropy change from a Landau theory plus Bean-Rodbell model. Interestingly, the coupling of lattice energy and electronic energy presents a positive value of up to 4.5% of the effective magnetic entropy change, producing a deleterious impact on the effective magnetic entropy change. The results suggest that the Mn5Ge2.9Ag0.1 system could be a very attractive material for room-temperature magnetic refrigeration applications.

The analysis of magnetic entropy change and long-range ferromagnetic order in Mn1−xAgxCoGe

MnCoGe alloy is a promising candidate for room-temperature magnetic refrigeration applications, and the magnetocaloric effect in this family has a close relationship with the nature of phase transition. In this work, we presented a systematic study focusing on the phase transition, magnetic entropy change, and magnetic interaction in four compositions. The Banerjee criterion, Landau theory, and universal behavior were performed to distinguish the characteristic of second-order transition. It is found that the theoretical magnetic entropy changes based on Landau theory are in good agreement with the experimental findings, indicating the reliability of this method to evaluate magnetocaloric property. Moreover, the fitting parameters determined from the rescaled magnetic entropy change curves and field dependence of magnetic entropy change are used to give a better understanding of phase transition and magnetic refrigerant performance. Reliable critical exponents from three techniques suggest long-range magnetic couplings in this system. Additionally, the differences in critical behavior with Ag substitution are described by calculation of density of the effective exponents (βeff and γeff) and exchange distance J(r). The very stable nature of phase transition and abundant availability make this system suitable for thermomagnetic power generation applications.

Giant low field magnetocaloric effect and magnetostructural coupling in MnCoGe1-xInx around room temperature

Effects on substitution of Ge by In on structural and magnetic properties are studied in MnCoGe1-xInx compounds. A small amount of In (2% and 5%) dopant can shift the martensite transformation temperature to room temperature and make it overlap with Curie temperature window, which results in a spin-lattice coupling and a large conventional magnetocaloric effect. Giant values of magnetic entropy change (△SM) are obtained in both magnetizing and demagnetizing processes in the vicinity of the magnetostructural transition. The maximum values of |△SM| for MnCoGe0.95In0.05 reach 21.4 and 25.4 J/kg K for a small magnetic field change △H = 2–0 and 0–2 T, respectively, which make it promising for room temperature magnetic refrigeration applications.

Mixed rare earth oxides derived from monazite sand as an inexpensive precursor material for room temperature magnetic refrigeration applications

An inexpensive perovskite type (REMIX)0.67Sr0.33MnO3 compound is synthesized via solid state method using mixed rare earth oxide precursor derived from monazite sand. Rietveld refinement of X-ray powder diffraction patterns confirms the compound is a mixture of rare earth manganites which is the major phase and CeO2 as the secondary phase. The compound shows a second order ferromagnetic to paramagnetic transition near room temperature and exhibits a magnetic entropy change (-ΔSM) of 3.28Jkg−1K−1 with a relative cooling power (RCP) of 120Jkg−1 and an adiabatic temperature change (ΔTad) of 2.11K at 310K under 50kOe magnetic field. The Debye temperature of the compound is found to be 543K and room temperature thermal conductivity is 4.26Wm−1K−1. The temperature variation of electrical resistivity shows a metal to insulator transition around 180K, which gets shifted towards higher temperature upon the application of magnetic field. The compound shows a large value of −ΔSM and this work makes an endeavor to develop low–cost materials for the magnetic refrigeration applications near the room temperature.

Effect of Mn Doping on the Structural, Magnetic, and Magnetocaloric Effect of Fe17Dy2 Compounds

Crystal structural and magnetic properties of polycrystalline (Fe1−x Mn x )17Dy2 (x = 0.0, 0.1, 0.2, and 0.3) compounds were studied by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) measurements. The results show that (Fe1−x Mn x )17Dy2 forms as a substitutional solid solution with the hexagonal Th2Ni17 type. The unit cell volume increases with Mn content. The Curie temperature (T C) can be tuned from 364 K for x = 0.0 to 80 K for x = 0.3. The magnetic transition at T C is a typical second-order ferromagnetic-paramagnetic transition. For an applied field change from 0 to 5 T, the maximum magnetic entropy change (| − ΔS M|) for (Fe1−x Mn x )17Dy2 (x = 0.0, 0.1, and 0.2) compounds are 3.9, 2.8, and 1.7 J kg−1 k−1, respectively. The high ΔS M, appropriate T C, and a high performance-to-cost ratio make (Fe1−x Mn x )17Dy2 compounds a candidate materials for room-temperature magnetic refrigeration applications.

Magnetic and magnetocaloric properties in second-order phase transition La1−xKxMnO3 and their composites

In this work, we present a detailed study on the magnetic properties and the magnetocaloric effect (MCE) of La1−xKxMnO3 compounds with x=0.05–0.2. Our results pointed out that the Curie temperature (TC) could be controlled easily from 213 to 306K by increasing K-doping concentration (x) from 0.05 to 0.2. In the paramagnetic region, the inverse of the susceptibility can be analyzed by using the Curie-Weiss law, χ(T)=C/(T−θ). The results have proved an existence of ferromagnetic clusters at temperatures above TC. Based on Banerjee's criteria, we also pointed out that the samples are the second-order phase transition materials. Their magnetic entropy change was calculated by using the Maxwell relation and a phenomenological model. Interestingly, the samples with x=0.1–0.2 exhibit a large MCE in a range of 282–306K, which are suitable for room-temperature magnetic refrigeration applications. The composites obtained from single phase samples (x=0.1–0.2) exhibit the high relative cooling power values in a wide temperature range. From the viewpoint of the refrigerant capacity, the composites formed out of La1−xKxMnO3 will become more useful for magnetic refrigeration applications around room-temperature.

Magneto-caloric effect of FexZryB100−x−y metallic ribbons for room temperature magnetic refrigeration

Among various amorphous magnetic materials, even though Fe-based materials do not have high magnetocaloric effect (MCE), their advantages of tunable Curie temperature (TC) and low cost have attracted considerable attention in regard to room temperature magnetic refrigeration applications. With the aim of enhancing the MCE, the influence of boron addition on Fe-based amorphous materials was investigated in this study. Fe94−xZr6Bx (x=5, 6, 8 and 10), Fe91−yZr9By (y=3, 4, 5, 6, 8 and 10) and Fe89−zZr11Bz (z=3, 4, 5, 6, 8 and 10) specimens were made in ribbon form and their magnetocaloric effect was investigated. The Curie temperature (TC) of all three series of ribbons underwent an almost linear increase, and the peak magnetic entropy change, |ΔSMpeak| (obtained in a magnetic field of 1.5T), generally increases with increasing boron content. The results further show that the Fe86Zr9B5 ribbon exhibits a relatively large |ΔSMpeak| value of 1.13J/kgK at 330K and a large refrigerant capacity value of 135.6J/kg under 1.5T. On the basis of these results, although there is still much scope for improvement before totally replacing the conventional cooling method, the Fe-based amorphous ribbon can be seen as a promising magnetocaloric material for room temperature magnetic refrigeration applications.

Wide temperature span of entropy change in first-order metamagnetic MnCo1−xFexSi

The crystal structure and magnetic properties of MnCoxFe1−xSi (x = 0–0.5) compounds were investigated. With increasing Fe content, the unit cell changes anisotropically and the magnetic property evolves gradually: Curie temperature decreases continuously, the first-order metamagnetic transition from a low-temperature helical antiferromagnetic (AFM) state to a high-temperature ferromagnetic state disappears gradually and then a spin-glass-like state and another AFM state emerge in the low-temperature region. The Curie transition leads to a moderate conventional entropy change. The metamagnetic transition not only yields a larger negative magnetocaloric effect at lower applied fields than in MnCoSi but also produces a very large temperature span (103 K for Δμ0H = 5 T) of ΔS(T), which results in a large refrigerant capacity. These phenomena were explained in terms of crystal structure change and magnetoelastic coupling mechanism. Because of the large isothermal entropy change, the wide working temperature span and the low cost, MnCo1−xFexSi compounds are promising candidates for near room-temperature magnetic refrigeration applications.

Magnetocaloric effect of Pr2Fe17−x Mn x alloys

Polycrystalline Pr2Fe17-xMnx (x = 0, 1, and 2) alloys were studied by X-ray diffraction (XRD), heat capacity, ac susceptibility, and isothermal magnetization measurements. All the alloys adopt the rhombohedral Th2Zn17-type structure. The Curie temperature increases from 283 K at x = 0 to 294 K at x = 1, and then decreases to 285 K at x = 2. The magnetic phase transition at the Curie temperature is a typical second-order paramagnetic- ferromagnetic transition. For an applied field change from 0 to 5 T, the maximum -DSM for Pr2Fe17-xMnx alloys with x = 0, 1, and 2 are 5.66, 5.07, and 4.31 Jkg -1 � K -1 , respectively. The refrigerant capacity (RC) values range from 458 to 364 Jkg -1 , which is about 70 %-89 % that of Gd. The large, near room temperature DSM and RC values, chemical stability, and a high performance-to-cost ratio make Pr2Fe17-xMnx alloys be selectable materials for room temperature magnetic refrigeration applications.

A significant reduction of hysteresis in MnFe(P,Si) compounds

The magnetocaloric effects in Mn1.3Fe0.7−x Co x P0.46Si0.54 compounds (x = 0, 0.025, 0.05 and 0.1) were investigated systematically. X-ray diffraction shows that the compounds crystallize in the Fe2P-type hexagonal structure with space group P-62m symmetry. Magnetic measurements show that the paramagnetic-ferromagnetic transition temperatures range from 247 to 298 K. The maximal magnetic entropy changes in the Mn1.3Fe0.7P0.46Si0.54 compound reaches 8.3 J/kgK for a field change from 0 to 1.5 T. The thermal hysteresis of these compounds is less than 3 K. The maximum adiabatic temperature change is 2.2 K in Mn1.3Fe0.7P0.46Si0.54 and Mn1.3Fe0.65Co0.05P0.46Si0.54 compounds for a field change from 0 to 1.48 T, indicating this material system has potential for room-temperature magnetic refrigeration applications.

Near room temperature magnetocaloric properties of Fe substituted La0.67Sr0.33MnO3

The effect of Fe substitution in the polycrystalline La0.67Sr0.33MnO3 has been investigated. Substitution of Fe decreases the Curie temperature of La0.67Sr0.33MnO3 from 370K to near room temperature in x<0.3 samples, which show well defined ferromagnetic–paramagnetic transition, whereas x>0.3 exhibit a frustrated glassy behaviour, evident from the ZFC and FC magnetization data. The magnetic entropy change calculated from the M–H–T data of x=0.05 and x=0.1 show broad peak and the respective values of −ΔSM and RCP are found to be about 2.8J/kgK, 166J/kg (at TC=275K) and 3.3J/kgK, 153J/kg (at TC=266K) under a field of 50kOe. Due to the wider distribution of the magnetic entropy, these two compounds can be used as refrigerants for room temperature magnetic refrigeration applications. The critical behaviour of the two compositions was also estimated from the field dependent magnetic entropy change.

Magnetic and magnetocaloric properties of Mn3−xFexSn2 (0.1 ⩽ x ⩽ 0.9)

The magnetic and magnetocaloric properties of Ni3Sn2-type (Pnma) Mn3−xFexSn2 compounds (0.1 ⩽ x ⩽ 0.9) have been investigated. Their thermomagnetic behaviour is characterized by three transitions whose temperature evolves with the Fe content: two successive second-order ferromagnetic-like transitions (258 K ⩽ TC1 ⩽ 290 K, 171 K ⩽ TC2 ⩽ 208 K) and a third transition at Tt corresponding to the appearance of a weak antiferromagnetic interaction (164 K ⩽ Tt ⩽ 206 K). The magnetization is kept almost constant throughout the series (∼5.4 μB/f.u. at 5 K). The −ΔSM (T) dependence is similar to that of a two-component hybrid material with peak maxima at TC1 and TC2 and a refrigerant capacity (q ∼ 1.9 J cm−3 for ΔH = 5 T) reaching at least 40% that of the best known magnetic refrigerants. The shape as well as the temperature span of the magnetocaloric response can be tuned by the iron content. This makes the low-cost Mn3−xFexSn2 alloys good candidates for near room temperature magnetic refrigeration applications, despite the moderate magnitude of the magnetocaloric effect (up to −ΔSM ∼ 26 mJ cm−3 K−1 for ΔH = 5 T).