Reversible Magnetic Entropy Change Research Articles

Large reversible multicaloric effects over a broad refrigeration temperature range in Co and B co-doped Ni–Mn–Ti alloys

Solid-state refrigeration is considered a promising alternative to traditional vapor compression refrigeration technology. Researchers demonstrated that Ni–Mn–Ti alloys have a remarkable elastocaloric effect. However, the Ni–Mn–Ti alloy can only operate under a uniaxial stress field due to its antiferromagnetic austenite, which narrows its range of refrigeration temperatures. Here, we activated the magnetism of the alloy by replacing some Ni atoms with Co atoms. The Ni–Co–Mn–Ti–B alloy demonstrates a reversible maximum magnetic entropy change(ΔSm) of 24.9 J kg−1 K−1 and achieves an adiabatic temperature change of 7.8 K under a 7 T magnetic field. Additionally, we demonstrate that adding boron (0.2%) can improve the mechanical properties and cyclic stability in Ni–Mn–Ti alloys. The elastocaloric effect of 21.3 K with high cycle stability (1013 cycles) were successfully achieved in the directionally solidified (Ni35Co15Mn35Ti15)99.8B0.2 alloy. Furthermore, we have demonstrated that the magnetoelastic coupling effect can effectively extend the refrigeration temperature range. The alloys achieved large caloric effects in the temperature range of 240 K–340 K. This provides a new strategy for designing high-performance materials for wide-temperature-domain refrigeration.

Impact of fast-solidification on all-d-metal NiCoMnTi based giant magnetocaloric Heusler compounds

Recently, the all-d-metal Ni(Co)MnTi based Heusler compounds are found to have a giant magnetocaloric effect (GMCE) near room temperature and manifest different functionalities like multicaloric effects, which can be employed for solid-state refrigeration. However, in comparison to other traditional Heusler compounds, the relatively large thermal hysteresis (ΔThys) and moderately steep ferromagnetic phase transition provides limitations for real applications. Here, we present that fast solidification (suction casting) can sufficiently tailor the GMCE performance by modifying the microstructure. Compared with the arc-melted sample, the magnetic entropy change of the suction-casted sample shows a 67% improvement from 18.4 to 29.4 Jkg−1K−1 for a field change (∆μ0H) of 5 T. As the thermal hysteresis has maintained a low ΔThys value (5.5 K) for the enhanced first-order phase transition, a very competitive reversible magnetic entropy change of 21.8 Jkg−1K−1 for ∆μ0H = 5 T is obtained. Combining high-resolution transmission electron microscopy (HRTEM) and positron annihilation spectroscopy (PAS) results, the difference in lattice defect concentration is found to be responsible for the significant improvement in GMCE for the suction-cast sample, which suggests that defect engineering can be applied to control the GMCE. Our study reveals that fast solidification can effectively regulate the magnetocaloric properties of all-d-metal NiCoMnTi Heusler compounds without sacrificing ΔThys.

Cyclic reversible martensitic transformation and magnetocaloric effect in a Ni51.0Mn20.8Ga22.4Cu5.8 alloy

Working materials exhibiting a large reversible magnetocaloric effect are necessary for improving the cooling efficiency of magnetic refrigeration. Herein, the cyclic reversibility of the martensitic transformation and magnetocaloric effect in a Ni51.0Mn20.8Ga22.4Cu5.8 alloy is investigated. The martensitic transformation exhibits small thermal and magnetic hystereses (∼6 K and ∼6.8 J/kg, respectively) and excellent reversibility upon 50 thermal and magnetic cycles owing to the good geometric compatibility of the martensite/austenite transferring interface. A reversible magnetic entropy change up to −21.7 J/kgK is achieved under 50 kOe after performing 50 magnetic cycles, indicating the excellent reversibility of the magnetocaloric effect in the alloy.

Large reversible magnetocaloric effect across the first-order magneto-structural transition in (Mn0.45Fe0.55) (Ni0.6Co0.4) Si alloy

Magnetic materials with reversible magnetocaloric effect across their respective first-order magneto-structural transitions (MST) have vital significance for further advancement towards the ultimate goal of practical magnetic cooling applications. In this present study, the reversibility of the MST is investigated by analyzing the isofield curves under different minor and major thermal hysteresis loops and the isothermal curves under different magnetic field cycles. The reversibility of the magnetocaloric effect (MCE) depends upon the width of the nucleation energy barrier existing across the MST. Minor hysteresis loops are found to be minimizing the energy loss by preventing the nucleation of the martensite phase and can be easily returned to the austenite phase immediately while switching from cooling to heating. A large reversible isothermal magnetic entropy change ΔSM of −14.4 J kg−1 K−1 nearly at 322 K is observed for the (Mn0.45Fe0.55) (Ni0.6 Co0.4) Si alloy under a low magnetic field change of 3 T. The observed large reversible MCE, very low magnetic field-induced hysteresis loss, and large reversible RCeffe ∼ 155 J kg−1 will be beneficial for reducing the energy loss during several magnetic field cycles in practical cooling applications which makes this alloy promising for the development of efficient magnetic refrigerants.

Structural, magnetic, and magnetocaloric characterization of NiMnSn microwires prepared by Taylor-Ulitovsky technique

We report the structural, magnetic, and magnetocaloric characterization of glass-coated Ni42.9Mn37.1Sn20.0 microwires produced by the Taylor-Ulitovsky method. Microwire samples crystallized into a single-phase austenite with the L21-type crystal structure (space group Fm3̄m, lattice parameter a ≈ 6.02 Å) and a Curie temperature of 349 K. A distinctive feature of the produced microwires is that saturation magnetization is reached at a very low magnetic field (∼0.15 T). For a magnetic field change of 3 T, the produced microwires showed a reversible maximum magnetic entropy change |ΔSM|max of 2.3 J kg−1 K−1 and a refrigerant capacity of 197 J kg−1, which are similar to the values reported by other austenitic NiMnSn alloys produced by rapid quenching techniques.

Magnetic and magnetocaloric properties of Pr2CuMnO6

We report on the structural, magnetic and transport properties of Pr2CuMnO6 prepared by the solid-state reaction method. X-ray diffraction and Rietveld refinement reveal an orthorhombic crystal structure (space group Pnma) with no trace of secondary phases in the prepared samples. FC and ZFC magnetization measurements show a second order ferromagnetic to paramagnetic (FM-PM) phase transition at 35 K confirmed further through investigations using the universal master curve and Arrott plots. The partial Cu-Mn ordering and lack of long-range order in the system are indicated by the absence of magnetic saturation up to a magnetic field of 7 T down to 5 K. A reversible magnetic entropy change (−ΔSm) with a maximum value of 1.47 Jkg−1K−1 and a relative cooling power of 96.37 Jkg−1 at the applied field of 7 T are observed around Tc.

Influence of Chemical Substitution and Light Element Insertion on the Magnetic Properties of Nanocrystalline Pr2Co7 Compound

It is well recognized that intermetallics based on rare-earth (R) and transition metals (T) display numerous interesting magnetic properties, leading to potential applications in different fields. The latest progress regarding magnetic properties and the magnetocaloric effect (MCE) in the nanostructured Pr2Co7 compound, as well as its carbides and hydrides, is reviewed in this paper. Some of this progress reveals remarkable MCE performance, which makes it attractive in the field of magnetic refrigeration at high temperatures. With the purpose of understanding the magnetic and magnetocaloric characteristics of these compounds, the crystal structure, microstructure, and magnetism are also brought into focus. The Pr2Co7 compound has interesting magnetic properties, such as a high Curie temperature TC and uniaxial magnetocrystalline anisotropy. It crystallizes in a hexagonal structure (2:7 H) of the Ce2Ni7 type and is stable at relatively low temperatures (Ta ≤ 1023 K), or it has a rhombohedral structure (2:7 R) of the Gd2Co7 type and is stable at high temperatures (Ta ≥ 1223 K). Studies of the magnetocaloric properties of the nanocrystalline Pr2Co7 compound have shown the existence of a large reversible magnetic entropy change (ΔSM) with a second-order magnetic transition. After its substitution, we showed that nanocrystalline Pr2Co7−xFex compounds that were annealed at Ta = 973 K crystallized in the 2:7 H structure similarly to the parent compound. The extended X-ray absorption fine-structure (EXAFS) spectra adjustments showed that Fe atoms preferably occupy the 12k site for x ≤ 1. The study of the magnetic properties of nanocrystalline Pr2Co7−xFex compounds revealed an increase in TC of about 26% for x = 0.5, as well as an improvement in the coercivity, Hc (12 kOe), and the (BH)max (9 MGOe) product. On the other hand, the insertion of C atoms into the Pr2Co7 cell led to a marked improvement in the TC value of 21.6%. The best magnetic properties were found for the Pr2Co7C0.25 compound annealed at 973 K, Hc = 10.3 kOe, and (BH)max = 11.5 MGOe. We studied the microstructure, hydrogenation, and magnetic properties of nanocrystalline Pr2Co7Hx hydrides. The crystal structure of the Pr2Co7 compound transformed from a hexagonal (P63/mmc) into an orthorhombic (Pbcn) and monoclinic (C2/c) structure during hydrogenation. The absorption of H by the Pr2Co7 compound led to an increase in the TC value from 600 K at x = 0 to 691 K at x = 3.75. The Pr2Co7H0.25 hydride had optimal magnetic properties: Hc = 6.1 KOe, (BH)max = 5.8 MGOe, and TC = 607 K. We tailored the mean field theory (MFT) and random magnetic anisotropy (RMA) methods to investigate the magnetic moments, exchange interactions, and magnetic anisotropy properties. The relationship between the microstructure and magnetic properties is discussed. The obtained results provide a fundamental reference for adapting the magnetic properties of the Pr2Co7, Pr2Co6.5Fe0.5, Pr2Co7C0.25, and Pr2Co7H0.25 compounds for potential permanent nanomagnets, high-density magnetic recording, and magnetic refrigeration applications.

Large reversible magnetic entropy change of R3Ni6Al2 (R = Dy, Ho and Er) compounds

Large magnetocaloric effect (MCE) and magnetic properties in R3Ni6Al2 (R = Dy, Ho and Er) compounds were systematically investigated. Large magnetic moment and low magnetic transition temperature play a decisive role in the magnetocaloric performance for R3Ni6Al2 (R = Dy, Ho and Er) compounds. Ho3Ni6Al2 compound shows the largest magnetic entropy change with the value of 19.7 J/kg K at ~20 K under field change of 0–5 T because of the large magnetic moment and moderate transition temperature. For Dy3Ni6Al2 compound, it exhibits the largest refrigeration capacity with the value of 394.5 J/kg due to the successive magnetic transitions. The Er3Ni6Al2 compound has a large MCE at ultra-low temperatures around 4 K. Furthermore, the second-order phase transition in R3Ni6Al2 (R = Dy, Ho, Er) compounds were confirmed according to Arrott plots, rescaled universal magnetic entropy change curves and mean field theory with negligible thermal and magnetic hysteresis. The large reversible MCE with low working temperatures indicates that R3Ni6Al2 compounds are potential excellent MCE materials for low-temperature magnetic refrigeration.

A strategy of optimizing magnetism and hysteresis simultaneously in Ni–Mn-based metamagnetic shape memory alloys

Due to the existence of the magnetic-field-induced reverse martensitic transformation, the Ni–Mn–Z alloys where Z is the p-block element of In, Sn or Sb exhibit several state-of-the-art magnetoresponsive properties. From the perspective of practical application, a major challenge of this compound is to strengthen the ferromagnetism and reduce the transitional hysteresis ΔTHys simultaneously. In this work, we report an alloying strategy to this issue, i.e., the partial substitutions of Co and Cu for Ni and the p-block element, respectively, by a combined study of experiment and ab-initio calculation in the Ni45Co5Mn36In14–xCux (x = 0–1.5) alloys. Results show that the Cu replacement for the p-block element (In) can effectively reduce ΔTHys owing to the improved geometrical compatibility between austenite and martensite. Moreover, the adopted alloying strategy of Cu hardly weakens the strong ferromagnetism of Ni(Co)–Mn–In, since the magnetism exhibits a weak dependence on the p-block element compared with Mn and Ni. The maximum reversible magnetic entropy change ΔSMMax of the Ni45Co5Mn36In13.3Cu0.7 directionally solidified sample at a magnetic field of 5 T is 13.8 J·kg−1·K−1. The refrigeration capacity RC and effective refrigeration capacity RCeff equal to 473.7 J·kg−1 and 270.2 J·kg−1, respectively. Both values belong to the highest one in the Ni–Mn-based alloys. Additionally, the working temperature window of the magnetocaloric effect is as wide as ~40 K. This work is expected to promote the design of advanced metamagnetic shape memory alloys.

Reversible low-field magnetocaloric effect in Ni-Mn-In-based Heusler alloys

Ni-Mn-$X$ ($X=\mathrm{In}$, Sn, and Sb) based Heusler alloys show a strong potential for magnetic refrigeration owing to their large magnetocaloric effect (MCE) associated with first-order magnetostructural transition. However, the irreversibility of the MCE under low field change of 0--1 T directly hinders its application as an efficient magnetic coolant. In this work, we systematically investigate thermal and magnetic properties, crystalline structure and magnetocaloric performance in $\mathrm{N}{\mathrm{i}}_{51\ensuremath{-}x}\mathrm{M}{\mathrm{n}}_{33.4}\mathrm{I}{\mathrm{n}}_{15.6}{\mathrm{V}}_{x}$ alloys. With the introduction of V, a stable magnetostructural transition near room temperature is observed between martensite and austenite. An extremely small hysteresis of 2.3 K is achieved for the composition $x=0.3$. Due to this optimization, the magnetic-field induced structural transition is partially reversible under 0--1 T cycles, resulting in a reversible MCE. Both magnetic and calorimetric measurements consistently show that the largest value for the reversible magnetic entropy change can reach about $5.1\phantom{\rule{0.16em}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}\mathrm{k}{\mathrm{g}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ in a field change of 0--1 T. A considerable and reversible adiabatic temperature change of \ensuremath{-}1.2 K by the direct measurement is also observed under a field change of 0--1.1 T. Furthermore, the origin of this small hysteresis is discussed. Based on the lattice parameters, the transformation stretch tensor is calculated, which indicates an improved geometric compatibility between the two phases. Our work greatly improves the MCE performance of Ni-Mn-$X$-based alloys and make them suitable as realistic magnetic refrigeration materials.

Giant reversible magnetocaloric effect in MnNiGe-based materials: Minimizing thermal hysteresis via crystallographic compatibility modulation

MnMX (M = Co or Ni, X = Si or Ge) alloys with strong magnetostructural coupling exhibit giant magnetic entropy change and are currently extensively studied. However, large thermal hysteresis results in serious irreversibility of the magnetocaloric effect in this well-known system. In this work, we report a low thermal hysteresis and large reversible magnetocaloric effect in a MnNiGe-based system. The introduction of Fe into both Ni and Mn sites can establish stable magnetostructural transitions from paramagnetic hexagonal to ferromagnetic orthorhombic phases. Fascinatingly, a low thermal hysteresis of 5.2 K is achieved in Mn0.9Fe0.2Ni0.9Ge alloy with a large magnetization difference of 62.1 A m2/kg between the two phases. These optimized parameters lead to a partially reversible phase transformation under a magnetic stimulus and bring about a large reversible magnetic entropy change of −18.6 Jkg−1K−1 under the field variation of 0–5 T, which is the largest value reported in MnMX system up to now. Moreover, this low-hysteresis magnetostructural transformation and large reversible magnetocaloric effect can be tuned by doping with Si in a wide temperature range covering room temperature. We also introduce geometrically nonlinear theory to discuss the origin of low hysteresis in MnMX alloys. A strong relation is found between thermal hysteresis and the change of c axis in the orthorhombic structure during the transition. Our work greatly develops the potential of MnMX alloys as magnetocaloric materials and is meaningful to seek or design a MnMX system with low thermal hysteresis.

Tuning the Reversible Magnetocaloric Effect in Ni–Mn–In‐Based Alloys through Co and Cu Co‐Doping

AbstractThe reversibility of the giant magnetocaloric effect (MCE) through the magnetic field–induced magnetostructural transformation in Ni–Mn–In‐based alloys is a key issue towards the potential magnetic refrigeration applications. In this work, Co and Cu are simultaneously doped to tune the reversible magnetocaloric properties associated with the magnetostructural transformation. Owing to the integration of large magnetization difference ΔM, suitable transformation entropy ΔStr, and narrow thermal hysteresis ΔThys in a Ni46Co3Mn35Cu2In14 alloy, the reversible field–induced inverse martensitic transformation is realized in a wide temperature range of 30 K under the field of 5T, yielding a maximum reversible magnetic entropy change ΔSMmax of 16.4 J kg−1 K−1. Moreover, under a low field change of 1.5T, a large reversible adiabatic temperature variation ΔTad of 2.5 K is also obtained, representing the highest value so far under the low field change of 1.5T in Ni–Mn‐based alloys. It is demonstrated that multi‐component alloying by combining the effects of appropriate substitutional elements is an effective way to develop high‐performance magnetocaloric materials.

Reversible magnetocaloric effect and critical behaviors in Mn1.9−xCoxSn compounds

The structure, magnetic properties and magnetocaloric effect in the Mn1.9−xCoxSn (x = 0, 0.2, 0.4) compounds have been investigated. The reversible magnetic-entropy changes of Mn1.9Sn and Mn1.7Co0.2Sn are 2.13 (209 K) and 1.08 (113 K) J kg−1 K−1, respectively, for magnetic field change between 0–5 T. The critical exponents in Mn1.9Sn and Mn1.7Co0.2Sn compounds have been determined. In the critical region, the data points of magnetization, field and temperature near fall into two universal curves. By analysis on the critical exponents, we thought that the short-range ferri-magnetic order occurs in x = 0 compound at T < and in x = 0.2 one at T > The analysis on long-range attractive interactions reveals the dominant long-range interactions in the vicinity of in both compounds, besides a little short-range ferro- or ferri-magnetic order.

Large reversible magnetic entropy change in rapidly solidified Ni0.895Cr0.105MnGe1.05 melt-spun ribbons

The crystal structure, and magnetic and magnetocaloric properties of rapidly solidified Ni0.895Cr0.105MnGe1.05 melt-spun ribbons is reported. The ribbon samples crystallize into a single-phase hexagonal Ni2In-type structure at room temperature. The as-quenched ribbons showed a second order magnetic transition at 192 ± 1 K at μoH = 5 mT. A magnetic-field-induced transition from an antiferromagnetic (AFM)-like to a ferromagnetic (FM) state of martensite structure was observed in annealed ribbons below the temperature of the martensitic transformation (TM ∼ 245 ± 1 K). The annealed ribbons undergo a first-order magnetostructural transition (MST) with a large maximum reversible magnetic entropy change of ΔSM = 16.1 J kg−1 K−1 (this is about a four-fold increase compared to the ΔSM observed for the bulk sample of the same nominal composition) and RC = 144 J kg−1 for μoΔH = 5 T at temperature T = TM ∼ 245 ± 1 K. The increase in the ΔSM peak value leads to an improved RC compared to that of the bulk sample (122 J kg−1). The observed MCE and quasi-reversible character of ΔSM at the MST illustrates the potential of Ni0.895Cr0.105MnGe1.05 ribbons for magnetic cooling technology.

Reversible magnetocaloric effect and critical exponent analysis in Mn-Fe-Ni-Sn Heusler alloys

We report the magnetic and magnetocaloric properties of Mn48-xFexNi41Sn11 (x = 8.5, 10.5) Heusler alloys. The temperature dependent magnetization curve (M vs T curve) reveals that these alloys show only second order ferromagnetic (FM) to paramagnetic (PM) transition at their Curie temperature (TC) and no structural transformation is observed. A large value of saturation magnetization (MS) ∼ 72.76 Am2/kg is observed at 80 K for x = 8.5 alloy as the alloy becomes purely austenite for this composition. A reversible magnetic entropy change of 1.02 JKg−1K−1 with moderate refrigerant capacity (RC) ∼ 40.2 J/kg are obtained near room temperature (∼305 K) for x = 8.5, across its TC due to a field change of 14 kOe only. The critical exponents are calculated for both the samples and found to exhibit long range ferromagnetic ordering in their austenite phase.

A large reversible room temperature magneto-caloric effect in Ni-TM-Co-Mn-Sn (TM = Ti, V, Cr) meta-magnetic Heusler alloys

Herein, we achieved a large reversible room temperature magneto-caloric effect (MCE) through synergic tuning of martensitic transformation (MT) temperatures and transition entropy change (ΔStr) via micro-alloying with transition metals (Ti, V, and Cr) in Ni45Co5Mn40Sn10 meta-magnetic Heusler alloys (MHAs). By the minor addition of TM, MT temperatures were brought down to below room temperature and ΔStr was reduced while maintaining narrow MT temperature range (ΔT) and large difference in magnetization (ΔM) of Ni45Co5Mn40Sn10 MHA. In particular, Ni43.8Cr1.2Co5Mn40Sn10 MHA exhibited a very large reversible room temperature magnetic entropy change (ΔSM) of 24.5 J/kg·K with a broad operating temperature window of ∼11 K at 5 T. Indeed, the MHA exhibited a very effective refrigeration capacity (RCeff) of 276 J/kg for 5 T, which is the largest value among the reported Ni-Mn-based MHAs. The decrease of ΔStr reduces the magnetic field required for completely reversible MT and accelerates the saturation of ΔSM, which leads to maximum RCeff value in the composition of MHA. Thus, we can conclude that smaller ΔStr with narrow ΔT and large ΔM is a key variable to develop MHA with reversible MCE under low magnetic field, which will ultimately give us a guideline for the tailor-made design of high-performance magneto-caloric materials.

Giant reversible magnetocaloric effect in a multiferroic GdFeO3 single crystal

The magnetocaloric properties of single crystalline ${\mathrm{GdFeO}}_{3}$ have been investigated in the temperature range 2--36 K by magnetization and heat-capacity measurements. Remarkably large and reversible magnetic entropy change, $\mathrm{\ensuremath{\Delta}}{S}_{\mathrm{m}}=\ensuremath{-}52.5$ J/kg K, has been observed for a field change of 0--9 T. The adiabatic temperature change, $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}$, is also found to be very large, 22 K, slightly above the antiferromagnetic ordering temperature (${T}_{N}^{\text{Gd}}=2.5$ K) of the ${\mathrm{Gd}}^{3+}$ moment, for a field change of 0--8 T. These magnetocaloric parameters remain large down to the lowest temperature measured and are significantly larger than that reported for the other members of rare-earth ($R$) orthoferrites ($R{\mathrm{FeO}}_{3}$) and several potential magnetic refrigerants in the same temperature range. Both $\mathrm{\ensuremath{\Delta}}{S}_{\mathrm{m}}$ and $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}$ are also quite large for a small field change. The large values of magnetocaloric parameters suggest that ${\mathrm{GdFeO}}_{3}$ could be considered as a potential refrigerant in low-temperature magnetic refrigeration technology, such as liquefaction of hydrogen in the fuel industry. Moreover, ${\mathrm{GdFeO}}_{3}$ has very low electrical conductivity and exhibits no thermal and field hysteresis in magnetization, fulfilling the necessary conditions for a good magnetic refrigerant.

Giant and reversible room-temperature magnetocaloric effect in Ti-doped Ni-Co-Mn-Sn magnetic shape memory alloys

The practical applications of magnetocaloric materials for magnetic refrigeration require not only large magnitude but also reversibility, as well as room-temperature operating temperature, of the magnetocaloric effect. However, it is a complex problem to simultaneously meet these demands in the Heusler-type Ni-(Co)-Mn-X (X = In, Sn, Sb, Ga) magnetic shape memory alloys which are a promising candidate for magnetocaloric materials, owing to the interdependence of magnetostructural transformation parameters. Here, through synergic tuning of magnetostructural transformation parameters via alloying with Ti in Ni42-xTixCo9Mn39Sn10 alloys, we achieved a large reversible room-temperature magnetocaloric effect. By alloying with a proper amount of Ti, the martensitic transformation temperature was brought down to room temperature and the sensitivity of transformation temperature to magnetic field change was greatly enhanced with the transformation entropy change still remaining a large value, while the thermal hysteresis and the transformation interval only slightly increased. Thus, the field required to induce the complete and reversible transformation was significantly reduced. As a result, a large reversible room-temperature magnetic entropy change ΔSm of 18.7 J kg−1 K−1 under 5 T was achieved in the Ni41Ti1Co9Mn39Sn10 alloy. This is the first report on reversible ΔSm in Ni-Mn-Sn-based Heusler alloys and the ΔSm we achieved represents the highest reversible ΔSm under 5 T reported heretofore in Ni-Mn-based Heusler alloys. Furthermore, the Ni41Ti1Co9Mn39Sn10 alloy shows good compressive properties and stable martensitic transformation during thermal cycling, beneficial for potential magnetocaloric applications. This study is instructive for the development of high-performance magnetocaloric materials for room-temperature magnetic refrigeration.

Reversible magnetocaloric effects and critical behaviors in Ce1-xPrxFe2

A systematic investigation of the magnetocaloric effects and critical behavior in Ce1-xPrxFe2 (x=0.02 and 0.06) has been performed. The partial replacement of Ce for Pr leads to a rapid increase in TC from 242K (x=0.02) to 256K (x=0.06). Along with this transition, reversible large magnetic entropy changes of 3.45 and 2.74Jkg−1K−1 under a magnetic field of 5T were found, respectively. The critical exponents (β, γ) has been obtained by modified Arrott plot. With these critical exponents, we find that the experimental M-T-H behavior below and above TC obeys scaling law. The critical analysis reveals that the gradual replacement of Ce for Pr tends to drive the system from the long-range-like (x=0.02) to the short-range-like (x=0.06) ferromagnetic order below TC.

Magnetocaloric properties of Eu1−xLaxTiO3 (0.01 ≤ x ≤ 0.2) for cryogenic magnetic cooling

We report magnetic and magnetocaloric (MCE) properties of polycrystalline Eu1−xLaxTiO3 samples over a wide composition range (0.01 ≤ x ≤ 0.20). It is found that the ground state changes from antiferromagnetic for x = 0.01 (TN = 5.2 K) to ferromagnetic for x ≥ 0.03 and the ferromagnetic Curie temperature increases from TC = 5.7 K for x = 0.03 to TC = 7.9 K for x = 0.20. The x = 0.01 sample shows a large reversible isothermal magnetic entropy change of −ΔSm = 23 (41.5) J/kg K and adiabatic temperature change of ΔTad = 9 (17.2) K around 6.7 K for a field change of μ0ΔH = 2 (5) Tesla. Although the peak value of −ΔSm decreases as La content increases, it is impressive in x = 0.2(−ΔSm = 31.41 J/kg K at T = 7.5 K for μ0ΔH = 5 T). The large value of MCE arises from suppression of the spin entropy associated with the localized moment (J = 7/2) of Eu2+:4f7 ions. This large MCE over a wide compositional range suggests that the Eu1−xLaxTiO3 series could be useful for magnetic cooling below 40 K.