Effective Refrigeration Capacity Research Articles

Microstructure and magnetocaloric effects of Mn1.2Fe0.8P0.6Si0.4B0.05 alloys prepared by ball milling and spinning methods

Abstract The Mn1.2Fe0.8P0.6Si0.4B0.05 alloys were prepared by ball milling and melt-spinning methods. The structure and magnetic characteristics of all samples were examined by X-ray diffraction, vibrating sample magnetometer and SEM. Results show that both the ribbon and bulk alloys can crystallize in a hexagonal Fe2P-type phase with some impurity phase. The lattice parameters, a and c, of Fe2P-type phase are 6.02960 A, 6.03033 A, and 3.42310 A, 3.44431 A for ribbon and bulk Mn1.2Fe0.8P0.6Si0.4B0.05 alloys, respectively. The Curie temperature increased by 20% from 165 K in bulk to 197 K in ribbon while thermal hysteresis and magnetic hysteresis decreased by 28% and 80% for ribbon sample, respectively. Moreover, the values of magnetic entropy change can be tuned from 15.7 J⋅kg−1⋅K−1 in bulk to 21.8 J⋅kg−1⋅K−1 in ribbon under 0–5 T, resulting in the effective refrigerant capacity (RCE) increasing from 238 to 286 J⋅kg−1. The nature of the phase transitions was studied through the Arrott plots, indicating that the samples undergo first-order ferro-paramagnetic phase transitions. The origin of magnetic hysteresis losses is also discussed deeply. Furthermore, this alloys with large magnetic entropy change could be an interest potential for future magnetic refrigeration applications.

Large room temperature adiabatic temperature variation in a Ni40Co8Mn42Sn10 polycrystalline alloy

For the potential applications in magnetic refrigeration, low-cost and high-performance refrigerants with large magnetocaloric effect at relatively lower field change are highly desired. In this work, we report a large adiabatic temperature variation for a low-field change of 1.5 T near room temperature in a Ni40Co8Mn42Sn10 bulk alloy. With the large magnetization difference between weak magnetic martensite and ferromagnetic austenite, this alloy exhibits significant inverse magnetocaloric effect. Under the field change of 5 T, large magnetic entropy change ΔSM of 21.6 J kg−1K−1 and effective refrigeration capacity RCeff of 293 J kg−1 were achieved. Moreover, a large ΔTad up to −4.4 K was obtained under the low-field change of 1.5 T, which is much higher than previously reported ΔTad values in Ni-Mn-Sn based alloys.

Enhanced magnetocaloric effect in Ni-Mn-Sn-Co alloys with two successive magnetostructural transformations

High magnetocaloric refrigeration performance requires large magnetic entropy change ΔSM and broad working temperature span ΔTFWHM. A fourth element doping of Co in ternary Ni-Mn-Sn alloy may significantly enhance the saturation magnetization of the alloy and thus enhance the ΔSM. Here, the effects of Co-doping on the martensite transformation, magnetic properties and magnetocaloric effects (MCE) of quaternary Ni47−xMn43Sn10Cox (x = 0, 6, 11) alloys were investigated. The martensite transformation temperatures decrease while austenite Curie point increases with Co content increasing to x = 6 and 11, thus broadening the temperature window for a high magnetization austenite (13.5, 91.7 and 109.1 A·m2/kg for x = 0, 6 and 11, respectively). Two successive magnetostructural transformations (A → 10 M and A → 10 M + 6 M) occur in the alloy x = 6, which are responsible for the giant magnetic entropy change ΔSM = 29.5 J/kg·K, wide working temperature span ΔTFWHM = 14 K and large effective refrigeration capacity RCeff = 232 J/kg under a magnetic field of 5.0 T. These results suggest that Ni40.6Mn43.3Sn10.0Co6.1 alloy may act as a potential solid-state magnetic refrigerant working at room temperature.

The phase transitions, magnetocaloric effect, and exchange bias in Mn49Ni42-xCoxSn9 alloys

The structure, phase transitions, magnetocaloric effect, and exchange bias effect in Mn49Ni42-xCoxSn9 (x = 0, 1, 3 and 5) ferromagnetic shape memory alloys have been systematically investigated. X-ray diffraction results measured at room temperature reveal that Mn49Ni42-xCoxSn9 alloys with x = 0, 1 present martensite structure, and Mn49Ni42-xCoxSn9 alloys with x = 3, 5 exhibit mixture phases of both martensite and austenite. The martensitic transformation and exchange bias field (HEB) are very sensitive to the Co content. In addition, large positive magnetic entropy changes were observed in these alloys due to the magnetic-field-induced transition from the paramagnetic martensitic phase to the ferromagnetic austenitic phase, and a large effective refrigeration capacity of 230.8 J/kg was obtained under the magnetic field change of 70 kOe in Mn49Ni37Co5Sn9 alloy. We realized a continuous tuning of the HEB from 534.7 Oe to 1113.0 Oe after field cooling in presence of 10 kOe.

Phase separation and its effect on the magnetic entropy change profile in an amorphous Gd48Co50Nb2 alloy

In the present work, we studied the microstructure, thermal and magnetic properties of a Gd48Co50Nb2 amorphous ribbon for the purpose of revealing the mechanism of the table-like magnetic entropy change (−ΔSm) profile of the ribbon. It was found that the amorphous ribbon was fully amorphous with only short-range orders. The two-step magnetic phase transitions indicate that there are two amorphous phases in the Gd48Co50Nb2 amorphous ribbon. The table-like −ΔSm profile of the Gd48Co50Nb2 amorphous ribbon is supposed to be due to the superposition of two −ΔSm peaks corresponding to two separated amorphous phases with different magnetic properties. The amorphous ribbon is expected to be a good candidate for magnetic refrigerant because of its high maximum −ΔSm and high effective refrigeration capacity of the specific table-like −ΔSm profile.

Table-like magnetocaloric effect and large refrigerant capacity of composite magnetic refrigerants based on LaFe11.6Si1.4Hy alloys

Composite magnetic refrigerants were prepared by physical mixing LaFe11.6Si1.4Hy alloys with different Curie temperatures (TC). The phase structures of these LaFe11.6Si1.4Hy alloys were analyzed by X-ray diffraction (XRD) and the magnetocaloric effect (MCE) and refrigerant capacity (RC) of these composite magnetic refrigerants were investigated by experiment and calculation in this paper. The magnetocaloric effect (MCE) and refrigerant capacity (RC) of these composite magnetic refrigerants were investigated by experiment and calculation in this paper. The results indicate the experimental magnetic entropy change (−ΔSM)–T curve corresponds reasonably with the (−ΔSM)–T curve calculated by the linear combination of (−ΔSM)–T curves of the single material. An optimal mixing ratio can make the composite magnetic refrigerant possess a table-like (−ΔSM)–T curve which is beneficial to magnetic Ericsson cycle. When three LaFe11.6Si1.4Hy alloys with different TC are mixed, the full width at half maximum (ΔTFWHM) of (−ΔSM)–T curves is about 48.7 K and the RC is about 177.76 J/kg under a magnetic field change of 2 T. The composite magnetic refrigerants based on LaFe11.6Si1.4Hy alloys can be promising candidates for near room temperature magnetic refrigeration and the work will be helpful to develop novel composite magnetic refrigerants with table-like MCE and large RC.

Tuning the magnetostructural transformation by wheel speed in Mn-Fe-Ni-Ge-Si alloy ribbons

The Mn-Fe-Ni-Ge-Si alloy ribbons are prepared by the melt spinning technique with different wheel speeds and the microstructure, magnetic and magnetocaloric properties are systematically investigated. All the samples reveal the coincident magnetostructural transformation from the ferromagnetic TiNiSi-type martensite to paramagnetic Ni2In-type austenite on heating. The magnetostructural transformation temperature decreases remarkably from 380 K to 320 K with the increase in wheel speed from 10 m/s to 30 m/s. Giant magnetocaloric effect with excellent magnetic reversibility is obtained and the effective refrigeration capacity shows an evident increase, namely 103.9, 125.3, and 185.9 J/kg for three ribbons (under a field change of 0–5 T), though the maximal magnetic entropy change peak value of 27.4 J/kg K is achieved for the sample at 20 m/s. All these features suggest that the wheel speed is an effective way to manipulate the magnetostructural transformation temperature and magnetocaloric properties for MnNiGe-based alloys. The underlying mechanisms are discussed.

Hydrostatic pressure modulated spin-reorientation transition and magnetocaloric effect in PrGa compound

The effect of hydrostatic pressure on the spin-reorientation transition and magnetocaloric effect in PrGa compound has been experimentally investigated. Because of the significant change of lattice parameter along with the spin reorientation, hydrostatic pressure can largely shift the spin reorientation temperature TSR from 28 K down to 16 K under 1.14 GPa, while magnetic transition at TC∼37 K hardly changes. Although the maximum entropy change ΔSM for a magnetic field change of 0–5T decreases from 9.2 J/kg K to 5.8 J/kg K as a pressure of 1.14 GPa was applied, an asymmetric broadening of ΔSM with magnetic field occurs due to the widening of metamagnetic transition window caused by pressure. As a result, a plateau develops on the ΔSM-T curve, and 10% improvement of effective refrigerant capacity RCeff has been achieved. The origin can be ascribed to the significant impact of the pressure on the lattice and crystal field interaction, which not only strengthens the first-order nature of the spin reorientation transition but also enlarges the distance between TSR and TC and broadens the temperature window of metamagnetic transition involving the specific spin alignment. The tunable TSR and enhanced RCeff by pressure in PrGa demonstrate that the compound can be useful in developing multi-field driven refrigeration technique.

Phase formation kinetics, hardness and magnetocaloric effect of sub-rapidly solidified LaFe11.6Si1.4 plates during isothermal annealing

High-temperature phase transition behavior and intrinsic brittleness of NaZn13-type τ1 phase in La–Fe–Si magnetocaloric materials are two key problems from the viewpoint of materials production and practical applications. In the present work, the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation was introduced to quantitatively characterize the formation kinetics of τ1 phase in sub-rapidly solidified LaFe11.6Si1.4 plates during the isothermal annealing process. Avrami index was estimated to be 0.43 (∼0.5), which suggests that the formation of τ1 phase is in a diffusion-controlled one-dimensional growth mode. Meanwhile, it is found that the Vickers hardness as a function of annealing time for sub-rapidly solidified plates also agrees well with the JMAK equation. The Vickers hardness of τ1 phase was estimated to be about 754. Under a magnetic field change of 30 kOe, the maximum magnetic entropy change was about 22.31 J/(kg·K) for plates annealed at 1323 K for 48 h, and the effective magnetic refrigeration capacity reached 191 J/kg.

Excellent mechanical properties and age stability of hydrogenated La0.8Ce0.2Fe12.5Mn0.2Si1.3Hδ plates with extra Fe

Herein, hydrogenated La0.8Ce0.2Fe12.5Mn0.2Si1.3Hδ plates as thin as 0.4–0.6 mm with extra Fe were prepared, whereupon the microstructure, mechanical properties, age stability, and magnetocaloric effect (MCE) were systematically investigated. It was demonstrated that the introduction of extra α-Fe largely enhanced the mechanical properties. The bending strength was about 61 MPa for a single 0.6 mm-thick plate, while the compressive strength was as much as 352 MPa for the stacked plates. Meanwhile, the hydride plates showed considerable MCE around room temperature. The maximal entropy change was 14.2 J/kgK around its Curie temperature TC = ∼298 K and the effective refrigeration capacity was 284 J/kg under a magnetic field change of 0–5 T. Moreover, the hydride plates exhibited excellent age stability and good thermal conductivity. No age splitting occurred, even when the plates were held at room temperature for more than one year, owing to full hydrogenation. Finally, room-temperature thermal conductivity was as large as 9.5 Wm−1K−1. All of these results demonstrate that the hydride plates with extra Fe are desirable magnetic refrigerants, which is beneficial to increase the working efficiency in a device.

Phase Transition Behavior and Magnetocaloric Effect in a Heusler Ni<sub>50</sub>Mn<sub>37</sub>Sn<sub>13</sub> Unidirectional Crystal

A unidireon heating, followed with a ferromagnetic- paramagnetic transition in austenite for the produced unidirectional crystal. Under a magnetic field change of 3 T, the total effective refrigeration capacity was strikingly enhanced up to 125 J/kg, nearly 64% higher than that of polycrystalline master alloy ctional crystal of Heusler Ni50Mn37Sn13 material was produced using a modified high-pressure optical zone-melting furnace. A structural transformation between weak-magnetization martensite and ferromagnetic austenite occurred first up(76 J/kg). The modified high-pressure optical zone-melting technique demonstrated high potentials for the fabrication of super-performance Heusler Ni-Mn-based magnetocaloric materials.

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.

Magnetic and magnetocaloric effects of Eu<sub>0.9</sub><i>M</i><sub>0.1</sub>TiO<sub>3</sub> (<i>M</i>=Ca, Sr, Ba, La, Ce, Sm) compounds

EuTiO<sub>3</sub> is a direct band-gap semiconductor material and exhibits antiferromagnetism with large magnetic entropy change around the liquid helium temperature. The ferromagnetic state can be changed into antiferromagnetic state through lattice constant change and electron doping by element substitution due to strong spin-lattice coupling coexistence of ferromagnetic coupling, and antiferromagnetic coupling. The values of magnetic entropy change can be effectively improved under low magnetic field change after changing into ferromagnetism. Samples of EuTiO<sub>3</sub> and Eu<sub>0.9</sub><i>M</i><sub>0.1</sub>TiO<sub>3</sub> (<i>M</i>=Ca, Sr, Ba, La, Ce, Sm) are prepared by the sol gel method. The Eu<sub>0.9</sub>Ca<sub>0.1</sub>TiO<sub>3</sub> exhibits the antiferromagnetism due to similar ion radius. The ferromagnetic coupling between Eu<sub>0.9</sub>Sr<sub>0.1</sub>TiO<sub>3</sub> and Eu<sub>0.9</sub>Ba<sub>0.1</sub>TiO<sub>3</sub> is enhanced, for alkaline earth metal (Sr and Ba) has larger ion radius, which is beneficial to improving the magnetocaloric effect under low magnetic field. Electron doping can inhibit the antiferromagnetic coupling because the extra carrier may occupy the Ti 3d and reduce the hybridization of Eu 4f-Ti 3d-Eu 4f. When the electron doping concentration is greater than 10%, the spin polarization rate of Ti 3d state on the Fermi surface is negative, resulting in the transition from antiferromagnetic to ferromagnetic state. When the Eu ions are replaced with the Sm ions (Sm ion radius is similar to Eu ion radius), the ferromagnetic coupling is enhanced. However, when the Eu ions are replaced with the La or Ce ions, the samples show strong ferromagnetism, for the lattice constant and electron doping are increased. A giant reversible magnetocaloric effect and large refrigerant capacity for each of Eu<sub>0.9</sub><i>M</i><sub>0.1</sub>TiO<sub>3</sub> (<i>M</i>=Sr, Ba, La, Ce) compounds are observed. Under the magnetic field change of 1 T, the values of maximum magnetic entropy change and refrigeration capacity are 9.8 J/(kg·K) and 36.6 J/kg for Eu<sub>0.9</sub>Sr<sub>0.1</sub>TiO<sub>3</sub>, and 10 J/(kg·K) and 45.1 J/kg for Eu<sub>0.9</sub>Ba<sub>0.1</sub>TiO<sub>3</sub>. The values of maximum magnetic entropy change of Eu<sub>0.9</sub>La<sub>0.1</sub>TiO<sub>3</sub> and Eu<sub>0.9</sub>Ce<sub>0.1</sub>TiO<sub>3</sub> are 10.8 J/(kg·K) and 11 J/(kg·K), respectively, which are larger than that of EuTiO<sub>3</sub> (9.8 J/(kg·K)). The values of refrigeration capacity are 39.3 J/kg and 51.8 J/kg, which are also improved compared with those of EuTiO<sub>3</sub>. In a word, the results suggest that these compounds could be considered as good candidates for low-temperature and low-field magnetic refrigerant.

Phase transition and magnetocaloric properties of Mn50Ni42-x Co x Sn8 (0 ≤ x ≤ 10) melt-spun ribbons.

The characteristics of magnetostructural coupling play a crucial role in the magnetic field-driven behaviour of magnetofunctional alloys. The availability of magnetostructural coupling over a broad temperature range is of great significance for scientific and technological purposes. This work demonstrates that strong magnetostrucural coupling can be achieved over a wide temperature range (222 to 355 K) in Co-doped high Mn-content Mn50Ni42-x Co x Sn8 (0 ≤ x ≤ 10) melt-spun ribbons. It is shown that, over a wide composition range with Co content from 3 to 9 at.%, the paramagnetic austenite first transforms into ferromagnetic austenite at TC on cooling, then the ferromagnetic austenite further transforms into a weakly magnetic martensite at TM. Such strong magnetostructural coupling enables the ribbons to exhibit field-induced inverse martensitic transformation behaviour and a large magnetocaloric effect. Under a field change of 5 T, a maximum magnetic entropy change ΔSM of 18.6 J kg-1 K-1 and an effective refrigerant capacity RCeff of up to 178 J kg-1 can be achieved, which are comparable with or even superior to those of Ni-rich Ni-Mn-based polycrystalline bulk alloys. The combination of high performance and low cost makes Mn-Ni-Co-Sn ribbons of great interest as potential candidates for magnetic refrigeration.

Table-like magnetocaloric effect and large refrigerant capacity in Gd65Mn25Si10-Gd composite materials for near room temperature refrigeration

Amorphous Gd65Mn25Si10 as well as crystalline Gd have technologically significant Curie temperature and large magnetic entropy change. Two types of composite materials Gd65Mn25Si10-Gd were fabricated: laminating Gd sheets and amorphous Gd65Mn25Si10 ribbons (multilayer composite) and hot pressing a mixture of amorphous Gd65Mn25Si10 thin ribbons, Gd particles and a small amount of Sn powders (bulk composite). A table-like magnetocaloric effect (MCE) in a wide, commercially useful, temperature span of 73 K (220 K-293 K) were observed in these composites. The values of full-width at half maximum of (−ΔSM) − T plots (ΔTFWHM) and enhanced refrigerant capacity (RC) for the multilayer and bulk composites are 212 K, 724 J/kg, and 248 K, 617 J/kg, respectively, for a field of 5 T. Large ΔTFWHM and RC values and the table-like (−ΔSM)max feature suggest that both multilayer and bulk Gd65Mn25Si10-Gd composites can meet the requirements of different magnetic refrigeration based on Ericsson-cycle.

Microstructural Feature and Magnetocaloric Effect of Mn50Ni40.5In9.5 Melt-Spun Ribbons

The microstructure and magnetocaloric properties of the melt-spun and annealed Mn50Ni40.5In9.5 ribbons were studied. It is shown that the post-annealing results in a considerable increase of the grain size for the initial austenite, where the columnar-shaped austenite grains almost run through the whole ribbon. Both the melt-spun and annealed ribbons consist of the mixture of austenite and martensite at room temperature, where a 8-layered modulated (8M) martensite structure was identified through selected area electron diffraction (SAED). Further High-angle Annular Dark-field (HAADF) characterizations reveal that the modulation period of 8M martensite is not homogeneous in one martensite plate. Due to strong magneto-structural coupling, the inverse martensitic transformation from a weak magnetic martensite to a strong magnetic austenite can be induced by the magnetic field, resulting in the inverse magnetocaloric effect around room temperature. For a field change of 5 T, the magnetic entropy change ΔSM of 3.7 J·kg−1·K−1 and 6.1 J·kg−1·K−1, and the effective refrigerant capacity RCeff of 52.91 J·kg−1 and 99.08 J·kg−1 were obtained for melt-spun and annealed ribbons, respectively. The improvement of the magnetocaloric properties after annealing should be attributed to the enhanced atomic ordering and magnetization difference between two phases, as well as the reduced hysteresis loss. In addition, both the melt-spun and annealed ribbons can work at a relatively wide temperature range, i.e., δTFWHM = 34 K for melt-spun ribbons and δTFWHM = 28 K for annealed ribbons.

Optimizing Magnetocaloric Properties of Heusler-Type Magnetic Shape Memory Alloys by Tuning Magnetostructural Transformation Parameters

Heusler-type magnetic shape memory alloys show a magnetostructural transformation from the low-magnetization phase to the high-magnetization phase upon the application of external magnetic fields. As a result, these alloys exhibit fascinating multifunctional properties, such as magnetic shape memory effect, magnetocaloric effect, magnetoresistance, and magnetic superelasticity. All these functional properties are intimately related to the coupling of the structural and magnetic transitions. Therefore, deliberate tuning of the magnetostructural transformation parameters is essential for obtaining optimal multifunctional properties. Here, we show that by tuning the magnetostructural transformation parameters, we are able to achieve a variety of novel magnetocaloric properties with different application potentials: (1) large magnetic entropy change of 31.9 J kg−1 K−1 under a magnetic field of 5 T; (2) giant effective magnetic refrigeration capacity (251 J kg−1) with a broad operating temperature window (33 K) under a magnetic field of 5 T; (3) large reversible field-induced entropy change (about 15 J kg−1 K−1) and large reversible effective magnetic refrigeration capacity (77 J kg−1) under a magnetic field of 5 T. The balanced tuning of magnetostructural transformation parameters of magnetic shape memory alloys may provide an instructive reference to the shape memory and magnetic refrigeration communities.

The Effect of a Multiphase Microstructure on the Inverse Magnetocaloric Effect in Ni–Mn–Cr–Sn Metamagnetic Heusler Alloys

Two Ni–Mn–Sn alloys substituted with 0.5 and 1 at.% Cr have been studied. The first alloy shows an average composition of Ni49.6Mn37.3Cr0.7Sn12.4 (e/a = 8.107), whereas the second has a multiphase microstructure with the matrix phase of an average Ni52.4Mn32.7Cr1Sn14 composition (e/a = 8.146). Both alloys undergo a reversible martensitic phase transformation. The Ni49.6Mn37.3Cr0.7Sn12.4 alloy transforms to the martensite phase at 239 K and, under the magnetic field change of μ0·ΔH = 1.5 T, gives the magnetic entropy change equal to 7.6 J/kg·K. This amounts to a refrigerant capacity in the order of 48.6 J/kg, reducible by 29.8% due to hysteresis loss. On the other hand, the alloy with a multiphase microstructure undergoes the martensitic phase transformation at 223 K with the magnetic entropy change of 1.7 J/kg·K (1 T). Although the latter spreads over a broader temperature window in the multiphase alloy, it gives much smaller refrigerant capacity of 16.2 J/kg when compared to Ni49.6Mn37.3Cr0.7Sn12.4. The average hysteresis loss for a field change of 1.5 T in the multiphase alloy is 2.7 J/kg, reducing the effective refrigerant capacity by 16.7%. These results illustrate that the key to gaining a large effective refrigerant capacity is the synergy between the magnitude of the magnetic entropy change and its broad temperature dependence.

Magnetostructural transformation and magnetocaloric effect in Mn-Ni-Sn melt-spun ribbons

The martensitic transformation and magnetic properties of Mn50Ni50-x Sn x $(7\le x\le 10)$ melt-spun ribbons were investigated. It is shown that the increase of Sn content results in a nearly linear decrease of martensitic transformation temperatures in the ribbons, with an average rate of 70 K per at % of Sn. In Mn50Ni40Sn10 ribbons, the field-induced reverse martensitic transformation from a weak magnetic martensite to a ferromagnetic austenite was realized due to the strong magnetostructural coupling. Under a field change of 5T, the large magnetic entropy change of 13.7 J kg-1K-1 and the effective refrigerant capacity of 72.9 Jkg-1 were obtained in Mn50Ni40Sn10 ribbons.

Achieving a table-like magnetocaloric effect and large refrigerant capacity in in situ multiphase Gd65Mn25Si10 alloys obtained by crystallization treatment

In situ multiphase structure Gd65Mn25Si10 alloys were fabricated by melt spinning and subsequent crystallization treatment. In the process of crystallization, the α-Gd, GdMn2 and Gd5Si3 phases precipitate in the amorphous matrix in turn. The Curie temperature (TC) values for the α-Gd crystallization phase and amorphous matrix can be tailored by tuning the crystallization treatment time. All three multiphase alloys obtained by crystallization treatment at 637 K for 20, 30 and 40 min, respectively, undergo multiple successive magnetic phase transitions. A table-like magnetic entropy change over a wide temperature range (~90–120 K) and a large full width at half maximum (ΔTFWHM) magnetic entropy change (~230 K) were achieved in the above-mentioned crystallized alloys, resulting in large refrigerant capacities (RCs). The enhanced RCs of the three crystallized alloys for a magnetic field change of 0–5 T are in the range of 541–614 J kg−1. Large ΔTFWHM and RC values and a table-like (−ΔSM)max feature obtained in in situ multiphase Gd65Mn25Si10 crystallized alloys make them suitable for potential application in efficient Ericsson-cycle magnetic refrigeration working in a temperature range from 74 to 310 K.