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The highly regarded Fe2P-based magnetocaloric materials are usually fabricated by ball milling, and require an additional extended annealing treatment at high temperatures (at temperatures up to 1423 K for several hours to days). In this work, we show that fabricating Mn1.3Fe0.6P0.5Si0.5 into the form of microwires attained 82.1 wt.% of the desired Fe2P phase in the as-cast state. The microwires show a variable solidification structure along the radial direction; close to the copper wheel contact, Fe2P phase is in fine grains, followed by dendritic Fe2P grains and finally secondary (Mn,Fe)5Si3 phase in addition to the dendritic Fe2P grains. The as-cast microwires undergo a ferro- to para-magnetic transition with a Curie temperature of 138 K, showing a maximum isothermal magnetic entropy change of 4.6 J kg−1 K−1 for a magnetic field change of 5 T. With further annealing, a two-fold increase in the maximum isothermal magnetic entropy change is found in the annealed microwires, which reveal 88.1 wt.% of Fe2P phase. [ABSTRACT FROM AUTHOR]

The desirable table-like magnetocaloric effect (MCE) was obtained by designing a new magnetic bed, which comprises three kinds of Gd-based microwire arrays with different Curie temperatures (TC). The TC interval among these wires is ~10 K. This new magnetic bed shows a smooth ferromagnetic to paramagnetic transition at ~100 K. In addition, a table-like magnetic entropy change (ΔSM) was obtained, ranging from ~92 K to ~107 K, with a maximum entropy change (−ΔSMmax) of 9.42 J/kgK for a field change (μ0ΔH) of 5 T. Notably, the calculated results of −ΔSM(T) corresponded to the experimental data for μ0ΔH = 5 T, suggesting that a microwire array-based magnetic bed with desirable magnetocaloric response can be designed. In addition, it was shown that a larger table-like temperature range and cooling efficiency can be achieved by increasing the interval of TC among microwire arrays. These important findings indicate that the newly designed magnetic bed is very promising for active magnetic cooling technology. [ABSTRACT FROM AUTHOR]

Ni45.6Fe3.6Mn38.4Sn12.4 microwires, with nanoscale γ-phase precipitates that enhance the magnetocaloric effects (MCEs) and mechanical properties, were prepared by a melt-extraction technique and subsequent high temperature annealing. The atomic ordering degree significantly increased after annealing, leading to a considerable increment in the structural entropy change (ΔStr) from 4.5 J/kg·K in the as-extracted microwire to 26.6 J/kg·K in the annealed one, and the magnetization difference (ΔM) from 35 A·m2/kg to 51 A·m2/kg under a magnetic field of 5.0 T. Consequently, a positive magnetic entropy change (ΔSM) peak of 15.2 J/kg·K with working temperature span (ΔTFWHM) of 12 K for the first-order martensite transformation followed by a negative ΔSM peak of −4.3 J/kg·K with ΔTFWHM = 50 K for the second-order magnetic transition under μ0ΔH = 5.0 T was achieved. By employing both magnetizing and demagnetizing processes for magnetic cooling, the two successive inverse and conventional MCEs in Ni–Fe–Mn–Sn microwires may show potential applications for micro-devices and systems. [ABSTRACT FROM AUTHOR]

High-quality Gd60Co15Al25 microwires with an average diameter of 40 µm were successfully fabricated by the melt-extraction method. The as-cast microwires undergo a second-order paramagnetic to ferromagnetic (PM-FM) transition at ∼100 K. Large values of the magnetic entropy change (−Δ SM ∼9.73 J kg−1 K−1) and the refrigerant capacity (RC ∼732 J kg−1) are achieved for a field change of 5 T. A careful analysis of critical exponents near the PM-FM transition indicates the significant effects of structural disorder on the long-range ferromagnetic interaction and the magnetocaloric response of the microwires. The excellent magnetocaloric properties make the Gd60Co15Al25 microwires very promising for use in magnetic refrigerators operating in the liquid nitrogen temperature range. [ABSTRACT FROM AUTHOR]

This work systematically investigated the effect of Fe content on the microstructure and magnetic transition behaviors of melt-extracting Mn-Fe-P-Si microwires. It was shown that the Fe content does not change the main phase of the samples, i.e. Fe 2 P compound, which decreased with the increasement of Fe content. The transition temperature (T tran) decreased from 311 to 245.5 K while the thermal hysteresis (T hys) increased from 9.5 to 22.5 K increasing Fe from 0.90 to 1.05. The samples realized the first order magnetic transition at x = 1.00 and 1.05, correspondingly the samples demonstrated large magnetic hysteresis losses (W y ,) and isothermal magnetic entropy change (− ∆ S iso peak ) at 5 T, 59.1 J kg−1 and 14.5 J kg−1 K−1 for the sample x =1.00, 58.4 J kg−1 and 15.8 J kg−1 K−1 for the sample x = 1.05. In contrast, the samples at x = 0.90 and 0.95 indicated second order transition character, and the W y and − ∆ S iso peak were much smaller, i.e. 14.8 J kg−1 and 10.3 J kg−1 K−1, 9.7 J kg−1 and 10.7 J kg−1 K−1 respectively for the samples x = 0.90 and 0.95. The largest effective refrigerant capacity (RCE , 293.7 J kg−1, 5 T) is found at x = 0.90. The reduced hysteresis and maintained competitive isothermal magnetic entropy change make the melt-extracting Mn-Fe-P-Si microwires with optimized Fe content as a promising magnetocaloric material family applied in real magnetic refrigeration applications. [Display omitted] • The MnFe x P 0.5 Si 0.5 microwires were fabricated by melt-extracted method. • The amount of Fe 2 P main phase increased with the Fe content x decreasing. • The phase transition character corresponds to second order with the Fe content < 1. [ABSTRACT FROM AUTHOR]

Abstract The atomic structure evolution of Gd 36 Tb 20 Co 20 Al 24 high entropy metallic glass microwire from room to cryogenic temperature has been studied by in-situ high energy synchrotron X-ray diffraction. During the cooling process, the atomic volume decreases. For short-range order, the coordination numbers of all atomic pairs increase. As the temperature decreases, bond lengths of large atom-small atom and small atom-small atom pairs keep decreasing whereas that of large atom-large atom pairs unexpectedly increases continuously. The mechanism of atomic structure evolution is proposed, which might be helpful for better understanding the low temperature magnetocaloric effect of high entropy metallic glasses. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

A novel type of bi-constituent wire composite was obtained by combining melt-extracted Gd 50 Al 30 Co 20 and Gd 55 Al 20 Co 25 microwire components with Curie temperature ( T C ) of 86 K and 110 K, respectively. For a field change of 5 T, the wire composite possesses a table-like feature spanning a temperature interval of 30 K with value of ∼8.6 J kg −1  K −1 , and enhanced refrigerant capacity (RC) and relative cooling power (RCP) values of ∼680 J kg −1 and ∼863 J kg −1 , respectively. The experimental results agree well with those calculated by a simple bi-composition model, demonstrating the possibility of designing wire-based composites with desirable magnetocaloric effects (MCE) for active magnetic refrigeration. [ABSTRACT FROM AUTHOR]

Very recently, we reported that Fe-doped Ni 50-x Fe x Mn 38.0 Sn 12.0 alloys exhibited enhanced magnetization difference Δ M between the martensite and austenite phases. Of note is that the alloy with x = 4.2 exhibits a strong metamagnetic transition behavior, i.e. magnetic-field-induced reverse martensite transformation, which is favorable for the magnetocaloric effects. Here, the enhanced magnetocaloric effect related to metamagnetic transition in the selected Ni 35.8 Fe 4.2 Mn 38.0 Sn 12.0 alloy was reported. This alloy exhibits a high magnetization difference Δ M of ∼58 A·m 2 /kg between martensite and austenite phases owing to the magnetic and structural coupling. The doping of Fe leads to a strong metamagnetic behavior, with austenite peak temperature shift Δ A p / Δ H reaching −2.4 K/T. As a result, the magnetic entropy change Δ S m increases rapidly from a starting critical magnetic field ∼0.2 T and then saturates at various finishing critical magnetic fields, depending on the working temperature. A sizable peak Δ S m of 33.8 J/kg·K with a working temperature interval of 7 K is obtained under a magnetic field of 5 T, which is responsible for a high relative cooling power RCP of 237 J/kg. These results suggest that Ni 45.8 Fe 4.2 Mn 38.0 Sn 12.0 alloy may act as a potential solid-state magnetic refrigerant. [ABSTRACT FROM AUTHOR]

Giant magnetocaloric effect in Ni-Mn-X (X=In, Sn, Sb) Heusler alloys has been revealed due to the significant shift of the martensite transformation temperatures under a bias magnetic field. However, the magnetic hysteresis during the magnetization and demagnetization cycles creates a large hysteresis loss and reduces the refrigeration capacity. Here we demonstrated that the magnetic hysteresis loss in Ni-Mn-Sb alloys was effectively reduced by Si-doping. The quaternary Ni 49.0 Mn 38.4 Sb 11.7 Si 0.9 alloy exhibited martensite and magnetic transitions around room temperature. Maximum magnetic entropy change Δ S m 9.4 J/kg K and working temperature interval 7.0 K were achieved attributed to the martensite transformation under a magnetic field of 5 T. Meanwhile, the average magnetic hysteresis loss for Ni 49.0 Mn 38.4 Sb 11.7 Si 0.9 alloy was 2.1 J/kg, much smaller than that for Ni 49.0 Mn 38.5 Sb 12.5 alloy, 11.4 J/kg. As a result, a refrigeration capacity of 50.2 J/kg was obtained in the Ni 49.0 Mn 38.4 Sb 11.7 Si 0.9 alloy. This result shows that Si-doped Ni-Mn-Sb alloys may act as a potential material system for magnetic refrigeration. [ABSTRACT FROM AUTHOR]

Small-sized materials with large surface to volume ratio favor heat transfer during magnetic refrigeration cycling and thus may help enhancing the refrigeration efficiency. Here, high Fe content Ni 44.9 Fe 4.3 Mn 38.3 Sn 12.5 polycrystalline microwires were prepared by a melt-extraction technique. The as-extracted microwires were annealed at 1173 K for 60 min, leading to significant grain growth and formation of a secondary Fe-rich γ phase. The annealed microwire exhibits larger magnetization difference ( ΔM ) between the austenite and martensite phases and smaller thermal hysteresis compared to the as-extracted microwire. The annealed microwire possesses a magnetic transition to austenite at 299 K, followed by a martensitic transformation (MT) from a ferromagnetic austenite to a weak-magnetic martensite at 208 K upon cooling. Under a magnetic field of 50 kOe, the annealed microwires show a maximum magnetic entropy change ΔS m of 6.9 J/kg·K and an effective refrigeration capacity RC eff of 78.0 J/kg over a broad working temperature span ΔT FWHM of 20 K around the MT. In addition, magnetic transition of the austenite gives rise to ΔS m − 3.7 J/kg·K and RC mag 232.5 J/kg with ΔT FWHM of 85 K under 50 kOe. [ABSTRACT FROM AUTHOR]

Ni-Mn-Sn alloys exhibit high magnetocaloric effect (MCE) during the magnetic-field-induced martensite to austenite phase transformation. However, the low magnetization of the austenite, narrow working temperature interval and high magnetic hysteresis reduced their magnetic refrigeration capacity. Here, the effects of Fe doping on the structural and magnetic transitions of Ni 50-x Fe x Mn 38 Sn 12 alloys were investigated. The doping of Fe higher than 2.9% induced the occurrence of a secondary γ phase, creating a dual phase alloy. The martensite transformation temperature significantly decreased with the occurrence of the secondary phase. However, the Curie temperatures of both austenite and martensite changed slightly with the formation of the secondary phase. As a result, the magnetostructural coupling, i.e. overlap of the structural and magnetic transitions between the ferromagnetic austenite and the paramagnetic martensite, occurred in the alloys with x = 0.5 - ∼4.2. Furthermore, the magnetization of the austenite and martensite both increased with increasing Fe content from x = 0 to x = 5.5, with the magnetization difference between the austenite and martensite saturating at x = 4.2. The dual phase Ni 45.8 Fe 4.2 Mn 38 Sn 12 alloy, exhibiting a magnetic field dependence of martensite transformation temperature ΔT M / μΔH - 0.28 K/kOe, showed a wider working temperature interval than that of the un-doped Ni 50 Mn 38 Sn 12 alloy. This demonstrated that the Ni 45.8 Fe 4.2 Mn 38 Sn 12 alloy might exhibit a high magnetic entropy change, wide working temperature interval and low magnetic hysteresis, and thus may be a promising magnetic refrigeration material. [ABSTRACT FROM AUTHOR]

Herein, we report high magnetocaloric performance of melt-extracted metallic glass Gd 60 Al 20 Co 20 microwires, which exhibit a large and reversible magnetocaloric effect (MCE). The isothermal magnetic entropy change (−Δ S m ) reaches as high as 10.1 J kg −1 K −1 and the refrigerant capacity (RC) has a large value of 681 J kg −1 for a field change of 5 T. The as-obtained Gd-based metallic glass microwires hold a great promise for multifunctional applications in MCE-based refrigeration of liquid nitrogen temperature range. [ABSTRACT FROM AUTHOR]

We reported the magnetocaloric properties of Heusler-type Ni 48 Mn 26 Ga 19.5 Fe 6.5 microwires with diameter of ∼50 μm which were fabricated by a precise melt-extraction method. The Fe-doped Ni–Mn–Ga microwires after chemical ordering heat-treatment exhibit negligible thermal and magnetic hysteresis along the axial direction due to their small magnetocrystalline anisotropy and display excellent magnetocaloric effect (MCE) for both magnetic (paramagnetic–ferromagnetic) phase transition and structural (austenite–martensite) phase transition. The maximum entropy change (−Δ S m ), ∼4.7 J kg −1 K −1 , is obtained during the structural transition induced by an external magnetic field of 50 kOe at a temperature of ∼361 K. Moreover, tiny positive magnetic entropy also appears when the applied field is lower than 5 kOe. [ABSTRACT FROM AUTHOR]

Highlights: [•] High-quality Gd55Al25Co20 metallic glass magnetocalorific fibers were melt-extracted. [•] They show superior MCE performance versus its counterpart in BMGs. [•] They have tensile strength of 1189MPa and high security threshold of 796MPa. [•] The excellent performances result from size effect and amorphous structure. [Copyright &y& Elsevier]

• The novel medium-entropy alloys were fabricated by melt-extraction and exhibit excellent magnetic entropy change. • The microwires show typical amorphous characteristics and second-order phase transition. • The microstructure of microwires near room temperature is studied by in-situ HEXRD. A melt-extracted HoErCo medium-entropy alloy (MEA) with large magnetic entropy change and excellent magnetic refrigerant capacity is successfully designed in this study. The microstructure evolution of these microwires near room temperature is studied by an in-situ high energy synchrotron X-ray diffraction (HEXRD). The wires show typical amorphous characteristics during room temperature to 250 K. For a field change of 5 T, the maximum magnetic entropy change (-Δ S M max) of the microwires reaches a maximum value of 15.0 J•kg−1 K−1. Magnetization measurements revealed a paramagnetic to ferromagnetic phase transition at T C ~16 K. The refrigerant capacity (RC) and relative cooling power (RCP) are 527 J•kg−1 and 600 J•kg−1, respectively. This investigation highlights the potential of HoErCo MEA microwires as promising magnetocaloric effect materials for cryogenic applications of magnetic cooling. [ABSTRACT FROM AUTHOR]

The effects of trace Fe-doping on the magnetic and magnetocaloric performances of Gd-based metallic microfibers were systematically and detailedly investigated in this article. Experimental results indicated that the Gd-based microfibers prepared by the rotated-dipping process are uniform and continuous, with typically amorphous structure characteristics and favorable thermal stability. Curie temperature T C of Gd-based amorphous microfibers increases with the rising of Fe content, and the T C of GdAlCoFe3 microfibers is the highest at 128.7 K (relatively increased by 15.3 K than before doping). Among the general magnetic performance indicators, the saturation magnetization M s of GdAlCoFe2 microfibers reaches a peak at 264.04 emu/g. Furthermore, the values of magnetocaloric performance indexes of Gd-based amorphous microfibers increase firstly and then decrease with the rising of Fe-doping amount. When the external magnetic field H ex = 50,000 Oe, the maximum magnetic entropy change -Δ S m max, refrigeration capacity RC and relative cooling power RCP of GdAlCoFe1 microfibers are 10.33 J/kg·K, 748.22 J/kg and 1006.90 J/kg, which increased by 0.07 times, 0.13 times and 0.16 times, respectively than before Fe-doping (namely -Δ S m max = 9.68 J/kg·K, RC = 663.79 J/kg, RCP = 871.73 J/kg). From the perspective of microstructural changes, Fe-doping results in the formation tendency of atomic clusters and nanocrystals in micro-regions, the orderly orientation of atoms appears, and the magnetic anisotropy increases accordingly. In addition, the 3d electron layer of the doped Fe element in Gd-Al-Co-Fe quaternary alloy system enhances the RKKY indirectly exchange coupling interaction and changes the state of magnetic entropy, which in turn leads to an increase in Curie temperature and an improvement in magnetocaloric performance. Since RC and RCP are the main indicators in engineering applications, the GdAlCoFe1 amorphous microfibers can be selected as a low-temperature magnetic refrigeration working medium to provide technical guarantee for the application of magnetic refrigeration technology. In comparison to Fe-doped Gd-based amorphous microfibers, # GdAlCoFe1 microfibers have enhanced magnetocaloric properties by coactions of atomic arrangement ordering transformation (AAOT) and magnetic moment ordering transformation (MMOT). Image 1 • Influence of Fe-doping amounts on the magnetocaloric properties was investigated systematically. • MCE properties of # GdAlCoFe1 amorphous fibers were enhanced effectively. • Interaction mechanism was illustrated from the perspective of atomic arrangement and magnetic moment ordering transformation. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEA) represent potentially disruptive materials across multiple industries, especially for refrigeration technologies. Building metal components layer-by-layer increases design freedom and manufacturing flexibility, thereby enabling high magnetic thermal properties of the multicomponent alloy. However, excessive alloying elements could limit the mass production potential, while prolonging the time to market. Here we demonstrate that a high performance magnetocaloric material can be synthesized from only three elements, HoErFe, by taking advantage of the combination of rare earth and transition elements. Novel medium-entropy alloys (MEA) are prepared by melt-extraction and exhibit excellent magnetocaloric properties. The amorphous/nanocrystalline structure of the microwires, which is confirmed by both transmission electron microscopy (TEM) and X-ray diffraction (XRD), gives the primary contribution to the MCE. The microwires undergo a ferromagnetic-paramagnetic (FM-PM) transition near the Curie temperature (T C = ~44 K), and a spin-glass (SG) behavior could be observed below the T C. The maximum magnetic entropy (-ΔS M max) was 9.5 J kg−1 K−1 under a field change of 5 T. Meanwhile, the refrigerant capacity (RC) and the relative cooling power (RCP) of the alloy microwires were 450 J·kg−1and 588 J kg−1, respectively. The high refrigeration efficiency and high magnetocaloric effect that is reversible make these novel metallic microwires attractive working materials for low-temperature magnetic refrigeration applications. • The novel medium-entropy alloys are prepared by melt-extraction and exhibit excellent magnetocaloric properties. • The wire composite shows a spin-glass behavior below Curie temperature. • The amorphous/nanocrystalline structure of the microwires exhibit enhanced magnetocaloric effect. [ABSTRACT FROM AUTHOR]

We report upon the excellent magnetocaloric effect in melt-extracted DyHoCo medium entropy microwires. The magnetic entropy change (-Δ S M) reaches a large value of ∼11.2 J kg−1 K−1 for a field change (μ 0 Δ H) of 5 T. The large value of -Δ S M is resulted from the large magnetic moments of Dy and Ho. In addition, the DyHoCo microwires show a good cooling efficiency; RC1, RC2 and RC3 are evaluated to be ∼530 J kg−1, ∼417 J kg−1 and ∼279 J kg−1, respectively, at μ 0 Δ H = 5 T. The DyHoCo microwires undergo a second-order paramagnetic-ferromagnetic transition at the Curie temperature of ∼35 K. The excellent magnetocaloric property makes the melt-extracted DyHoCo microwires a promising refrigerant for cryogenic cooling application. Image 1 • Dy 33.3 Ho 33.3 Co 33.4 medium entropy microwires were fabricated by melt-extraction. • DyHoCo microwires possess an amorphous structure and SOMT. • DyHoCo microwires show the excellent MCE performance. [ABSTRACT FROM AUTHOR]

• High entropy Gd 19 Tb 19 Er 18 Fe 19 Al 25 microwires were fabricated by melt-extraction. • Gd 19 Tb 19 Er 18 Fe 19 Al 25 microwires show amorphous structure and SOMT. • Gd 19 Tb 19 Er 18 Fe 19 Al 25 microwires show broaden working temperature range. In this paper, the magnetocaloric effect (MCE) of a high-entropy Gd 19 Tb 19 Er 18 Fe 19 Al 25 amorphous microwires fabricated by melt-extracted method are investigated systematically. These microwires exhibit a second-order phase transition from ferromagnetic to paramagnetic states at the Curie temperature of 97 K. The zero-field-cooling (ZFC) and field-cooling (FC) magnetization curves are irreversible when the temperature lower than the Curie temperature due to the spin glassy freezing behavior. The peak magnetic entropy change (Δ S M pk ) for a field change from 0 to 5 T reaches ~5.94 J/kg∙K. In accordance to two criteria refrigerant capacity, the values of refrigerant capacity (RC) and relative cooling power (RCP) reach ~569 J/kg and ~733 J/kg at a field change of 5 T, respectively. These results suggest that the melt-extracted Gd 19 Tb 19 Er 18 Fe 19 Al 25 microwires exhibit good MCE and have great potential to use as one kind of high temperature magnetic refrigeration material. [ABSTRACT FROM AUTHOR]

Ferromagnetic shape memory Ni–Mn-Ga alloys exhibit magnetostructural coupling during the Curie points, which may alter their magnetocaloric effect (MCE). Here MCE of Ni–Mn-Ga alloy microwires are tuned by Fe-doping. The chemical ordering annealed Ni 49·6 Mn 25.5 Ga 22.6 Fe 2.3 (Fe2), Ni 49·6 Mn 25 Ga 21 Fe 4.4 (Fe4) and Ni 48 Mn 26 Ga 19.5 Fe 6.5 (Fe6) microwires have diameters of ~30–50 μm and grain sizes of ~2–5 μm. The magnetic entropy changes (Δ S m) of the microwires increase with external magnetic fields, then reach a positive peak and finally decrease to negative peak at a high field. The direct (negative Δ S m , DMCE) and inverse (positive Δ S m , IMCE) MCEs are attributed to microscopic and mesoscopic couplings in microwires. In addition, the specific features of MCEs are also controlled by the magnetization difference (Δ M) between martensite and austenite phases. Interestingly, the DMCE and IMCE are component dependent. At high Δ M , the linearly decreasing region is dominant and Fe4 and Fe6 microwires produce a negative Δ S m at high magnetic fields due to the microscopic coupling with free electron valence ratio e / a = 7.692 and 7.725. On the other hand, the Δ M is small in Fe2 microwire, which has a positive Δ S m because mesoscopic coupling is dominant with e / a = 7.607; the Δ S m is highest when a single variant martensite occurs, then decreases linearly with increasing magnetic fields. The transition from positive to negative values in Δ S m with the applied fields is related to the counterbalance of mesoscopic and microscopic couplings at e / a = 7.66. The study found that, the specific features of the MCE in the present Ni–Mn-Ga-Fe microwires have been found to be controlled by the magnetization difference between martensite/austenite phases (Δ M = M M - M A). At small Δ M , the ΔS m is first positive, reaches a maximum under a critical magnetic field (e.g. 7.6 kOe for Fe2 where a single variant martensite state occurs), and decreases linearly with H for higher fields. For high values of Δ M , the linearly decreasing region is dominant (e.g. Fe6). Image 1 • Ni–Mn-Ga-Fe microwires with fine grains were fabricated by melt-extraction. • The mixed direct and inverse MCEs caused by the magnetostructural coupling. • The MCE can be adjusted by changing the content of Fe. [ABSTRACT FROM AUTHOR]