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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]

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]

We report enhancements of both Curie temperature and magnetic refrigerant capacity in Gd 50 (Co 69.25 Fe 4.25 Si 13 B 13.5 ) 50 microwires, which were fabricated by the melt-extraction method. For a field change of 5 T, the maximum magnetic entropy change (−Δ S M max ), the refrigerant capacity (RC) and relative cooling power (RCP) reached high values of 6.56 J kg −1 K −1 , 625 J kg −1 and 826 J kg −1 , respectively. While the RC is similar to those of our previously reported GdAlCo microwires, a much broader working temperature range of ∼126 K and a higher Curie temperature of 170 K make the Gd 50 (Co 69.25 Fe 4.25 Si 13 B 13.5 ) 50 microwires more attractive for active magnetic refrigeration. [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]

• 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]

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]

The microstructure and magnetic properties including magnetocaloric performance of as-prepared and heat-treated La(Fe,Ni) 11.5 Si 1.5 alloys were systematically investigated. The experimental results indicate that the as-prepared La(Fe,Ni) 11.5 Si 1.5 alloys are composed of α-Fe phase and LaFeSi phase, and the saturation magnetization M s can achieve 159.1 emu/g, as for the larger content of ferromagnetic α-Fe phase. The peritectic reaction occurs during vacuum annealing process, and the decrease of α-Fe phase content reduced the hysteresis loss, meanwhile the NaZn 13 -type structure (1:13 phase) generated. In particular, the magnetocaloric properties of La(Fe,Ni) 11.5 Si 1.5 alloys annealed at 1373 K are superior to that of annealed at 1323 K. And the magnetic entropy change (-Δ S m) of the alloys annealed at 1373 K is up to 20.87 J kg−1 K−1, while Refrigeration Capacity (RC) reaches 415.59 J kg−1 at a magnetic field of 5 T. From the perspective of solid-phase reaction dynamics, the increase of annealing temperature could beneficially accelerate the peritectic reaction process, and result in the increasing content of 1:13 phase, thereby enhancing their magnetocaloric characteristics. Therefore, the microstructure and magnetocaloric properties of La(Fe,Ni) 11.5 Si 1.5 alloys could be effectively modulated by optimizing the annealing process, and it also provides a significant technical reference for the practical application of room-temperature Magnetic Refrigeration (MR) technology. Magnetocaloric properties of La(Fe,Ni) 11.5 Si 1.5 alloys based on NaZn 13 -type structure are distinctly enhanced by modulation of vacuum annealing treatment and Ni-doping. Image 1 • Effects of impurity phases on the magnetic properties were studied in detail. • The saturation magnetization and hysteresis loss of as-prepared alloy are larger than them of heat-treated alloy. • The formation of La(Fe,Ni,Si) 13 (1:13) phase in the alloy is promoted by annealed at higher temperature. • Magnetocaloric properties of La(Fe,Ni) 11.5 Si 1.5 alloy can be effectively improved by rising annealing temperature. [ABSTRACT FROM AUTHOR]

Gd-based metallic microfibers have been the research highlights due to the significant magnetocaloric effect. Herein, the atomic cluster micro-regions are constructed in Gd-based microfibers to further improve the magnetocaloric effect. The results show that the continuous and amorphous microfibers with excellent softly magnetic and thermal stability properties are obtained. The maximum magnetic entropy change -Δ S m max of Gd-based microfibers increases first and then decreases with Ni alloying degree increase. Among which, the better magnetocaloric properties is obtained in (Gd 60 A 20 lCo 20) 95 Ni 5 microfibers. The maximum magnetic entropy change, refrigeration capacity (RC), and relative cooling power (RCP) at 5 T reach 11.57 J/kg K, 834.14 J/kg, and 1138.16 J/kg, respectively. The outstanding magnetocaloric properties of microfibers are attributed to the indirect interaction coupling caused by Ni elements and the atomic cluster micro-regions, which lead to a fundamental shift in magnetic entropy. The findings of this study promote the application of Gd-based microfibers in the field of magnetic refrigeration. • The excellent magnetocaloric properties are obtained in GdAlCoNi5 microfibers after Ni alloyed. • The -Δ S m max, RC and RCP of GdAlCoNi5 microfibers reach 11.57 J/kg·K, 834.14 J/kg and 1138.16 J/kg, respectively. • The atomic cluster micro-regions promote the transformation of magnetic entropy disorder to order after Ni alloyed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nanocrystalline Fe-containing GdTbCoAl high-entropy-metallic-glass were attained. • Curie temperature is tuned by Fe-doping in a wide temperature range of 81–108 K. • Magnetic entropy change 7.6–8.9 J kg−1 K−1 for 5 T were achieved. • The dual-phase structure with T C distribution enhances the cooling efficiency. Through designing the composition and processing approach, the non-equiatomic (Gd 36 Tb 20 Co 20 Al 24) 100-x Fe x (x = 0, 1, 2 and 3 at.%) high-entropy-metallic-glass (HE-MG) alloy microwires were successfully fabricated by melt-extraction technique. The microstructure and magnetocaloric properties of the microwires were systematically investigated. The microwires possess tunable Curie temperatures, i.e. 81–108 K, above the typical rare-earth (RE) containing HE-MG reports. The high Curie temperatures are attributed to the designed composition. Magnetocaloric response peak values of Fe-containing GdTbCoAl alloy microwires range 7.6–8.9 J kg−1 K−1 (5 T), which are comparable to those of many outstanding RE-containing magnetocaloric HE-MGs. The characteristics of the melt-extraction method, combining with compositional effects, favor the formation of amorphous and nanocrystalline phases. The increase in the cooling efficiency for microwires with higher Fe content can be attributed to the broadening of the Curie temperature distribution induced by the composition difference between nanocrystalline phase and amorphous matrix. The designed composition and the melt-extraction processing approach for Fe-containing GdTbCoAl alloys can tune their Curie temperatures towards a temperature range of natural gas liquefaction and improve their magnetocaloric properties. This demonstrates that Fe-containing GdTbCoAl HE-MG composite microwires have great potential as high-performance magnetic refrigerants. [ABSTRACT FROM AUTHOR]

Herein, the influence of annealing current intensities on magnetic properties of Gd-based microfibers was systematically investigated. The experimental results indicated that the as-prepared microfibers have amorphous structure and excellent thermal-stability, and the Curie temperature T C of which slightly change before and after annealing. The general magnetic physical magnitudes (M s , M r , μ 0 H c and μ m) of microfibers increase firstly and then decrease with the rising of annealing current intensities, and those of the microfibers annealed at 90 mA microfibers are more obvious (M s = 255 A m2/kg and μ m = 0.38 ± 0.01). Similarly, the magnetocaloric parameters of microfibers also increase firstly and then decrease with the rising of current intensities. At 5 T of magnetic field change μ 0 Δ H , the maximum magnetic entropy change Δ S m max and refrigerant capacity RC of 90 mA annealed metallic microfibers are 12.77 J/(kg·K) and 906 J/kg, respectively, and which remarkably increased in compared with the as-prepared state, respectively. From the microstructural evolution perspective, a certain intensity current annealing induces the tendency of micro-regional clusters and nanocrystals, forming atomic ordered regions, and the internal residual stress release with a reduction of magnetic anisotropy. Meanwhile, the magnetic ordering and the critical magnetic-moment rotational driving-force were changed after Fe-doping, resulting in effective improvement of refrigerant capacity. Accordingly, the current-annealed Gd-Al-Co-Fe microfibers can be adopted as low-temperature magnetic refrigeration working-medium, which also provides a theoretical foundation for magnetic refrigeration technology application. Magnetocaloric properties of Gd-Al-Co-Fe metallic microfibers current-annealed at 90 mA are significantly improved according to the microstructural evolution and magnetic ordering modulation. Image 1 • Effects of current annealing intensities on the magnetic properties were investigated in detail. • MCE characteristics of Gd-Al-Co-Fe microfibers could be obviously improved at 90 mA. • Magnetocaloric mechanism is illustrated by the perspective of structural evolution and magnetic ordering transformation. [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]

The enhanced magnetocaloric properties are studied in melt-extracted Gd 36 Tb 20 Co 20 Al 24 metallic glass microwires. The Curie temperature is ∼91 K for these microwires which show promising applications at liquid nitrogen range. The microwires possess spin glass phase in low temperature and spin freezing temperature is 60 K. Notably, the maximum magnetic entropy change (–Δ S M max), the relative cooling power (RCP) and the refrigerant capacity (RC) reach high values of 12.36 J kg−1K−1, 948 J kg−1 and 731 J kg−1, respectively, under a field change of 5 T. The large –Δ S M max originates from the high effective magnetic moment. Meanwhile, the spin fluctuation, the exchange integral fluctuation of metallic glass and the second order paramagnetic-ferromagnetic transition enlarge the phase transition range. Image 1 • Gd 36 Tb 20 Co 20 Al 24 metallic glass microwires were prepared by melt-extracted method. • The microwires show the maximum magnetic entropy change of 12.36 J. kg−1K−1. • The microwires exhibit refrigerant capacity of 731 J. kg−1. [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]