Magnetocaloric effect and critical behavior in melt-extracted Gd₆₀Co₁₅Al₂₅microwires

Abstract

High-quality Gd 60 Co 15 Al 25 microwires with an average diameter of 40 mm were successfully fabricated by the meltextraction method. The as-cast microwires undergo a secondorder paramagnetic to ferromagnetic (PM-FM) transition at $100 K. Large values of the magnetic entropy change (ÀDS M $9.73 J kg À1 K À1 ) and the refrigerant capacity (RC $732 J kg 1 Introduction Magnetic refrigeration (MR) based on the magnetocaloric effect (MCE) of magnetic refrigerant materials with a first-order magnetic transition (FOMT) or a second-order magnetic transition (SOMT) has attracted growing interest in the scientific community, due to its advantages (e.g., high-cooling efficiency, environmental friendliness, low noise, and compactness) over conventional gas compression-based cooling techniques [1]. Beside Gd, one of the best refrigerant candidates for sub-room temperature magnetic refrigeration [2], a large number of alloys including GdSiGe [3], LaFeSi [4], and MnFePAs [5] exhibiting giant MCEs have been developed for roomtemperature MR, and some of them have also been exploited in low-temperature MR [6]. It has been reported that the larger magnetic enetropy change (DS M ) is observed in a FOMT material but is concentrated in a narrower temperature range, as compared to a SOMT material that shows the smaller magnetic entropy change over a broader temperature range [7]. As a result, the larger refrigerant capacity (RC), which depends both on the magnitude of DS M and on

Enhanced Curie temperature and cooling efficiency in melt-extracted Gd50(Co69.25Fe4.25Si13B13.5)50 microwires

“…The fitted result is shown in Fig. 5a, which yields n = 0.77, in good agreement with those reported previously for the Gd-Al-Co microwires [16][17][18][19][20][21]. This value of n is also close to that reported previously for typical Fe-based amorphous alloys (n = 0.75) [34], but deviates from the mean-field theoretical value (n = 0.67) [33].…”

“…The amorphous structure of the microwires can also be predicted based on Inoue's three rules of thumb [26]: 1 ) 50 microwires is ~70 K higher than those of our previously reported Gd-Al-Co amorphous microwires (T C ~100 K) [16][17][18][19][20][21]. It has been reported that relative to GdCo binary alloys [28], the Al addition enhanced the MCE but reduced the Curie temperature in GdCoAl ternary alloys [29].…”

“…However, producing amorphous magnetic wires with diameters less than 1 mm using traditional fabrication techniques has remained a challenging task. Appling a precision homemade melt-extraction technique with greater quenching rates, we have been successful in preparing a new class of high quality Gd-based microwires such as GdCoAl that possess enhanced MCE and RC [16][17][18][19][20][21]. In these GdCoAl microwires, Al was used to enhance amorphous structure and hence MCE, but decreased the Curie temperature of the initial alloy.…”

The Magnetocaloric Composite Designed by Multi‐Gd‐Al‐Co Microwires with Close Performances

“…In addition, the refrigeration capacity (RC) of the wire composite was also calculated using Equation : where T 1 and T 2 are the onset and offset temperatures of full width at half‐maximum ( δ FWHM ) of the calculated −Δ S M ‐ T curves. The obtained RC of the composite was ≈665 J kg −1 at µ 0 Δ H = 5 T. The value was higher than that of ≈622 J kg −1 for Gd 50 Al 25 Co 25 wires, similar to that of ≈652 J kg −1 for the Gd 55 Al 25 Co 20 wire and lower than that (≈732 J kg −1 ) for the Gd 60 Al 25 Co 15 wires . The composite sample shows the average performance among its components.…”

“…The results of −Δ S M at different temperatures and applied fields are plotted in the 3D form in Figure a. The maximum magnetic entropy change () of the composite reaches ≈9.98 J kg −1 K −1 for a field change of 5 T, showing a similar performance compared with its components (slightly higher than that of the Gd 55 Al 25 Co 20 wire and the Gd 60 Al 25 Co 15 wire of ≈9.67 and 9.73 J kg −1 K −1 , respectively, but lower than that of the Gd 50 Al 25 Co 25 wire of ≈10.3 J kg −1 K −1 as shown in Figure b and c).…”