† Corresponding author. E-mail:
Project supported by the National Natural Science Foundation of China (Grant Nos. 51671119 and 51871139), the Chongqing Research Program of Basic Research and Frontier Technology, China (Grant No. cstc2018jcyjAX0329 and cstc2018jcyjAX0444), and the Key Project of Science and Technology Research Program of Chongqing Education Commission of China (Grant No. KJZD-K201900501).
A small amount of Ni was added into the binary Gd50Co50 amorphous alloy to replace Gd in order to obtain ternary Co50Gd50 − xNix (x = 1, 2, and 3) amorphous alloys. Compared to the binary Gd50Co50 amorphous alloy, the Co50Gd50 − xNix amorphous alloys show an enhanced Curie temperature (TC) with a weakened formability. The maximum magnetic entropy change (
Energy efficiency and environmentally friendliness have become the most urgent requirement of refrigeration technology due to the increasing energy shortage and environmental deterioration. Therefore, efforts have been made to develop new climate-friendly refrigeration solutions with high efficiency. The magnetic refrigeration (MR) technology, by using the endothermic and exothermic characteristic of a refrigerating medium upon the variation of the magnetic field, has displayed promising potential due to its compactness, high efficiency, energy saving, and environmental harmlessness.[1–5]
As the working materials play a critical role in the efficiency of the magnetic refrigerator, numerous magnetic alloys that exhibit fine magneto-caloric effect (MCE) have been studied intensively in recent years.[5–25] Amongst these MCE materials, the amorphous alloys display better mechanical properties and corrosion resistance, in addition to their excellent magnetic proprieties. For instance, the Gd-based amorphous alloys show considerable prospects as magnetic refrigerants based on their soft magnetic performance with negligible magnetic hysteresis at different temperatures, the ultrahigh refrigeration capacity (RC) corresponding to their broadened magnetic entropy change (−ΔSm) peak, and especially their tunable Curie temperature (TC) over a wide range of composition.
However, as the situation in the Gd–Co binary metallic glasses,[23–25] the glass formability (GFA) and MCE of the Gd-based amorphous alloys become worse with the increasing TC.[8–22] Therefore, although the multicomponent Gd-based bulk metallic glasses show high glass formability and outstanding MCE at low temperature, the Gd-based amorphous alloys can only be fabricated into thin ribbons when improving the TC to near the room temperature and their maximum magnetic entropy change (
Samples with nominal compositions of Co50Gd50 − xNix (x = 1, 2, 3, 4, and 5) were firstly prepared into ingots by arc-melting of pure Gd, Co, and Ni metals (purity ≥ 99.9 at.%) for several times under a Ti-gettered Ar atmosphere, and then quenched into ribbons with a thickness of 30–40 μm by a single roller melt-spinning method. The structural characteristics of the as-spun ribbons were tested by the Rigaku x-ray diffraction (XRD, model D\max-2550) using Cu Kα radiation. The thermal properties of the amorphous ribbons were obtained from the differential scanning calorimetry (DSC) curves measured by a Perkin-Elmer calorimeter (DIAMOND) at a heating rate of 20 K/min. The temperature dependence of magnetization (M–T) curves and the isothermal magnetization (M–H) curves were measured in a Quantum Design physical properties measurement system (PPMS, model 6000), and the magnetic proprieties of Curie temperature (TC) and magnetic entropy change (−ΔSm) were calculated from the M–T and M–H curves accordingly.
Figure
DSC measurements under a heating rate of 20 K/min were performed to obtain the thermodynamic parameters of the Co50Gd50 − xNix (x = 1, 2, and 3) amorphous ribbons. As shown in Fig.
![]() | Fig. 2. DSC traces of the Co50Gd50 − xNix (x = 1, 2, and 3) amorphous ribbons obtained at a heating rate of 20 K/min. |
![]() | Table 1. Thermal, magnetic, and magnetocaloric properties of the Co50Gd50 − xNix (x = 1, 2, and 3) and Gd50Co50 amorphous alloys. . |
Figure
The M–T curves of the Co50Gd50 − xNix (x = 1, 2, and 3) metallic glasses were measured to reveal the magnetic transition temperature of the alloys. The Curie temperature TC, as shown in Fig.
In order to investigate the mechanism for the improvement of the magnetic transition temperature of the Co50Gd50 − xNix (x = 1, 2, and 3) amorphous alloys, we constructed the compositional dependence of TC for the Co50Gd50 − xNix amorphous alloys, as shown in Fig.
It is common that in the Gd–(TM)-based amorphous alloys, there exist at least three kinds of interactions between the matrix elements: the direct 3d–3d electronic interaction between the transition elements that contain the unfilled 3d shell and the indirect coupling of 4f–4f electronic interaction form the RE elements. Besides the respective interactions of the compositional elements themselves, there also exists the 3d–4f interaction between the different atoms. Referring to the previous research on the Gd–TM amorphous alloys,[14,25] the 3d–4f indirect interaction is considered to be negligible compared with other interactions in determining the Curie temperature of the samples. Therefore, for Gd50Co50 − yNiy (x = 2 and 5) amorphous alloys with a constant proportion of RE elements, the changed TC of the alloys should have little relation with the RE interactions and could be mainly ascribed to the 3d–3d direct interaction between the transition metals.[20] On the other hand, the decreasing TC with Ni content in the Gd50Co50 − yNiy (y = 2 and 5) amorphous alloys is understandable because the magnetic moment of Ni is smaller than that of Co, which means the reduced 3d–3d interactions between the transition metals. The effect of Ni substitution on the TC of the Co50Gd50 − xNix metallic glasses, however, is more complicated. The nominal magnetic moment (μnom.) of the Co50Gd50 − xNix amorphous alloys decreases from 6.352μB for x = 1, to 6.302μB for x = 2 and to 6.256μB for x = 3 because the magnetic moment of Ni is much smaller than that of Gd. However, the effective magnetic moment (μeff) calculated according to the Curie–Weiss law, as shown in the inset of Fig.
The temperature dependence curves of −ΔSm under various magnetic fields of the Co50Gd50 − xNix amorphous alloys were obtained by measuring the magnetic performance as shown in Fig.
![]() | Fig. 4. The −ΔSm vs. T curves for the Co50Gd50 − xNix amorphous ribbons: (a) x = 1, (b) x = 2, and (c) x = 3. |
![]() | Fig. 5. The ![]() ![]() |
From another point of view, the cooling efficiency, as an important parameter of the magnetic refrigeration material, can be evaluated in a more intuitive way through considering the adiabatic temperature rise (ΔTad) of the alloys. By measuring the heat capacity Cp(T) of the sample, as shown in the inset of Fig.
![](cpb_29_5_056401/cpb_29_5_056401_ieqn23.gif)
In summary, we added a small amount of Ni to Gd50Co50 binary amorphous alloy and obtained Co50Gd50 − xNix (x = 1, 2, and 3) amorphous ribbons with improved Curie temperature. The glass forming ability remains stable under the substitution of 1 at.% Ni, while the substitution of 2–3 at.% Ni weakens the thermal stability and GFA of the alloy. The MCE of the Co50Gd50 − xNix (x = 1, 2, and 3) amorphous alloys was studied. It was found that with the increasing TC of the Co50Gd50 − xNix amorphous alloys,
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[3] | |
[4] | |
[5] | |
[6] | |
[7] | |
[8] | |
[9] | |
[10] | |
[11] | |
[12] | |
[13] | |
[14] | |
[15] | |
[16] | |
[17] | |
[18] | |
[19] | |
[20] | |
[21] | |
[22] | |
[23] | |
[24] | |
[25] | |
[26] | |
[27] | |
[28] |