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Magnetocaloric effect and refrigeration performance in RE60Co20Ni20 (RE = Ho and Er) amorphous ribbons
Journal of Magnetism and Magnetic Materials 498 (2020) 166179
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Research articles
Magnetocaloric effect and refrigeration performance in RE60Co20Ni20 (RE = Ho and Er) amorphous ribbons Yaming Wang, Dan Guo, Bingbing Wu, Shuhua Geng, Yikun Zhang
T
⁎
State Key Laboratory of Advanced Special Steels & Shanghai Key Laboratory of Advanced Ferrometallurgy & School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China
A R T I C LE I N FO
A B S T R A C T
Keywords: RE60Co20Ni20 (RE = Ho and Er) Amorphous ribbons Magnetocaloric effect Magnetic properties Magnetic refrigeration
The magnetism and magnetocaloric performances of rapidly solidified RE60Co20Ni20 (RE = Ho and Er) amorphous ribbons have been investigated in this work. Both ribbons undergo a second-ordered magnetic transition from ferromagnetic (FM) to paramagnetic (PM) state. The magnetocaloric performances of RE60Co20Ni20 (RE = Ho and Er) ribbons have been characterized using magnetic entropy change (ΔSM), temperature averaged entropy change (TEC), relative cooling power (RCP) as well as refrigeration capacity (RC). With the external magnetic field change from 0 to 5 T, the maximal ΔSM values (−ΔSMmax) for Ho60Co20Ni20 and Er60Co20Ni20 are calculated to be 18.4 and 15.5 J/kg-K, respectively. The corresponding RCP (RC) values reach 668.2 (518.5) and 403.2 (320.3) J/kg. The present investigation highlights the potential of RE60Co20Ni20 ribbons as magnetic refrigerant materials at low temperature region.
1. Introduction The traditional vapor-compression technique, which is meeting the growing needs of people for a long time, has a few apparent disadvantages, including high energy consumption, low conversion rate, unfriendly to the environmental protection, etc. Magnetic cooling (MC) obtained through magnetocaloric effect (MCE) has been considered as a potential cooling technology for its advantages like high conversion rate and environmental friendliness [1–7]. MCE is a phenomenon that the magnetic part of the entropy changes (temperature of the system) with the changing applied magnetic field. Thus, MCE is usually characterized by the adiabatic temperature change (ΔTad) or/and isothermal magnetic entropy change (−ΔSM). As the important section of MC technology, magnetic materials with large and reversible MCEs have a direct effect on the cooling efficiency of magnetic refrigerators. For this purposes, several kinds of materials with giant MCEs have been realized, such as (La,M)MnO3 [8,9], MnAs [10,11], La(Fe,Si)13 [12,13], MnTX [14,15], Ni-Mn-X [16,17] and some rare earth (RE) based materials [18–27]. In the past two decades, amorphous alloys have attracted tremendous attention with respect to their outstanding properties due to its special character of the absence of long range ordering [28–30]. Thanks to the metastable microstructures, the magnetic crystalline anisotropy in amorphous alloys is averaged, which induced an
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outstanding soft ferromagnetic performance. Moreover, amorphous alloys also present high corrosion resistance, good wear resistance, and remarkable mechanical performances, since the grain boundary, dislocation and other defects are absence, which is of practical importance [28–33]. Compared with crystalline materials, RE-based amorphous MR materials usually display much broader MCE peaks, which is good to obtain good refrigeration capacity (RC). Additionally, the RE-based amorphous alloys possess an adjustable Curie temperature (TC) and good thermal stability, which makes the materials more suitable for application in MR. Zheng et al. found Gd95Fe2.8Al2.2 amorphous alloy show excellent magnetocaloric performances around room temperature [34]. Li et al. [10] have studied the magnetic properties and MCE of equi-atomic ErGdHoCoCu ribbons, and a table-like MCE was observed around a wide temperature zone of 25–75 K. Very recently, large reversible MCEs was found in Tm60Co20Ni20 ribbons under low magnetic field changes [35]. To further understand the magnetism and magnetocaloric performances of RE-based amorphous MR materials, Ho60Co20Ni20 and Er60Co20Ni20 melt-spun ribbons were fabricated successfully. Both ribbons undergo a second order magnetic transition, which induced large MCEs and attractive RC. 2. Experimental details The alloy ingots (~8 g) with compositions of Ho60Co20Ni20 and
Corresponding author. E-mail address: [email protected] (Y. Zhang).
https://doi.org/10.1016/j.jmmm.2019.166179 Received 1 September 2019; Received in revised form 28 October 2019; Accepted 19 November 2019 Available online 20 November 2019 0304-8853/ © 2019 Elsevier B.V. All rights reserved.
Journal of Magnetism and Magnetic Materials 498 (2020) 166179
Y. Wang, et al.
Fig. 1. The XRD patterns for melt-spun Ho60Co20Ni20 (a) and Er60Co20Ni20 (b) ribbons at room temperature; The DSC trace for Ho60Co20Ni20 (c) and Ho60Co20Ni20 (d) ribbons with a heating rate of 22 K/min.
taken as a key factor to describe the glass forming ability (GFA), and the obtained ΔT values are 17.4 and 51.3 K for Ho60Co20Ni20 and Er60Co20Ni20, respectively. Significantly, Er60Co20Ni20 ribbons have a better GFA than that of Ho60Co20Ni20. The temperature dependence of magnetization M(T) curves for RE60Co20Ni20 (RE = Ho and Er) ribbons with the field (H) of 1 T are given in Fig. 2 (left scale). M shows a rapid decrease with increasing T at low temperatures, and then decrease very slowly with further increasing temperature. The deduced reciprocal susceptibility 1/χ(T) curves for RE60Co20Ni20 (RE = Ho and Er) are given in the right scale of Fig. 2. By a linear fitting, it is found that the high temperature 1/χ satisfies the Curie-Weiss law: χm−1 = (T − θp) Cm , where Cm and θp represent the Weiss constant and paramagnetic Curie temperature. The deduced θp are 35.9 and 11.0 K for Ho60Co20Ni20 and Er60Co20Ni20, respectively. The positive θp value means that the magnetic transition is ferromagnetic. The insets of Fig. 2 give the M(T) curves under 0.2 T for RE60Co20Ni20 (RE = Ho and Er) by the field-cooled (FC) and zero-fieldcooled (ZFC) modes. We can see that the MFC and MZFC curves of both ribbons can overlap with each other well, declaring that there is no thermal hysteresis and it is a second-order magnetic transition (SOMT) characteristics. The Curie temperatures (TC) for RE60Co20Ni20 ribbons are determined by finding the lowest point of dMFC/dT-T curves (insets of Fig. 2), and the obtained values are approximately 20.4 and 11.5 K for RE = Ho and Er, respectively. Fig. 3(a) and (b) shows the M (H) curves measured at some selected temperatures around TC at various magnetic fields up to 5 T for Ho60Co20Ni20 and Er60Co20Ni20, respectively. M increases rapidly under a low H when T ≤ TC, and then it nearly approaches saturation under H of 1 T, illustrating the ribbons are in ferromagnetic (FM) state. In contrast, M shows a linear increase with the increasing H when T is away from TC, illustrating the system is in paramagnetic (PM) state. Arrott plots are evolved from the M-H curves, which is also a useful way to determine the order of magnetic transition. According to Banerjee’s criterion, when the slope of any point on the curve is positive, it means
Er60Co20Ni20 were prepared by arc-melting with high purity Ho, Er, Co and Ni under Ar atmosphere. The ingots were re-melted over 5 times to reach a better homogeneity, and the losses of for both ingots are ~0.25 wt%. The Ho60Co20Ni20 and Er60Co20Ni20 ribbons have been fabricated by single copper melt-spinning technology with the surface linear speed of 38 m/s. The structure of Ho60Co20Ni20 and Er60Co20Ni20 ribbons was checked by X-ray diffraction (XRD, Cu-Kα radiation, Bruker D8), the thermal analysis was examined by differential scanning calorimeter (DSC, STA449F3) under argon atmosphere. The magnetic data for Ho60Co20Ni20 and Er60Co20Ni20 ribbons were collected by physical properties measurement system (PPMS-9, QD Company).
3. Results and discussion The XRD patterns for melt-spun Ho60Co20Ni20 and Er60Co20Ni20 ribbons that were recorded at room temperature are given in Fig. 1(a) and (b), respectively. It is evident that only broad diffraction peaks instead of sharp or crystalline peaks can be seen, indicating the formation of armorphous phase in both ribbons. The DSC traces of Ho60Co20Ni20 and Er60Co20Ni20 ribbons are displayed in Fig. 1(c) and (d), respectively. One obvious exothermic peak together with an endothermic peak can be observed in each alloy composition, which corresponds to crystallization and melting feature. Then, the initial crystallization temperature Tx and melting temperature Tm are ascertained to be 638.5 K and 1052.0 K for Ho60Co20Ni20, as well as 380.6 K and 800.7 K for Er60Co20Ni20, respectively. In order to acquire directly the glass transition signals, the DSC curves around the glass transition temperatures are given in the insets of Fig. 1(c) and (d), respectively. Furthermore, the glass transition temperatures Tg of 621.5 K and 294.3 K for Ho60Co20Ni20 and Er60Co20Ni20 are noted, respectively. The initial crystallization temperature Tx and melting temperature Tm are also obtained to be 638.5 K and 1052.0 K for Ho60Co20Ni20, as well as 380.6 K and 800.7 K for Er60Co20Ni20, respectively. Generally, the temperature interval of undercooled liquid ΔT, equal to Tx − Tg, is 2
Journal of Magnetism and Magnetic Materials 498 (2020) 166179
Y. Wang, et al.
that the magnetic transition is second-order one. On the contrary, if the slope of any point on the curve is negative, indicating that it is firstorder one. As shown in Fig. 3(c) and (d), the slopes of both Arrott curves are positive, i.e., the magnetic transition for RE60Co20Ni20 (RE = Ho and Er) ribbons are second order. The isothermal magnetic entropy change (ΔSM) with the changing of external magnetic field and temperature can be calculated by Maxwell formula [5,36–38]:
ΔSM =
∫0
Hmax
(∂M (H , T ) ∂T )H dH
(1)
The ΔSM (T) curves for Ho60Co20Ni20 and Er60Co20Ni20 are displayed in Fig. 4(a) and (b), respectively. The value of −ΔSM increases with increasing T and gets the maximum (−ΔSMmax) at ~TC, and decreasing when T is away from the TC. The values of −ΔSM max for Ho60Co20Ni20 are 10.2 (0–2 T) and 18.4 J/kg-K (0–5 T). In parallel, While, the temperature at −ΔSMmax for Er60Co20Ni20 has a slight shift with increasing H, the values of −ΔSMmax are 9.7 (0–2 T) and 15.5 J/kg K (0–5 T), respectively. Furthermore, Griffith et al. [39] have introduced the conception of Temperature averaged Entropy Change (TEC) to check the performances of the MCE materials, and it is calculated as the dependence of ΔH under a certain temperature rang (ΔTlift):
TEC (ΔTlift ) =
⎧ 1 max ΔTlift Tmid ⎨ ⎩
ΔTlift Tmid + 2 ΔTlift mid − 2
∫T
ΔS (T )(ΔH , T ) dT
⎫ ⎬ ⎭
(2)
Herein, Tmid means the temperature at the center of the average. Unequal values of ΔTlift (2 and 5 K) are chosen to study whether the TEC at different temperature ranges are different. Obviously, the values of TEC(2) under various ΔH are much closer to −ΔSMmax than these of TEC(5) for both ribbons, as listed in Table 1. The magnetic field change dependence of −ΔSMmax and TEC(5) for Ho60Co20Ni20 and Er60Co20Ni20 are given in Fig. 5(a) and (b), respectively. Similar to –ΔSMmax, a nearly linear increase can be noted in TEC(5) for RE60Co20Ni20 (RE = Ho and Er) ribbons.
Fig. 2. The magnetization (M, left scale) and reciprocal susceptibility (1/ χ = H/M, right scale) as a function of temperature for (a) Ho60Co20Ni20 and (b) Er60Co20Ni20 ribbons. The inset shows the temperature dependence of magnetization (M, left scale) at the magnetic fields of H = 0.2 T measured in the field cooled (FC) and zero field cooled (ZFC) modes for (a) Ho60Co20Ni20 and (b) Er60Co20Ni20 ribbons, and the radio dM/dT (right scale) vs. T curves for (a) Ho60Co20Ni20 and (b) Er60Co20Ni20 ribbons.
Fig. 3. A series of M(H) curves measured around TC at various magnetic fields up to 5 T for (a) Ho60Co20Ni20 and (b) Er60Co20Ni20 ribbons; The Arrott plots (H/M vs. M2) around TC with increasing H only for (c) Ho60Co20Ni20 and (d) Er60Co20Ni20 ribbons. 3
Journal of Magnetism and Magnetic Materials 498 (2020) 166179
Y. Wang, et al.
Fig. 4. Temperature dependence of magnetic entropy change −ΔSM at the magnetic field range of 0–5 T for (a) Ho60Co20Ni20 and (b) Er60Co20Ni20; universal curves for (c) Ho60Co20Ni20 and (d) Er60Co20Ni20.
quantitatively. The calculations method of RC and RCP are as follows:
Table 1 The values of −ΔSMmax, TEC(2) and TEC(5) for RE60Co20Ni20 (RE = Ho, Er) amorphous ribbons under various magnetic field changes from 0 to 1 T to 0–5 T. Materials
ΔH (T)
−ΔSMmax (J/kg-K)
TEC(2) (J/kg-K)
TEC(5) (J/kg-K)
Ho60Co20Ni20
0–1 0–2 0–3 0–4 0–5
6.1 10.2 13.4 16.3 18.4
6.0 10.1 13.3 16.2 18.3
5.8 9.9 13.0 16.0 18.0
Er60Co20Ni20
0–1 0–2 0–3 0–4 0–5
6.0 9.7 12.6 14.1 15.5
5.8 9.6 12.1 13.9 15.4
5.5 9.2 11.8 13.7 15.2
RC =
∫T
Thot
cold
|ΔSM | dT
RCP = −ΔSM × δTFWHM
(4) (5)
where Thot and Tcold are the corresponding temperatures of full width half maximum (δTFWHM) when the −ΔSM gets the maximum value. As shown in Fig. 4(a) and (b), both amorphous materials have wider temperature window, which may result in higher values of RC and RCP. Fig. 5(c) and (d) represent the curves of RC-H (T) and RCP-H (T) calculated by the above formulas. The values of RC and RCP for Ho60Co20Ni20 and Er60Co20Ni20 are 518.5 and 668.2 J/kg, 457.2 and 590.9 J/kg under the external field of 5 T, respectively. The MCE parameters of −ΔSMmax and RC for Ho60Co20Ni20 and Er60Co20Ni20 ribbons together with some other previously reported solids at the similar work temperature regimes with ΔH of 0–5 T are summarized in Table 2 for comparison. It is evident that the MCE parameters for the present Ho60Co20Ni20 and Er60Co20Ni20 ribbons compare favorably with other reported materials and could be potential candidates for cryogenic MR materials.
Franco et al. [40] presented another method to prove the SOMT of some materials, i.e. “universal curve”, which is evolved from the −ΔSM-T (K) curve, the Y axis of the curve is ΔSM (T)/ΔSMmax, which is also called normalized magnetic entropy change ΔS′, θ is used as the X axis:
4. Conclusions
− (T − TC ) (Tr1 − TC );T ≤ TC θ=⎧ ⎨ ⎩ (T − TC ) (Tr 2 − TC );T > TC
To summarize, RE60Co20Ni20 (RE = Ho, Er) amorphous ribbons have been prepared successfully, both ribbons display excellent magnetic refrigeration performances. The values of TC are ascertained to be ~20.4 K for Ho60Co20Ni20 and ~11.5 K for Er60Co20Ni20, respectively. Around TC, both ribbons are undergoing a FM-PM transition, which is the symbol of SOMT. For 0–5 T magnetic field change, the values of −ΔSMmax and TEC(5) are 18.4 and 18.0 J/kg-K, as well as 15.5 and 15.2 J/kg-K for Ho60Co20Ni20 and Er60Co20Ni20, respectively. Correspondingly, the values of RCP (RC) are 668.2 (518.5) J/kg, as well as 403.2 (320.3) J/kg, respectively. The present results make RE60Co20Ni20 (RE = Ho, Er) amorphous ribbons become the potential
(3)
where Tr1 (below TC) and Tr2 (above TC) denote two reference temperatures and their corresponding ΔSM(Tr1)/ΔSMmax = ΔSM(Tr2)/ ΔSMmax = 0.6. The normalized ΔSM(T)/ΔSMmax-θcurves for Ho60Co20Ni20 and Er60Co20Ni20 ribbons are displayed in Fig. 4(c) and (d), respectively. It is significant that all rescaled curves are almost unaffected by the magnetic field and collapse into only one universal curve, which further confirm that both ribbons undergo a SOPT. Refrigeration capacity (RC) and relative cooling power (RCP) have used to describe the performance of magnetocaloric material 4
Journal of Magnetism and Magnetic Materials 498 (2020) 166179
Y. Wang, et al.
Fig. 5. The maximum magnetic entropy change (−ΔSMmax) and Temperature-averaged Entropy Change (TEC) as a function of ΔH for (a) Ho60Co20Ni20 and (b) Er60Co20Ni20 ribbons. (c) Refrigeration capacity (RC) and (d) relative cooling power (RCP) of Ho60Co20Ni20 and Er60Co20Ni20 respectively.
Acknowledgements
Table 2 The magnetic transition temperatures TM (TC or TN) and the MCE parameters of −ΔSMmax, RCP and RC for RE60Co20Ni20 (RE = Ho, Er) amorphous ribbons as well as some other MR materials under the magnetic field change of 0–5 T. Materials
TC (K)
−ΔSMmax (J/kgK)
RCP (J/ kg)
RC (J/kg)
Refs.
Ho60Co20Ni20
20.4
18.4
668.2
518.5
Er60Co20Ni20
11.5
15.4
403.2
320.3
Tm60Co20Ni20 Er2Ni2Ga Er60Cu20Al20 Er60Al16Co20Ni4 HoAgAl HoNi2B2C HoPdIn HoNiAl2 Ho57Cu25Al18 Tm4PdMg ErCoC Er60Ni30Co10 Dy36Ho20Co20Al24 Gd2NiSi3 HoCoAl
6.7 7.1 13.3 – 18 5 23 7.8 22.8 6 10 11.5 23 16 10
17.1 9.6 12.2 16.5 10.3 17.7 14.6 14.0 11.8 14.9 18.7 12.1 9.49 ~13 21.5
273 240 359 – 344 283 496 213 482 287 371 342 – ~310 ~660
– 151 279 326 – 206 374 171 385 229 – 265 326 – –
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Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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Journal of Magnetism and Magnetic Materials 498 (2020) 166179
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Research articles
Magnetocaloric effect and refrigeration performance in RE60Co20Ni20 (RE = Ho and Er) amorphous ribbons Yaming Wang, Dan Guo, Bingbing Wu, Shuhua Geng, Yikun Zhang
T
⁎
State Key Laboratory of Advanced Special Steels & Shanghai Key Laboratory of Advanced Ferrometallurgy & School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China
A R T I C LE I N FO
A B S T R A C T
Keywords: RE60Co20Ni20 (RE = Ho and Er) Amorphous ribbons Magnetocaloric effect Magnetic properties Magnetic refrigeration
The magnetism and magnetocaloric performances of rapidly solidified RE60Co20Ni20 (RE = Ho and Er) amorphous ribbons have been investigated in this work. Both ribbons undergo a second-ordered magnetic transition from ferromagnetic (FM) to paramagnetic (PM) state. The magnetocaloric performances of RE60Co20Ni20 (RE = Ho and Er) ribbons have been characterized using magnetic entropy change (ΔSM), temperature averaged entropy change (TEC), relative cooling power (RCP) as well as refrigeration capacity (RC). With the external magnetic field change from 0 to 5 T, the maximal ΔSM values (−ΔSMmax) for Ho60Co20Ni20 and Er60Co20Ni20 are calculated to be 18.4 and 15.5 J/kg-K, respectively. The corresponding RCP (RC) values reach 668.2 (518.5) and 403.2 (320.3) J/kg. The present investigation highlights the potential of RE60Co20Ni20 ribbons as magnetic refrigerant materials at low temperature region.
1. Introduction The traditional vapor-compression technique, which is meeting the growing needs of people for a long time, has a few apparent disadvantages, including high energy consumption, low conversion rate, unfriendly to the environmental protection, etc. Magnetic cooling (MC) obtained through magnetocaloric effect (MCE) has been considered as a potential cooling technology for its advantages like high conversion rate and environmental friendliness [1–7]. MCE is a phenomenon that the magnetic part of the entropy changes (temperature of the system) with the changing applied magnetic field. Thus, MCE is usually characterized by the adiabatic temperature change (ΔTad) or/and isothermal magnetic entropy change (−ΔSM). As the important section of MC technology, magnetic materials with large and reversible MCEs have a direct effect on the cooling efficiency of magnetic refrigerators. For this purposes, several kinds of materials with giant MCEs have been realized, such as (La,M)MnO3 [8,9], MnAs [10,11], La(Fe,Si)13 [12,13], MnTX [14,15], Ni-Mn-X [16,17] and some rare earth (RE) based materials [18–27]. In the past two decades, amorphous alloys have attracted tremendous attention with respect to their outstanding properties due to its special character of the absence of long range ordering [28–30]. Thanks to the metastable microstructures, the magnetic crystalline anisotropy in amorphous alloys is averaged, which induced an
⁎
outstanding soft ferromagnetic performance. Moreover, amorphous alloys also present high corrosion resistance, good wear resistance, and remarkable mechanical performances, since the grain boundary, dislocation and other defects are absence, which is of practical importance [28–33]. Compared with crystalline materials, RE-based amorphous MR materials usually display much broader MCE peaks, which is good to obtain good refrigeration capacity (RC). Additionally, the RE-based amorphous alloys possess an adjustable Curie temperature (TC) and good thermal stability, which makes the materials more suitable for application in MR. Zheng et al. found Gd95Fe2.8Al2.2 amorphous alloy show excellent magnetocaloric performances around room temperature [34]. Li et al. [10] have studied the magnetic properties and MCE of equi-atomic ErGdHoCoCu ribbons, and a table-like MCE was observed around a wide temperature zone of 25–75 K. Very recently, large reversible MCEs was found in Tm60Co20Ni20 ribbons under low magnetic field changes [35]. To further understand the magnetism and magnetocaloric performances of RE-based amorphous MR materials, Ho60Co20Ni20 and Er60Co20Ni20 melt-spun ribbons were fabricated successfully. Both ribbons undergo a second order magnetic transition, which induced large MCEs and attractive RC. 2. Experimental details The alloy ingots (~8 g) with compositions of Ho60Co20Ni20 and
Corresponding author. E-mail address: [email protected] (Y. Zhang).
https://doi.org/10.1016/j.jmmm.2019.166179 Received 1 September 2019; Received in revised form 28 October 2019; Accepted 19 November 2019 Available online 20 November 2019 0304-8853/ © 2019 Elsevier B.V. All rights reserved.
Journal of Magnetism and Magnetic Materials 498 (2020) 166179
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Fig. 1. The XRD patterns for melt-spun Ho60Co20Ni20 (a) and Er60Co20Ni20 (b) ribbons at room temperature; The DSC trace for Ho60Co20Ni20 (c) and Ho60Co20Ni20 (d) ribbons with a heating rate of 22 K/min.
taken as a key factor to describe the glass forming ability (GFA), and the obtained ΔT values are 17.4 and 51.3 K for Ho60Co20Ni20 and Er60Co20Ni20, respectively. Significantly, Er60Co20Ni20 ribbons have a better GFA than that of Ho60Co20Ni20. The temperature dependence of magnetization M(T) curves for RE60Co20Ni20 (RE = Ho and Er) ribbons with the field (H) of 1 T are given in Fig. 2 (left scale). M shows a rapid decrease with increasing T at low temperatures, and then decrease very slowly with further increasing temperature. The deduced reciprocal susceptibility 1/χ(T) curves for RE60Co20Ni20 (RE = Ho and Er) are given in the right scale of Fig. 2. By a linear fitting, it is found that the high temperature 1/χ satisfies the Curie-Weiss law: χm−1 = (T − θp) Cm , where Cm and θp represent the Weiss constant and paramagnetic Curie temperature. The deduced θp are 35.9 and 11.0 K for Ho60Co20Ni20 and Er60Co20Ni20, respectively. The positive θp value means that the magnetic transition is ferromagnetic. The insets of Fig. 2 give the M(T) curves under 0.2 T for RE60Co20Ni20 (RE = Ho and Er) by the field-cooled (FC) and zero-fieldcooled (ZFC) modes. We can see that the MFC and MZFC curves of both ribbons can overlap with each other well, declaring that there is no thermal hysteresis and it is a second-order magnetic transition (SOMT) characteristics. The Curie temperatures (TC) for RE60Co20Ni20 ribbons are determined by finding the lowest point of dMFC/dT-T curves (insets of Fig. 2), and the obtained values are approximately 20.4 and 11.5 K for RE = Ho and Er, respectively. Fig. 3(a) and (b) shows the M (H) curves measured at some selected temperatures around TC at various magnetic fields up to 5 T for Ho60Co20Ni20 and Er60Co20Ni20, respectively. M increases rapidly under a low H when T ≤ TC, and then it nearly approaches saturation under H of 1 T, illustrating the ribbons are in ferromagnetic (FM) state. In contrast, M shows a linear increase with the increasing H when T is away from TC, illustrating the system is in paramagnetic (PM) state. Arrott plots are evolved from the M-H curves, which is also a useful way to determine the order of magnetic transition. According to Banerjee’s criterion, when the slope of any point on the curve is positive, it means
Er60Co20Ni20 were prepared by arc-melting with high purity Ho, Er, Co and Ni under Ar atmosphere. The ingots were re-melted over 5 times to reach a better homogeneity, and the losses of for both ingots are ~0.25 wt%. The Ho60Co20Ni20 and Er60Co20Ni20 ribbons have been fabricated by single copper melt-spinning technology with the surface linear speed of 38 m/s. The structure of Ho60Co20Ni20 and Er60Co20Ni20 ribbons was checked by X-ray diffraction (XRD, Cu-Kα radiation, Bruker D8), the thermal analysis was examined by differential scanning calorimeter (DSC, STA449F3) under argon atmosphere. The magnetic data for Ho60Co20Ni20 and Er60Co20Ni20 ribbons were collected by physical properties measurement system (PPMS-9, QD Company).
3. Results and discussion The XRD patterns for melt-spun Ho60Co20Ni20 and Er60Co20Ni20 ribbons that were recorded at room temperature are given in Fig. 1(a) and (b), respectively. It is evident that only broad diffraction peaks instead of sharp or crystalline peaks can be seen, indicating the formation of armorphous phase in both ribbons. The DSC traces of Ho60Co20Ni20 and Er60Co20Ni20 ribbons are displayed in Fig. 1(c) and (d), respectively. One obvious exothermic peak together with an endothermic peak can be observed in each alloy composition, which corresponds to crystallization and melting feature. Then, the initial crystallization temperature Tx and melting temperature Tm are ascertained to be 638.5 K and 1052.0 K for Ho60Co20Ni20, as well as 380.6 K and 800.7 K for Er60Co20Ni20, respectively. In order to acquire directly the glass transition signals, the DSC curves around the glass transition temperatures are given in the insets of Fig. 1(c) and (d), respectively. Furthermore, the glass transition temperatures Tg of 621.5 K and 294.3 K for Ho60Co20Ni20 and Er60Co20Ni20 are noted, respectively. The initial crystallization temperature Tx and melting temperature Tm are also obtained to be 638.5 K and 1052.0 K for Ho60Co20Ni20, as well as 380.6 K and 800.7 K for Er60Co20Ni20, respectively. Generally, the temperature interval of undercooled liquid ΔT, equal to Tx − Tg, is 2
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that the magnetic transition is second-order one. On the contrary, if the slope of any point on the curve is negative, indicating that it is firstorder one. As shown in Fig. 3(c) and (d), the slopes of both Arrott curves are positive, i.e., the magnetic transition for RE60Co20Ni20 (RE = Ho and Er) ribbons are second order. The isothermal magnetic entropy change (ΔSM) with the changing of external magnetic field and temperature can be calculated by Maxwell formula [5,36–38]:
ΔSM =
∫0
Hmax
(∂M (H , T ) ∂T )H dH
(1)
The ΔSM (T) curves for Ho60Co20Ni20 and Er60Co20Ni20 are displayed in Fig. 4(a) and (b), respectively. The value of −ΔSM increases with increasing T and gets the maximum (−ΔSMmax) at ~TC, and decreasing when T is away from the TC. The values of −ΔSM max for Ho60Co20Ni20 are 10.2 (0–2 T) and 18.4 J/kg-K (0–5 T). In parallel, While, the temperature at −ΔSMmax for Er60Co20Ni20 has a slight shift with increasing H, the values of −ΔSMmax are 9.7 (0–2 T) and 15.5 J/kg K (0–5 T), respectively. Furthermore, Griffith et al. [39] have introduced the conception of Temperature averaged Entropy Change (TEC) to check the performances of the MCE materials, and it is calculated as the dependence of ΔH under a certain temperature rang (ΔTlift):
TEC (ΔTlift ) =
⎧ 1 max ΔTlift Tmid ⎨ ⎩
ΔTlift Tmid + 2 ΔTlift mid − 2
∫T
ΔS (T )(ΔH , T ) dT
⎫ ⎬ ⎭
(2)
Herein, Tmid means the temperature at the center of the average. Unequal values of ΔTlift (2 and 5 K) are chosen to study whether the TEC at different temperature ranges are different. Obviously, the values of TEC(2) under various ΔH are much closer to −ΔSMmax than these of TEC(5) for both ribbons, as listed in Table 1. The magnetic field change dependence of −ΔSMmax and TEC(5) for Ho60Co20Ni20 and Er60Co20Ni20 are given in Fig. 5(a) and (b), respectively. Similar to –ΔSMmax, a nearly linear increase can be noted in TEC(5) for RE60Co20Ni20 (RE = Ho and Er) ribbons.
Fig. 2. The magnetization (M, left scale) and reciprocal susceptibility (1/ χ = H/M, right scale) as a function of temperature for (a) Ho60Co20Ni20 and (b) Er60Co20Ni20 ribbons. The inset shows the temperature dependence of magnetization (M, left scale) at the magnetic fields of H = 0.2 T measured in the field cooled (FC) and zero field cooled (ZFC) modes for (a) Ho60Co20Ni20 and (b) Er60Co20Ni20 ribbons, and the radio dM/dT (right scale) vs. T curves for (a) Ho60Co20Ni20 and (b) Er60Co20Ni20 ribbons.
Fig. 3. A series of M(H) curves measured around TC at various magnetic fields up to 5 T for (a) Ho60Co20Ni20 and (b) Er60Co20Ni20 ribbons; The Arrott plots (H/M vs. M2) around TC with increasing H only for (c) Ho60Co20Ni20 and (d) Er60Co20Ni20 ribbons. 3
Journal of Magnetism and Magnetic Materials 498 (2020) 166179
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Fig. 4. Temperature dependence of magnetic entropy change −ΔSM at the magnetic field range of 0–5 T for (a) Ho60Co20Ni20 and (b) Er60Co20Ni20; universal curves for (c) Ho60Co20Ni20 and (d) Er60Co20Ni20.
quantitatively. The calculations method of RC and RCP are as follows:
Table 1 The values of −ΔSMmax, TEC(2) and TEC(5) for RE60Co20Ni20 (RE = Ho, Er) amorphous ribbons under various magnetic field changes from 0 to 1 T to 0–5 T. Materials
ΔH (T)
−ΔSMmax (J/kg-K)
TEC(2) (J/kg-K)
TEC(5) (J/kg-K)
Ho60Co20Ni20
0–1 0–2 0–3 0–4 0–5
6.1 10.2 13.4 16.3 18.4
6.0 10.1 13.3 16.2 18.3
5.8 9.9 13.0 16.0 18.0
Er60Co20Ni20
0–1 0–2 0–3 0–4 0–5
6.0 9.7 12.6 14.1 15.5
5.8 9.6 12.1 13.9 15.4
5.5 9.2 11.8 13.7 15.2
RC =
∫T
Thot
cold
|ΔSM | dT
RCP = −ΔSM × δTFWHM
(4) (5)
where Thot and Tcold are the corresponding temperatures of full width half maximum (δTFWHM) when the −ΔSM gets the maximum value. As shown in Fig. 4(a) and (b), both amorphous materials have wider temperature window, which may result in higher values of RC and RCP. Fig. 5(c) and (d) represent the curves of RC-H (T) and RCP-H (T) calculated by the above formulas. The values of RC and RCP for Ho60Co20Ni20 and Er60Co20Ni20 are 518.5 and 668.2 J/kg, 457.2 and 590.9 J/kg under the external field of 5 T, respectively. The MCE parameters of −ΔSMmax and RC for Ho60Co20Ni20 and Er60Co20Ni20 ribbons together with some other previously reported solids at the similar work temperature regimes with ΔH of 0–5 T are summarized in Table 2 for comparison. It is evident that the MCE parameters for the present Ho60Co20Ni20 and Er60Co20Ni20 ribbons compare favorably with other reported materials and could be potential candidates for cryogenic MR materials.
Franco et al. [40] presented another method to prove the SOMT of some materials, i.e. “universal curve”, which is evolved from the −ΔSM-T (K) curve, the Y axis of the curve is ΔSM (T)/ΔSMmax, which is also called normalized magnetic entropy change ΔS′, θ is used as the X axis:
4. Conclusions
− (T − TC ) (Tr1 − TC );T ≤ TC θ=⎧ ⎨ ⎩ (T − TC ) (Tr 2 − TC );T > TC
To summarize, RE60Co20Ni20 (RE = Ho, Er) amorphous ribbons have been prepared successfully, both ribbons display excellent magnetic refrigeration performances. The values of TC are ascertained to be ~20.4 K for Ho60Co20Ni20 and ~11.5 K for Er60Co20Ni20, respectively. Around TC, both ribbons are undergoing a FM-PM transition, which is the symbol of SOMT. For 0–5 T magnetic field change, the values of −ΔSMmax and TEC(5) are 18.4 and 18.0 J/kg-K, as well as 15.5 and 15.2 J/kg-K for Ho60Co20Ni20 and Er60Co20Ni20, respectively. Correspondingly, the values of RCP (RC) are 668.2 (518.5) J/kg, as well as 403.2 (320.3) J/kg, respectively. The present results make RE60Co20Ni20 (RE = Ho, Er) amorphous ribbons become the potential
(3)
where Tr1 (below TC) and Tr2 (above TC) denote two reference temperatures and their corresponding ΔSM(Tr1)/ΔSMmax = ΔSM(Tr2)/ ΔSMmax = 0.6. The normalized ΔSM(T)/ΔSMmax-θcurves for Ho60Co20Ni20 and Er60Co20Ni20 ribbons are displayed in Fig. 4(c) and (d), respectively. It is significant that all rescaled curves are almost unaffected by the magnetic field and collapse into only one universal curve, which further confirm that both ribbons undergo a SOPT. Refrigeration capacity (RC) and relative cooling power (RCP) have used to describe the performance of magnetocaloric material 4
Journal of Magnetism and Magnetic Materials 498 (2020) 166179
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Fig. 5. The maximum magnetic entropy change (−ΔSMmax) and Temperature-averaged Entropy Change (TEC) as a function of ΔH for (a) Ho60Co20Ni20 and (b) Er60Co20Ni20 ribbons. (c) Refrigeration capacity (RC) and (d) relative cooling power (RCP) of Ho60Co20Ni20 and Er60Co20Ni20 respectively.
Acknowledgements
Table 2 The magnetic transition temperatures TM (TC or TN) and the MCE parameters of −ΔSMmax, RCP and RC for RE60Co20Ni20 (RE = Ho, Er) amorphous ribbons as well as some other MR materials under the magnetic field change of 0–5 T. Materials
TC (K)
−ΔSMmax (J/kgK)
RCP (J/ kg)
RC (J/kg)
Refs.
Ho60Co20Ni20
20.4
18.4
668.2
518.5
Er60Co20Ni20
11.5
15.4
403.2
320.3
Tm60Co20Ni20 Er2Ni2Ga Er60Cu20Al20 Er60Al16Co20Ni4 HoAgAl HoNi2B2C HoPdIn HoNiAl2 Ho57Cu25Al18 Tm4PdMg ErCoC Er60Ni30Co10 Dy36Ho20Co20Al24 Gd2NiSi3 HoCoAl
6.7 7.1 13.3 – 18 5 23 7.8 22.8 6 10 11.5 23 16 10
17.1 9.6 12.2 16.5 10.3 17.7 14.6 14.0 11.8 14.9 18.7 12.1 9.49 ~13 21.5
273 240 359 – 344 283 496 213 482 287 371 342 – ~310 ~660
– 151 279 326 – 206 374 171 385 229 – 265 326 – –
This work This work [35] [22] [41] [42] [43] [44] [45] [46] [31] [47] [48] [49] [50] [51] [52]
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Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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