magnetocaloric effect of gd based microwires from binary to quaternary system

Peng1 1Institute for Composites Science Innovation InCSI, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, People’s Republic of China 2Department of Phy

Magnetocaloric effect of Gd-based microwires from binary to quaternary system

Y F Wang, F X Qin, Y H Wang, H Wang, R Das, M H Phan, and H X Peng

Citation: AIP Advances 7, 056422 (2017); doi: 10.1063/1.4975356

View online: http://dx.doi.org/10.1063/1.4975356

View Table of Contents: http://aip.scitation.org/toc/adv/7/5

Published by the American Institute of Physics

Articles you may be interested in

Universal field dependence of conventional and inverse magnetocaloric effects in DyCo2Si2

AIP Advances 121, 043901043901 (2017); 10.1063/1.4974302

Magnetocaloric effect of Gd-based microwires

from binary to quaternary system

Y F Wang,1 F X Qin,1, a Y H Wang,1 H Wang,1 R Das,2 M H Phan,2

and H X Peng1

1Institute for Composites Science Innovation (InCSI), School of Materials Science

and Engineering, Zhejiang University, Hangzhou 310027, People’s Republic of China

2Department of Physics, University of South Florida, Tampa, Florida 33620, USA

(Presented 3 November 2016; received 23 September 2016; accepted 15 November 2016;

published online 30 January 2017)

We have studied the magnetocaloric effect (MCE) of Gd-based amorphous microwires from binary to quaternary system We find that with increase of components from binary GdNi to ternary GdNiCo, there is a significant increase in magnetic entropy change (∆Sm) from 1.43 to 2.73 J · kg-1·K-1and an increase of temperature inter-val from 90K to 115K; further comparison between the quaternary GdNiCoDy and ternary GdNiCo shows a continuing increase of temperature interval while retaining the similar ∆Sm Such an improvement of MCE can be ascribed to the enhance-ment of amorphicity with increasing number of components, which leads to the improved magnetic softness and homogeneity The increase of the Curie tempera-ture with increasing number of components also indicates the enhanced Ruderman– Kittel–Kasuya–Yosida (RKKY) magnetic interactions caused by the addition of alloying elements as comparing binary, ternary and quaternary system or by opti-mized composition in terms of such as Ni/Co ratio in a typical ternary system of GdNiCo These results have demonstrated that appropriately designed Gd-based microwires are very useful for active magnetic refrigeration in the liquid nitrogen

temperature regime © 2017 Author(s) All article content, except where

other-wise noted, is licensed under a Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/ ) [http://dx.doi.org/10.1063/1.4975356]

Modern society relies very much on readily available refrigeration Current refrigeration tech-nology for cooling applications is mainly based on vapor compression, which has already reached

an upper limit of cooling efficiency and is harmful to our living environment due to the usage of hazardous gas such as chlorofluorocarbons (CFCs) and hydro-chlorofluorocarbons (HCFCs).1 To meet the requirement of environmental friendliness and energy saving, magnetic refrigeration (MR) based on the magnetocaloric effect (MCE),2emerges as the most promising alternative to conven-tional refrigerators, through a long time of continuous and in-depth research.3The MCE is defined

as the adiabatic temperature change (∆Tad) of a magnetic material in response to a varying mag-netic field (like magnetization and demagnetization), the essence of which is the isothermal magmag-netic entropy change (∆Sm) due to the aligning or disturbing of the magnetic dipoles of atoms when a field

is applied or removed So ∆Tadand ∆Smare often considered to be two important parameters for characterizing MCEs in magnetic materials In view of its practical application, however, the refrig-erant capacity (RC) is a more reasonable figure to characterize the cooling efficiency of magnetic materials, which is defined as the integration of −∆Sm(T) from the temperature of cold sink to hot sink in an ideal refrigeration cycle.4Therefore, a desired magnetocaloric material should possess a large magnetic entropy change (∆Sm) over a wide temperature range, resulting in the large RC.5On account of the giant magnetocaloric effect (GMCE) discovered in Gd5(SixGe1-x)4(0<xϕϕ≤0.5),6

a Corresponding author: faxiangqin@zju.edu.cn

2158-3226/2017/7(5)/056422/6 7, 056422-1 © Author(s) 2017

056422-2 Wang et al. AIP Advances 7, 056422 (2017)

namely the alloy with a significantly large MCE, much effort has been devoted to first-order mag-netic transition(FOMT) materials Many families of alloys have proved to exhibit large ∆Sm, such

as MnAs1-xSbx,7MnFeP1-xAsx and NiMnGa Heusler alloys,9 but there are still some challenging issues that restrict the implementation of these FOMT materials; the temperature change is restricted

to a relatively narrow temperature range, and the large thermal and field hysteresis losses in the temperature range of interest are detrimental to the active magnetic refrigeration.10By contrast, stud-ies11 – 14have shown that the materials with a second–order magnetic transition (SOMT) have smaller MCEs but span over broader temperature ranges, thus leading to the larger RC values and negligible hysteresis losses As a consequence, in single phase materials, it is difficult to attain large ∆Sm and large RC at the same time, which means a wide and high platform in the diagram of ∆Smvs T and

is necessary to Ericsson cycle

To overcome the difficulty, metallic glasses seem to be a good solution, because of a series of progress achieved in property studies of rare-earth based materials.15–17Since the heavy rare-earth based amorphous materials have a large magnetic moment, which determine them a large magnetic entropy change, and a tunable ordering temperature, these materials are excellent magnetic refriger-ants, as compared to Fe based, Co based and Pd based amorphous materials Among the amorphous materials, Gd-based metallic glasses18–20appear a great potential in magnetic refrigeration The peak value of −∆Smfor Gd53Al24Co20Zr3bulk metallic glass (BMG) reaches 9.40Jkg-1K-1, which is com-parable with that of pure Gd as known with a high cost, in the work.21Notably the RC (590Jkg-1) of the BMG is much larger than that of the FOMT material, Gd5Si2Ge2, due to a much wide temperature range of the large ∆Sm The previous work of Qin et al.22has shown the larger values of −∆Sm and

RC in Gd53Al24Co20Zr3microwire samples relative to their bulk counterparts Current efforts are to improve the MCE and increase the Curie temperature of Gd alloy microwires

In this paper, a series of Gd-based microwires, including binary, ternary and quaternary com-ponents, were fabricated and their magnetocaloric properties were systematically characterized The enhancements of both the MCE and Curie temperature achieved in these microwires make them promising candidates for AMR applications

Gd based microwires of composition Gd71Ni29, Gd55Ni10Co35, Gd55Ni15Co30, Gd55Ni20Co25 and Gd53Ni24Co20Dy3were prepared using a melt-extraction method The specific production process

is described below: The ingot, i.e precursor alloy with the same composition of the microwires finally obtained, was manufactured from raw materials Gd (99.9%), Ni (99.9%), Co (99.9%) and Dy (99.9%)

in argon gas atmosphere by arc-melting The melt extraction process was performed using a cooper wheel with of 160 mm and 60◦knife edge, with a linear velocity of the wheel rim fixed at 30 m min-1 and a feed rate of the molten material of 90µm s-1 The morphology of microwires was observed

by a field emission scanning electron microscope (SEM Utral 55) at 5kV The amorphous structure

of the microwires was examined by the X-ray diffraction characterization using SHIMADZU

XRD-6000 with Cu Ka radiation The magnetic properties were measured utilizing a commercial Physical Property Measurement System (PPMS-9T) from Quantum Design in a temperature range of 10-300K and with a magnetic field up to 2T

Figure1 shows the X-ray diffraction (XRD) patterns of the Gd based amorphous microwires with the binary, ternary and quaternary components (Gd71Ni29, Gd55Ni20Co25, Gd53Ni24Co20Dy3 respectively) The profile indicates a high diffraction peak exists between 30◦ to 35◦ and a more broader and lower diffraction peak distributes around a larger angle, which is agreed with the previous work.5,21By comparison, there is an appreciable peak in the Gd71Ni29XRD pattern, however, the peak gets lower and indistinct and has a slight trend to the right with component increasing There

is a mixture of crystalline and amorphous phases in Gd71Ni29and a fully amorphous state is formed

in Gd55Ni20Co25and Gd53Ni24Co20Dy3 This phenomenon can be demonstrated by the empirical rule,23 that multicomponent systems consisting of more than three components can enhance glass forming ability (GFA).The picture of the cross section shows the roundness of microwires is poor, suggesting that the fabrication parameters need to be optimized in order to receive better roundness The temperature dependence of magnetization was measured under a field of 0.2T between 50K and 300K, as shown in Fig.2a The ternary Gd55Ni20Co25 and quaternary Gd53Ni24Co20Dy3have

a similar behavior, with magnetization decreasing rapidly to zero when heating, indicating a change

FIG 1 XRD patterns of the binary Gd 71 Ni 29 , the ternary Gd 55 Ni 20 Co 25 and quaternary Gd 53 Ni 24 Co 20 Dy 3 amorphous microwires The inset picture shows the cross section of the microwires.

occurs till Tc, after which the magnetization reduces much more slowly At room temperature, the material is paramagnetic, which is consistent with that of ternary and quaternary samples The picture illustrates that there is a single homogeneous magnetic phase in ternary and quaternary amorphous microwires and dual magnetic phases in binary amorphous microwires because of the coexistence of crystalline and amorphous phases The Curie temperatures, Tc, which are defined as the temperature

at the minimum of dM/dT, are 121K, 129K and 141K for binary, ternary and quaternary amorphous microwires (Fig.2b) The Curie temperatures are much lower than that of the crystalline Gd (293K), which is resulted from the structural disordering and the addition of alloying elements.5 Figure2c shows the M-T curves of ternary Gd55Ni10+5xCo35-5x(x=0, 1, 2) also under a 0.2T field in a temperature range of 50K-300K The three amorphous alloys show a similar rapid decrease with increasing temperature, suggesting a homogeneous single magnetic phase The Tcvalues obtained for the three alloys are 189K, 157K and 129K, respectively (Fig.2d), indicating that the content of Ni and Co has

a significant effect on Tc, more Co and less Ni resulting in a higher Tc This is consistent with what has been reported in Ref.24, which elucidates the phenomenon using a theoretical model based on

FIG 2 Temperature (T) dependence of magnetization (M) taken at 0.2T (a) for Gd 71 Ni 29 , Gd 55 Ni 20 Co 25 , Gd 53 Ni 24 Co 20 Dy 3

and (c) for ternary Gd 55 Ni 10+5x Co 35-5x (x=0, 1, 2); dM/dT (b) for Gd 71 Ni 29 , Gd 55 Ni 20 Co 25 , Gd 53 Ni 24 Co 20 Dy 3 and (d) for

Gd Ni Co (x=0, 1, 2).

056422-4 Wang et al. AIP Advances 7, 056422 (2017)

FIG 3 Isothermal magnetization curves at different temperatures for (a) Gd 71 Ni 29 , (b) Gd 55 Ni 10 Co 35 , (c) Gd 55 Ni 15 Co 30 , (d) Gd 55 Ni 20 Co 25 and (e) Gd 53 Ni 24 Co 20 Dy 3

hypothetical “GdCo” and real GdNi compound, reasoning that enhanced effective magnetic exchange interactions resulted from Ni sites replaced by Co lead to this phenomenon

The MCE of the Gd-based amorphous microwires was evaluated by measuring the isothermal magnetization curves at different temperatures Fig.3 (a–e)shows the results of the isothermal mag-netization, measured with a field step of 200Oe in a range of 0-20kOe and temperature intervals of

FIG 4 Magnetic entropy changes −∆S m under different magnetic field for (a) Gd 71 Ni 29 , (b) Gd 55 Ni 10 Co 35 , (c)

TABLE I Maximum entropy change, −∆S m , peak temperature, T p , Curie temperature,T c , and RC, for the present samples.

Materials T c (K) T p (K) µ 0 ∆H(T) −∆S m (J/kg·K) RC(J/kg)

10K away from the Tcand 5K around the Tc The plots show the magnetization reaches its saturation state rapidly at a low field, with little magnetic hysteresis loss The behavior suggests that Gd based amorphous microwires have excellent soft magnetic properties, which is desired for AMR Based on the isothermal magnetization curves (M-H), Arrott plots25exhibit all positive slopes of H/M-M2(not shown here), indicating that all Gd-based amorphous microwires possess a typical SOMT feature, which is desirable for the magnetic refrigeration over wide temperature span

The isothermal entropy change(∆Sm) is calculated through the M-H curves by using Maxwell equation.26 The plots of −∆Sm −T are displayed in Fig 4, under a magnetic field range from 0-2T for all the samples As shown, all samples have broad and large peaks, which can result in a large RC The peak value of −∆Smis 1.56J/Kg+K, 2.51 J/Kg+K, 3.55J/Kg+K, 2.89J/Kg+K and 2.68 J/Kg+K for Gd71Ni29, Gd55Ni10Co35, Gd55Ni15Co30, Gd55Ni20Co25and Gd53Ni24Co20Dy3at a 2T field, respectively For a more intuitive comparison, −∆Sm and RC values of the present samples are summarized in Table I The binary amorphous microwires have the minimum −∆Sm, while

Gd55Ni15Co30 shows the highest −∆Sm value, demonstrating that composition have a significant impact on the MCE By optimization of component and proportion of the composition, superior MCE can be attained in Gd-based amorphous microwires

To evaluate the RC of the samples, the value of RC is defined as the integration of −∆Smfrom the cold end to the hot end in an ideal refrigeration cycle It should be noted that the temperatures at half maximum of the peak are usually used as the integration interval Fig.5shows the comparison of RC-H plots of different microwires The RCs of the samples increase with the increasing field The largest RC value is obtained in ternary Gd55Ni15Co30at a 2T magnetic field, approaching 325J/Kg, corresponding with the largest −∆Smvalue

The MCE performance of the microwires is strongly dependent on the composition and microstructure There exists a relation between the composition and Curie temperature: increas-ing the atomic ratio of Co/Ni can yield a larger Curie temperature This can be understood as

an appropriate ratio of Ni and Co ions has enhanced Ruderman–Kittel–Kasuya–Yosida (RKKY) magnetic interactions and hence induced the maximum polarization Another important factor is the

FIG 5 H dependence of RC for all the studied samples.

056422-6 Wang et al. AIP Advances 7, 056422 (2017)

number of elements involved as more components can to some extent benefit the formation of amor-phous structure, which is likely to lead to a broadened temperature span.5This explains why we see the Gd55Ni15Co30 ranks NO.1 and the Gd53Ni24Co20Dy3 the second in terms of RC ranking It is expected with optimization of the composition of the quaternary system, the RC can be significantly improved to overtake the ternary system in any case

In summary, we have studied the MCE of a set of Gd-based microwires with different composition from binary to quaternary It is found that the key indices of MCE performance such as Curie temper-ature, entropy change and cooling capacity are governed by the amorphicity of the microwires and composition through the RKKY magnetic interactions The improvement of amorphous microwires engineering technique and exploration of optimized composition recipe are therefore anticipated to yield better MCE microwires for active refrigeration applications

ACKNOWLEDGMENTS

FXQ would like to thank the financial support of NSFC No 51671171 and No 51501162, and

‘National Youth Thousand Talent Program’ of China and ‘Hundred Talents Program’ of Zhejiang University

1 V Franco, J S Bl´azquez, B Ingale, and A Conde, Annu Rev Mater Res.42, 305–342 (2012).

2P Weiss and A Piccard, “Le ph´enom`ene magn´etocalorique,” J Phys (Paris), 5th Ser 7, 103–109 (1917).

3 V K Pecharsky and K A Gschneidner, J Magn Magn Mater.200(1-3), 44 (1999).

4V K Pecharsky, K A Gschneidner, and A O Tsokol, Rep Prog Phys 68(6), 1479 (2005).

5 F X Qin, N S Bingham, H Wang, H X Peng, J F Sun, V Franco, S C Yu, H Srikanth, and M H Phan, Acta Mater.

61(4), 1284 (2013).

6 V K Pecharsky and K A Gschneidner, Phys Rev Lett.78(23), 4494 (1997).

7 H Wada and Y Tanabe, Appl Phys Lett.79(20), 3302 (2001).

8 O Tegus, E Br¨uck, K H J Buschow, and F R de Boer, Nature415, 150 (2001).

9 F Albertini, F Canepa, S Cirafici, E A Franceschi, M Napoletano, A Paoluzi, L Pareti, and M Solzi, J Magn Magn Mater.272-276, 2111 (2004).

10 V Provenzano, A J Shapiro and R D Shull, Nature429 (6994), 853 (2004).

11 R Caballero-Flores, V Franco, A Conde, K E Knipling, and M A Willard, Appl Phys Lett.98(10), 102505 (2011).

12 S C Paticopoulos, R Caballero-Flores, V Franco, J S Bl´azquez, A Conde, K E Knipling, and M A Willard, Solid State Commun.152(16), 1590 (2012).

13 Z W Wang, P Yu, Y T Cui, and L Xia, J Alloys Compd.658, 598 (2016).

14 P Yu, N Z Zhang, Y T Cui, L Wen, Z Y Zeng, and L Xia, J Alloys Compd.655, 353 (2016).

15B Zhang, R J Wang, D Q Zhao, M X Pan, and W H Wang, Phys Rev B 70(22) (2004).

16 S Li, R J Wang, M X Pan, D Q Zhao, and W H Wang, J Non-Cryst Solids354(10-11), 1080 (2008).

17 X K Xi, S Li, R J Wang, D Q Zhao, M X Pan, and W H Wang, J Mater Res.20(09), 2243 (2011).

18 X C Zhong, B B Gao, Z W Liu, Z G Zheng, and D C Zeng, J Alloys and Compd.553, 152 (2013).

19 Q Y Dong, B G Shen, J Chen, J Shen, F Wang, H W Zhang, and J R Sun, Solid State Commun.149(9-10), 417 (2009).

20 J X Min, X C Zhong, Z W Liu, Z G Zheng, and D C Zeng, J Alloys and Compd.606, 50 (2014).

21 Q Luo, D Q Zhao, M X Pan, and W H Wang, Appl Phys Lett.89(8), 081914 (2006).

22 N S Bingham, H Wang, F Qin, H X Peng, J F Sun, V Franco, H Srikanth, and M H Phan, Appl Phys Lett.101(10),

102407 (2012).

23 A Inoue, T Zhang, W Zhang, and A Takeuchi, Mater Trans JIM37, 99 (1996).

24 Y Mudryk, D Paudyal, T Prost, L S Chumbley, V K Pecharsky, and K A Gschneidner, Acta Mater.92, 18 (2015).

25 S K Banerjee, Phys Lett.12, 16 (1964).

26A H Morrish, The Physical Principles of Magnetism (Wiley, New York, 1965).