Comparable magnetocaloric properties of melt-extracted Gd36Tb20Co20Al24 metallic glass microwires

Journal Pre-proof Comparable magnetocaloric properties of melt-extracted Gd36Tb20Co20Al24 metallic glass microwires Hangboce Yin, Yongjiang Huang, Ying Bao, Sida Jiang, Peng Xue, Songshan Jiang, Huan Wang, Faxiang Qin, Ze Li, Shuchao Sun, Yunfei Wang, Hongxian Shen, Jianfei Sun PII:

S0925-8388(19)32156-5

DOI:

https://doi.org/10.1016/j.jallcom.2019.06.085

Reference:

JALCOM 50983

To appear in:

Journal of Alloys and Compounds

Received Date: 14 January 2019 Revised Date:

4 June 2019

Accepted Date: 7 June 2019

Please cite this article as: H. Yin, Y. Huang, Y. Bao, S. Jiang, P. Xue, S. Jiang, H. Wang, F. Qin, Z. Li, S. Sun, Y. Wang, H. Shen, J. Sun, Comparable magnetocaloric properties of melt-extracted Gd36Tb20Co20Al24 metallic glass microwires, Journal of Alloys and Compounds (2019), doi: https:// doi.org/10.1016/j.jallcom.2019.06.085. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.

1

Comparable magnetocaloric properties of

2

melt-extracted Gd36Tb20Co20Al24 metallic

3

glass microwires

4

Hangboce Yin a, Yongjiang Huang a, *, Ying Bao a, Sida Jiang a, Peng Xue a, Songshan

5

Jiang a, Huan Wang b, Faxiang Qin b, Ze Li a, Shuchao Sun a, Yunfei Wang b,

6

Hongxian Shen a, *, Jianfei Sun a

7

a

8

150001, China

9

b

School of Materials Science and Engineering, Harbin Institute of Technology, Harbin

Institute for Composites Science Innovation, School of Materials Science and

10

Engineering, Zhejiang University, Hangzhou, 310027, China

11

*E-mail address: [email protected] (Y. J. Huang), [email protected] (H.

12

X. Shen).

13

14

Abstract

15

The enhanced magnetocaloric properties are studied in melt-extracted

16

Gd36Tb20Co20Al24 metallic glass microwires. The Curie temperature is ~ 91 K for these

17

microwires which show promising applications at liquid nitrogen range. The

18

microwires possess spin glass phase in low temperature and spin freezing temperature

19

is 60 K. Notably, the maximum magnetic entropy change (–∆SMmax), the relative

1

1

cooling power (RCP) and refrigerant capacity (RC) reach high values of 12.36 J•kg-1K-1,

2

948 J•kg-1 and 731 J•kg-1, respectively, under a field change of 5 T. The large –∆SMmax

3

originates from the high effective magnetic moment. Meanwhile, the spin fluctuation,

4

the exchange integral fluctuation of metallic glass and the second order

5

paramagnetic-ferromagnetic transition enlarged the phase transition range.

6

Keywords:

7

refrigeration.

8

1. Introduction

Megnetocaloric

effect;

Metallic

glass;

Microwires;

Magnetic

9

Owing to excellent efficiency and environmental friendliness [1-4], magnetic

10

refrigerants, based on the magnetocaloric effect (MCE), show promising applications

11

in refrigeration devices [5]. MCE is an intrinsic feature of magnetic materials, which

12

can be characterized by magnetic entropy change (∆SM). The decrease of ∆SM will

13

release heat under an external magnetic field [6], whereas the increase of ∆SM will

14

absorb heat when the magnetic field is removed. The generated heat of MCE

15

materials under varying fields should be transferred between the materials and the

16

target or environment. Therefore, the heat-exchange of the MCE materials in cooling

17

system should be effective and it has been certified that a microwire shape with a

18

micro-size diameter satisfies this demand [7,8].

19

Based on the magnetic phase transition, MCE materials can be divided into first

20

order magnetic transition (FOMT) and second order magnetic transition (SOMT) 2

1

materials. SOMT materials usually process broadened magnetic phase transition with

2

negligible thermal and magnetic hysteresis [9-11]. Metallic glasses (MGs) are typical

3

SOMT materials, and show excellent MCE performances owing to their structural

4

disorder effect. Our previous work indicated that GdCoAl metallic glass microwires

5

showed MCE of ~10 J•kg-1K-1 and refrigerant capacity (RC) of 600 J•kg-1 at field

6

change of 5 T [9-11]. Recently, RE36RE20Co20Al24 MG alloys have received great

7

attention in magnetic refrigeration for the enhanced MCE [12-14]. Dy36Ho20Co20Al24

8

[13] and Tb36Ho20Co20Al24 [14] MGs exhibit excellent magnetic entropy change (∆SM)

9

of 9.49 J•kg-1K-1 and 8.94 J•kg-1K-1, respectively under a field change of 5 T.

10

In this regard, this work designs a MG with RE36RE20Co20Al24 component which

11

contains more Gd element in order to achieve higher Curie temperature and a large

12

magnetic moment. The fabricated Gd36Tb20Co20Al24 (at. %) MG microwires using

13

melt-extraction method combined the excellent MCE and broadened magnetic phase

14

transition. The results show that the designed Gd36Tb20Co20Al24 MG microwires

15

possess excellent ∆SM and broad working temperature range, which have promising

16

applications for magnetic refrigerants working in nitrogen liquefaction temperature

17

range.

18

2. Experimental details

19

Alloy ingots with a nominal composition of Gd36Tb20Co20Al24 were prepared by

20

arc melting a mixture of pure metals with purities higher than 99.9% in a Ti-gettered 3

1

high-purity Ar atmosphere, followed by suction casting into copper molds to form an

2

alloy rod with a diameter of 10 mm and a length of ~50 mm. Subsequently, the

3

continuous and circular Gd36Tb20Co20Al24 MG microwires were extracted by a

4

precision home-made melt-extraction facility. The details of the preparation process

5

can be found in previous literatures of our group [15-18]. As described, the rod was

6

placed in a boron nitride (BN) crucible and re-melted by a high frequency induction

7

furnace. Then the melt was extracted by a molybdenum (Mo) wheel with a diameter

8

of 320 mm and 60o knife-edge. Finally, the microwires were formed under their

9

surface tension and natural gravity. The constant linear velocity of the Mo wheel rim

10

was fixed at 30 m/s and the chosen feeding rate of the molten alloy was 15~30 µm/s.

11

The structure of the microwires was identified by the X-ray diffraction (XRD) with Cu

12

Kα radiation. Thermal analysis was carried out on a differential scanning calorimeter

13

(DSC) at a heating rate of 10 K/min. The microstructural observations of the

14

microwires were performed by scanning electron microscopy (SEM, FEI Quanta

15

200FEG) equipped with energy dispersive spectrometer (EDS) and high resolution

16

transmission electron microscopy (HRTEM, FEI Talos F200X). Selected area electron

17

diffraction (SAED) was also used to further analyze the structure for the microwires.

18

The magnetic measurements were performed by a commercial Magnetic Property

19

Measurement System (SQUID-VSM) from Quantum Design in the temperature range

20

of 15~170 K, and the applied magnetic field was up to 5 T. Multi-microwires were used

21

to test the magnetic properties, which were parallel and were completely filled with a 4

1

non-magnetic plastic tube of 1 mm in inner diameter, 2.5 mm in outer diameter, and 3

2

mm in length.

3

3. Result and discussion

4

3.1. Structural characterization

5

As-prepared Gd36Tb20Co20Al24 MG microwires have a uniform diameter of ~40

6

µm, as shown in Fig 1a. The compositional analysis obtained by EDS in Fig. 1a

7

shows that the actual composition of microwires is very close to their nominal

8

composition. The XRD pattern and DSC trace of the microwires are shown in Fig. 1b.

9

There is a typical broad halo pattern with only a broad diffuse peak and without Bragg

10

peak in the XRD pattern, demonstrating the representative characteristic of

11

amorphous structure. The DSC trace exhibits an obvious endothermic characteristic

12

due to glass transition followed by two sharp exothermic peaks related to

13

crystallization, certifying the nature of amorphous structure. The glass transition

14

temperature (Tg), the temperature for the onset of crystallization (Tx) and melting

15

temperature (Tm) are determined to be 586 K, 630 K and 958 K, respectively. The

16

microwires possess excellent glass forming ability, confirmed by the broad

17

supercooled liquid region (∆Tx= Tx - Tg = 44 K). The amorphous feature of the

18

microwires is further confirmed by the HRTEM image and the corresponding SAED

19

pattern. The HRTEM image in Fig 1c shows a homogeneous and featureless contrast

20

without any noticeable long-range atomic order. The corresponding SAED pattern in 5

1

the inset of Fig 1c confirms the solely amorphous phase of microwires, one strong

2

inner diffraction ring with a rather faint and diffuse halo. This result agrees well with

3

the XRD and DSC analysis, describing their amorphous characteristic of the

4

Gd36Tb20Co20Al24 MG microwires. The amorphous structure of the as-prepared

5

Gd36Tb20Co20Al24 MG microwires also can be predicted based on Lu’s empirical

6

concept [19]:

7


[Eu( − )] + [Eu( − )] + [Eu( − )] + [Eu( − )] = 1

8


∆ = ∆ = ∆

9

where α, β, γ and δ are constants, ∆HGd-Co, ∆HGd-Al, ∆HTb-Co and ∆HTb-Al are heat of

10

mixing for the clusters Gd-Co, Gd-Al, Tb-Co and Tb-Al, respectively. Constants α, β,

11

γ and δ can be quickly calculated by substituting heat of mixing of these atomic pairs

12

(-22 kJ/mol for the Gd-Co pair, -39 kJ/mol for the Gd-Al pair, -23 kJ/mol for the

13

Tb-Co pair, and -39 kJ/mol for the Tb-Al pair [20]) into Eqs. (1) and (2). The results

14

show that α=0.32, β=0.18, γ=0.31, and δ=0.18, and the composition is

15

Gd35.8Tb20.2Co20.2Al23.8, calculated based on four binary eutectics Gd72Co28, Gd68Al32,

16

Tb64Co36 and Tb1.8Al98.2 [21]. The calculated chemical composition based on Lu’s

17

empirical concept, is very close to the present composition. This suggested that the

18

studied alloy here is an excellent glass former.

19

3.2. Magnetic property

!

= ∆

!

(1) (2)

20

The temperature dependence of magnetization (M-T) results of zero-field cooling

21

(ZFC) and field cooling (FC) for Gd36Tb20Co20Al24 MG microwire is measured from 6

1

5 to 300 K under a field of 200 Oe, shown in Fig. 2a. The Curie temperature (TC) is

2

determined by the peak value of dM/dT results for the sharp magnetic phase transition

3

[9-11,13]. However, as can be seen from Fig. 2a and its inset, the M-T and the dM/dT

4

curves are broadened. Therefore, the peak value ~ 81 K, shown in the inset of Fig. 2a,

5

may not signify the Curie temperature (TC). An extrapolation method is used for the

6

linear part of the M-T curve at the phase transition, crossing the temperature axis at ~

7

91 K. The broadness can be ascribed to the extended phase transition and the

8

elemental distribution in the microwires. The Arrott plots (M2 vs. H/M), as presented

9

below, confirms that 91 K is the TC of the microwires. Table 1 summarizes the Curie

10

temperature (TC) of this microwires and many other reported bulk RE36RE20Co20Al24

11

MGs. The studied microwires show higher TC due to the Gd element which possesses

12

higher Curie temperature than other rare elements [22]. ZFC curve clearly shows a

13

peak, and the ZFC and FC curves begin to diverge near the peak position, showing a

14

distinct spin-glass-like behavior [23]. From the maximum value of the ZFC curve, the

15

spin freezing temperature (Tf) of the studied microwires can be obtained to be 60 K

16

[14,23,24]. To clarify the critical dynamics of the spin-glass transition, AC

17

susceptibility measurements were carried out at different frequencies for

18

Gd36Tb20Co20Al24 MG microwires under a field of 2 Oe. As the frequency increases,

19

the peak intensity decreases and the peak shifts to higher temperatures, as shown in the

20

inset of Fig. 2b. For the slowing down of the dynamics at the transition, the relaxation

21

time (τmax=1/ω) and the length diverges follow the power law, as follows [25] 7

1

τ#$% = &' × )

* +

− 1,

-.

(3)

2

where ω is the frequency, Ts is the ideal freezing temperature, zv is the critical

3

exponent, τ0 is related to the relaxation time of individual atomic magnetic moment.

4

zv and τ0 is 4-12 and ~10-12-10-13s, respectively, for canonical spin glass systems [24].

5

A critical divergence can be seen from the excellent fitting result of the experimental

6

data by Eq. (3), as shown in Fig. 2b. The fitting results are listed as follows, Ts=77 K,

7

zv=7.6 and τ0=~10-13 s, typical values of canonical spin glasses.

8

In order to further characterize the magnetic behavior of the microwires, the ratio

9

of applied field H and magnetization M (i.e. H/M) is calculated based on the FC curve

10

in different temperatures, as shown in Fig. 2c. This curve shows that

11

Gd36Tb20Co20Al24 MG microwire obeys the Curie-Weiss law above the TC [26]. The

12

slopes of the paramagnetic Curie points are positive, which means that the dominated

13

exchange interaction of the microwire is paramagnetic-ferromagnetic near the TC.

14

According to Curie-Weiss law, the Curie-Weiss temperature (θp) and the Curie

15

constant (C) are obtained to be 97 K and 5.62 emu•K-1mol-1, respectively by fitting

16

the line parts of the curve, as depicted in Fig. 2b. The Curie constant (C) also can be

17

calculated as: 3 /01 23 4(456)78

18

=

19

and the effective magnetic moment (µeff) can be calculated by:

20

;<== = g?@(@ + 1);A

21

(4)

9:8

(5)

where n represents the amount of substance for the microwire composition, NA 8

1

represents the Avogadro constant, g represents the Lande factor, J represents the total

2

angular momentum, kB represents Boltzmann constant, and µB represents Bohr

3

magneton. Then the effective magnetic moment (µeff) of studied microwire is

4

calculated to be ~6.7 µB based on Eqs. (4) and (5).

5

3.3. Magnetocaloric property

6

In order to characterize the MCE of Gd36Tb20Co20Al24 MG microwires, the

7

measurements of isothermal magnetization (M-H) curves are carried out at

8

temperature ranging from 15 to 170 K with a temperature interval of 10 K and

9

deceasing to 5 K when close to TC under various magnetic fields up to 5 T, and the

10

results are shown in Fig. 3a. At low magnetic fields and low temperature, the

11

magnetization varies rapidly, and upon further increasing the magnetic field, the

12

magnetization tends to be saturated, which shows the typical ferromagnetic behavior

13

[12]. Contrarily, microwire shows paramagnetic behavior at high temperature.

14

Therefore, from low temperature to high temperature, a ferromagnetic-paramagnetic

15

transition happens in the microwires.

16

Based on isothermal M-H curves, the Arrott plots are plotted to identify the order

17

of magnetic phase transition and the Curie temperature, as shown in Fig. 3b. The

18

tangent slopes of all curves are positive, illustrating a second-order magnetic

19

transition (SOMT) of the Gd36Tb20Co20Al24 MG microwire according to the Banerjee

20

criterion [27]. This results correspond to the above analysis of M-T and M-H curves.

21

Second-order magnetic transition always means that the thermal and magnetic 9

1

hysteresis are negligible and the magnetic phase transition are broadened, which could

2

promote the practical applications of active magnetic refrigerators [10]. The Arrott

3

plots also indicate that the Curie temperature ranges between 90 K and 95 K,

4

corresponding to the above result of M-T curve and confirming that 91 K is the Curie

5

temperature.

6 7 8 9

The –∆SM of the Gd36Tb20Co20Al24 MG microwire can be calculated from the isothermal M-H curves, using the Maxwell relationship [28,29] and integral method: I

GH

∆BC (, ) = B(, ) − B(, 0) = F' JKL ) G ,  ≈ − ∑R I

ST56 )∆R

6

OPQ 5 O

(ST − (6)

10

where S is the magnetic entropy, UVW is the maximum external magnetic field and

11

Mi and Mi+1 are the magnetizations under the field of Hj and at the temperatures of Ti

12

and Ti+1, respectively. Fig. 4 shows the calculated –∆SM as a function of temperature

13

under different applied fields. Large –∆SM for the Gd36Tb20Co20Al24 MG microwire

14

can be found around the TC. With increasing magnetic field, the –∆SM increases

15

significantly. The peak value (–∆SMmax) for this microwire reaches 12.36 J•kg-1K-1

16

under a field change (µ0∆H) of 5 T at ~ 87 K, which is comparable to those of the

17

most RE36RE20Co20Al24 magnetocaloric MGs as listed in Table 1. It is obvious that

18

the temperature of maximum magnetic entropy change, Tp ~ 87 K, is not

19

corresponding to the Tc, which may be attributed to the strengthened ferromagnetic

20

coupling of spin clusters at high field [13]. The high –∆SMmax is related with the high

21

effective magnetic moment as discussed above for the large magnetic moments of rear 10

1 2

earth elements [30,31]. Here the relationship between –∆SMmax and applied field change is studied using

3

Eq. (7) [32-34]:

4

UVW −∆BC ∝ /

5

where n represents a local exponent. The fitted result of n is ~0.835 at Tp ~ 87 K as

6

shown in Fig. 5a. The value is much higher than the value of ~2/3 based on mean field

7

theory [35], and also higher than those of GdAlCo glassy wires (~0.74) [36]. Mean

8

field theory usually fails to describe materials in the field dependence of magnetic

9

entropy change near transition temperature [37]. In addition, deviation from the value

10

(7)

of 2/3 may due to the local inhomogeneities in the MG microwires [35,38].

11

For a refrigeration application, magnetocaloric materials are expected to own a

12

large magnetic entropy change and a wide working temperature range. Therefore,

13

only concerning a large –∆SMmax is not enough when characterizing the magnetic

14

properties of magnetocaloric materials. For this situation, the refrigerant capacity (RC)

15

and/or relative cooling power (RCP) of the microwires are studied here. RCP and RC

16

can be obtained using the following equation [10,30,39-41]:

17

UVW UVW Y Z = −∆BC × [\IH = −BC (] − 6 )

(8)

18

RC = F 3 −∆BC ()

(9)

19

where FWHM is the full-width at half-maximum, and 6 and ] represent the onset

20

and offset temperatures of [\IH , respectively. The calculated values of RCP and

21

RC under different magnetic field changes are shown in Fig. 5b and summarized in

Q

11

1

Table 1. The values of RCP and RC for the microwires are determined to be 948

2

J·kg-1 and 731 J·kg-1 under a field change of 5 T, respectively. In spite of the large –

3

∆SMmax, such high values of RCP and RC can be ascribed to the wide phase transition

4

range due to the spin fluctuation [24], the exchange integral fluctuation of metallic

5

glass [31,42] and the second order paramagnetic-ferromagnetic transition [9,10]. For

6

spin-glass phase, magnetic moments are frozen into the equilibrium orientations,

7

however there is no long-range order structure in the studied microwires. Therefore, it

8

is more difficult for magnetic moments of spin-glass phase to be frozen than the

9

ferromagnetic materials [43,44], which could widen the magnetic transition

10

temperature range.

11

Conclusion

12

In summary, melt-extracted Gd36Tb20Co20Al24 MG microwires are fabricated,

13

which possess respectable magnetocaloric properties. The Curie temperature is 91 K

14

and the –∆SMmax is 12.36 J•kg-1K-1 at µ0△H = 5 T. The excellent MCE performances

15

are closely related to the high effective magnetic moment. The microwires show a spin

16

freezing temperature of 60 K. Notably, the obtained MG shows high values of RCP

17

and RC of 948 J•kg-1 and 731 J•kg-1, respectively, under a field change of 5 T with

18

broadened phase transition range. This can be attributed to the spin fluctuation, the

19

exchange

20

paramagnetic-ferromagnetic transition and the large –∆SMmax. Therefore, the design of

integral

fluctuation

of

metallic

12

glass,

the

second

order

1

RE36RE20Co20Al24 metallic glass is beneficial for the cooling system.

2

3

Acknowledgments

4

The authors would like to acknowledge the financial support from the National

5

Natural Science Foundation of China under Grant Nos. 51871076, 51671070,

6

51801044, 51827801, 51671071, 51601168, and 51671171.

7

8

9 10 11 12

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4 5

18

1

Figure captions

2 3

Fig. 1 (a) EDS spectrum with inset showing its SEM image, (b) DSC trace and XRD

4

pattern (inset), and (c) HRTEM image and SAED pattern (inset) of the

5

Gd36Tb20Co20Al24 MG microwire.

6 7

Fig. 2 (a) Temperature dependence of the ZFC and the FC magnetization, with inset

8

showing the dM/dT versus temperature curves, (b) The relaxation time versus

9

temperature for Gd36Tb20Co20Al24 MG microwires and the χ’ at frequencies ranging

10

from 10 to 800 Hz under a field of 2 Oe, and (c) temperature vs. the ratio of applied

11

field H and magnetization M (i.e. H/M) of the microwires under a field of 200 Oe.

12 13

Fig. 3 (a) The isothermal magnetization (M-H) curves, and (b) the corresponding

14

Arrott conversion H/M vs M2 curves of the Gd36Tb20Co20Al24 MG microwire at

15

different temperatures.

16 17

Fig. 4 Magnetic entropy change (–∆SM) of the Gd36Tb20Co20Al24 MG microwire as a

18

function of temperature under different applied fields.

19 20

Fig. 5 (a) Magnetic field dependence of the maximum magnetic entropy change

21

UVW (−∆BC ) and the fitted result, and (b) magnetic field dependence of the calculated

22

RC and RCP values. 19

Table 1 The magnetocaloric parameters of the present microwires and bulk RE36RE20Co20Al24 MGs reported in previous literatures. Form

Tc (K)

-△SM (J•kg-1K-1)

RC(J•kg-1)

Gd36Tb20Co20Al24

Microwire

91

12.36

731

This work

Dy36Ho20Co20Al24

Bulk

23

9.49

417

[13]

Gd36Y20Co20Al24

Bulk

53

7.76

459

[45]

Tb36Ho20Co20Al24

Bulk

~30

8.94

[14]

Tb36Er20Co20Al24

Bulk

~27

7.89

[14]

Tb36Gd20Co20Al24

Bulk

~62

8.4

[14]

Tb36Y20Co20Al24

Bulk

~42

~6.3

[14]

Tb36Sm20Co20Al24

Bulk

~58

~6.5

[14]

Tb36Pr20Co20Al24

Bulk

~38

~5.6

[14]

Research Highlights 1. Gd36Tb20Co20Al24 metallic glass microwires were prepared by melt-extracted method. 2. The microwires show the maximum magnetic entropy change of 12.36 J•kg-1K-1. 3. The microwires exhibit refrigerant capacity of 731 J•kg-1.