<span class='text_page_counter'>(1)</span><div class='page_container' data-page=1>

Nguyen Thi Mai

a,b

, Nguyen Hai Yen

c

, Pham Thi Thanh

c

, Tran Dang Thanh

c

,

Dinh Chi Linh

c

, Vu Manh Quang

d

, Nguyen Mau Lam

d

, Nguyen Le Thi

c,e

,

Nguyen Thi Thanh Huyen

f

, Do Thi Kim Anh

b

, Nguyen Huy Dan

c,*

a_{The College of Printing Industry, Phuc Dien, Bac Tu Liem, Ha Noi, Viet Nam}

b_{Hanoi University of Science, Vietnam National University, 334 Nguyen Trai, Thanh Xuan, Ha Noi, Viet Nam}

c_{Institute of Material Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Ha Noi, Viet Nam}
d_{Hanoi Pedagogical University, No. 2, 32 Nguyen Van Linh, Phuc Yen, Vinh Phuc, Viet Nam}

e_{Hong Duc University, 565 Quang Trung, Dong Ve, Thanh Hoa, Viet Nam}
f_{Quang Ninh University of Industry, Yen Tho, Dong Trieu, Quang Ninh, Viet Nam}

a r t i c l e i n f o

Article history:

Received 15 February 2017
Received in revised form
17 February 2017
Accepted 19 February 2017
Available online 27 February 2017

Keywords:

Magnetocaloric effect
Magnetic phase transition
Heusler alloy

Critical parameter
Melt-spinning method

a b s t r a c t

Ni50
xCoxMn50
yAly(x¼ 7 and 9; y ¼ 17, 18 and 19) alloy ribbons were prepared by melt-spinning with a

tangential velocity of copper wheel of 40 m s
1. X-ray diffraction patterns reveal multi-crystalline phase
behavior in the fabricated ribbons. The shape of thermomagnetization curves clearly depends on Co and
Al concentrations. The Curie temperatures (TC) of the alloy ribbons strongly increase with increasing the

Co concentration and slightly decrease with increasing the Al concentration. The martensitic-austenitic
phase transition in the alloy ribbons can be manipulated by tuning Co and Al concentrations. The
maximum magnetic entropy changejDSmjmaxof about 0.75 J kg
1K
1for afield change of 12 kOe at

TCz 364 K was achieved for the Ni43Co7Mn32Al18ribbon. Critical analysis using the Arrott-Noaks and

KouveleFisher methods demonstrates the existence of a long-range ferromagnetic order in this ribbon.
© 2017 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi.
This is an open access article under the CC BY license ( />

1. Introduction

The magnetocaloric effect (MCE) is defined as the heating or
cooling of a magnetic material when a magneticfield is applied. The
MCE occurs in a magnetic solid as a result of the entropy variation
due to the coupling of the magnetic spin system with the magnetic
field. Since the discovery of the MCE, it has been widely utilized in
magnetic materials to reach low temperatures. Nowadays, there is a
great deal of interest in using the MCE as an alternative technology

for refrigeration. The magnetic refrigeration offers the prospect of
an energy-efficient and environmentally friendly alternative to the
common vapor cycle refrigeration technology used today[1_e5].

Among magnetocaloric materials, NieMn-based Heusler alloys
are emerging as a promising candidate[6]. Recently, Ni-Mn-based

alloys have been reported to exhibit the large magnetocaloric
ef-fects, including both the conventional and inverse magnetocaloric
effects [7e9]. Besides that, the shape memory effect and other
interesting properties have also been observed[10e12]. In the
Ni-Mn-Al Heusler alloys, the Neel temperature TN z 300 K was

found to be virtually independent of composition[13]. The
Ni-Mn-Al alloys with their relatively low cost and high ductility are a
potentially attractive candidate material as a magnetic refrigerant.
The partial substitution of Co for Ni in these alloys has been
re-ported to have a strong effect on the martensitic-austenitic
trans-formation which greatly enhanced the MCE[14e16]. Despite some
previous efforts[7,16_e18], a clear understanding of the
magneto-caloric effect and its association with the magnetic phase transition
and magnetic interactions characterized by critical exponents in
Ni-Co-Mn-Al alloys has not been reached.

To address this, we have systematically investigated the
mag-netic, magnetocaloric and critical properties of Ni50
xCoxMn50
yAly

(x¼ 7 and 9; y ¼ 17, 18 and 19) rapidly quenched ribbons.

* Corresponding author.

E-mail address:(N.H. Dan).

Peer review under responsibility of Vietnam National University, Hanoi.

/>

</div>
<span class='text_page_counter'>(2)</span><div class='page_container' data-page=2>

2. Experimental

Six alloy ingots with nominal compositions of Ni50
x

-CoxMn50
yAly(x¼ 7 and 9; y ¼ 17, 18 and 19) were prepared from

pure elements (99.9%) of Ni, Co, Mn and Al using the arc-melting
method in Argon gas. The melt-spinning method was then used
to fabricate the alloy ribbons with a tangential velocity of copper
wheel of 40 m s
1. The structure of the alloys was investigated by
powder X-ray diffraction (XRD) technique using CuKa radiation

with measuring step of 0.02at room temperature. The magnetic
properties and magnetocaloric effects of the alloys were
charac-terized on a vibrating sample magnetometer with temperature
range of 77e500 K and maximum magnetic field of 12 kOe.
3. Results and discussion

The XRD patterns taken at room temperature (Fig. 1) show that
crystalline phases of L10(face centered cubic), B2 (body centered

cubic) and 10M (orthorhombic) are formed in the ribbons. Most of
the samples mainly contain B2 and L10 phases. The 10M phase

appears in the ribbons with high concentrations of Al and Co. The
change of the structure would probably affect magnetic and
mag-netocaloric properties of the alloys.

The magnetic properties of the samples were characterized by
magnetization versus temperature (M-T) measurements (Fig. 2a).
The results show that the shape of M-T curves clearly depends on Co
and Al concentrations. For examples, the magnetization of the
sample with x_{¼ 7 increased from ~0.7 emu/g for y ¼ 17 to ~7.7 emu/g}

for y¼ 19. The Curie temperatures of the alloy ribbons strongly
increased with increasing the Co concentration and slightly
decreased with increasing the Al concentration. By increasing the Co
concentration from 7 at.% to 9 at.%, the Curie temperature (TC)

strongly increased from ~364 K (for x¼ 7 and y ¼ 18) to ~ 394 K (for
x¼ 9 and y ¼ 18). The magnetization of Ni50
xCoxMn33Al17ribbons

are also increased considerably with the substitution of Co for Ni.
The martensitic-austenitic phase transition in the alloy ribbons can
be tuned by adjusting Co and Al concentrations.

In this series of samples, the Ni43Co7Mn32Al18ribbon shows two

strong magnetic phase transitions near a room temperature region.
Therefore, it was chosen as a representative one for analyzing
magnetic and magnetocaloric properties. The magnetocaloric effect
in the ribbon was assessed by the magnetic entropy change (

D

Sm)

as functions of temperature and magnetic field using Maxwell

relationship:

D

Sm¼
ZH2

H1


vM

vT


H

dH (1)

From a series of experimental curves M(T) (Fig. 2b), the
corre-sponding M(H) curves can be deduced (Fig. 3a). Fig. 3b shows

D

Sm(T) curves of the Ni43Co7Mn32Al18ribbon for different magnetic

field changes (

D

H¼ 1, 4, 8, and 12 kOe). For

D

H¼ 12 kOe, the
maximum magnetic entropy changes (j

D

Smjmax) are determined to

be about 0.43 and
0.74 J kg
1K
1for the conventional (negative)
and inverse (positive) magnetocaloric effects, respectively. As

Fig. 1. XRD patterns of Ni50
xCoxMn50
yAlyribbons with x¼ 7 (a) and x ¼ 9 (b).

Fig. 2. Thermomagnetization curves of Ni50
xCoxMn50
yAly(x¼ 7 and 9; y ¼ 17, 18 and 19) ribbons measured in a magnetic field of 100 Oe (a) and thermomagnetization curves of

</div>
<span class='text_page_counter'>(3)</span><div class='page_container' data-page=3>

expected, thej

D

Smjmaxincreases with increasing the magneticfield

(the inset ofFig. 3b).

The temperature dependence of

D

Smfor different appliedfield

changes for the second-order phase transition of materials can be
described by the so-called “universal master” curves [19e21].
Based on the

D

Sm(T) curves, the

D

Sm=

D

Smax versus

q

plots are

constructed. White

q

value is determined by the formula:

q

ẳ


T
TCị=Tr1
TCị; T  TC

T
TCÞ=ðTr2
TCÞ; T> TC (2)

where Tr1and Tr2are the temperatures of the two reference points.

For the present study, they are selected as those corresponding to

D

SmTr1;2ị ẳ k:

D

Smaxk ẳ 0:5ị. This choice of k does not affect the

actual construction of the universal curve, as it implies only
pro-portionality constant.Fig. 4a shows the universal master curve of
the Ni43Co7Mn32Al18ribbon. All

D

Sm(T) data are well collapsed onto

a universal master curve, affirming the nature of second-order
magnetic transition of the material. This is an interesting
prop-erty of second-order phase transition materials and is distinct from
first-order phase transition materials.

It has been shown that the magnetic orders of materials
exhibiting in a second-order magnetic phase transition can be
assessed by the critical parameters using Arrott plots [22]. The
Arrott plots, H/M versus M2(Fig. 4b), were constructed from the
M(H) data. It can be observed that the M2eH/M curves are
non-linear at low magnetic field and linear at high magnetic field.
Values of the spontaneous magnetization (MS) and the inverse

initial susceptibility (

c

0
1) at different temperatures were derived

from Arrott plots. The critical parameters of

b

,

g

and TCrelate to the

two above quantities via the following equations:

MSTị ẳ M0
ịH < 0; (3)

c

1₀ Tị ẳH0
M0

r _{> 0;} ₍₄₎

where M0, H0and D are the critical amplitudes andε ¼ ðT
TCÞ=TC

is the reduced temperature.

The linear extrapolation from highfield to the intercepts with
the M2 and H/M axes gives the values of MS(T) and

c

0
1(T),

respectively. The critical parameters TC,

b

and

g

were obtained from

fitting MS(T) and

c

0
1(T) data (Fig. 5a) following the according

formulas (3) and (4), while

d

was calculated by using the Widom
scaling relation, equation

d

¼ 1 þ

g

=

b

(5)[23]. The Ni43Co7Mn32Al18

ribbon possesses TC ¼ 364.21 ± 0.61 K,

b

¼ 0.469 ± 0.048,

g

¼ 0.951 ± 0.035 and

d

z 3.027. The critical parameters can be
obtained more accurately by the KouveleFisher method[25]. Like
Arrott-Noakes method, MS(T) and

c

10 ðTÞ are determined by

plot-ting M1/bversus (H/M)1/gcurves. The critical parameters of

b

and

g

relate to the two above quantities by these equations:

MSẵdMS=dT
1ẳ T
TCị=

b

(6)
Fig. 3. Magneticeld dependence of the magnetization at different temperatures (a) andDSm(DH¼ 1, 4, 8, and 12 kOe) versus temperature (inset shows the field dependence of

jDSmjmax) (b) of the Ni43Co7Mn32Al18ribbon.

</div>
<span class='text_page_counter'>(4)</span><div class='page_container' data-page=4>

c

1₀ Tịhd

c

1₀ Tị.dTi
1ẳ T
TCị=

g

(7)

The critical parameters TC,

b

and

g

obtained fromtting MS(T)

and

c

0
1(T) data by using the accordingformulas (6) and (7).Fig. 5b

shows the KouveleFisher curves of the Ni43Co7Mn32Al18 ribbon

withfitting results of TCz 364 K,

b

z 0.462 and

g

z 0.948. Based

on the Widom scaling relation, the

d

value was calculated to be
3.051. Clearly, the critical parameter values determined from the
KouveleFisher method are in good agreement with those obtained
by the Arrott-Noakesfittings. These critical parameters are quite
close to those of the mean-field model (

b

¼ 0.5,

g

¼ 1 and

d

¼ 3)
characterizing materials with long-range ferromagnetic
in-teractions [24]. In a previous study, it has been shown that
Ni50Mn50
xSnx(x¼ 13 and 14) alloy ribbons show a short-range

ferromagnetic order for x_{¼ 13 but a long-range ferromagnetic}
or-der for x¼ 14 at temperatures just below Tc, indicating that that Sn
addition tends to drive the system, in the austenitic ferromagnetic
phase, from the short-range (x¼ 13) to long-range (x ¼ 14)
ferro-magnetic order[16]. The long-range ferromagnetism has recently
been reported for Co50
xNixCr25Al25(x¼ 0 and 5) alloys[17]. In the

present case, the presence of Co and Al seem to establish a
long-range ferromagnetic order in the Ni43Co7Mn32Al18ribbon, thus

fa-voring the conventional (negative) magnetocaloric effect rather
than the inverse (positive) magnetocaloric effect. Nevertheless, a
systematic study on effects of various Co and Al contents on the
magnetic ordering and magnetocaloric effect in Ni50
xCoxMn33Al17

ribbons will be essential to fully understand their relationship.
4. Conclusion

The rapidly quenched Ni_50
xCoxMn50
yAly(x¼ 7 and 9; y ¼ 17,

18 and 19) ribbons exhibit multi-crystalline phases of the L10, B2

and 10M types. The Curie temperature of the alloy ribbon strongly
increases with increasing the Co-concentration and slightly
de-creases with increasing the Al-concentration. For afield change of
12 kOe, the maximum magnetic entropy change of the Ni43

C-o7Mn32Al18 ribbon is about 0.43 and
0.74 J kg
1 K
1 for the

negative and positive magnetocaloric effects, respectively. This
sample exhibits a long-range ferromagnetic order at temperatures
just below the TC.

Acknowledgments

This work was supported by the National Foundation for Science
and Technology Development (NAFOSTED) of Viet Nam under
Grant numbers of 103.02e2014.35. Part of the work was done in

Key Laboratory for Electronic Materials and Devices and Laboratory
of Magnetism and Superconductivity, IMS-VAST, Viet Nam.

References

[1] O. Tegus, E. Brück, K.H. Buschow, F.R. Boer, Transition-metal-based magnetic

refrigerants for room-temperature applications, Nature 415 (2002) 6868.
[2] X. Zhang, B. Zhang, Z. Yu, Z. Liu, W. Xu, G. Liu, Combined giant inverse and

normal magnetocaloric effect for room-temperature magnetic cooling, Phys.
Rev. B 76 (2007) 132403.

[3] E. Bruck, Developments of magnetocaloric refrigeration, Appl. Phys. 38 (2005)
381.

[4] Y.B. Yang, X.B. Ma, X.G. Chen, J.Z. Wei, R. Wu, J.Z. Han, H.L. Du, C.S. Wang,
S.Q. Liu, Y.C. Yang, Y. Zhang, J.B. Yang, Structure and exchange bias of
Ni50Mn37Sn13ribbons, Appl. Phys. 111 (2012) 07A916.

[5] E.C. Passamani, V.P. Nascimento, C. Larica, A.Y. Takeuchi, A.L. Alves,
J.R. Provetib, M.C. Pereirac, J.D. Fabrisd, The influence of chemical disorder
enhancement on the martensitic transformation of the Ni50Mn36Sn14

Heusler-type alloy, Alloys Compd. 509 (2011) 7826.

[6] T. Krenke, E. Duman, M. Acet, E.F. Wassermann, X. Moya, Ll. Ma~nosa, A. Planes,
Inverse magnetocaloric effect in Ni-Mn-Sn alloys, Nat. Mater 4 (2005) 450.
[7] A. Biswas, T.L. Phan, N.H. Dan, P. Zhang, S.C. Yu, H. Srikanth, M.H. Phan, The

scaling and universality of conventional and inverse magnetocaloric effects in
Heusler alloys, Appl. Phys. Lett. 103 (2013) 162410.

[8] E. Stern-Taulats, P.O. Castillo-Villa, L. Ma~nosa, C. Frontera, S. Pramanick,

S. Majumdar, A. Planes, Magnetocaloric effect in the low hysteresis Ni-Mn-In
metamagnetic shape-memory Heusler alloy, J. Appl. Phys. 115 (2016) 173907.

[9] A.M. Aliev, A.B. Batdalov, I.K. Kamilov, V.V. Koledov, V.G. Shavrov,
V.D. Buchelnikov, J. García, V.M. Prida, B. Hernando, Magnetocaloric effect in
ribbon samples of Heusler alloys NieMneM (M ¼ In,Sn), Appl. Phys. Lett. 97
(2016) 212505.

[10] S. Singh, L. Caron, S.W. D'Souza, T. Fichtner, G. Porcari, S. Fabbrici, C. Shekhar,
S. Chadov, M. Solzi, C. Felser, Large magnetization and reversible
magneto-caloric effect at the second-order magnetic transition in Heusler materials,
Adv. Mater. 28 (2016) 3321.

[11] V.K. Pecharsky, K.A. Gschneidner, A.O. Pechasky, A.M. Tishin,
Thermody-namics of the magnetocaloric effect, Phys. Rev. B 64 (2011) 144406.
[12] A. Planes, L. Ma~nosa, M. Acet, Magnetocaloric effect and its relation to

shape-memory properties in ferromagnetic Heusler alloys, Appl. Phys. 21 (2009)
233201.

[13] S. Morito, T. Kakeshita, K. Hirata, K. Otsuka, Magnetic and martensitic
trans-formations in Ni50Mn50-xAlx, Acta Mater 46 (1998) 5377.

[14] R. Kainuma, Y. Imano, W. Ito, Y. Sutou, H. Morito, S. Okamoto, O. Kitakami,
K. Oikawa, A. Fujita, T. Kanomata, K. Ishida, Magneticfield-induced reverse
transformation in B2-type NiCoMnAl shape memory alloys, Nature 439 (2006)
957.

[15] X. Xu, W. Ito, T. Kanomata, R. Kainuma, Entropy change during martensitic
transformation in Ni50
xCoxMn50
yAlymetamagnetic shape memory alloys,

Entropy 16 (2014) 1808.

[16] The-Long Phan, P. Zhang, N.H. Dan, N.H. Yen, P.T. Thanh, T.D. Thanh,
M.H. Phan, S.C. Yu, Coexistence of conventional and inverse magnetocaloric
effects and critical behaviors in Ni50Mn50-xSnx(x¼ 13 and 14) alloy ribbons,

Appl. Phys. Lett. 101 (2012) 212403.

[17] J. Panda, S.N. Saha, T.K. Nath, Critical behavior and magnetocaloric effect in
Co50
xNixCr25Al25(x¼ 0 and 5) full Heusler alloy system, J. Alloys Compd. 644

(2015) 930.

[18] H.C. Xuan, F.H. Chen, P.D. Han, D.H. Wang, Y.W. Du, Effect of Co addition on
the martensitic transformation and magnetocaloric effect of Ni-Mn-Al
ferro-magnetic shape memory alloys, Intermetallics 47 (2014) 31.

</div>
<span class='text_page_counter'>(5)</span><div class='page_container' data-page=5></div>

<!--links-->
<a href=' /><a href=' />