Achieving a table-like magnetic entropy change across the ice point of water with tailorable temperature range in Gd-Co-based amorphous hybrids

Article abstract of DOI:10.1016/j.jallcom.2017.06.254

Alloys exhibiting table-like magnetic entropy change (?ΔS_m) profiles are regarded as ideal magnetic refrigerants for the Ericsson magnetic refrigeration cycle. In this work, we fabricated two Gd-Co-based amorphous hybrids using various combinations of Gd₅₀Co₅₀, Gd₅₀Co₄₈Fe₂, Gd₅₀Co₄₈Mn₂ and Gd₅₀Co₄₅Mn₅ amorphous ribbons with Curie temperatures ranging from 245 K to 278 K, and obtained table-like ?ΔS_m profiles across the ice point of water within different temperature ranges. The maximum ?ΔS_m and refrigeration capacity of the amorphous hybrids were higher than those of other amorphous alloys or composites with flattened ?ΔS_m values near room temperature, indicating that amorphous hybrids are good candidates for magnetic refrigerants in house-hold magnetic refrigerators.

Full text of DOI:10.1016/j.jallcom.2017.06.254

Journal of Alloys and Compounds 723 (2017) 197e200
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Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
Achieving a table-like magnetic entropy change across the ice point of
water with tailorable temperature range in Gd-Co-based amorphous
hybrids
,
, *
L.Y. Ma a, L.H. Gan a, K.C. Chan b, D. Ding a b, L. Xia a
a Laboratory for Microstructure, Institute of Materials, Shanghai University, Shanghai, 200072, China
b Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, Hung Hom, Hong Kong
a r t i c l e i n f o
a b s t r a c t
Article history:
Alloys exhibiting table-like magnetic entropy change (ꢀ
DSm) profiles are regarded as ideal magnetic
refrigerants for the Ericsson magnetic refrigeration cycle. In this work, we fabricated two Gd-Co-based
Received 28 February 2017
Received in revised form
22 June 2017
Accepted 23 June 2017
Available online 24 June 2017
amorphous hybrids using various combinations of Gd50Co50
Gd50Co45Mn5 amorphous ribbons with Curie temperatures ranging from 245 K to 278 K, and obtained
table-like ꢀ Sm profiles across the ice point of water within different temperature ranges. The
maximum ꢀ Sm and refrigeration capacity of the amorphous hybrids were higher than those of other
Sm values near room temperature, indicating that
, Gd50Co48Fe2, Gd50Co48Mn2 and
D
D
amorphous alloys or composites with flattened ꢀ
D
Keywords:
Amorphous alloy
Hybrids
amorphous hybrids are good candidates for magnetic refrigerants in house-hold magnetic refrigerators.
© 2017 Published by Elsevier B.V.
Table-like magnetic entropy change
Refrigeration capacity
1. Introduction
thermodynamic cycle (e.g., the Ericsson cycle), a specific table-like
profile of the MCE, where ꢀ
temperature in the cooling region, provides optimal efficiency.
Obviously, even the broadened ꢀ Sm peaks of SOMPT materials are
unable to match the required MCE profile, let alone the sharp but
Sm peaks of alloys undergoing a first order magnetic
phase transition. More recently, efforts have been spent on
achieving table-like magnetic entropy change around room tem-
perature in some of the amorphous alloys or amorphous compos-
DSm is a constant with respect to
The magneto-caloric effect (MCE) is the temperature change of a
magnetic material under an external magnetic field. Magnetic al-
loys with excellent MCE can be applied as working materials in
newly developed refrigeration technologies, namely, magnetic
refrigeration (MR) [1e5]. MR technology has attracted increasing
attention because of many advantages such as compactness,
high effectiveness, low energy consumption and environmental
safety over traditional gas compression technology [2e10]. As a
result, magneto-caloric alloys have been intensively investigated
and the number of MCE materials investigated has increased
exponentially [11e22].
D
narrow ꢀ
D
ites [11e15]. However, the maximum ꢀ
DSm values of these
amorphous alloys or composites are not high enough for them to be
used as magnetic refrigerants [12,13], and the temperature range of
the table-like ꢀ
not tailorable [11]. Fortunately, the method used to obtain
flattened ꢀ Sm profile in the amorphous composite provides us
with a useful way of achieving table-like ꢀ Sm within a tailorable
temperature range by selecting amorphous alloys with appropriate
Sm peaks [11]. According to our
DSm of the single phase amorphous alloy is
It is commonly accepted that a better MCE material is one that
can supply the maximum amount of cooling over a widest tem-
perature range [9e16]. Therefore, alloys undergoing a second order
magnetic phase transition (SOMPT) with a substantial peak value of
D
D
magnetic entropy change (ꢀ
magnetic refrigerants due to their broadened magnetic entropy
Sm) peaks. However, for the practical application of MCE
D
Spmeak) seem to be ideal candidates for
Curie temperatures (Tc) and ꢀ
D
preliminary work, we have obtained several Gd-Co-based amor-
phous alloys with excellent MCE near the freezing temperature of
water [17e19]. These amorphous alloys play important roles as
basic alloys for fabricating the Gd-Co-based amorphous hybrids
with table-like magnetic entropy change across the ice point of
water within tailorable temperature ranges. In the present work,
change (ꢀ
D
materials as magnetic refrigerants when utilizing
a certain
* Corresponding author.
E-mail address: xialei@shu.edu.cn (L. Xia).
http://dx.doi.org/10.1016/j.jallcom.2017.06.254
0925-8388/© 2017 Published by Elsevier B.V.

198
L.Y. Ma et al. / Journal of Alloys and Compounds 723 (2017) 197e200
we fabricated two amorphous hybrids using a combination of
Gd50Co50, Gd50Co48Fe2, Gd50Co48Mn2 and Gd50Co45Mn5 amor-
phous ribbons with Tc ranging from 245 K to 278 K, according to a
particular fraction (wt%), and obtained table-like MCE profiles near
the freezing point of water, with a width of 20e40 K. The amor-
phous hybrids are expected to be applied as magnetic refrigerants
in house-hold refrigerators.
2. Experimental methods
Gd50Co50, Gd50Co48Fe2, Gd50Co48Mn2 and Gd50Co45Mn5 ingots
were prepared separately by arc-melting Gd, Co, Fe and Mn -
elements with a purity of at least 99.9% (at%) under a titanium-
gettered argon atmosphere. As-spun ribbons of each ingot
were prepared under a pure argon atmosphere by a single copper
wheel with a surface speed of about 30 m/s. The amorphous
structures of the as-spun ribbon were checked by X-ray diffraction
(XRD) on
radiation. Gd50Co50, Gd50Co48Fe2, Gd50Co48Mn2 and Gd50Co45Mn5
amorphous ribbons with approximate dimensions mm
(long) ꢁ 0.6 mm (wide) ꢁ 40 m (thick) were glued together ac-
a Rigaku D\max-2550 diffractometer using Cu Ka
8
m
cording to specific fractions (wt%) for magnetic measurements. The
first amorphous hybrid sample (sample 1) was fabricated by gluing
together with 70% (wt%) Gd50Co48Fe2 and 30% (wt%) Gd50Co48Mn2
amorphous ribbons; while the second amorphous hybrid sample
(sample 2) was glued together with 65% (wt%) Gd50Co48Fe2, 25%
(wt%) Gd50Co45Mn5 and 10% (wt%) Gd50Co50 amorphous ribbons.
The magnetic properties of the amorphous ribbons and the hybrid
samples were measured by a Quantum Design Physical Properties
Measurement System (PPMS 6000). The applied field was parallel
to the longitudinal direction along the length of the sample in order
to minimize the demagnetization factor.
3. Results and discussion
Fig. 1 shows the XRD patterns of the Gd50Co50, Gd50Co48Fe2,
Gd50Co48Mn2 and Gd50Co45Mn5 as-spun ribbons. The ribbons are
predominantly amorphous without any obvious crystalline peaks
on the XRD patterns. The temperature dependence of the magne-
tization (M-T) curves for the Gd50Co50, Gd50Co48Fe2, Gd50Co48Mn2
and Gd50Co45Mn5 amorphous ribbons measured under a field of
0.03 T are shown in Fig. 2 (a). Tc values of the amorphous alloys are
obtained from the derivative of their M-T curves. As marked clearly
Fig. 2. (a) M-T curves of the Gd50Co50, Gd50Co48Fe2, Gd50Co48Mn2 and Gd50Co45Mn5
amorphous ribbons under a field of 0.03 T, (b) the (ꢀ
DSm)-T curves of the amorphous
ribbons under a field of 5 T.
on the M-T curves, the Tc of the Gd50Co50 amorphous alloy is
enhanced to about 277 K by minor Fe addition, but decreases with
Mn addition to about 258 K for the Gd50Co48Mn2 amorphous rib-
bon and to about 245 K for the Gd50Co45Mn5 amorphous ribbon.
There are three kinds of exchange interactions in Gd-Co amorphous
alloys: the indirect Gd-Gd, Gd-Co interactions and the direct Co-Co
interaction [17e19]. The direct Co-Co interaction plays an impor-
tant role in determining the Tc of the amorphous alloys, while the
magnetic behavior of these alloys is mainly determined by the in-
direct interactions. Therefore, the improved Tc of the Gd50Co48Fe2
amorphous alloy is closely related to the enhanced Co-Co interac-
tion by the minor Fe addition, and the reduced Co-Co interaction in
the Gd50Co48Mn2 and Gd50Co45Mn5 amorphous alloys leads to the
decrease of Tc with Mn addition.
The temperature dependence of the magnetic entropy change
((-DSm)-T) curves under a field of 5 T for the Gd50Co50, Gd50Co48Fe2,
Gd50Co48Mn2 and Gd50Co45Mn5 amorphous ribbons derived from
their isothermal magnetization (M-H) curves according to the
thermodynamic Maxwell equation are shown in Fig.
The ꢀ
Spmeak of the amorphous alloys obviously increases with the
decrease of their Curie temperatures, which follows the relation-
2 (b).
D
ship between ꢀ
D
Spmeak and Tc proposed by Belo et al. from mean field
Fig. 1. XRD patterns of the Gd50Co50, Gd50Co48Fe2, Gd50Co48Mn2 and Gd50Co45Mn5 as-
spun ribbons obtained at a wheel surface speed of 30 m/s.
theory [23].

L.Y. Ma et al. / Journal of Alloys and Compounds 723 (2017) 197e200
199
These amorphous alloys provide ideal basic alloys for the
fabrication of Gd-Co-based amorphous hybrids with table-
according to the thermodynamic Maxwell equation, as shown in
Fig. 4.
like ꢀ
D
Sm profiles across the ice point of water within a tailorable
Fig. 4 (a) shows the (ꢀ
field of 5 T. Hybrid sample 1 shows a table-like ꢀ
temperature range of 20 K, while hybrid sample 2 shows a flattened
D
Sm)-T curves for the two samples under a
temperature range. According to the results obtained in FeZrB(Cu)
amorphous composites, the dipolar interaction between the
amorphous ribbons can be neglected [12]. Therefore, the magnetic
DSm within a
-D
Sm within a temperature range of 40 K. The maximum ꢀ
DSm is
entropy change of the amorphous hybrid (ꢀ
DSm(hybrid)) fabricated
about 4.32 J kgꢀ1Kꢀ1 for hybrid sample 1 and about 4.26 J kgꢀ1Kꢀ1
for sample 2 under 5 T, both of which are over 12% higher than that
of the amorphous Gd50Co45Fe5 alloy [11] and over 73% higher than
by lamination of several amorphous ribbons is:
X
that of the amorphous FeZrB(Cu) composite [12]. The (ꢀ
DSm)-T
n
ꢀDSmðhybridsÞ ¼
i¼1;2;:::;nwi ꢁ ð ꢀ
DSmÞi
(1)
curves for the hybrid samples under various magnetic fields are
shown in Fig. 4 (b) and (c). The hybrid samples show table-
where wi is the weight fraction of an amorphous ribbon [11e15].
We calculated ꢀ Sm(hybrid) of various hybrids composed of
different amorphous ribbons according to various weight fractions,
Sm
profiles across the ice point of water. In this work, we employed
two hybrids composed of two or three ribbons with a working
temperature range of 20 K and 40 K across the ice point of water in
order to ascertain the effectiveness of Equation (1).
The isothermal magnetization (M-H) curves for the hybrid
sample 1 measured at temperatures ranging from 150 K to 310 K
and hybrid sample 2 measured at temperatures ranging from 150 K
to 320 K are shown in Fig. 3 (a) and (b), respectively. From these M-
like ꢀ
DSm profiles under various magnetic fields, indicating the
validity of Equation (1) due to the negligible dipolar interaction
between the different amorphous ribbons.
D
and found that several hybrids exhibit perfect table-like ꢀ
D
Another important figure of merit for the MCE materials is the
refrigeration capacity [7, 11, 12, 24], which can be calculated in two
ways: RCP ¼ ꢀ
D
Spmeak
ꢁ
D
Tm (where
D
Tm is the temperature range at
R
T2
the half maximum of the ꢀ
D
Spmeak), and RC ¼
ꢀ
D
SmðT; HÞdTÞ
Tm). As
T1
(where T1 and T2 are the onset and ending temperatures of
D
the T1 and T2 values of the two samples are out of the temperature
range of the (ꢀ
DSm)-T curve measured in the present work, RCP is
much larger than 691 Jkg-1 for sample 1 and much larger than 686
Jkgꢀ1 for sample 2; RC is much larger than 526 Jkg-1 for sample 1
H curves, we obtained the (ꢀ
DSm)-T curves of the hybrid samples
Fig. 4. (a) The table-like magnetic entropy change of amorphous hybrid samples
within temperature range of about 20 K and 40 K, respectively, (b) the table-like
magnetic entropy change of amorphous hybrid sample 1 under various fields, and
(c) the table-like magnetic entropy change of amorphous hybrid sample 2 under
various fields.
Fig. 3. M-H curves of the amorphous hybrids: (a) sample 1, and (b) sample 2.

200
L.Y. Ma et al. / Journal of Alloys and Compounds 723 (2017) 197e200
and much larger than 548 Jkg-1 for sample 2. Both the RCP and RC
values for the hybrid samples are larger than those of other ma-
refrigerants in house-hold refrigerators with a tailorable tempera-
ture range.
ꢀ
terials with table-like or flattened ꢀ
D
Sm profile [11e15]. P. Alvarez
Acknowledgements
et al. have recently proposed a new method to evaluate the
refrigeration capacity for practical devices operating through a
The work described in this paper was supported by the National
Nature Science Foundation of China (Grant Nos. 51671119 and
51271103), the Research Grants Council of the Hong Kong Special
Administrative Region, China (Project No. PolyU 511212).
reversible Ericsson cycle between the cold (Tcold) and hot (Thot
reservoirs [13]: RCeff ¼ ꢀ Sm T, where T ¼ ThotꢀTcold. In case of
materials showing a table-like - Sm profile, T is the temperature
range of the table-like - Sm. Therefore, RCeff is about 42 J/kg under
)
D
ꢁ
D
D
D
D
D
2 T and about 86 J/kg under 5 T for hybrid sample 1; about 77 J/kg
under 2 T and about 166 J/kg under 5 T for hybrid sample 2. RCeff of
sample 1 is much higher than that of the FeZrB(Cu) amorphous
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