Supplementary Information
Giant magnetocaloric effect in isostructural MnNiGe-CoNiGe system by
establishing a Curie-temperature window
E. K. Liua, H. G. Zhanga, G. Z. Xua, X. M. Zhanga, R. S. Maa, W. H. Wanga, J. L. Chena,
H. W. Zhanga, G. H. Wua1, L. Fengb, X. X. Zhangc
a
State Key Laboratory for Magnetism, Beijing National Laboratory for Condensed Matter
Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
b
College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024,
China
c
Core Labs, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-
6900, Saudi Arabia
1
Author to whom correspondence should be addressed; E-mail: ghwu@iphy.ac.cn
1
1. Differential scanning calorimetry (DSC) thermal analysis for
stoichiometric MnNiGe.
0.06
M
-1
DSC / mW mg
Exotherm.
TN
0.04
H ea
0.02
ting
Tt
0.00
M
TN
-0.02
-0.04
X=0
-0.06
300
350
Tt
400
450
Co
oli
500
ng
550
Temperature / K
Figure S1. DSC thermal analysis for phase transitions of stoichiometric MnNiGe (x = 0).
The martensitic transformation occurs at 460 K upon cooling, which is in paramagnetic state
as it is higher than the Néel temperature TNM of 356 K.
2
2. Analysis of low-temperature magnetic behavior for Mn0.9Co0.1NiGe.
As seen in Figure S2(a), in the whole temperature region, the martensite gains high
magnetizations owing to the introduced Co-Mn interaction (analyzed in Fig. 4 in main
context). At high temperatures (above 150 K), the ferromagnetic (FM) coupling introduced by
Co-Mn interaction dominates the martensite. The martensite gets easy to saturate with welldefined saturation fields of 13, 20 and 30 kOe for 230, 200 and 150 K, respectively. The
magnetization increases with lowering temperature, which can be also seen in (b). Compared
with the similar cases in MnNi1-xCoxGe 1 and MnNi1-xFexGe 2 systems, it seems that the native
antiferromagnetic (AFM) coupling left in martensite matrix can be enhanced again at low
temperatures. This makes the martensite very difficult to saturate. The saturation fields at 100,
50 and 5 K thus become very large (much higher than 50 kOe). At the same time, the
magnetization in 50 kOe also decreases with lowering temperature (also see (b)), due to the
enhanced AFM interaction. A magnification of low-field magnetization, M (H) curves (c)
reveals that there is a crossover at about 3 kOe between low-temperature and hightemperature M (H) curves. This indicates a metamagnetization happening around 3 kOe.
Further magnification of low-field M (H) curves (d) reveals that, at 1 kOe, the lowtemperature M (H) curves are higher than high-temperature M (H) curves. This corresponds
to an increase in thermomagnetization, M (T) curve in 1 kOe with lowering temperature. M
(T) curves in 1 and 50 kOe shown in (b) reproduce the M (T) curves of this sample in Figs. 3a
and 3b in the main context. The remarkable difference between low-temperature and hightemperature M (H) curves indicates there exists a striking competition between FM and AFM
exchange interactions and a complex magnetic behavior is present in Co-substituted
martensite phase of Mn0.9Co0.1NiGe.
Here it should be pointed out that the FM-to-AFM like transition in 50 kOe field at 100
K leads to a visible decrease of the magnetization. Nevertheless, the strong FM coupling
established above 100 K, providing a high magnetization and a large magnetization change
(ΔM) is enough to bring about magnetic-field-induced magnetoresponsive effects accross the
martensitic transitions.
3
80
80
(b)
(a)
70
75
50
5K
50 K
100 K
150 K
200 K
230 K
40
30
20
10
70
M / emu g
M / emu g
-1
-1
60
1 kOe
50 kOe
65
3.25
3.00
x = 0.1
2.75
0
0
10
20
30
40
50
0
50
H / kOe
20
7
-1
15
M / emu g
-1
150
T/K
200
250
8
(c)
M / emu g
100
10
5
(d)
6
5
4
3
2
Crossover
1
1
2
3
0.5
4
H / kOe
1.0
H / kOe
1.5
2.0
Figure S2. Analysis of low-temperature magnetic behavior for Mn0.9Co0.1NiGe. (a)
Isothermal magnetization behavior of martensite phase of Mn0.9Co0.1NiGe at various
temperatures. (b) Magnetizations in 50 kOe at various temperatures from (a). (c) and (d)
Magnifications of low-field M (H) curves from (a).
4
3. Atomic site preference and related magnetic coupling in Co-substituted
MnNiGe martensite.
According to the atomic site-preference rule,3,4 as shown in Figure S3, in isostructural
MnNiGe-CoNiGe system, Co and Mn atoms with more covalent electrons than Ni atom
jointly occupy 2a sites, forming local Co-4Mn atom configuration (a). In stoichiometric
MnNiGe,5,6 with near zero-moment of Ni and Ge atoms, a spiral AFM coupling between Mn
moments is formed (b). After Co substitution, Co-Mn FM coupling in the local Co-4Mn atom
configuration is formed (c). Probing the origin of this behavior is an interesting topic for
further investigation. Each Co atom supports 4 nearest-neighbour Mn atoms to form parallel
moment arrangements.
Figure S3. Atomic site preference and magnetic coupling in Co-substituted MnNiGe
martensite. (a) Atomic site preference. (b) Mn-Mn spiral AFM structure. (c) Co-Mn FM
structure.
5
4. Magnetocaloric effect (MCE) of Mn0.8Co0.2NiGe.
As shown in Fig. 3 in the main text, the MT of Mn0.8Co0.2NiGe decreases below the
Curie temperature of austenite (TCA = 129 K), resulting in two successive transitions of a
second-order spontaneous magnetization around TCA and a first-order FM-to-FM MT around
Tt. The isothermal M (H) curves across the spontaneous magnetization and the martensitic
transformation (MT) (from 200 to 60 K) are measured, as shown in Fig. S4(a). Across the MT
(below 110 K), the temperature loop process method was also adopted, like the case in
Mn0.9Co0.1NiGe in the main text. Using Maxwell relation and these isothermal M (H) curves,
the magnetic entropy changes (ΔSm) are obtained, as shown in Fig. S4(b). Corresponding to
the two successive phase transitions, two peaks of ΔSm are observed. Due to the descent of the
magnetic entropy in both transitions, both MCEs show the same sign (negative). Distinctly,
compared with the MCE of Mn0.9Co0.1NiGe in the Curie-temperature window (TW), the MCE
in the first-order MT (Peak 1) in Fig. S4(b) becomes very small, leaving only -5 J kg-1 K-1 for
field change (ΔH) of 50 kOe. This is mainly because that, when the MT lowers below the TW,
the ΔM between the FM austenite and the FM martensite decreases abruptly (26 emu g-1, half
that of Mn0.9Co0.1NiGe, see Fig. 3b in main text). Simultaneously, the sharpness of the MT
becomes weak and the MT lasts over a wide temperature range. From the measurements of
isothermal M (H) curves, it has been confirmed that there is no magnetic-filed-induced
metamagnetic MT since the small ΔM cannot provide enough Zeeman energy for this sample.
It should be further pointed out that there are some other characters for this sample. Just
because of the wide temperature range of the MT, the peak of ΔSm also spans from 110 to 70
K. By integrating the ΔSm (T) curve over the full width at half maximum,7 a refrigerant
capacity (RC) value of 125 J kg-1 is produced over a wide temperature range, which is clearly
comparable with that of Mn0.9Co0.1NiGe. At the same time, this MCE is reversible, like the
MCE (Peak 2) in the spontaneous magnetization, since there is no magnetic hysteresis loop in
M (H) curves, indicating that the hysteresis loss is negligible. This means that, closely related
to the TW established in this study, two successive peaks of ΔSm in this sample are obtained
and an especial candidate for magnetic cooling can be expected over a very wide temperature
range.
6
200 K
190 K
180 K
170 K
165 K
160 K
155 K
150 K
145 K
140 K
130 K
120 K
110 K
105 K
100 K
95 K
90 K
85 K
80 K
75 K
70 K
65 K
60 K
(a)
60
-1
Magnetization (emu g )
75
45
30
15
0
0
10
5
20
30
H (kOe)
40
Peak 1 (Tt)
(b)
H=10
H=20
H=30
H=40
H=50
4
-1
-1
Sm / J kg K )
50
3
kOe
kOe
kOe
kOe
kOe
A
Peak 2 (TC )
2
1
0
60
80
100
120
140
160
180
200
Temperature / K
Figure S4. MCE of Mn0.8Co0.2NiGe. (a) Isothermal M (H) curves of Mn0.8Co0.2NiGe across
the spontaneous magnetization and MT. (b) Isothermal magnetic entropy changes in various
field changes.
7
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8