Magnetostructural transition behavior in Fe-doped Heusler Mn–Ni–In ribbon materials

Journal of Magnetism and Magnetic Materials 417 (2016) 267–271

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Magnetostructural transition behavior in Fe-doped Heusler Mn–Ni–In ribbon materials Hongwei Li a,b,c, Yue Fang d, Shutong Feng d, Qijie Zhai a,b,c, Zhiping Luo e, Hongxing Zheng a,b,c,d,n a

State Key Laboratory of Advanced Special Steels, Shanghai University, Shanghai 200072, China Shanghai Key Laboratory of Advanced Ferrometallurgy, Shanghai University, Shanghai 200072, China c School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China d Laboratory for Microstructures, Shanghai University, Shanghai 200072, China e Department of Chemistry and Physics, Fayetteville State University, Fayetteville, NC 28301, USA b

art ic l e i nf o

a b s t r a c t

Article history: Received 20 April 2016 Received in revised form 19 May 2016 Accepted 24 May 2016 Available online 26 May 2016

In the present work, we investigated magnetostructural transition behavior in Mn-rich Heusler Mn50
xFexNi41In9 (x ¼ 0, 1, 2, 3 at%) ribbon materials. Microstructural observations showed that substituting Mn with Fe in Mn50Ni41In9 led to striking grain refinement from ∼50 μm to 5–10 μm, and formation of a secondary phase when Fe content was increased up to 2 at%. Differential scanning calorimetric and thermomagnetic measurements indicated that a paramagnetic-ferromagnetic transition in austenite occurred first, followed with a weak-magnetic martensitic transition upon cooling for the Mn50
xFexNi41In9 (x ¼0, 1, 2). In case of Mn47Fe3Ni41In9, the martensitic transformation happened between paramagnetic austenite and weak-magnetic martensite, without the presence of the magnetic transition in austenite. The effective refrigeration capacity of Mn49Fe1Ni41In9 reached 137.1 J kg
1 under a magnetic field change of 30 kOe. & 2016 Elsevier B.V. All rights reserved.

Keywords: Heusler Mn–Ni–In Martensitic transformation Magnetic transition Magnetocaloric effect

1. Introduction Heusler Ni–Mn based materials attracted much attention due to their potential magnetic refrigeration applications [1,2]. As proposed in previous literature, two key issues need to be clarified so as to take full advantages of the first-order martensitic transformation: the first one is on the complex crystal structure of the low-temperature martensite, and the second one is the compositional dependence of the martensitic transformation [3]. Modulated four- and five-layered orthorhombic, seven-layered monoclinic (4O, 10M and 14M), and unmodulated double tetragonal (L10) martensites have been observed in Heusler Ni–Mn–Sn [4]. The martensitic transformation would occur between austenite and martensite with various magnetic states [5–8] and generally, the materials demonstrated giant magnetocaloric effect when the martensitic transformation takes place between ferromagnetic austenite and weak-magnetic martensite. That is, the austenite should undergo a paramagnetic-ferromagnetic transition prior to the martensitic transformation upon cooling [9]. For example, Aguilar-Ortiz et al. reported giant room-temperature n Corresponding author at: State Key Laboratory of Advanced Special Steels, Shanghai University, Shanghai 200072, China. E-mail address: [email protected] (H. Zheng).

http://dx.doi.org/10.1016/j.jmmm.2016.05.087 0304-8853/& 2016 Elsevier B.V. All rights reserved.

inverse magnetocaloric effect in Ni42Fe8Mn40Sn10 ribbons, where the magnetic entropy change across the martensitic transformation reached 11 J kg
1 K
1 under a magnetic change of 50 kOe, whereas the maximum magnetic entropy change dramatically decreased to 2 J kg
1 K
1 in Ni50Mn40Sn10 ribbons because the latter martensitic transformation happened between paramagnetic austenite and weak-magnetic martensite [10]. Recently, more studies focused on the Mn-rich Heusler Mn–Ni–In materials because it was expected to hold the promise for higher saturation magnetization materials [11–13]. Wu et al. [14] observed improved magnetization discrepancy between austenite and martensite in Mn50Ni37Co3In10 alloy. Llamazares et al. [15] reported a L21-type single-phase austenite and a 14M monoclinic martensite in Mn50Ni40In10 ribbons, which exhibited large magnetocaloric effect around room temperature. From the viewpoint of materials fabrication, melt-spinning technique has been emphasized considering several advantages for the fabrication and application of high-performance magnetocaloric materials [16–18]. Firstly, it could produce homogeneous and chemically-ordered materials without additional extended high-temperature heat treatment. Secondly, it is favorable to obtain textured materials with improved magnetic and mechanical properties. Thirdly, the geometry of ribbon materials is well suited for fast heat exchange with the heat transfer fluid in a

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H. Li et al. / Journal of Magnetism and Magnetic Materials 417 (2016) 267–271

magnetocaloric device. Therefore, in this work, we systematically investigated the effect of Mn substitution by Fe in the Mn50Ni41In9 melt-spun ribbons. Particularly, the magnetostrutural transition behaviors and magnetocaloric effect were studied.

Intensity

Fe3

*

* 2. Experimental procedure

Fe2

*

Four ribbon samples with nominal compositions of Mn50
xFexNi41In9 (x ¼0, 1, 2, 3 at%) were investigated in the

*

20

30

50

60

70

(422)

Table 1 Chemical compositions of the matrix and secondary phase in Mn–Fe–Ni–In annealed ribbons (at%).

(420)

(400)

(220) 40

(311)

Fe0

(200)

Fe1

80

2 theta (degree)

Fe0 Fe1 Fe2 Fe3

Matrix Matrix Matrix Secondary phase Matrix Secondary phase

Mn

Fe

Ni

In

49.56 48.63 47.29 55.54 46.48 53.66

0 1.01 1.98 10.26 2.93 13

41.0 41.0 41.3 30.48 41.2 30.04

9.44 9.36 9.43 3.72 9.39 3.30

Fig. 1. XRD patterns of Mn–Fe–Ni–In annealed ribbons at room temperature.

50μ μm

10μm

10μm

10μm

Fig. 2. Backscattered scanning electron images of Mn–Fe–Ni–In annealed ribbons at room temperature. (a) Fe0, (b) Fe1, (c) Fe2, and (d) Fe3.

Heat flow

endo

H. Li et al. / Journal of Magnetism and Magnetic Materials 417 (2016) 267–271

973 K for 4 h. X-ray diffraction technique (XRD DLMAX–2200) was employed to detect the phases and crystal structures. Differential scanning calorimetric measurement (NETZSCH DSC 204 F1) was carried out at heating/cooling rates of 10 K min
1. Microstructural observations were conducted using a field-emission scanning electron microscope (SEM, JSM-6700F) with an energy dispersive spectroscopy system (EDS). Magnetization measurements were performed by a physical property measurement system (PPMS-9) using the vibrating sample magnetometer module. The magnetic field was applied along the length direction (rolling direction) of the ribbons.

Fe3

Fe2

Fe1 heating

As=279K

Fe0 Mf=265K

210

240

Af=301K

cooling

Ms=286K

270

300

269

330

Temperature (K) Fig. 3. Differential scanning calorimetric charts of Mn–Fe–Ni–In annealed ribbons.

present work, hereinafter referred to as Fe0, Fe1, Fe2 and Fe3, respectively. The as-cast ingots about 8 g were prepared using high-frequency induction melting in quartz tubes from Mn (99.5 wt%), Fe (99.99 wt%), Ni (99.99 wt%) and In (99.99 wt%) elements under argon atmosphere. After the ingots were melted and hold for 3 min, the ribbons were in-situ fabricated using the melt-spinning technique at a linear speed of 10 m s
1. The resultant ribbons were ∼20 mm long, 4–6 mm wide and 30–35 μm thick. All the ribbons were sealed in quartz tubes and annealed at

3. Results and discussion The XRD patterns of the Mn–Fe–Ni–In annealed ribbons are shown in Fig. 1. All the main diffraction peaks are well indexed as a L21-type austenite (bcc structure) [11]. With the Fe substitution, one can see that it is clear that the diffraction peak (400) of austenite shifted towards high-angle regime, indicating that the unit cell shrunk slightly with small Fe atom (atom radius r¼0.124 nm) replacement for large Mn atom (r¼0.135 nm). Two weak diffraction peaks at 49.6° and 72.6° appeared when Fe content increased up to 2 at%, which corresponded well to γ phase (fcc structure) [19]. Fig. 2 shows the backscattered scanning electron images. Pure austenite with an average grain size of 50–100 μm is obtained in the Mn50Ni41In9 ribbons at room temperature (Fig. 2a). With 1 at% Fe substitution for Mn in Fig. 2b, the grains refine strikingly to 5–10 μm. Further increasing Fe

Fig. 4. Temperature dependence of magnetization for Mn–Fe–Ni–In annealed ribbons under a magnetic field of 100 Oe upon heating and cooling.

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(a)

255K

(b)

50

250K

30 245K

20 240K 235K 230K

10

260K

40

ΔT=5K

40

Magnetiztion (emu/g)

Magnetization (emu/g)

50

30

320K

20

10

0

0 0

5

10

15

20

25

30

0

5

10

Magnetic Field (kOe)

20

25

30

(c)

20

300

320

(d)

-1

-1

Hysteresis loss (Jkg )

-1

Entropy change (Jkg K )

9

15

Magnetic Field (kOe)

6

3

0

15

10

5

0 -3 220

240

260

280

300

320

Temperature (K)

220

240

260

280

Temperature (K)

Fig. 5. (a) and (b) Isothermal magnetization curves of the Fe1 annealed ribbons under a magnetic field change of 30 kOe upon heating; (c) Temperature dependence of the magnetic entropy change ΔSM and (d) the hysteresis loss.

content to 2 at%, the grain size keeps almost unchanged, and a secondary phase forms along the grain boundaries (Fig. 2c). More secondary phase appears even inside the grains when Fe content was increased up to 3 at%, as shown in Fig. 2d. These results agree well with the XRD results. EDS results (Table 1) indicate that the secondary phase is Fe-rich and In-poor with average chemical compositions of Mn55.54Fe10.26Ni30.48In3.72 and Mn53.66Fe13Ni30.04In3.30 for Fe2 and Fe3 annealed ribbons, respectively. Differential scanning calorimetric charts are plotted in Fig. 3. Taking Fe0 ribbon as an example, large exothermic and endothermic peaks are associated with the first-order martensitic and reverse transformations, respectively. The characteristic temperatures of martensitic transformation, including the martensite start and finish (Ms, Mf) and austenite start and finish temperatures (As, Af) are determined to be 279 K, 265 K, 279 K and 301 K, respectively. With 1 at% Fe substitution, the transformation temperature decreased about 35 K. With 2 at% and 3 at% substitution, the transformation temperatures increased slightly compared to Mn49Fe1Ni41In9 owing to the formation of secondary phase. In order to clarify the magnetic states, the field cooling and field heating M(T) curves were measured under 100 Oe, as shown in Fig. 4. Except Fe3 ribbon, the Fe0, Fe1 and Fe2 ribbons show a similar tendency. A sharp increase of magnetization is firstly observed upon cooling, and upon further decreasing temperature, a sudden drop of magnetization occurs, corresponding to the martensitic transformation. Whereas upon heating, the reverse martensitic transformation from weak-magnetic martensite to ferromagnetic austenite happens. It should be noted that for Fe0, Fe1 and Fe2, the magnetization intensities of austenite upon heating are lower than these upon cooling, which can be attributed to the

overlap between martensitic and magnetic transitions. In case of Fe3 ribbon, one can deduce that the martensitic transformation happens directly between paramagnetic austenite and weak-magnetic martensite according to the weaker magnetization intensities. Generally the change of martensitic transformation temperatures can be explained from two aspects: electron concentration (e/a) and unit-cell volume. Theoretically speaking, it is reasonable that Fe substitution for Mn would cause an increase of e/a. Here, it is assumed that the valence electrons per atom are 7 (3d54s2) for Mn and 8 (3d64s2) for Fe, respectively. Meanwhile, the volume of unit-cell would shrink with the replacement of a larger Mn atom by a smaller Fe atom. According to the general principle, both factors would give rise to the austenite metastable and therefore lead to a higher transformation temperature [5,20]. However, the Fe1 results obtained in the present study are on the contrary. We ascribed this to a striking refinement of grain size. That is, the grain refinement plays a dominant role for the change of martensitic transformation in Fe1 sample. The change in Fe2 and Fe3 samples mainly related to the formation of the secondary phase, which changed the matrix composition, as shown in Table 1. Fig. 5a and b shows the isothermal magnetization curves M–H of the Fe1 annealed ribbons. The M–H curves were measured at a temperature interval of 5 K. The sample was firstly cooled down to the lowest measurable temperature with zero-field, and then heated up to 320 K under the magnetic field change of 30 kOe. The stripped area marked in Fig. 5a stands for the hysteretic losses which was caused by the first-order field-induced metamagnetic martensitic transformation. One can see that the sample occurs the martensitic transformation within 230 K and 255 K, and

H. Li et al. / Journal of Magnetism and Magnetic Materials 417 (2016) 267–271

magnetic transition in austenite from 260 K to 320 K (Fig. 5b). In the present study, the magnetic entropy changes (ΔSM) shown in Fig. 5c were calculated using the classical Maxwell relation [21]. The corresponding hysteresis loss is shown in Fig. 5d. One can see that the maximum values of ΔSM are about 9.3 J kg
1 K
1 and
2.2 J kg
1 K
1 for the martensitic and magnetic transitions, respectively; and the corresponding refrigeration capacity of Mn49Fe1Ni41In9 annealed ribbons reaches 69.9 J kg
1 and 83.8 J kg
1 at a magnetic field change of 30 kOe through integrating the magnetic entropy change [22]. After subtracting the average hysteresis losses (16.6 J kg
1) resulted from the martensitic transformation, the total effective refrigeration capacity reaches 137.1 J kg
1, lower than the Fe0 (184.2 J kg
1, 30 kOe) [23] and comparable with Mn50Ni40In10 melt-spun ribbon (148 J kg
1, 30 kOe) [24].

4. Conclusions In summary, the magnetostructural transitions and magnetocaloric property of Mn-rich Mn50
xFexNi41In9 (at%, x ¼0, 1, 2, 3) ribbons were studied, and the following conclusions can be obtained. (1) All ribbons are L21-type cubic austenite at room temperature. Fe substitution for Mn resulted in striking grain refinement, and formation of a secondary phase when Fe content was increased up to 2 at%. (2) With 1 at% Mn replacement by Fe, both martensitic and magnetic transition temperatures were lowered down about 33 K. Further increasing Fe to 2 at%, both transitions increased slightly and overlapped largely. When Fe content was increase to 3 at%, the magnetic transition in austenite disappeared and the martensitic transformation occurred between paramagnetic austenite and weak-magnetic martensite. The maximum effective refrigeration capacity of Fe1 ribbon reached 137.1 J kg
1 under a magnetic field change of 30 kOe.

Acknowledgments The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (51474144, 51201096).

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