Magnetic properties and magnetocaloric effect in Ni–Mn–Sn alloys

doi:10.1016/j.jmmm.2014.08.061

Journal of Magnetism and Magnetic Materials

Volume 374, 15 January 2015, Pages 372-375

https://doi.org/10.1016/j.jmmm.2014.08.061 Get rights and content

Highlights

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Crystalline phases and magnetic properties in Ni₅₀Mn_50−xSn_x alloys (x=0–40).
•
Simultaneous transitions of structural and magnetic phases.
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Coexistence of positive and negative giant magnetocaloric effect in Heusler alloys.
•
Tuning giant magnetocaloric effect in room temperature region.

Abstract

Magnetic and magnetocaloric properties in Ni₅₀Mn_50−xSn_x alloys with wide range of the Sn-concentration (x=0–40) were investigated. The alloys were prepared by arc-melting and subsequently annealing at 850 °C for 4 h. The X-ray diffraction analyses manifest the formation of the crystalline phases (Ni₂MnSn, NiMn, Ni₃Sn₂, Mn₃Sn, and MnSn₂) in the alloys with various compositions and fabrication conditions. With increasing x, the saturation magnetization first increases from near zero (at x=10) to above 40 emu/g (at x=20) and then decreases to below 10 emu/g (at x=40) for both the as-melted and annealed cases. The martensitic–austenitic transition was observed in the alloys with a narrow range of x (13–15). The magnetic transitions in the alloy can be controlled by changing Sn-concentration. The alloy reveals both the positive and negative entropy changes with quite large magnitude (∆S_m>1 J/kg K with ∆H=12 kOe) with appropriate compositions and annealing conditions.

Introduction

Ni–Mn–Sn Heusler alloys have been attracting a lot of scientists by virtue of their giant magnetocaloric effect (GMCE) and application potential for magnetic refrigeration at room temperature [1], [2], [3], [4], [5], [6], [7], [8]. Both the positive (inverse) and negative (normal) GMCEs could be observed in these alloys by changing composition and fabrication conditions. The positive GMCE is believed to relate to a transformation between martensite and austenite phases. The coexistence of ferromagnetic (FM) and antiferromagnetic (AFM) orders was also observed in the alloys. Adding other elements such as Cu, Co, Al etc. [9], [10], [11], [12], [13], [14], [15], [16] and changing fabrication conditions [17], [18], [19], [20] are common ways to understand the magnetic mechanism and achieve the desired GMCEs for the alloys. The magnetic orders and the magnetocaloric effects in Ni–Mn–Si alloys were found to be very sensitive to their composition and fabrication conditions. Therefore, systematic studies on these alloys are still needed. The compositions of the alloys in most of published papers are rather limited. In this work, we investigated magnetic and magnetocaloric properties in the Ni₅₀Mn_50−xSn_x alloys with a wide range of the Sn-concentration (x=0–40) to make more clear the variation trend versus composition of magnetic and magnetocaloric properties of the material.

Section snippets

Experiment

Alloys with nominal compositions of Ni₅₀Mn_50−xSn_x (x=0, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30 and 40) were prepared from pure metals (4 N) of Ni, Mn and Sn by using an arc-melting method. A part of each sample was annealed at 850 °C for 4 h in a vacuum of 10⁻⁵ Torr and then quenched to room temperature by Ar-flow. The quenching rate was about 100 °C per minute. The structure of the samples was examined by means of powder X-ray diffraction (XRD) on a Siemens D5000 X-Ray diffractometer with

Results and discussion

Fig. 1 shows room temperature powder-XRD patterns of the as-melted and annealed Ni_0.5Mn_0.5−xSn_x alloys in the range of 30–65°. Crystalline phases of Ni₂MnSn, NiMn, Ni₃Sn₂, Mn₃Sn and MnSn₂ are identified from these patterns. The number and relative intensity of diffraction peaks, i.e. crystalline structure, are varied with varying the Sn-concentration (x) for both the as-melted and annealed cases. The Mn₃Sn phase is a main phase with low values of x, while the Ni₃Sn₂ phase is dominated at high

Conclusion

The Ni₅₀Mn_50−xSn_x alloys with a wide range of Sn-concentration (x=0–40) were fabricated by arc-melting and subsequently annealing. The influence of composition and fabrication conditions on structure, magnetic properties and magnetocaloric effect was investigated systematically. The formation of crystalline phases of Ni₂MnSn, NiMn, Ni₃Sn₂, Mn₃Sn, MnSn₂ was observed. The coexistence of various magnetic orders was revealed by both the magnetic hysteresis and thermomagnetization measurements. The

Acknowledgment

This work was supported by the National Foundation for Science and Technology Development (NAFOSTED) of Vietnam under Grant numbers of 103.02–2011.23 and 103.02–2010.28 and the Converging Research Center Program funded by the Ministry of Science, ICT and Future Planning, Korea (2014048835). A part of the work was done in the Key Laboratory for Electronic Materials and Devices, and Laboratory of Magnetism and Superconductivity, Institute of Materials Science, VAST, Vietnam.

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Citation Excerpt :
Fig. 2(a) shows the temperature dependence of the magnetization M of Ni2Mn1.48Sn0.52 measured in an applied field of 1 kOe after a zero-field cooling (ZFC) and a field-cooling (FC) process. The overall behavior of the temperature variation of M, M(T), is consistent with previous results [8,10,15,22,23]. In the ZFC process, the sample was first cooled to 1.8 K from room temperature under zero magnetic field; at this temperature the magnetic field of 1 kOe was applied and the magnetization was measured at this constant field with increasing temperature up to 400 K. Then, without removing the external field, the magnetization was measured with decreasing temperature, i.e., the FC process.
The results of experimental investigations of the crystal structure, magnetization and Mössbauer spectroscopy of the Heusler alloy Ni₂Mn_1.48Sn_0.52 are reported. The alloy undergoes the martensitic transition from the L2₁-type cubic structure into 4O-type orthorhombic structure with a thermal hysteresis of ∼23 K. The martensitic transition temperature T_M is 309 K. The Curie temperature in the austenitic phase T_C^A of Ni₂Mn_1.48Sn_0.52 is found to be 316 K. The Mössbauer spectra from the high temperature paramagnetic state at 330 K and the martensitic state at 283 K were both singlets, showing a typical paramagnetic feature in the narrow temperature range just below T_M. With further decrease of temperature, the ferromagnetic ordered state also appears in the martensitic phase. The Curie temperature in the martensitic phase T_C^M is found to be 256 K. Furthermore, the exchange bias effect is observed in the temperature range 1.8 K ≤ T ≤ T_B (∼130 K), where T_B is an exchange bias blocking temperature. The values of a hyperfine magnetic field at Sn nuclei of Ni₂Mn_1.48Sn_0.52 fall significantly below the molecular magnetic field approximation for S = 1. On the basis of the experimental results, the electronic and magnetic properties of Ni₂Mn_1.48Sn_0.52 are discussed.
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Magnetic properties and magnetocaloric effect in Ni–Mn–Sn alloys

Highlights

Abstract

Introduction

Section snippets

Experiment

Results and discussion

Conclusion

Acknowledgment

Scr. Mater.

J. Alloys Compd.

J. Mater. Sci. Technol.

J. Magn. Magn. Mater.

J. Alloys Compd.

J. Alloys Compd.

Nat. Mater.

Phys. Rev. B

Phys. Rev. B

Phys. Rev. B