CommunicationThe effect of hydrostatic pressure on martensitic transition and magnetocaloric effect of Mn44.7Ni43.5Sn11.8 ribbons
Introduction
Currently, conventional refrigeration techniques are still based on the compression and expansion cycle of hazardous gases. The heavy use of these refrigerants inevitably has created and exacerbated many global environmental problems. In order to solve these problems, great efforts are being made to develop new solid-state refrigeration technologies that promise to be more efficient and environmentally friendly. The potential magnetic refrigeration materials such as the intermetallic Gd-Si-Ge [1], La(Fe13-xSix) [2], other rare-earth compounds [3], and Ni–Mn-based Heusler alloys [[2], [3], [4], [5], [6], [7]] have been extensively studied in recent years. These caloric materials show reversible thermal changes in response to changes of applied external fields, such as magnetocaloric, electrocaloric and mechanocaloric (elastocaloric or barocaloric) effects [8]. Due to the fact that hydrostaticc pressure is easier to achieve than strong magnetic field, the barocaloric materials have attracted considerable attention, such as Ni44.6Co5.5Mn35.5In14.4 [9], Ni-Mn-In(Ga) [10], Mn3NiN [11], AgI [12]. It is found that the barocaloric effect of these compounds is accompanied by the first-order structural phase transformation. At the same time hydrostatic pressure can act as a parameter to tune the martensitic transition temperature [13].
In non-stoichiometric Ni–Mn-based Heusler family, a magneto-structural coupled state leads to a temperature-induced martensitic transition, which is between two crystallographic phases with significantly different magnetic structures. However, the change of high magnetic entropy is always concentrated in a small temperature range under the state of magnetic structure coupling, which is obviously not conductive to practical applications. So far, some methods have prominent effect on tuning working temperature interval, such as applying external fields, introducing doping element or sample fragmentation [[14], [15], [16]].
Our previous research has been reported that a large magnetoresistance in highly textured Mn44.7Ni43.5Sn11.8 melt spun ribbons. Under a lower magnetic field of 10 kOe, a giant MR of 25% was obtained at 276 K [17], which was twice larger than that of polycrystalline alloys. The process is also accompanied by the first-order structural phase transformation. More interestingly, when the magnetic field decreases, the large negative MR of the ribbons from the field-induced transition remains constant at 273 K. The reason of above properties may be that magnetocrystalline anisotropy causes the domain walls displacement or twin variants reorientation to be frozen in a certain angle. As we know, in ferroic materials, such as ferroelastic, ferroelectric, and ferromagnetic materials, large caloric effects are expected in the region where the ferroic property spontaneously emerges [18]. These novel properties evoke us to further investigate hydrostatic pressure effect on the martensitic transformation(MT) and magnetocaloric effect(MCE) of Mn44.7Ni43.5Sn11.8 ribbons.
Section snippets
Experiment
The precursor ingot was prepared by induction melting with nominal composition of Mn44.7Ni43.5Sn11.8 under a high-purity argon atmosphere. Subsequently, the ingot was induction melted in a quartz tube and melt-spun at a wheel surface speed of 15.0 m s−1. At the same time, the copper wheel was cooled by circulating cooling water system. The resulting ribbons were annealed at 1073 K for 1 h and cooled in the vacuum furnace. Microstructure and chemical composition of the ribbons were determined by
Results and discussion
The typical SEM image on the cross section of the annealed Mn44.7Ni43.5Sn11.8 ribbon is shown in Fig. 1(a). The annealed fracture morphology shows that the longer axis of the columnar grain has a tendency to align perpendicularly to the free surface of the ribbon. The XRD patterns of melt-spun and annealed ribbons measured at room temperature are presented in Fig. 1(b). It is clear that both of the samples have the cubic L21-type structure and crystal directions [400] are preferentially
Conclusions
In summary, highly textured Heusler alloy Mn44.7Ni43.5Sn11.8 ribbons were prepared by melt spinning. The XRD patterns indicate that the crystal directions [400] are preferentially oriented perpendicular to the ribbon surface. The of 19.3 K GPa−1 is obtained in the vicinity of room temperature due to the strong correlation of magnetic exchange interaction with the Mn–Mn distances in our Mn-rich ribbons. As a result, a broadening of working temperature range for magnetic refrigeration was
Acknowledgments
This work is supported by the Scientific Activities of Selected Returned Overseas Professionals in Shanxi Province, Shanxi Scholarship Council of China (Grant No. 2016–092), The Natural Science Foundation of Shanxi Province (No. 201901D111267), The China Scholarship Council (No. 201808140031), China Postdoctoral Science Foundation funded project (Grant No. 2015M571285), The Emerging Industry Leadership Talent Program of Shanxi Province (No. 2019042), The Recruitment Program of Global Experts of
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