Magnetocaloric effect of Ni-Fe-Mn-Sn microwires prepared by melt-extraction technique

摘要

Small-sized materials with large surface to volume ratio favor heat transfer during magnetic refrigeration cycling and thus may help enhancing the refrigeration efficiency. Here, high Fe content Ni44.9Fe4.3Mn38.3Sn12.5 polycrystalline microwires were prepared by a melt-extraction technique. The as-extracted microwires were annealed at 1173 K for 60 min, leading to significant grain growth and formation of a secondary Fe-rich gamma phase. The annealed microwire exhibits larger magnetization difference (Delta M) between the austenite and martensite phases and smaller thermal hysteresis compared to the as-extracted microwire. The annealed microwire possesses a magnetic transition to austenite at 299 K, followed by a martensitic transformation (MT) from a ferromagnetic austenite to a weak-magnetic martensite at 208 K upon cooling. Under a magnetic field of 50 kOe, the annealed microwires show amaximum magnetic entropy change Delta S-m of 6.9 J/kg center dot K and an effective refrigeration capacity RCeff of 78.0 J/kg over a broad working temperature span Delta T-FWHM of 20 K around the MT. In addition, magnetic transition of the austenite gives rise to Delta S-m-3.7 J/kg center dot K and RCmag 232.5 J/kg with Delta T-FWHM of 85 K under 50 kOe. (C) 2016 Elsevier Ltd. All rights reserved.