Abstract
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 1173K for 60min, leading to significant grain growth and formation of a secondary Fe-rich γ phase. The annealed microwire exhibits larger magnetization difference (ΔM) 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 299K, followed by a martensitic transformation (MT) from a ferromagnetic austenite to a weak-magnetic martensite at 208K upon cooling. Under a magnetic field of 50kOe, the annealed microwires show a maximum magnetic entropy change ΔSm of 6.9J/kg·K and an effective refrigeration capacity RCeff of 78.0J/kg over a broad working temperature span ΔTFWHM of 20K around the MT. In addition, magnetic transition of the austenite gives rise to ΔSm −3.7J/kg·K and RCmag 232.5J/kg with ΔTFWHM of 85K under 50kOe.
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