Influence of Annealing on Martensitic Transformation and Magnetic Entropy Change in Ni37.7Co12.7Mn40.8Sn8.8 Magnetic Shape Memory Alloy Ribbon

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The microstructure, martensitic transformation and magnetic properties of Ni37.7Co12.7Mn40.8Sn8.8 high temperature magnetic shape memory ribbon subjected to different annealing temperature were investigated. Annealing up to 1073 K slightly raised the transformation temperatures and the transformation interval, while annealing at 1173 K considerably decreased the transformation temperature and strongly widened the transformation interval due to the formation of a second phase. The as-spun and annealed ribbon at 973 K exhibited giant magnetic entropy changes of around 15 J/kg K under 15 kOe magnetic field above 400 K. Further increasing annealing temperature caused a decrease of the magnetic entropy change. To achieve a large magnetocaloric effect while keeping an elevated transformation temperature, an appropriate annealing parameter should be carefully considered.