Enhanced magnetic refrigeration properties in Mn-rich Ni-Mn-Sn ribbons by optimal annealing.

The influence of annealing time on temperature range of martensitic phase transition (ΔT(A-M)), thermal hysteresis (ΔThys), magnetic hysteresis loss (ΔMhys), magnetic entropy change (ΔS(M)) and relative refrigeration capacity (RC) of the Mn-rich Ni43Mn46Sn11 melt spun ribbons have been systematically studied. By optimal annealing, an extremely large ΔS(M) of 43.2 J.kg(-1)K(-1) and a maximum RC of 221.0 J.kg(-1) could be obtained respectively in a field change of 5 T. Both ΔT(A-M) and ΔThys decreases after annealing, while ΔMhys and ΔS(M) first dramatically increase to a maximum then degenerates as increase of annealing time. A large effective cooling capacity (RC(eff)) of 115.4 J.kg(-1) was achieved in 60 min annealed ribbons, which increased 75% compared with that unannealed ribbons. The evolution of magnetic properties and magnetocaloric effect has been discussed and proved by atomic ordering degree, microstructure and composition analysis.