Wheel speed-dependent martensitic transformation and magnetocaloric effect in Ni–Co–Mn–Sn ferromagnetic shape memory alloy ribbons

Abstract This study investigated systematically the effects of different wheel speeds (10–30 m/s) on the structural, microstructural, magnetic, and magnetocaloric properties of as-spun and annealed Ni–Co–Mn–Sn ribbons. The ribbons comprised a mixture of austenite with L21 cubic structure and non-modulated martensite with L10 tetragonal structure. Both as-spun and annealed ribbons showed an increase in the reverse martensitic transformation temperature (Tm) and a decrease in the thermal hysteresis (Thys) when the wheel speed was increased from 10 m/s to 25 m/s. Unexpectedly, the Tm decreased and the Thys increased in the ribbons prepared with a wheel speed of 30 m/s. This finding may be attributed to the appearance of the γ-precipitated phase, which was lacking in the other samples. The martensitic transformation with a large magnetocaloric effect can be tailored in a wide temperature range, i.e., 30 K for the as-spun ribbons and 33 K for the annealed ribbons. The as-spun ribbons prepared at 15 m/s and annealed ribbons prepared at 25 m/s achieved large effective refrigerating capacities of 48.8 and 47.8 J/kg, respectively, in the field change of 0–1 T. These results provided significant insights into the effects of wheel speed on the magnetic and functional properties, as well as into the underlying mechanisms, of Ni–Mn-based multifunctional ribbon alloys.