Long-range ferromagnetism and magnetocaloric effects in rapidly quenched Ni50−xCoxMn50−yAly ribbons

Ni50−xCoxMn50−yAly (x = 7 and 9; y = 17, 18 and 19) alloy ribbons were prepared by melt-spinning with a tangential velocity of copper wheel of 40 m s−1. X-ray diffraction patterns reveal multi-crystalline phase behavior in the fabricated ribbons. The shape of thermomagnetization curves clearly depends on Co and Al concentrations. The Curie temperatures (TC) of the alloy ribbons strongly increase with increasing the Co concentration and slightly decrease with increasing the Al concentration. The martensitic-austenitic phase transition in the alloy ribbons can be manipulated by tuning Co and Al concentrations. The maximum magnetic entropy change |ΔSm|max of about 0.75 J kg−1 K−1 for a field change of 12 kOe at TC ≈ 364 K was achieved for the Ni43Co7Mn32Al18 ribbon. Critical analysis using the Arrott-Noaks and Kouvel-Fisher methods demonstrates the existence of a long-range ferromagnetic order in this ribbon.