A strategy of optimizing magnetism and hysteresis simultaneously in Ni–Mn-based metamagnetic shape memory alloys

Abstract

Due to the existence of the magnetic-field-induced reverse martensitic transformation, the Ni–Mn–Z alloys where Z is the p-block element of In, Sn or Sb exhibit several state-of-the-art magnetoresponsive properties. From the perspective of practical application, a major challenge of this compound is to strengthen the ferromagnetism and reduce the transitional hysteresis ΔTHys simultaneously. In this work, we report an alloying strategy to this issue, i.e., the partial substitutions of Co and Cu for Ni and the p-block element, respectively, by a combined study of experiment and ab-initio calculation in the Ni45Co5Mn36In14–xCux (x = 0–1.5) alloys. Results show that the Cu replacement for the p-block element (In) can effectively reduce ΔTHys owing to the improved geometrical compatibility between austenite and martensite. Moreover, the adopted alloying strategy of Cu hardly weakens the strong ferromagnetism of Ni(Co)–Mn–In, since the magnetism exhibits a weak dependence on the p-block element compared with Mn and Ni. The maximum reversible magnetic entropy change ΔSMMax of the Ni45Co5Mn36In13.3Cu0.7 directionally solidified sample at a magnetic field of 5 T is 13.8 J·kg−1·K−1. The refrigeration capacity RC and effective refrigeration capacity RCeff equal to 473.7 J·kg−1 and 270.2 J·kg−1, respectively. Both values belong to the highest one in the Ni–Mn-based alloys. Additionally, the working temperature window of the magnetocaloric effect is as wide as ~40 K. This work is expected to promote the design of advanced metamagnetic shape memory alloys.