Martensitic transformation behaviors of all-<italic>d</italic>-metal Heusler Mn<sub>50</sub>Ni<sub>50−</sub><sub><italic>x</italic></sub><sub>−</sub><sub><italic>y</italic></sub>Fe<sub><italic>x</italic></sub>Ti<sub><italic>y</italic></sub> alloys

Abstract

<p indent="0mm">A series of Mn₅₀Ni₅₀₋_{<italic>x</italic>}₋_{<italic>y</italic>}Fe_{<italic>x</italic>}Ti_{<italic>y</italic>} all-<italic>d</italic>-metal Heusler alloys ribbon samples were fabricated, and the effect of dual element Fe- and Ti-doping on the Martensitic transformation (MT) has been studied systemically. For the alloys with same Fe content, the increase of Ti content would stabilize the B2 parent phase and then reduce the MT temperature. In addition, the MT temperature also decreases with the increase of Fe in the Ti8 alloys, suggesting that the substitution of Fe for Ni atoms could stabilize the B2 parent phase. Meanwhile, part of 5M martensite transforms into L1₀ martensite with increasing Fe content higher than 2 in the Ti8 alloys, causing the decrease of thermal hysteresis. This result reveals that the driving force of the MT between L10 martensite and parent phase is lower than that between 5M martensite and parent phase. On the contrary, the MT temperature increases slightly with increasing Fe content for the <italic>y</italic>&gt;8 alloys, which is due to the possible disordered occupation of Fe atoms. The introduction of Fe has a ferromagnetic activation to establish the weak ferromagnetic ordering and increase the Curie temperature. A large change of resistivity is observed during the MT transition, which is due to the electron scattering effect of the distinct lattice distortion in martensite. Furthermore, proper annealing treatment could eliminate the effect of disordered occupation of Fe atoms and stabilize the B2 parent phase, resulting in the reduction of MT temperature for all Ti-doped samples. The present work suggests that a series of MT transitions could be obtained by dual element Fe- and Ti-doping, and it provides the candidates for future research on magnetocaloric and elastocaloric materials.