Probing martensitic transformation, kinetics, elastic and magnetic properties of Ni2-xMn1.5In0.5Cox alloys

Abstract

The martensitic transformation, kinetics, elastic and magnetic properties of the Ni2-xMn1.5In0.5Cox (x = 0-0.33) ferromagnetic shape memory alloys were investigated experimentally and theoretically by first-principles calculations. First-principles calculations show that Co directly occupies the site of Ni sublattice, and Co atoms prefer to distribute evenly in the structure. The optimized lattice constants are consistent with the experimental results. The martensitic transformation paths are as follows: PA ↔ FA ↔ 6 MFIM ↔ NMFIM when 0 ≤ x < 0.25; PA ↔ FA ↔ 6 MFM ↔ NMFIM with 0.25 ≤ x < 0.3 and PA ↔ FA ↔ NMFM with 0.3 ≤ x ≤ 0.33 for Ni2-xMn1.5In0.5Cox (x = 0-0.33) alloys. The fundamental reasons for the decrease of TM with increasing Co content are explained from the aspects of first-principles calculations and martensitic transformation kinetics. The component interval of the magnetostructural coupling is determined as 0 ≤ x ≤ 0.25 by first-principles calculations. Furthermore, the origin of the demagnetization effect during martensitic transformation is attributed to the shortening of the nearest neighboring distances for Ni-Ni (Co) and Mn-Mn. Combining the theoretical calculations with experimental results, it is verified that the TM of the Co6 alloy is near room temperature and its magnetization difference ΔM is 94.6 emu/g. Therefore, magnetic materials with high performance can be obtained, which may be useful for new magnetic applications.