Investigation of route to martensitic transition in Ni-Mn-In shape memory alloys

摘要

The temperature dependent x-ray diffraction and magnetization measurements on the off stoichiometric Ni_2Mn_(1+x)In_(1-x) alloys have confirmed the appearance of martensite at critical Mn concentration of x=0.35. The high temperature phase of all the alloys have cubic L21 structure with the lattice constant steadily decreasing with increase in Mn concentration. Martensitic transition begins to appear in Ni_2Mn_(1.35)In_(0.65) at about 197K and the structure seems to adopt two phases including the major cubic along with the modulated monoclinic phase. This has been explained on the basis of number of Mn-Ni-Mn hybridized pairs that are responsible for inducing martensitic transition.