Effect of Fe substitution on the phase stability and magnetic properties of Mn-rich Ni–Mn–Ga ferromagnetic shape memory alloys

The influence of Fe additions on the martensitic transformation and magnetic properties of Mn-rich Ni–Mn–Ga alloys was investigated by substituting either 1 at% Fe for each atomic species or by substituting Ni with varying amounts of Fe. The magnetic structure of the alloys was studied using 57Fe Mössbauer spectroscopy. Mössbauer spectra revealed typical paramagnetic features in Mn-rich Ni–Mn–Ga–Fe alloys owing to the preferential site occupancy of Fe atoms at Ni sites. The evolution of the magnetic properties and phase stability has been correlated with the chemical and atomic ordering in these alloys.

Research highlights
► Fe atoms preferentially occupy Ni sites over vacant Ga sites in Mn-rich Ni–Mn–Ga alloys.
► Such chemical order suppresses the magnetic hyperfine field of Fe atoms due to the interaction with the surrounding Ga and Mn atoms.
► Accordingly, the Curie temperature and saturation magnetization decrease.
► This short range ordering also influences the phase stability.