Phase diagram of Fe-doped Ni-Mn-Ga ferromagnetic shape-memory alloys

TL;DR

This study investigates how Fe doping affects the structural and magnetic phase transitions in Ni-Mn-Ga ferromagnetic shape-memory alloys, revealing that Fe alters transformation temperatures and phase stability governed by electron concentration.

Contribution

It provides new insights into the role of Fe substitution in tuning phase transitions and stability in Ni-Mn-Ga alloys, highlighting differences from ternary systems.

Findings

Fe addition shifts magnetic transition temperatures higher.

Fe substitution lowers martensitic and premartensitic transformation temperatures.

Phase stability correlates with electron per atom concentration, but with different scaling than in ternary systems.

Abstract

We have studied the effect of Fe addition on the structural and magnetic transitions in the magnetic shape memory alloy Ni-Mn-Ga by substituting systematically each atomic species by Fe. Calorimetric and AC susceptibility measurements have been carried out in order to study the magnetic and structural transformation properties. We find that the addition of Fe modifies the structural and magnetic transformation temperatures. Magnetic transition temperatures are displaced to higher values when Fe is substituted into Ni-Mn-Ga, while martensitic and premartensitic transformation temperatures shift to lower values. Moreover, it has been found that the electron per atom concentration essentially governs the phase stability in the quaternary system. However, the observed scaling of transition temperatures with $e/a$ differs from that reported in the related ternary system Ni-Mn-Ga.