Controlling Magnetic-Field-Induced Shape Memory Response in Polycrystalline Off-Stoichiometry Fe _47-x Mn _{24 <b>+</b> x} Ga ₂₉ Microwires

The ferromagnetic shape memory (FSM) behavior of glass-coated Fe_{47‑<i>x</i>} Mn_24+<i>x</i> Ga₂₉ (x = 0-8 at. %) microwires has been investigated through temperature-dependent magnetization and <i>ac</i> magnetic susceptibility measurements. Magnetization measurements as a function of temperature reveal an abrupt increase and decrease in magnetization upon cooling and heating, respectively, indicating characteristic thermal hysteresis (<i>ΔT</i> _<i>hys</i> ) behavior typically associated with a magnetic-field-induced "diffusionless" martensitic transformation. The magnitude and width of <i>ΔT</i> _<i>hys</i> are strongly correlated with the Fe/Mn atomic ratio; notably, the Fe₄₅Mn₂₆Ga₂₉ microwire exhibits a very large <i>ΔT</i> _<i>hys</i> width of 98 K, which is attributed to local deformation involving the motion of Fe and Mn atoms. Furthermore, an antiferromagnetic transition is observed in a low-temperature region, shifting from 22 to 41 K depending on composition. This shift is attributed to variations in local exchange interactions arising from unequal occupation of Fe and Mn 3<i>d</i> orbitals. These findings highlight a compositionally driven design strategy that enables precise tuning of FSM behavior, making Fe-Mn-Ga microwires promising candidates for use in tunable magnetic actuation and sensing technologies.