Characterization and properties of ferromagnetic shape memory alloys

Ni-Mn-Ga shape memory alloys are employed for applications in actuators and sensing devices. These alloys exhibit ferromagnetic shape memory effect with large reproducible strains in moderate magnetic fields. This work presents a study of the effect of composition and annealing treatment on the microstructure and magnetic properties in Mn-rich off-stoichiometric Ni-Mn-Ga alloys. Modulated martensitic structure (c/a <1) with hierarchical twins was found at room temperature in alloys with Mn >= 28 at.% whereas the alloy containing higher Ga (>22 at.%) revealed austenitic structure at room temperature. Ferromagnetic nature of the alloys was confirmed by the magnetization curves. It is demonstrated that a maximum of 400 parts per million strain was measured in the alloy with 7 M martensitic structure at room temperature. (C) 2011 Elsevier Inc. All rights reserved.