Ferromagnetic shape memory alloys: An overview

Ferromagnetic shape memory alloys (FSMA) have the unique capability to exhibit the thermoelastic martensitic transformation and rearrangement of martensitic variants by applying a magnetic filed, in addition to temperature and/or stress changes as in conventional shape memory alloys. The different mechanisms which can produce a shape change under a magnetic field and their relation with the magnetocrystalline anisotropy are discussed. The transformation sequences and martensitic structures are reviewed, particularly in Ni-Mn-Ga alloys as the best known system and representative of the martensites appearing in most FSMA systems. Some transformation features of more recently developed FSMA, namely Ni-Co-Al and Co-Ni-Ga, are also considered.