Magnetic and magnetomechanical properties of Ni₂MnGa

Magnetocrystalline anisotropy and magnetostrictive properties are reported for the austenitic and martensitic phases of ferromagnetic shape memory Heusler alloy Ni₂MnGa. In the low-temperature martensitic phase, the phenomenon of field-induced variant rearrangement provides a mechanism which can produce large strains, while at the same time causing anomalous effects in the apparent anisotropy. These anomalies and their effects on measured M-H and torque curves are clarified. Magnetomechanical experiments were performed in the martensitic phase to characterize the work output of a suitably oriented specimen at various stresses, and with proper stress biasing of the initial microstructure produced the largest magnetostrictive strains to date of 4.3%.