Temperature dependence of reversible field-induced strain and magnetization changes in Ni-Mn-Ga single crystals

The alloys close to stoichiometric Ni₂MnGa with Mn excess are prepared by a directional solidification method. Three single crystal alloys having 5M martensitic structure and exhibiting the magnetic shape memory effect (MSME) are studied at room temperature. The martensite-to-austenite transformation temperature varies from 314 K to 343 K. The MSME of the crystals or structural reorientation is then evaluated by simultaneous measurements of the magnetization and strain in slowly changing magnetic field at different temperatures and at a constant compressive stress. The magnetization changes observed during the MSME reflect the structural reorientation or martensitic variant redistribution of the crystals.