Effect of external magnetic field on transformation strain and microstructure of NiMnGa magnetic shape memory alloy

The effect of external magnetic field on martensitic transformation and transformation strain of Ni₅₂Mn_24.6Ga_23.4 (at%) single crystal were described, and the mechanism of enhancement of magnetic field on transformation strain was discussed. It was found that transformation strain is up to 0.3% without external field. With the increasing of magnetic field along the [001] direction transformation strain increases linearly. The maximum strain is 3.5% in 6.37×10⁵ A/m field. Upon cooling to M_f temperature in magnetic field, the oriented martensite forms and the martensite bands become broad, while the substructure of martensite twins keeps unchanged. It was shown that the orientation of martensite variants in magnetic field enhances the transformation strain.