Magnetocrystalline anisotropy constant and twinning stress in martensite phase of Ni–Mn–Ga

We have examined rearrangement of martensite variants driven by magnetic field for 10M martensite in Ni2MnGa and 2M martensite in Ni2.14Mn0.92Ga0.94 in a wide temperature range below each transformation temperature. The following results are obtained: (i) the twinning plane of the 10M martensite moves by the application of magnetic field, but that of 2M martensite does not at any temperature, (ii) in order to explain such difference, we have evaluated the maximum of the magnetic shear stress acting across the twinning plane ( τ mag m ), which is calculated by using the magnetocrystalline anisotropy constant (Ku) measured in this study, and the twinning shear stress (τreq) obtained by compressive test in this study for the 10M and 2M martensites, and have confirmed whether or not the relation of τ mag m > τ req is satisfied for 10M martensite and that of τ mag m < τ req is satisfied for 2M martensite. As a result, the above condition is satisfied at any temperatures for 10M and 2M martensites.