Magnetic anisotropy and the shape memory phase transition in Ni52Mn26Ga22

Torque measurements of magnetocrystalline anisotropy energies, made on (1 0 0) and (1 1 0) oriented planar disc samples of the shape memory alloy Ni52Mn26Ga22 as a function of temperature and applied directional field cooling are reported. The results confirm small values for the anisotropy constants in the austenite phase (Phys. Rev. B 65 (2002) 134422). Optical observations reveal the influence of applied stresses and magnetic fields on the mobility of the phase transition and twin boundaries. Lorentz mode TEM observations from a (1 1 0) planar foil reveal the interactions between magnetic and anti-phase domain boundaries as the specimen is thermally cycled through the transition temperature.