TEM studies of crystallographic and magnetic microstructures in Ni-based ferromagnetic shape memory alloys

Magnetic domains in the L21 phase of Ni2Mn(Al,Ga) – a series of ferromagnetic Heusler alloys, which can undergo martensitic transformations in cases of off-stoichiometric compositions – have been studied by the defocus mode of Lorentz microscopy. One-to-one correspondence was observed between the magnetic domain walls and antiphase boundaries (APBs). The result indicates that the APBs are strong pinning sites for the motion of magnetic domain walls. Effects of applying a weak magnetic field to the magnetic domains were studied by in situ observations of Lorentz microscopy.