Electron holography studies on magnetic domains in ferromagnetic shape memory alloys

Magnetization distribution in ferromagnetic shape memory alloys has been studied by electron holography and Lorentz microscopy. The observations have revealed that a martensite variant, which is a crystallographic domain in ferromagnetic shape memory alloys, is divided into several 180° magnetic domains in a Ni ₂MnGa alloy. The magnetization vectors of the 180° domains are basically oriented along the easy magnetization axis due to the high magnetocrystalline anisotropy of the martensite. Close relations between the magnetic domains and the antiphase domains in the parent phase of a Ni ₅₁Fe ₂₂Ga ₂₇ alloy were also revealed by in situ observations with electron holography.