The martensitic structure and magnetic domain structure of Fe1-xNix system (0.30≤x≤0.32) were investigated by means of non-contact atomic force microscopy and magnetic force microscopy. The martensite has a stripe domain structure whose period decreases with the Ni composition. The magnetic anisotropy constant in the martensite was estimated to be 2×104 J/m3, whose magnitude is the same order as that of Fe or Ni metal.
