Observation of magnetic ripple and nanowidth domains in a layered ferromagnet

We investigated ferromagnetic domain structures on nanometer to micrometer scale for single crystals of a layered ferromagnet, La(2-2x)Sr(1+2x)Mn2O7 (0.32 < or = x < or = 0.40), as functions of x and temperature by means of Lorentz electron microscopy. We have succeeded in observing the evolution of magnetic ripple structure, dynamically, related to a spin reorientation transition where the magnetization direction switches between parallel and perpendicular to the layers. Our high-resolution magnetic domain imaging revealed that the ripple state is characterized by the evolution of magnetic nanowidth domains.