Electron holography of ferromagnetic nanowires

Off-axis electron holography has been applied in order to investigate quantitatively the remanent magnetization state of single ferromagnetic Co₉₃Cu₇ and Ni nanowires, respectively. The magnetization reversal of an individual Co₉₃Cu₇ nanowire has been followed by observing a series of remanent states, obtained ex-situ by applying different external magnetic field sweeps parallel to the nanowire axis. The relation between mis-oriented crystal grains and non-uniform magnetization states has been studied by the combination of electron holography and conventional transmission electron microscopy. Nickel nanowires have been heated in-situ to temperatures above the Curie temperature and cooled down again. The magnetic state during the heating experiment was followed by a series of electron holograms. A single Ni nanowire was examined in detail. It was observed to be uniformly magnetized before the heating cycle. The ferromagnetic state spontaneously formed upon cooling from above the Curie temperature, exhibited a magnetic state with two antiparallel magnetic domains.