Electron holography of ferromagnetic nanowires

Off-axis electron holography has been applied in order to investigate quant itatively 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 state s, obtained ex-situ by applying different external magnetic field sweeps pa rallel to the nanowire axis. The relation between mis-oriented crystal grai ns 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 t emperature and cooled down again. The magnetic state during the heating exp eriment was followed by a series of electron holograms. A single Ni nanowir e was examined in detail. It was observed to be uniformly magnetized before the heating cycle. The ferromagnetic state spontaneously formed upon cooli ng from above the Curie temperature, exhibited a magnetic state with two an tiparallel magnetic domains. (C)1999 Acta Metallurgica Inc.