Imaging magnetic flux-closure domains and domain walls in electroless-deposited CoNiB nanotubes

Abstract

Magnetic nanotubes are predicted to host mag- netic domains and domain walls with a topology different from that for at elements[1, 2]. Com- pared to cylindrical nanowires, reports on mag- netism of isolated metallic nanotubes are scarce and so far no material has given rise to well- defined magnetic domains. Here we report the fabrication of high-aspect ratio CoNiB nanotubes by electroless plating inside a porous template. Through imaging, we evidenced multiple mag- netic domains and domain walls in these nano- tubes. Surprisingly, magnetization in the do- mains is orthoradial (azimuthal, vortex-like), a situation not anticipated by theory for long nano- tubes. The material is therefore technologically appealing for a dense 3D magnetic device such as the racetrack memory[3] (based on shifting mag- netic walls), as ux-closure domains should efi- ciently prevent cross-talk related to internal di- polar fields. Further, we show tuning of a growth- induced anisotropy and thus of the magnetic state of the tube by annealing