Magnetization Dynamics of an Individual Single-Crystalline Fe-Filled Carbon Nanotube

The magnetization dynamics of individual Fe-filled multiwall carbon-nanotubes (FeCNT), grown by chemical vapor deposition, are investigated by microresonator ferromagnetic resonance (FMR) and Brillouin light scattering (BLS) microscopy and corroborated by micromagnetic simulations. Up to now, only static magnetometry measurements are available. They suggest that the FeCNTs consist of a single-crystalline Fe nanowire throughout the length. The number and structure of the FMR lines and the abrupt decay of the spin-wave transport seen in BLS indicate, however that the Fe filling is not a single straight piece along the length. Therefore a stepwise cutting procedure was applied in order to investigate the evolution of the ferromagnetic resonance lines as a function of the nanowire length. Our results show that the FeCNT is indeed not homogeneous along the full length but is built from 300-400 nm long single-crystalline segments. These segments consist of magnetically high quality Fe nanowires with almost the bulk values of Fe and with a similar small damping in relation to thin films, promoting the FeCNTs as appealing candidates for spin-wave transport in magnonic applications.