Magnetization Dynamics of an Individual Single‐Crystalline Fe‐Filled Carbon Nanotube (original) (raw)

motivated by a broad range of applications for magnetoresistive devices, optical meta-materials, cell-DNA separators, drug delivery vectors, [7,8] and wave based information transport. [9] Both, the high stability of their magnetic equilibrium state against external perturbations, as well as their robust domain walls, which propagate with velocities faster than the spin wave phase velocity, promote them as appealing candidates for racetrack memory devices and for information transport and processing using spin waves in magnonic applications. Various bottom-up synthesis routes for the preparation of magnetic nanowires exist; including for example electrodeposition based on porous membrane templates [1] and pyrolysis of metal-organic precursors. In particular the pyrolysis of ferrocene allows for the formation of iron-filled carbon nanotubes (FeCNT), i.e., multiwall carbon nanotubes, which contain single-phase single-crystalline iron nanowires, [10-14] where the body-centered cubic iron phase dominates. Furthermore, iron nanowires with various crystal orientations can be found with no prevalent orientation. [13] The diameters of the carbon nanotubes and the embedded iron nanowires are in the range of 30-100 and 10-40 nm, respectively. [13] The magnetization dynamics of individual Fe-filled multiwall carbonnanotubes (FeCNT), grown by chemical vapor deposition, are investigated by microresonator ferromagnetic resonance (FMR) and Brillouin light scattering (BLS) microscopy and corroborated by micromagnetic simulations. Currently, 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 is applied in order to investigate the evolution of the ferromagnetic resonance lines as a function of the nanowire length. The results show that the FeCNT is indeed not homogeneous along the full length but is built from 300 to 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 FeCNTs as appealing candidates for spin-wave transport in magnonic applications.