Controlled filling of Permalloy into one-end-opened carbon nanotubes

Controlled filling of Permalloy into a one-end-opened carbon nanotube (∼40 nm in inner diameter, 900 nm in length) array embedded in an anodic aluminium oxide film was achieved by an electrochemical route. Thanks to the electron-microscopically transparent carbon nanotubes, the time course of the electrochemical deposition process was readily visualized by means of transmission electron microscopy, revealing that Permalloy filling started from the pore bottom of the carbon nanotubes. This novel bottom-up filling opens a route to controllable filling of materials of interest into carbon nanotubes with one open end. The magnetic properties of the controlled filled carbon nanotubes in the array were studied. Interestingly, even in the case of isolated Permalloy nanoparticles inside the carbon nanotubes in the array, prominent magnetic anisotropy with an easy magnetization direction along the carbon nanotube axis was observed. In addition to the Permalloy-filled carbon nanotube array as embedded in the anodic aluminium oxide film, individual carbon nanotubes filled with Permalloy were also obtained.