Growth and nanoscale magnetic properties of ferromagnetic nanowire encapsulated inside carbon nanotubes

We synthesize ferromagnetic Co nanowire, and Co/Pd multisegment nanowires encapsulated inside multi-walled carbon nanotubes CNTs (MWCNTs) by plasma-enhanced chemical vapor deposition (PECVD). High-resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED) patterns and energy dispersive X-ray spectroscopy (EDS) were used to characterize the microstructures and elemental analyses of the nanowires. Quantitative magnetization measurements of Co nanowires encapsulated inside MWCNTs were experimentally established by TEM off-axis electron holography at room temperature. The MWCNTs grew up to 100-110 nm in diameter and 1.5-1.7 μm in length. The typical bright-field TEM images revealed both Co nanowire and Co/Pd multisegment nanowires encapsulated inside vertically aligned MWCNTs on the same substrate. The composition of metal encapsulated inside MWCNTs were characterized by EDS. Experimental results revealed that the Co nanowire encapsulated inside MWCNT was always presented as the face-centered-cubic (fcc) Co structure. The component of magnetic induction was then measured to be 1.2 ± 0.1 T based on TEM off-axis electron holography results, which is lower than the expected saturation magnetization of fcc Co bulk of 1.7 T. The partial oxidation of the ferromagnetic metal during the process and the magnetization direction may play an important role in the determination of the quality of the remanent states. The ferromagnetic metal nanowires encapsulated inside CNTs demonstrate very high potential in providing the required magnetic properties, low dimensionality, and small volume for future nanoscale devices.