Filled-carbon nanotubes: 1 D nanomagnets possessing uniaxial magnetization axis and reversal magnetization switching

The present study aims to control the direction of magnetization in Fe₃C, Co and Ni nanorods filled inside carbon nanotube (CNT). This control has been achieved during growth by modifying thermal chemical vapor deposition (CVD) system. As-grown in situ filled-CNTs were found to exhibit permanent magnetization. These CNTs have been characterized by using scanning electron microscopy (SEM), X-ray diffraction, Raman spectroscopy and transmission electron microscopy (TEM). Afterwards, direction of magnetization in Fe₃C, Co or Ni nanorod filled inside CNT has been further probed by using magnetic force microscopy (MFM). MFM measurements reveal that nanorod exhibits single domain behavior and direction of magnetization, instead of being controlled either by shape or magneto crystalline anisotropy, has been found to be influenced by magnetic field gradient, produced in modified thermal CVD system. Direction of magnetization has been found either along tube axis in vertical grown CNTs or in radial direction i.e. perpendicular to the tube axis in randomly grown CNTs. Besides investigated structural and magnetic properties, plausible growth model of in situ filling as well as mechanism to understand unique magnetization behavior has been proposed.