Enhanced magnetism in Fe-filled carbon nanotubes produced by pyrolysis of ferrocene

Abstract

By optimization of the synthesis of ferromagnetic-filled carbon nanotube ensembles on Si substrates (catalytic decomposition of ferrocene) and following annealing at 645°C, marked hysteresis loops can be measured by the alternating-gradient method. Unusually high coercivities and strong anisotropies with an easy magnetic axis parallel to the alignment of the nanotubes are observed from the as-grown samples, whereas an enhanced magnetic saturation moment (up to a factor of 2) and a decreased anisotropy are realized after annealing at 645°C. The increase of the magnetic saturation moment of the Fe-filled carbon nanotube ensembles is caused by the entire transformation within the tubes of the γ-Fe and Fe3C phases to ferromagnetic α-Fe and graphite. X-ray diffraction with different glancing incidence shows that the γ-Fe is predominantly at the tips of the nanotubes, while the iron carbide resides closer to the substrate. However, after the annealing process only α-Fe is found. At an annealing temperature of 675°C the nanotube structures are destroyed and the magnetic characteristics are dramatically altered (viz., the disappearance of anisotropy and reduction in coercivity).

Synthesis, Properties, and Applications of Ferromagnetic‐Filled Carbon Nanotubes

“…XRD patterns of the Fefilled samples, synthesized by both LSCVD and SSCVD, generally reveal the three typical peak series corresponding to the c-Fe (fcc), a-Fe (bcc), and Fe 3 C phases, which is in agreement with the actual phases in the Fe-C phase diagram. [27] In our investigations, the as-grown filled carbon nanotube ensembles always featured the bcc-iron as the main component. Hitherto, in an individual nanotube, only the bcc phase, or the fcc phase mixed with a minor fraction of iron carbide could be detected.…”

Recent developments in inorganically filled carbon nanotubes: successes and challenges

“…There are several reports on the synthesis of CNTs filled with Fe, Co, Ni, Sn, Ga and In [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. In order to prepare them, high-temperature chemical vapor deposition (CVD) techniques have usually been employed [30,31].…”

Peeling off effects in vertically aligned Fe3C filled carbon nanotubes films grown by pyrolysis of ferrocene

“…The high coercivities of these structures have been reported to depend strongly on crystal anisotropy, shape anisotropy, degree of alignment of the MWCNTs and exchange coupling or bias interactions 6,15,16 . The synthesis of these films is generally performed by chemical vapour deposition (CVD) of an organometallic precursor known as ferrocene on the top of thermally oxidized Si/SiO 2 substrates [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] .Commonly used fabrication methods are solid-source CVD (SSCVD) and liquidsource CVD (LSCVD) 19 . The decomposed metallocenevapour has been reported to contain Fe, H 2 , CH 4 , C 5 H 6 and other hydrocarbon species 19 that react on the substrate surface to form the metal particles from which the MWCNTs and single crystal filling will grow simultaneously.…”

“…For more than a decade films of aligned multiwall carbon nanotubes (MWCNTs) filled with ferromagnetic α-Fe and Fe 3 C have been an important subject of research owing to their attractive magnetic properties [1][2][3][4][5][6][7][8][9][10][11][12] . These structures can indeed exhibit extremely large coercivities of 0.…”