Characterization and magnetic response of multiwall carbon nanotubes filled with iron nanoparticles of different aspect ratios

• Magnetic properties of MWCNTs encapsulated with Fe-NPs of different aspect ratios are presented.
• MWCNTs were produced by a low cost simple one step approach without noble gas flow.
• The aspect ratio of trapped Fe-NPs is ~10, 5 and 2, respectively for three samples.
• Enhanced values of Hc are observed (~2.6 kOe at 10 K) due to dipolar interaction and shape anisotropy.
• However, Hc values hardly show any variation for three samples at 300 K.

Three samples of multiwall carbon nanotubes (MWCNT) [TF200, TF150 and TF100, where T and F stand for toluene and ferrocene respectively, and numeral denotes the amount (mg) of ferrocene] filled with iron-nanoparticles (Fe-NPs) of different aspect ratios are grown by chemical vapor deposition of toluene–ferrocene mixture. Energy dispersive X-ray analysis shows a systematic variation in the intensities of peak corresponding to Fe, indicating that Fe is present in different amounts in the three MWCNT samples. The lengths of Fe-NPs lie in the range of 200–250; 80–120; and 30–40 nm for TF200, TF150 and TF100, respectively, as estimated statistically from transmission electron microscopy micrographs. However, the diameter of the encapsulated Fe-NPs does not vary significantly for different samples and is 20–30 nm for all samples. Hysteresis loop measurements on these MWCNT samples were done at 10, 150 and 300 K up to an applied field of 1.5 T. At 10 K, values of coercivity are 2584, 2315, and 2251 Oe for TF200, TF150 and TF100 respectively. This is attributed to the strong shape anisotropy of the Fe-NPs and significant dipolar interactions between them. Further, M–H loops reveal that saturation magnetization of TF200 is almost four times that of TF100 at all temperatures.

Enhanced values of coercivity (~2.6 kOe at 10 K) are observed in MWNTs filled with rod-shaped iron-nanoparticles of different aspect ratios (~10, 5, and 2). Figure optionsDownload as PowerPoint slide