## 3 Results  
### Characterization of the Magnetic Properties of MWCNTs and MWCNT/ PDMS Nanocomposite  
To better understand the magnetic properties of the MWCNT particles, SEM/EDS was performed on the MWCNTs. This test was useful to analyse the elemental composition and search for contaminants remaining from the fabrication process. Figure 4 presents an SEM-backscattered electron image of the MWCNT, showing contrasting particles identified by EDS as based on aluminium. The fabrication of the NC7000 MWCNT uses alumina substrate for the iron catalyst, which under the MWCNT synthesis conditions (high-temperature environment with carbon-rich gas) may reduce to aluminium carbide, Al4C3 [20].  
The SQUID analysis presented in Figure 5 showed that the MWCNTs and the MWCNT/PDMS present both ferromagnetism and diamagnetism. By analysing the magnetisation curve for the MWCNTs, it is noticeable that the ferromagnetic properties dominate at lower fields (between \(-6000\) and \(6000\) Oe), and the diamagnetism dominates at higher fields. This behaviour could be associated with the ferromagnetic saturation since the diamagnetism keeps changing linearly with the magnetic field. The diamagnetic property could be associated with the different materials; it could be due to the magnetic properties of MWCNTs or the catalysts (alumina or Al4C3). The ferromagnetic response could be related to the presence of iron, a ferromagnetic material that was also identified by SEM/EDS.  
Figure 3: Bending tests with an applied force of 6.6 N, (**a**) press and (**b**) release motion.  
showed a combination of diamagnetism and ferromagnetism. They concluded that the diamagnetism arose from the multi-walled nanotubes, and the ferromagnetism was due to the presence of iron nanoparticles derived from the fabrication process.  
Another example is the work of [PERSON] et al., 2020 [22], which reported that CNTs grown from alumina by CVD show significant ferromagnetic properties, even though the catalyst materials showed diamagnetic properties.  
By analysing Figure 5b in detail, it is possible to notice a dominant ferromagnetic effect [23]. The measured coercivity (Hc), retentivity (Mr), and saturation magnetisation (Ms) of the MWCNT particles at 300 K were 84.81 Oe, 0.13 emu/g, and 1.07 emu/g, respectively. The results demonstrate that the magnetic properties of the MWCNTs are invariant in the temperature range studied, from 300 to 380 K.  
As expected, when compared with the particles, the lower concentration of the MWCNTs (5 wt.%) and the polymeric nature of PDMS decrease the overall ferromagnetic properties in the nanocomposite. Analysing Figure 5d, it is presented a ferromagnetic curve. The measured coercivity (Hc), retentivity (Mr), and saturation magnetisation (Ms) of the nanocomposite at 300 K were 93.02 Oe, 0.004 emu/g, and 0.03 emu/g, respectively. Similar to the MWCNT particles, the 5 wt.% MWCNT/PDMS also shows a dominant ferromagnetic effect at lower fields (between \(-6000\) and \(6000\) Oe) and a dominant diamagnetic behaviour at fields between 6000 and 50,000 Oe.  
It is also noticeable that the nanocomposite has a stronger diamagnetic behaviour than the MWCNT particles. This increase in the diamagnetic behaviour could be associated with the PDMS matrix. In the work of [PERSON] et al. [24], it was possible to observe a similar behaviour. When the authors tested samples with and without the PDMS matrix, a dominant diamagnetism was also present for higher fields.