# Magnetic Nanoparticles as Mediators for Magnetic Hyperthermia Therapy Applications: A Status Review
## 3 Results and Discussion
### Transmission Electron Microscopy  
Figures 14-17 show the TEM analysis of as-synthesized maghemite and the CM-dextran-coated maghemite MNPs, (Mg, Ti)-ferrite MNPs, as-prepared and thermally homogenized Ni\({}_{0.725}\)Cu\({}_{0.275}\) MNPs, and of NiCu MNPs embedded in the silica matrix. The nanoparticle size and the crystallinity were characterized by TEM using a JEOL 2010F microscope. The MNPs were deposited on a cooper-grid-supported, perforated, transparent carbon film. Figure 14 shows as-prepared maghemite MNPs (a) and the maghemite NP coated with CM-dextran (b) [27]. The main reason that the coated particles have a smaller average particle size is that they were centrifuged, which removes the larger particles from the magnetic fluid. Using TEM images, we also determined the size of the nanoparticles, which was about 14.5 nm for the maghemite nanoparticles and 12.0 nm for the maghemite nanoparticles coated with CM-dextran. When we compare the size estimated with [PERSON]'s equation, the results are consistent with or very similar to the XRD results. Figure 14: TEM micrographs of (**a**) as-prepared maghemite particles (A), (**b**) coated maghemite with CM-dextran. Figure 15: Particles of sample B with mechanically strained particle = x (**a**), consisting of nanocrystallites = y (**b**), enlarged view (**c**), and a typical image of the milled powder (**d**). Figure 15 shows the (Mg, Ti)-ferrite MNPs with a size of a few hundred nanometers [26]. The particle marked with x (b) shows contours that could have been formed by the mechanical strain. According to what was said or found by XRD analysis, TEM images confirm the formation of crystalline components and nanosized crystalline components. So, we can confirm with certainty that the sample consists of two types of crystallites. In Figure 15a, we see very large nanoparticles larger than a hundred nanometers, while in Figure 15b,c we see nanocrystallites. In Figure 16 (above), we see a TEM image of prepared NiCu MNPs (microemulsion method) and the corresponding electron diffraction [41]. The corresponding electron diffraction shows a combination of two cubic FCC structures (Ni-Cu, NiCuO). Using TEM images, we were able to determine the size of the nanoparticles, which ranged from 3 to 10 nm. Figure 16 (below) shows a TEM image of thermally homogenized MNPs (750 \({}^{\circ}\)C, 5 h under H\({}_{2}\)/Ar atmosphere) and their corresponding electron diffraction showing larger agglomerated particles of Ni-Cu and NiCuO structure. Homogenization resulted in a relatively broad distribution of nanoparticle sizes, ranging from a few tens of nm to several hundreds of nm. The samples were homogenized, but on the other hand, homogenization led to agglomeration, which we do not want in the case of use in MH. Figure 16: TEM image (**a**) and corresponding electron-diffraction pattern of the as-prepared MNPs (**b**) (microemulsion method). TEM image (**c**) and corresponding electron-diffraction pattern of the thermally homogenized particles (**d**). Figure 17: (**A**) Typical TEM images of MNPs of sample Ni\({}_{67.5}\)Cu\({}_{32.5}\) embedded in a silica matrix and (**B**) bare alloy particles and the corresponding histogram. Figure 17A shows the NiCu alloy MNPs embedded in the silica matrix (sol-gel method) [103]. Spherical, non-agglomerated grains with a relatively uniform size distribution were observed. The sol-gel method proved to be very promising as the nanoparticles were spherical despite homogenization and no agglomeration occurred due to the silica matrix. Figure 17B shows a TEM image of the bared MNPs after leaching. Using a TEM image, we also determined the size of the nanoparticles after leaching (Figure 17B), the nanoparticles are about 16.6 nm in size, which is consistent with the results of XRD analysis, or later, as we will see, with magnetic measurements. In Figure 18, we see a TEM image of mechanically milled Cu-Ni, sample C (Cu\({}_{27.5}\)Ni\({}_{72.5}\)) [55].