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Figure 6.3 shows the TEM and HRTEM images of the core/shell and hollow
MNPs. In the case of the core/shell MNPs, both the core and shell are crystalline.
The measured lattice spacing of the core corresponds to the (110) lattice planes of
alpha iron and that of the shell to the (311) planes of the spinel iron oxide. The Fe
core is single crystalline, however, the oxide shell is composed of small crystallites
which are oriented randomly. In the case of the hollow MNPs, the shell is composed
of randomly oriented grains that stick together to make a hollow shell.
Fig. 6.3 TEM and HRTEM images of the core/shell Fe/γ-Fe 2 O 3 (a, b) and hollow γ-Fe 2 O 3 (c,
d) MNPs; Inset (a) shows a histogram of the particle size distribution and inset (c) shows SAD
pattern of hollow nanoparticles. The scale bar is 20 nm in Fig. (a, c) and is 5 nm in Fig. (b, d)
Fig. 6.4 a ZFC (solid symbols) and FC (open symbols) magnetization versus temperature curves
for 9 nm (spheres) and 18 nm (squares) hollow γ-Fe 2 O 3 MNPs. M–H loops taken at 300 and 50 K
for the 9 nm (b) and 18 nm (c) hollow γ-Fe 2 O 3 MNPs. Reprinted from [15], with the permission
of AIP Publishing