Figure 2
SEM images of bare γ-Fe 2 O 3 nanoparticles after solvent drying. In absence of the alternating magnetic field (a) and in presence of alternating magnetic field with different frequency (1 kHz (b), 5 kHz (c), 10 kHz (d), 50 kHz (e), 100 kHz (f), and 20 Hz (g)). The concentration of sample was 12.5 μg/ml. The naturally drying sample showed amorphous aggregates, while the field-treated samples showed more or less one-dimensional orientation. With the frequency increasing, the chain-like assembly was more and more obvious. However, for the 20-Hz alternating magnetic field, the field-treated sample re-showed the amorphous aggregates to some extent, meaning that the alternating magnetic field of the frequency had not induced the assembly of γ-Fe2O3 nanoparticles.