The synthesis of magnetite nanoparticles with controlled size
has long been of scientific and technological interest. Magnetite
(Fe3O4) is a common magnetic iron oxide that has a cubic inverse
spinel structure with oxygen forming a fcc closed packing and Fe
cations occupying interstitial tetrahedral sites and octahedral sites.1
The electrons can hop between Fe2+ and Fe3+ ions in the octahedral
sites at room temperature, rendering magnetite an important class
of half-metallic materials.2 Its particle dispersions have been widely
used as ferrofluid in, for example, rotary shaft sealing, oscillation
damping, and position sensing.3 The use of properly coated
magnetite nanoparticles in clinical medicine has also intensified.
With proper surface coating, these magnetic nanoparticles can be
dispersed into water, forming water-based suspensions.4 Such a
suspension can interact with an external magnetic field and be
positioned to a specific area, facilitating magnetic resonance imaging
for medical diagnosis5 and AC magnetic field-assisted cancer
therapy.6 All these technological and medical applications require
that the nanoparticles are superparamagnetic with sizes smaller than
20 nm and the overall particle size distribution is narrow so that
the particles have uniform physical and chemical properties.
However, producing magnetite particles with the desired size and
acceptable size distribution without particle aggregation has consistently
been a problem