Magnetic and Mössbauer spectroscopy studies of nanocrystalline iron oxide aerogels

A sol-gel synthesis was used to produce iron oxide aerogels. These nanocrystalline aerogels have a pore-solid structure similar to silica aerogels but are composed entirely of iron oxides. Mössbauer experiments and x-ray diffraction showed that the as-prepared aerogel is an amorphous or poorly crystalline iron oxide, which crystallized as a partially oxidized magnetite during heating in argon. After further heat treatment in air, the nanocrystallites are fully converted to maghemite. The particles are superparamagnetic at high temperatures, but the magnetic properties are strongly influenced by magnetic interactions between the particles at lower temperatures