  Magnetic and structural properties of magnetite nanoparticles stabilized in
polyvinyl-alcohol thin films are investigated by using X-ray diffraction (XRD),
transmission electron microscopy (TEM), electron paramagnetic resonance (EPR)
and static magnetometry techniques. The nanoparticles have well-defined
crystallinity, and are superparamagnetic at room temperature. Their size
distribution is characterized by the distinct log-normal law (with average
diameters near 5-7 nm) and slight maximum near 70-80 nm. The EPR spectra and
static magnetization data demonstrated pronounced anomalies in the interval
between 130 K (corresponding to Verwey transition) and 200 K. The experimental
data obtained can be understood on the basis of the half-metallic electronic
structure, complex temperature behavior of the magnetic anisotropy, along with
effects of "weak magnetic-electron" sublattice of magnetite.
