  We report an experimental study of the CoFe2O4/CoFe2 nanocomposite, a
nanostructured material formed by hard (CoFe2O4) and soft (CoFe2) magnetic
materials. The precursor material, cobalt ferrite (CoFe2O4), was prepared using
the conventional stoichiometric gel-combustion method. The nanocomposite
material was obtained by reducing partially the precursor material using
activated charcoal as reducing agent in air and argon atmospheres, at 800 and
900 C respectively. The magnetic hysteresis loops demonstrate that, in general,
prepared nanocomposite samples display single magnetic behavior, indicating
exchange coupling between the soft and hard magnetic phases. However, for
nanocomposite samples prepared at higher temperatures, the hysteresis
measurements show steps typical of two-phase magnetic behavior, suggesting the
existence of two non-coupled magnetic phases. The studied nanocomposites
presented coercivity (HC) of about 0.7 kOe, which is considerably lower than
the expected value for cobalt ferrite. A huge increase in HC (>440%) and
maximum energy product (about 240%) was obtained for the nanocomposite after
high energy milling processing.
