Phase formation and magnetic properties of CoFe2O4/CoFe2 nanocomposites

Nanosize CoFe2O4 particles were synthesized via thermal decomposition of a mixed oxalate precursor; the mean ferrite particle size between 5 nm and 35 nm is tailored through variations of the decomposition temperature. Ferrite particles of 22 nm and 14 nm size were subsequently heated in Ar/5%H-2 atmosphere at 315 degrees C for various holding times. The resulting nanocomposites consist of spinel ferrite, CoO and CoFe2, with the alloy concentration increasing with dwell time. Room temperature hysteresis loops exhibit a single-phase reversal behavior and remanence enhancement. An increase of the maximum energy product was observed as well. Hysteresis loops at 5 K, however, show two-phase behavior indicating that no exchange coupling is active.