Electron paramagnetic resonance of ferrite nanoparticles

Three types of iron-based oxide nanoparticles (weight compositions Fe2O3, B aFe2O4, and BaFe12O19) embedded in a polyethylene matrix are studied using the electron paramagnetic resonance technique. All nanoparticles are found to be multiphase. Thermal variations of electron paramagnetic resonance spe ctra reveal the presence of two phases in the Fe2O3 nanoparticles. One such phase undergoes an antiferromagnetic-like transition near 6 K. Nanoparticl es of BaFe2O4 demonstrate a resonance anomaly near 125 K that could indicat e the presence of a magnetic phase. Reduced magnetic anisotropy in BaFe12O1 9 nanoparticles may be related to either structural imperfection or particl e smallness (effective diameter of less than 10 nm). Our data clearly show that low temperature experiments are desirable for the correct identificati on of nanoparticles by means of the electron paramagnetic resonance techniq ue. (C) 2001 American Institute of Physics.