Magnetic and optical properties of Fe3O4 nanoparticle ferrofluids prepared by coprecipitation technique

Nanometer size Fe₃O₄ particles were fabricated by chemical coprecipitation technique. The particle shape and size are affected by the PH value of the reactive solutions. The ferrofluids were fabricated with the Fe₃O₄ particles as magnetic particles, ammonium oleate as surfactant, and de-ionized water as solvent. Optical transmission of Fe₃O₄ nanoparticle ferrofluids was investigated as a function of incident optical wavelengths between 450 and 750 nm and applied magnetic fields up to 150 Oe. In general, for samples with lower PH value, the particles are small and agglomerate together, however, for samples with higher PH value, the particles are larger and distributed uniformly. Samples precipitated with higher PH value show larger variation of the transmittance (ΔT). This can be understood by our transmission electron microscope and X-ray diffraction pattern studies. The behavior of agglomeration for samples with lower PH value relates to the smaller variation of the optical transmission to the magnetic field