Method for fabricating Fe3O4 nanoparticles using H2O2 and its comparison with coprecipitation method

Fe3O4 nanoparticles were successfully synthesized from an aqueous Fe(OH)2 colloid under nearly neutral condition by oxidizing it with HO. The morphology, structure, and magnetic properties were characterized and measured by transmission electron microscopy (TEM), x-ray diffraction (XRD), vibrating sample magnetometer, and superconducting quantum interference devices (SQUID). The TEM image shows that the sample consists of well-dispersed spherical particles with diameter about 18 nm, and has a cubic spinel structure according to XRD. The m6ssbauer spectrum at room temperature is fitted using two sextet spectrum corresponding to Fe ions at A site and B site, and the results show that the hyperfine field of the sample is a little smaller than that of bulk value, and crystalline defects exist in the sample. The saturation magnetization of the sample fabricated by using H2O2 is 67 × 10-3A · m2/g, and the Verwey transition was observed at 20 K, but the magnetization of the sample fabricated by coprecipitation is only 46 × 10-3A · m2/g when the applied field is 1 Tesla, and the Verwey transition was not observed in our temperature range of measurement. In addition, the superparamagnetic blocking temperature of the sample fabricated by coprecipitation was observed at 178 K.