Tuning magnetic properties of cobalt ferrite nanoparticles by hematite amount

Abstract

Cobalt ferrite nanoparticles were produced using two different preparation methods: the conventional solid-state synthesis and the chemical co-precipitation. The initial proposal was to analyze the preparation route influence on magnetic and structural properties of the resulting samples. In the solid-state reaction, a heat treatment at 1200 °C for 4 h was alternated with grinding to increase the method efficiency. On the other hand, the synthesis by chemical co-precipitation was performed with different flow by adding the alkaline solution (NaOH). The preparations were performed at 4 different flow regimes: by the abrupt addition of alkaline solution and by a continuous flow at 0.05 ml/s, 1.2 ml/s and 2.0 ml/s. Finally, the resulting powder from each sample was divided into 4 equal parts and heat-treated at 600 °C for different times: 0 h (untreated), 5 h, 10 h and 20 h. Using X-ray diffraction, two crystalline phases were identified (cobalt ferrite and hematite) and the corresponding average crystal size was calculated. Magnetic measurements were performed as a function of the applied magnetic field at 5 K and at 300 K resulting in great differences if compared the studied samples. The magnetizations as a function of temperature with a constant applied field at field-cooled and zero field-cooled regimes were performed for better understanding of resulting materials. Thus, magnetic measurements were efficient and highly sensitive to detect secondary-phase effects in magnetic compounds.