Phase stabilization of magnetite (Fe3O4) nanoparticles with B2O3 addition: A significant enhancement on the phase transition temperature

• B2O3 addition to magnetite nanoparticles enhances the superparamagnetism.
• The phase transition temperature of magnetite to hematite increases by 200 °C.
• B2O3 addition increases the activation energy of magnetite.

Magnetite nanoparticles (MNPs) are extensively investigated for biomedical applications, particularly as contrast agents for Magnetic Resonance Imaging and as drug delivery agent and heat mediators for cancer therapy. Tuning the magnetic properties of the magnetite nanoparticles with doping of foreign atoms has a crucial importance for determining the application areas of these materials and so attracts much interests. On the other hand the doping with foreign atoms requires high temperature annealing, and it causes a phase transition to the hematite phase above 400 °C. In this work the phase transition temperature from the magnetite to the hematite phase has been increased by 200 °C, which is the highest enhancement reported in literature. It was achieved by addition of the appropriate amounts of B2O3. Our experiments indicates that the 5.0 wt% of B2O3 addition stabilizes and keeps the existence of single phase magnetite up to 600 °C.