**8. Conclusions**

Exploration related to the use of natural materials for functional materials has been applied in this study. Natural iron sand with the dominant magnetite (Fe3O4) content has been successfully synthesized through the chemical coprecipitation method as a starting material for producing hematite (α-Fe2O3). α-Fe2O3 has been successfully used as the source of Fe3+ ions to synthesize calcium ferrite and bismuth ferrite nanoparticles. The calcium ferrite powders synthesized by the chemical dissolved technique produce nano-sized crystals with the dominant phases of CaFe4O7 and Ca4Fe14O25. The calcium ferrite powder has soft magnetic properties at room temperature which is attributed to the presence of dominant ferromagnetic phase and also oxygen vacancy in the nanoparticles. Magnetic parameters, such as saturation magnetic, are comparable to the barium-calcium hexaferrites, so that these nanoparticles have the potential application as microwave-absorbing materials. The bismuth ferrite powder, synthesized by the sol-gel method, exhibits multiferroic properties. The undoped BiFeO3 possesses a weak ferromagnetism at room temperature. The magnetic parameters can be enhanced by Ni doping in the form of BiFe0.9Ni0.1O3 nanoparticles. On the other hand, the electrical properties, i.e., dielectric constant, permittivity, and electrical conductivity, can be improved by Pb doping in the nanoparticles of Bi0.9Pb0.1FeO3. The multiferroic behaviors

are strongly determined by the nano-sized effects, the presence of oxygen vacancies and impurities, and also the doping type affecting the phase stability in the perovskite structure of BiFeO3 crystals. Considering the importance of applying these ferrite-based nanoparticles, investigations for obtaining pure phases of the nanoparticles from natural resources are very important and need further study.
