Fe3O4 particles were synthesized from platelet α-FeOOH particles by a liquid-phase reduction process using tetra-ethylene glycol as reduction agent, for their application in hyperthermia or thermoablation therapies that employ hysteresis-loss heating. Fe3O4 particles 60–100 nm in size were finally obtained by heating. The saturation magnetization of the obtained particles increased with the heating time to reach a maximum value of approximately 80 Am2/kg. In contrast, the coercive force of the particles was nearly constant at approximately 12–13 kA/m and was independent of the heating time. Lattice image observation of the synthesized Fe3O4 particles revealed to obtain single crystals. On the basis of experimental results, it was concluded that the single-crystal Fe3O4 particles were formed by recrystallization through the dissolution and precipitation of iron ions from α-Fe2O3 formed by the dehydration of α-FeOOH. The recrystallization of the Fe3O4 particles was promoted with increasing α-FeOOH particle content in tetra-ethylene glycol up to about 0.022 g/mL.
