Change of Magnetic Properties and Structure in Fe3O4 Films on Si Substrates with Annealing Temperature

We have investigated the magnetic properties and structure of Fe3O4 films on Si substrates before and after annealing at various temperatures, T-a. The saturation magnetization and the coercivity in the Fe3O4 films are observed at all Ta. They markedly increase with increasing T-a up to 873 K, and their values become maximum at T-a = 873 K. Furthermore, they slightly decrease above T-a = 873 K. The Fe3O4 phase mainly exists in the films at all T,. In addition, the alpha-Fe2O3 phase (hematite) is also formed in the films above T. = 873 K. On the basis of these results, it is found that the growth of Fe3O4 phase by annealing is mainly dominant in the change of magnetic properties in the Fe3O4 film up to T-a = 873 K and that the formation of alpha-Fe2O3 Phase influences the change of magnetic properties in the Fe3O4 film above T-a = 873 K.