Ferromagnetic amorphouslike oxide films of the Fe2O3-Bi2O3-PbTiO3 system prepared by rf-reactive sputtering

In this paper, the magnetic properties of ferromagnetic oxide films of the ternary Fe2O3-Bi2O3-PbTiO0 system prepared by rf-reactive sputtering are presented. As-sputtered films deposited at a substrate temperature below 400 °C are amorphous and behave paramagnetically. Amorphous films like these whose composition corresponds to the perovskite solid solution of BiFeO3 -PbTiO3 become crystalline with a perovskite structure on annealing in air, but no distinct spontaneous magnetization appears. On the contrary, in certain compositions in the Fe2O3 -Bi2O3 -PbTiO3 system, the samples retain a glassy (or amorphouslike) state even when the samples were annealed at around 600 °C. Also a spontaneous magnetization appears at room temperature. The maximum room-temperature saturation magnetization 4πMs achieved in this system is 1.67 kG with the composition 0.74Fe2O3 -0.16Bi2O3 -0.10PbTiO3. Experiments imply that the amorphous state is essential for establishment of strong ferromagnetism in the sputtered oxide films. Mössbauer spectroscopy and x-ray photoelectron spectroscopy were performed to examine the microscopic properties of the films that lead to ferromagnetism. The optical transmissivity and magneto-optical Faraday effect of the films are also discussed.