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

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Abstract
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.