Magnetic properties of amorphous-like oxides of the Bi2O3-Fe2O3-PbTiO3 system synthesized by sol-gel method

Similar to films rf-sputtered in an argon and oxygen mixed gas, amorphous-like oxides (films and powders) with the ternary Bi2O3-Fe2O3-PbTiO3 system prepared by sol-gel method develop a considerably large spontaneous magnetization after being annealed above Ta = 500 °C in air. The magnetization of gel-coated films showed a sharp maximum IS exceeding 0.1 T in a narrow region with the Fe2O3-rich compositions when annealed around Ta = 700 °C, where samples showed halo-patterns in X-ray diffraction, retaining the amorphous state, while further increase in Ta results in a rapid decrease in magnetization, where X-ray diffraction lines assigned to para- and/or antiferromagnetic oxide precipitates such as α-Fe2O3, BiFeO3, and Bi2Fe4O9, were apparent. It may be concluded that spontaneous magnetization arises from nano-ferrimagnetic clusters which cannot be detected by X-ray diffraction. In order to elucidate its microscopic origin, Mössbauer measurement was also carried out.