Magnetic properties of BiFeO3-BaTiO3 and BiFeO3-PbTi(Zr)O3 glassy sputtered films

Abstract

Magnetic properties of glassy oxide films which exhibit ferromagnetism and ferroelectricity simultaneously above room temperature prepared by reactive rf sputtering are presented. Nominal film composition is the solid solution compound system expressed by (1−x)BiFeO₃‐x ABO₃, x=0–1 where ABO₃ denotes ferro‐ (antiferro‐) electric perovskites, such as BaTiO₃, PbTiO₃, and PbZrO₃. Spontaneous magnetization 4πM_s for as‐deposited films is small behaving paramagnetically and does not show the compositional dependence. After annealing at temperatures of 600–700 °C in either air or PbO atmosphere, considerably large 4πM_s exceeding 1 kG appears at the solid solution composition. All samples with large 4πM_s are x‐ray amorphous and a rapid decrease in 4πM_s takes place after annealing at higher temperatures (≳800 °C), where still unidentified crystallites are precipitated. Mössbauer absorption spectra were done to understand the origin of ferromagnetism. Besides pronounced magnetic (and/or dielectric) properties, these films have a high transmittance from visible through near‐infrared regions, so that they are expected to be useful as optoelectronic device materials.