Transparent ferromagnetic films coexisting with ferroelectricity of the BiFeO3-PbTiO3 system fabricated by reactive RF-sputtering.

In an attempt to fabricate transparent ferromagnetic materials coexisting with ferroelectricity above room temperature, we have examined reactive rf-sputtered films of solid solution compounds with (BiFeO3)1-x(PbTiO3)x, x=0 to 1. The targets were mixed powders of Bi2O3, α-Fe2O3, PbTiO3 and PbO, in which the first two components were used to synthesize BiFeO3 by 1 : 1 mixing in mol. % and the last component was added by 5 mol. % with respect to PbTiO3 to compensate the evaporation loss of lead during sputtering. As-grown samples deposited at about 400°C are amorphous but have noticeably large saturation magnetization 4πMs=210 G and saturation dielectric polarization of Ps=0. 092 μC/cm2 at room temperature. The samples are turned into polycrystalline by post-heat treatment at 700°C for 2 hours in air and 4πMs is increased to about twice as large as the initial one, while Ps is, in most samples, rather decreased. The samples have a high transmittance in the wavelength of visible through near-infrared. The refractive index n of BiFeO3 film is 3.0 at λ=700 nm.