Transparent Ferromagnetic Films Coexisting with Ferroelectricity of the BiFeO3-PbTiO3 System Fabricated by Reactive RF-Sputtering

Reactive rf-sputtered films of solid solution compounds with (BiFeO3)1-x(PbTiO3)x (x = 0 to 1), were examined in an attempt to fabricate transparent ferromagnetic materials which are also ferroelectric above room temperature. The targets were mixed powders of Bi2O3, ¿-Fe2O3, PbTiO3 and PbO, in which the first two components were used to synthesize BiFeO3 by 1:1 mixing in mol.%, and PbO was added by 5 mol.% with respect to PbTiO3 to compensate for the evaporation loss of lead during sputtering. As-grown samples deposited at about 400°C are amorphous but have noticeably large saturation magnetization of 4¿Ms = 210 G and saturation dielectric polarization of Ps = 0.092 ¿C/cm² at room temperature. The samples are turned polycrystalline by post-heat treatment at 700°C for 2 hours in air and 4¿Ms is increased to about twice the initial value, while Ps is, in most samples, somewhat lower. The samples have a high transmittance in the visible through near-infrared wavelengths. The refractive index n of BiFeO3 film is 3.0 at ¿ = 700 nm.