Optical characteristic of sol-gel synthesized lead lanthanum titanate-cobalt iron oxide multiferroic composite thin film

摘要

In the present work, we have investigated the optical characteristics of (1 -x) Pb_(0.85)La_(0.15)TiO_3 (PLT15)-x CoFe_2O_4 (CFO) (x, volume fraction of CFO 0.0 < x < 0.12) composite multiferroic thin films. It has been demonstrated that the analysis of wavelength dispersion of refractive indices is an effective tool to comment on the magnetostrictive (CFO) phase distribution in perovskite (PLT15) matrix. Thus, in case of 0-3 type (1 - x) PLT15-X CFO composite films, it has been demonstrated that as long as CFO phase is distributed homogeneously in PLT15 matrix, the measured refractive indices follow Sellmeir dispersion formalism. Interestingly, for percolative magnetostrictive phase (CFO) distribution, the refractive index variation of the composite films deviates from the Sellmeir type dispersion. Absorption coefficient and the band gap energy are estimated for PLT15 and (1 - x) PLT15-X CFO composite films with varying CFO volume contents. Both refractive indices and packing fraction of (1 - x) PLT15-X CFO composite films are found to be marginally reduced with the increase in CFO volume contents. The band gap of these films is found to be systematically reduced with the increase in CFO volume contents. The change in band gap is argued to be due to cation/(s) diffusion across PLT15 and CFO interface.