Relative thickness effects on multiferroic Bi0.9Gd0.1Fe0.96Mn0.04O3/NiFe2O4 bilayered thin films

Multiferroic bilayered thin films consisting of Bi0.9Gd0.1Fe0.96Mn0.04O3 (BGFM) and NiFe2O4 (NFO) layers with different relative thicknesses were prepared on a general Pt/Ti/SiO2/Si substrate by using a chemical solution deposition method. The influence of the thickness fraction on the properties including microstructure, chemical state, dielectric, leakage current, ferroelectric and ferromagnetic properties of the BGFM/NFO bilayered thin films was investigated. XPS analysis reveals that increase the relative thickness of NFO can lead to increase the electron density around Bi ions of BGFM, and Fe2+ ions are the dominant species for BGFM. Raman spectra suggest that the tetragonality (c/a) of BGFM decrease with increase in the thickness fraction of NFO, which further decreases the spontaneous polarization of the film. With increasing in the relative thickness of NFO, the compressive stress in NFO decreases substantially, resulting in the abrupt reduction in magnetization. The BGFM/NFO (560/70) composite film exhibits both promising ferroelectric and magnetic behaviors at room temperature. Its remanent polarization is measured to be 130 μC/cm2 and the saturation magnetization is 140 emu/cm3 with a small coercive field of 148 Oe (normalized to the NFO layer).