Layered Perovskite NLaFe_1-xCo_xO₃-Bi₄Ti₃ O₁₂ Film Preparation And Multiferroic Properties Research

It is necessary to attain multifunctionality in a small device.Single-phase room-temperature multiferroics have aroused great interest in recent years.In order to synthesize single-phase room-temperature multiferroic materials,this dissertation conceives inserting the antiferromagnetic LaFeO₃?LFO?unit into the ferroelectric Bi₄Ti₃O₁₂?BTO?matrix of layered perovskite.Both single-phase multiferroic1.5LaFeO₃-Bi₄Ti₃O₁₂?1.5LFO-BTO?and LaFe_1-xCo_xO₃-Bi₄Ti₃O₁₂(LF_1-xC_x-BTO)thin films were successfully prepared on?111?Pt/Ti/SiO₂/Si through a sol-gel process.In this thesis,the effect of preparation conditions on the electrical properties of 1.5LFO-BTO films is firstly discussed,then the ferroelectricity,dielectricity and magnetism properties of 1.5LFO-BTO thin films as well as their magneto-dielectric effect are presented.Finally,the multiferroic properties of LFO-BTO thin films with different Co-doping contents are addressed.The main results and conclusions are listed as below:1.Polycrystalline single-phase 1.5LFO-BTO thin films of layered perovskite were deposited on Pt/Ti/SiO₂/Si substrates by using a sol-gel route.The effects of depositon conditions?including sintering atmosphere,heating rate and annealing temperature?on the microstructures and ferroelectric properties of the 1.5LFO-BTO films were investigated.It was found that the thin films annealed in flowing oxygen and at rapid heating rate of 120?/s exhibit the best ferroelectricity with the largest remanent polarization value.2.Random-oriented 1.5LFO-BTO films present room-temperature multiferroic properties with the remanent polarization 2P_r²7.20?C/cm² and saturated magnetization M_s⁴.28 emu/cm³.Moreover,under the magnetic field of 0.5 T,room-temperature magneto-dielectric effect with magneto-dielectric coefficient of ¹.03%was observed,which arises from the charge ordering of Fe²⁺and Fe³⁺in the films.Both temperature-dependent dielectric spectrum and X-ray photoelectron spectroscopy data reveals the coexistencea of Fe²⁺and Fe³⁺in the 1.5 LFO-BTO films.3.The room-temperature multiferroic properties of LFO-BTO films with different Co-doping contents??0.5 mol%?were studied.It was found that with increasing Co contents,their lattice parameter goes up,remanent polarization decreases and dielectric constant?_r increases monotonously.In addition,the LFO-BTO films with Co contents of 0.1 mol%show the largest remanent magnetization M_r value,indicating the the most remarkable room-temperature ferromagnetism.