Preparation Of NSmFeO₃-Bi₄Ti₃O₁₂ Thin Film And Study Of Its Multiferroic Properties

With the development of modern industries and technologies,multiferroic has been attracting more attention not only due to its combination of ferroelectricity?FE?,ferromagnetism?FM?and/or ferroelasticity in one single homogeneous phase,but also for its applications on new type of sensors,data storage,and spintronics.In this thesis,nSmFeO₃-Bi₄Ti₃O₁₂?n=0.5,1.0,1.5,2.0?thin films with Aurivillus-phase were prepared by Sol-Gel method,and room temperature multiferroic properties are obtained by combining FE and FM units at atomic level.The micro-structures,ferroelectricity,magnetism,leakage current,dielectric properties and magnetoelectric coupling of the thin films were also investigated.In addition,the electrocaloric effect of[111]oriented0.74Pb(Mg_1/3Nb_2/3)O₃-0.26PbTiO₃ single crystal was investigated.The main contents are as follows:1?SmFeO₃-Bi₄Ti₃O₁₂2 multiferroic thin films with four-layered Aurivillus-phase were deposited on?111?Pt/Ti/SiO₂/Si substrates by Sol-Gel process.The thin films exhibit remarkable room-temperature multiferroic properties with 2P_r⁴8?C/cm² and M_s⁰.43 emu/cm³.More importantly,the magnetodielectric effect is observed at room temperature,which may originate from the spin reorientation under applied magnetic fields by affecting the interaction between the local dipoles of Fe²⁺and Fe³⁺.The coexistence of Fe²⁺and Fe³⁺was confirmed with both X-ray photoelectron spectra and dielectric relaxation spectrum.2?The effects of SmFeO₃ content on the microstructure,dielectric properties,leakage properties and multiferroic properties of the thin films were studied.By our research shows that with the increasing of SmFeO₃ content?1?the interplanar spacing d as well as volume V decrease gradually,?2?the dielectric constant decreases gradually,?3?the leakage current gradually increases,?4?the ferroelectricity decreases gradually,?5?the magnetism increases gradually.3?The 0.74PMN-0.26PT single crystal with single phase was prepared by a modified Bridgman technique.The electrocaloric?EC?effect was investigated by indirect and direct methods.The maximum values of?T_EC and?T/?E are 0.62 K and 5.2×10^-6KmV^-1 at 100°C under the electric field of 12 kV/cm by indirect methods,derived from Maxwell's relation.While the maximum value of?T_EC and?T/?E are 0.63 K and 2.1×10^-7 KmV^-1 at 100°C under the electric field of 4 kV/cm by direct methods.