Study On Magnetoelectric Coupling Effect Of Bismuth-based Oxide Composite Films

The multiferroic composite film is composed of ferroelectric and ferromagnetic phase on the mesoscopic scale through a certain connection.Due to the strong coupling effect between the typical ferromagnetic and ferroelectric phases,the multi-iron composite films generally show strong magnetic coupling effect.Therefore,multiferroic thin films have wide application prospects in electromagnetic integrated devices such as electrical magnetic signal conversion,polymorphic information storage and so on.They are currently one of the leading research directions in condensed matter physics and multiferroic materials.In this paper,a lead-free single layer bismuth based perovskite Bi_0.5(K_0.15Na_0.85)_0.5TiO₃?BKNT?in combination with Ga_0.8Fe_1.2O₃?GFO?formed 2-2type composite film was synthesized by chemical sol-gel process.The microstructure,domain structure,ferroelectric,piezoelectric,magnetic and magnetoelectric coupling effects of Bi_0.5(K_0.15Na_0.85)_0.5Ti O₃/Ga_0.8Fe_1.2O₃ composite films were investigated at room temperature.It was found that the bilayer composite film formed a good interface coupling and observed the clear electrical domain structure.The strong magnetic coupling effect is formed between ferromagnetic GFO and ferroelectric BKNT.The magnetoelectric voltage coefficient of GFO/BKNT composite film can reach 30.89mV/cm?Oe.Experiments found Ga_0.8Fe_1.2O₃?GFO?films with excellent magnetic properties at room temperature.In order to obtain higher quality of magnetoelectric composite films,bismuth basic perovskite structure Na_0.5Bi_4.5Ti₄O₁₅?NBT?is introduced as a piezoelectric phase and Ga_0.8Fe_1.2O₃ film as ferromagnetic phase to form 2-2 type multiferroic composite film.Because NBT belongs to the four layered perovskite structure,compared with the simple perovskite structure.There is a?Bi₂O₂?²⁺layer in the crystal structure,containing two?Bi₂O₂?²⁺bismuth oxygen layered structure.The?Bi₂O₂?²⁺layer can compensate for the space charge and reduce the leakage current,so the?Bi₂O₂?²⁺layer plays a positive role in the materials.That is,the ferroelectric properties of the layered perovskite ferroelectric thin films may be improved in comparison with the simple perovskite.So,GFO/NBT composite films possessed good ferroelectric,leakage and piezoelectric properties.GFO/NBT composite film also obtained strong magnetoelectric coupling effect.In the experiment,the magnetoelectric voltage coefficient?_E=79.32 mV/cm?Oe was measured at low frequency f=600 Hz under magnetic field of H=7k Oe.The results show that the dielectric response of GFO/NBT composite film will also change under the action of the bias magnetic field,and the MDC value of the magnetodielectric constant is 3.35%under 3k Oe magnetic field,and the strong magnetodielectric effect is obtained.Through the above experiments,the magnetism is obtained in the lead-free bismuth based ferroelectric films,forming of the multiferroic magnetoelectric compo-site films.At the same time,the composite films had good magnetic coupling charac-teristics.The present work provides a new idea for the research of lead-free magne-toelectric composite films and provides an opportunity for its application in magneto-electric fields such as multi-state memories,magnetoelectric converters and so on.