The Electrical Characteristic Of The Ferroelectric BiFeO₃ Film Influenced By Magnetic Field

In the decades of rapid change of information,there has been a lot of interest in basic science andapplied technology due to the existence of many kinds of iron order and magnetoelectric coupling effect.This makes multi-iron materials have great application potential in high density memory,electromechanical devices and spin electronic devices.As a good performance material,BiFeO₃（BFO）,which is a good material in the multi-iron material,has poured into the eyes of the researchers.BFO which does not contain toxic elements such as lead,is pollution-free,environmentally friendly,and has good chemical stability.As a typical single phase multiferroelectic material,BiFeO₃（BFO）is the only material exhibiting multiferroelectric property at room temperature with the high Curie temperature（T_C¹100 K）and Neel temperature（T_N⁶40 K）and also have excellent properties such as ferroelectric anti-ferromagnetism,structural tunability,photovoltaic properties,etc.,which have great application prospects in many fields.However,the high leakage current density in BFO caused by the Bi deficiencies and oxygenvacancies(V_Bii and V_O)seriously affects its properties and limits devise applications.Because the process of preparing,BFO nanostructures is quite strict,we will get BFO nanomaterials with lattice defects,which will seriously affect the properties of the materials,but the production of defects is inevitable.So researchers have solved this problem in a variety of ways,such as doping（self-doping and other doping,elemental substitution,and other reagents）to improve the properties of BFO films.In order to prevent this phenomenon,researchers try to change the structure of BFO by changing the external conditions without changing the structure of BFO.To optimize the properties of BFO,for example:adding lasers,the BFO film has a photoelectric effect,and it can produce photogenerated carriers,so that the charge inside the BFO film will be recombined and distributed.Thus,the properties of BFO thin films can be changed.In recent years,with the miniaturization and refinement of ferroelectric and piezoelectric devices,as well as the increasing interest in the study of the growth behavior of internal structures,more and more additional physical examination can be applied to optimize the properties of the materials studied.In the process of testing,different experimental methods are used to test the materials,so it is more and more meaningful to characterize the properties of materials on a nanometer scale..A variety of advanced microscopic characterization techniques based on AFM（atomic force microscope）have emerged as the times require.With the help of AFM,the relationship between internal defects and material properties can be explored,as well as the additional experimental conditions of AFM.It provides basic research basis for wider application of materials.In this work,the properties of BFO thin films are awakened by the method of external magnetic field.By controlling the magnitude and direction of magnetic field,the properties of BFO films can be improved by means of various observation methods（atomic force microscope,pressure-electric microscope,atomic force microscope,pressure-electric microscope）.The effects of magnetic field intensity on ferroelectric properties and electrical properties of BFO/NSTO dopedBiFeO₃/Nb:Sr₂TiO₃ heterojunction were investigated by electrostatic microscope,surface Kelvin probe microscope,conducting atomic force microscope and scanning electron microscope.The main contents of the study are as follows:1.BFO ceramic target with high quality were prepared successfully by the solid-state reaction method.The Bi/Fe ratio is 1.25.because Bi elements are very volatile,in order to prevent the loss in the sintering process of Bi,but also to prevent bulk ceramic target uneven heating,sintering process using powder embedded method,the other makes Bi the amount of a little more,good compact ceramic targets were prepared;2.the growth of BFO thin films was monitored on the substrate of strontium titanate doped with niobium oxide by pulsed laser deposition（PLD）.First,the growth of BFO thin films was monitored by high energy electron gun（RHEED）.Due to the high oxygen pressure during cooling,RHEED was turned off.The NSTO here is used as the base electrode.Of course,the lattice mismatch between BFO and NSTO is also small,and the structure growth of BFO will not change too much.3.The microcosmic ferroelectric and electrical properties of BFO thin films have been studied by means of various scanning probe microscopes（AFM、PFM、EFM,KPFM and CAFM）.1.The microcosmic ferroelectric and electrical properties of BFO thin films have been studied by changing the applied magnetic field intensity.The crystal quality of the BFO thin films is good,no heterophase is produced,and the surface is flat and compact;2.the ferroelectric layer of BFO thin film shows spontaneous polarization upward.With the increase of magnetic field intensity,the spontaneous polarization and piezoelectric response of BFO thin films increase,and the surface potential of BFO thin films increases with the enlarge4.surface charge density.Conductivity and leakage current of heterostructure Weakening,rectifying characteristic is obvious;3.In order to further understand the properties of bismuth ferrate thin films,we observed the retention properties of bismuth ferrate films with the same magnetic field intensity,and measured them every 5 hours through a time interval of 0h-10h-15h.Our conclusion is that bismuth ferrate thin films have a very good retention at high magnetic field intensity,with little change;4.In order to eliminate the influence of magnetic field direction on the properties of bismuth ferrate thin films,we changed the magnetic field intensity of bismuth ferrate thin films in a single point test.The results show that the influence of magnetic field intensity on the properties of bismuth ferrate films can be almost ignored.However,the properties of bismuth ferrate thin films were affected only in the presence of magnetic field intensity,these results can be explained by polarization discontinuity theory and band theory.