Theoretical Study On Magnetoelectric Couplinf Properties For Perovskite Oxide Heterostructures

With the rapid development of information science and technology,multiferroic materials with magnetoelectric coupling have become the most promising applications in the field of microelectronics such as high density non-volatile random memories and novel types of sensors.Among them,perovskite oxides have attracted extensive attention as a class of materials with rich physical properties,especially magnetoelectric multiferroic perovskite oxide films.The reason why magnetoelectric multiferroic materials are attracted much attention is that this material makes it possible to develop ferroelectric and ferromagnetic functions.For example,magnetic potential can be supplemented by potential to build four-state storage devices,and the coupling behavior between ferromagnetic and ferroelectric states can induce new properties independent of these two states.Although magnetoelectric materials have a wide range of applications,the single-phase perovskite multiferroic materials are still scarce due to limited conditions in nature,and in the actual application is faced with enormous challenges,such as the magnetoelectric coupling performance is weaker,smaller electric polarization and curing temperature lower,so it is urgent to find magnetoelectric multiferroic materials that can stably exist at room temperature.With the continuous progress of thin film preparation technology in recent years,perovskite oxide composite materials with different coupling properties can be prepared by means of pulse laser deposition or molecular beam epitaxy.This composite material induces the rearrangement of lattice and electron at the interface,so that the material presents more controllable and rich novel physical properties,including magnetoelectric coupling,quantum Hall effect,two-dimensional electron gas,interfacial superconductivity and so on.In addition,the physical properties of the perovskite oxide heterostructures can also be regulated by strain or doping.Therefore,perovskite oxide heterostructures have become a research hotspot in the field of materials in recent years.With the development of quantum mechanics and the continuous progress of computer science and technology,the method of theoretical calculation and simulation has become an important means to study the physical properties of materials.Because it is not limited by experimental conditions,the method of calculating and simulating material properties can not only verify the experimental results,but also provide theoretical guidance for the experiment,which is an important bridge between theory and experiment.In this paper,based on first-principles calculation method,the magnetoelectric coupling performance,electronic properties,magnetic anisotropy and the physical mechanism of perovskite oxide heterostructures are predicted and analyzed.The specific research work is as follows:1.Interface robust magnetoelectric coupling effect in ferromagnetic/ferroelectric BiFeO₃/KNbO₃heterostructures.In this work,when the heterostructure composed of multiferroic BiFeO₃ and ferroelectric KNbO₃have been constructed,the magnetic properties,electronic properties and magnetic anisotropy of two kinds of heterostructures with different interfaces（KF-type and NB-type）are simulated based on first-principles calculation method.It is found that the magnetic order of BiFeO₃ changes from antiferromagnetism to ferromagnetism and the easily magnetized axis also reversely transforms between in-plane and out-plane by reversing the polarization direction of KNbO₃ for KF-type heterostructures,showing strong magnetoelectric coupling properties.The polarized states–P KNbO₃ does not change the insulativity of BiFeO₃ films,but+P KNbO₃ makes BiFeO₃ films half metal.In this way,under the polarization electric field of KNbO₃,BiFeO₃ films realizes the non-volatile electrical control from antiferromagnetic insulator to ferromagnetic half-metal.This work will provide an effective method for realizing non-volatile electrical control and its application in spintronic devices.2.Magnetoelectric coupling properties of YTiO₃/BiFeO₃ heterostructures under ferroelectric polarization and epitaxial strain.It is very important to find perovskite multiferroic materials with ferroelectric and ferromagnetic properties in scientific research,and it is of great significance for future magnetoelectric nanodevices.In this work,the effects of epitaxial strain and ferroelectric polarization on electronic properties and magnetoelectric coupling in YTiO₃/BiFeO₃ heterostructures are investigated using first-principles calculations.It is found that the size and direction of magnetic moment of Ti atom are controlled by strain and polarization,and then induce the heterostructure to realize reversible conversion of A-type antiferromagnetic,G-type antiferromagnetic and ferromagnetic.In addition,the ferroelectric polarization switch can also adjust the conductivity of the heterostructure,so that it changes from an insulator to half-metal,and the spin polarization changes from 0%to nearly 100%.Further studies revealed that polarization and strain induced the change of Ti-O bond length at the interface and the transfer and rearrangement of Ti-3d state electrons,resulting in a strong magnetoelectric coupling effect of YTiO₃/BiFeO₃ heterostructures It provides theoretical guidance for the design and implementation of information memory,spintronic devices and multifunctional nanoelectronic devices.