The Study Of Electric Field Control Of Magnetization In Ferromagnetic/Ferroelectric Heterostructure Based On X-ray Magnetic Circular Dichroism

With the discovery of interlayer anti ferromagn eti c coupling,giant magnetoresistance and tunneling magnetoresistance,spintronics has been an emerging subject since the 1980s.The research and application of spintronics bring the magnetic information storage technology to a new level.However,traditional spintronics devices require an external magnetic field or electric current to control the magnetization of the ferromagnetic layer in order to further realize the electron's spin injection and detection.This increases the difficulty of device miniaturization as well as the large energy loss,which could not meet the increasing requirements for higher density,higher speed and lower energy consumption of the next-generation devices.Therefore,it is necessary to find a more suitable way of magnetization manipulation to realize the above-mentioned requirements.The magnetoelectric coupling effect of the electric field controlled magnetization is a potential alternative approach.It plays an increasingly important role in spintronics and electronic information technology.To understand the fundamental magnetoelectric coupling mechanism and find more magnetoelectric coupling materials with excellent performance is highly desired to realize the nonvolatile information storage with low power consumption and higher density.In this thesis,the magnetoelectric coupling effect and the corresponding mechanism of artificial multiferroic of CoFeB/PMN-PT(011)heterostructure at room temperature are discussed.In magnetized CoFeB/PMN-PT(011)heterostructure,the large scale magnetization change is manipulated by the pure electric field at room temperature.In the demagnetized samples,the 180° reversal of magnetization is realized by pure electric field instead of magnetic field.The X-ray magnetic circular dichroism under in-situ electric field is carried out for demagnetized CoFeB/PMN-PT(011)to study the atomic level mechanism of this novel magnetoelectric coupling effect.In terms of application aspect,we have done the performance test of the electric field controlled magnetization model for the CoFeB/PMN-PT(011)system,including the electric field controlled magnetization switch and pulse voltage controlled magnetic fatigue performance test.Finally,the related work of graphene spintronic devices based on this magnetoelectric coupling effect is also introduced.The first chapter mainly includes:(1)Development of information technology,the basic knowledge of magnetism and the magnetic storage in the field of information technology.(2)History and achievements of multiferroic materials.(3)Research history and achievements of magnetoelectric coupling.(4)Application of multiferroic magnetoelectric coupling system in spintronics.(5)Brief introduction of X-ray magnetic circular dichroism technology.(6)Our research works of this thesis.The second chapter introduces the experimental research methods and experimental equipment used in this research in terms of sample preparation,structure and morphology characterization,performance test,mechanism investigation of physical property and nanofabrication of devices.The third chapter is the main research part of CoFeB/PMN-PT(011)heterostructure.We obtain large scale nonvolatile electric field controlled magnetization at room temperature.In terms of mechanism,we confirm the magnetoelectric coupling mechanism of interface strain regulation in CoFeB/PMN-PT(011)structure through the experimental exploration of phase transition before and after polarization of PMN-PT(011)under in-situ electric field and the simulation of different strain patterns.Similarly,the magnetoelectric coupling effect of demagnetized sample is also characterized.We find that the 1800 magnetization reversal can be achieved by using pure electric field at room temperature.In view of this special magnetoelectric coupling phenomenon,we further carry out the X-ray magnetic circular dichroism of synchrotron radiation source under in-situ electric field for the demagnetized sample.The microscopic mechanism of this magnetoelectric coupling process is explained at the atomic scale.Experimental results show that the magnetoelectric coupling is due to the uniaxial magnetic anisotropy of Fe and Co atoms.Under the control of electric field,the orbital magnetic moment of Fe atom in CoFeB is more anisotropic,which determines the 180° magnetization reversal in CoFeB.The fourth chapter introduces the related work of graphene spintronic devices based on the pure electric field regulation of the magnetoelectric coupling system.In addition,another project of freestanding YBCO high temperature superconducting thin film during the master career is also introduced.The fifth chapter gives the summary,innovation points and future work prospective.