Interfacial Properties And Field Manipulation Of Transition Metal Oxide Thin Films

With the rise of artificial intelligence and the super fast development of electronic information industry,Moore's law is difficult to accurately predict the development law of semiconductor industry.In addition,the emergence of power consumption problems such as the heating of electronic devices poses great challenges to the traditional semiconductor industry.Transition metal oxides,with their new physical mechanism,have become a new direction in the development of electronics,bringing new opportunities to the rapidly developing electronic information industry.The ferromagnetic La0.7Sr0.3Mn O3(LSMO)thin film shows a large magnetoelectric coupling effect,and the ferroelectric Ba Ti O3(BTO)thin film can produce rich interface effects through the ferroelectric polarization reversal.Therefore,the ferroelectric/ferromagnetic multiferrous superlattice has good quantum manipulation.Although the relevant work of LSMO/BTO superlattices(SL)has been studied,the effect of interfacial strain-driven lattice distortion on the magnetic properties of superlattices has not been fully studied.In this paper,we propose the mechanism of the effect of epitaxial strain on the interfacial magnetism,which extends the new idea of the study of complex metal oxides.In addition,the ferromagnetic oxide metal electrode/ferroelectric interface provides a more efficient way to regulate junction tunneling current through interface effects.In particular,the mechanism of the interinterface magnetic exchange between LSMO and BTO on the tunneling resistance effect(TER)has not been revealed.Based on this,the ferroelectric tunnel junction of LSMO/BTO/NSTO was prepared by pulsed laser deposition method,and the switching ratio of the devices in the tunnel junction(FTJ)was improved through the interface effect of the applied electric field.Finally,the study on transport properties and magnetic properties of the heterostructure formed by 4d and 5d transition metal oxide films,Sr Ru O3(SRO)and Sr Ir O3(SIO),is extended to lay a foundation for the subsequent spin-current detection.In this paper,we use pulsed laser deposition technology to prepare transition metal oxide films and devices.According to different material systems and structural forms,the specific research content is divided into the following three parts:(1)Effect of epitaxial strain on LSMO/BTO SL interface magnetic propertiesIn order to eliminate the coupling between adjacent interfaces due to thin single-layer film,we chose the thicker LSMO(30 uc)and BTO(25 uc)layers as a period.After obtaining high quality LSMO/BTO superlattices,the influence of period on the magnetic properties of LSMO/BTO SL was investigated.The results show that the saturation magnetization of the SL decreases with the increase period,and the magnetization axis tends to be more in-plane.Combining theory and electron microscopy,it is shown that the interfacial phase transition caused by lattice distortion caused by epitaxial strain,it is the key to affect interfacial magnetic properties.This phase transition will accumulate with the increase of the number of interfaces and eventually change the magnetic properties of the SL.(2)Ferroelectric modulation TER of LSMO/BTO/NSTO FTJWe first prepared the LSMO/BTO/NSTO(Nb:SrTi O3)FTJ.Compared with Pt/BTO/NSTO FTJ,the tunneling current switch ratio of LSMO/BTO/NSTO FTJ is two orders of magnitude higher than that of Pt/BTO/NSTO tunnel junction.This significant improvement is mainly due to cation diffusion and magnetic exchange at the LSMO/BTO interface.When changing the direction of the applied electric field,the Mn3+/Mn4+ ratio is changed by the cation diffusion at the interface,thus affecting the interface resistance and tunneling resistance.The high and low resistance state is modulated by ferroelectric polarization.In addition,the low temperature tunneling of the LSMO/BTO/NSTO FTJ was investigated.It found that the competition interfacial magnetic exchange interaction and the electron-electron interaction of the LSMO layer in the low temperature region caused the jump of tunneling resistance.(3)Study on transport properties of 4d and 5d metal oxide filmsIt was found that different growth temperature and oxygen partial pressure directly affected the transport properties of SIO and SRO films.According to the comparison experiment,SIO and SRO films grown at low temperature and low oxygen pressure show insulation,and even metal-insulator transformation will occur at low temperature.However,the quality of SIO and SRO films growing at high temperature and high oxygen partial pressure is optimal,and they have good crystallinity and typical perovskite structure,as well as metallic properties and negative magnetoresistance at low temperature.Under the same growth conditions,SRO films also have good transport characteristics and low temperature anomalous hall effect.In addition,the electrical transport characteristics of SRO/BTO/NSTO heterojunction were investigated.Due to growth temperature,oxygen partial pressure and other factors,as well as the large stress mismatch between SRO and BTO film,the transport properties of SRO were finally affected,resulting in metal-insulator transformation at low temperature.By studying the new physical properties of transition metal oxides and exploring new devices with oxide interface effects,a new path can be opened for the development of transition metal oxides in information electronics and the application of spintronic devices.