Manipulation Of Magnetic And Electric Properties In Manganite-based Thin Films And Heterostructures

With the development of information technology towards high speed,high density and low consumption,the demands for multifuctional materials and devices are rapidly increasing.Manganites demonstrate large amounts of novel and interesting physics behavior due to various degrees of freedom,which provides a large stage for design of magnetic and electric properties and promotes the advances in spintronic materials and devices.In comparison to the rich physics phenomena,the methods for manipulation of magnetic and electric behavior are still limited.Thus,how to explore new mechanisms and techiniques for the manipulation of magnetic and electric behavior is the key problem during the development of spintronics towards multifunctional applications.This dissertation focuses on manganite-based thin films and heterostructures and systematically studies the influence of light on spin transport properties via the light illumination of LED.A new mechanism of optical control of mangetism is proposed on the basis of the half-metallic electronic structure.Followingly,a novel type of spintronic devices with remarkable optical response is proposed and achieved.Meanwhile,on the basis of oxygen octahedral tilting,new methods are developed for the control of exchange coupling and magnetic anisotropy.A remarkable variation in magnetoresistance of La_1/2Sr_1/2MnO_3-??LSMO?is observed under light illumination,indicating an increased saturation field and a weakened magnetic anisotropy in LSMO induced by light.Then it's proposed that based on the photon-induced spin transition,the magnetism in half-metallic systems can be modulated.Followingly,a type of photon-gated spin transistor is proposed and designed with partial area of the device under light exposure,where a sudden increase of resistance is observed under light illumination.In this way,opitcal control of spin transport is achieved taking advantage of the discontinuity of DOS caused by the photon-induced spin transition,demonstrating the transient advantage of optical control.The chemical valence of LSMO is altered via redox,accompanied by the variation of the spin polarization at the excited state,which leads to an enhancement of the photon-induced spin transition.Thus,the photon-induced resistance change of the photon-gated spin transistor is increased from 0.3%to60%,offering a possible way for the application of this type of spintronic devices.According to the analysis about the relationship between octahedral tilting and exchange coupling at the ideal G-type antiferromagnet/ferromagnet interface,it's proposed that oxygen octahedral tilting is the key to the formation of exchange bias at the interface.Then the pattern and scale of octahdral tilting at the interface of SrMnO₃/La_2/3Sr_1/3MnO₃ are modulated via substrate selection and thickness design,consequently achieving a qualitative and semi-quantitative control of exchange bias via the control of octahedral tilting.It is observed that taking advantage of the exchange coupling due to octahedral tilting,the antiferromagnetic moments in thin SrCoO_2.5 turn to the out-of-plane direction when the ferromagnetic moments in thick La_2/3Sr_1/3MnO₃align in plane.In turn,the in-plane alignment of antiferromagnetic moments in thick SrCoO_2.5 results in a tendency of perpendicular magnetocrystalline anisotropy in thin La_2/3Sr_1/3MnO₃.In this way,utilizing the perpendicular alignment of magnetic moments induced by octahedral titling,the alignment of magnetic moments is manipulated,offering a novel way to explore the multifunctional applications of oxygen octahedral tilting.