Study On The Preparation And Properties Of Pervoskite Oxides Superlattice

The wealth of interesting physical implication and potential application prospects on the technology led the pervoskite oxides heterostructures to be one of hot research issues in the field of materials science. It not only help us to get a deeper understanding of the interaction among spin, charge, lattice phonon and orbit freedoms in strong interaction system, and at the same time it’s meaningful for us to know better about the relationships between structure and physical properties of materials and design with multi-functional. For the past decades, with the continuous development of epitaxial film preparation technology for epitaxial films, an incredible variety of interface physical phenomena has been realized by researchs. The appearance of Ferromagnetism and superconductivity in the interface between two antiferromagnetic materials; novel forms of improper ferroelectricity has been induced by non-polar pattern of AFD. The emergence of these new phenomenas and octahedral distortion, rotations coupling in the interface and interface effects, such as charge transfer and spin frustration are well connected. Moreover, thanks to the perfect epitaxy of perovskite oxides, the heterostructures devices have a significant meaning on the integration of multi-function of perovskite structure materials. This thesis focuses on the high quality superlattices which consist of typical CMR perovskite manganites La0.7Sr0.3MnO3and La0.67Ca0.33MnO3, the orthoferrite SmFeO3and the itinerant ferromagnet SrRuO3. On one hand, the octahedral distortion and rotational patterns at the interface are controlled via strain states and then new functionalities are emerged. On the other hand, we improve the electronic and magenetic properties of ultra thin LCMO by interface effect such as charge transfer.We divide this thesis into6chapters.Chapter1:As the exordium part of this paper, first of all, we give a introduction to the crystallographic structure and basic physical properties of typical perovskite oxides. Then on one hand, we review three promising strategies that improve the physical properties through tuning the octahedral connectivity via epitaxial strain, interfacial coupling and coherent superlattice formation. On the other hand, we describe the emergence of new phenomenas in the pervoskite oxides heterostructures are well connected with interface effects, such as charge transfer and spin frustration.Chapter2:In this section, we give a detail presentation on superlattices sample preparation and measurement methods, including atomic force microscope (AFM), pulsed laser deposition (PLD), reciprocal space maps (RSM), x-ray diffraction (XRD), and low-temperature measurement systems (VSM、SQUIDand PPMS) are introduced.Chapter3:We prepare a series of superlattice samples consist of SmFeO3with strong orthogonality and perovskite CMR Lao.7Sro.3Mn03(LSMO) on NdGaO3substrate and then discover different stress relaxation compared with single LSMO thin films. And the easy axis of magnetization and magnetic transition temperature are altered with the changing of strain states, which verify the connectivity between structure and properties in superlattice.Chapter4:A series of superlattice samples consist of CMR Lao.67Cao.33Mn03and itinerant ferromagnet SrRuO3are grown with high quality. In the ultra thin samples, the paramagnetic insulating-ferromagnetic metal state transition temperature which is not affected by LCMO and SRO layer thickness achieved LCMO bulk’s level.We exclude some possible effect, such as epitaxy strain and interdiffusion at the interface and believe the transfer of itinerant electron in SRO lead the change of the ratio of Mn3+/Mn4+in the LCMO layer, and then enhance double exchange interaction, improve its transition temperature.Chapter5:In order to further study the potential materials with magnetoelectric coupling effect, in this chapter, we explore the conditions for the preparation of high quality DyFeO3epitaxial films.By changing subsrates and the growth oxygen pressure, the optimal growth conditions-735℃,6Pa are selected to prepare a series of DyFeO3epitaxial films with different thickness. After annealing, clear sharp atomic steps appeare in the films, which prove the high quality of our epitaxial films.Chapter6:This thesis’s mainly innovation points are introduced.