Preparation,Magnetic And Transpoert Properties Of Several Perovskite Manganese Oxide Thin Films

As a typical representative of associated electron system,perovskite-type manganese-oxide film has many novel magnetic effects,metal insulator transition,magnetoresistance effect and other functional characteristics due to the strong interaction between spin,charge,orbit and lattice,and is easy to control.Therefore,it has great theoretical and application value in high density memory,magnetic sensor,new spintronics device and other fields.In this paper,a variety of LSMO and LMO polycrystalline and epitaxial thin films were prepared on quartz glass and（001）SrTiO₃ single crystal substrates by magnetron sputtering.The effect of preparation process on the microstructure of the thin films was investigated.In order to obtain the best technological parameters of film growth,the intrinsic relationship between the O₂/Ar flow ratio and the crystal structure,surface morphology and surface chemical states of LSMO and LMO polycrystalline films was studied in detail.And we clarified the effect mechanism of oxygen content,non-stoichiometric ratio and Mn³⁺/Mn⁴⁺valence ratio on the macroscopic magnetic properties of the films.Meanwhile,the magnetic and transport properties of LSMO epitaxial films under different strains were preliminarily explored.This paper has laid a certain research foundation for the design and application of perovskite-type manganese oxide film.The main work is as follows:（1）LSMO polycrystalline films were prepared on quartz glass by magnetron sputtering technology.The effects of sputtering pressure,sputtering power and post-annealing temperature on the deposition quality of LSMO polycrystalline films were studied,and the optimal conditions for preparing LSMO polycrystalline films were obtained.The prepared LSMO films have typical tripartite perovskite structure,with high crystal quality,regular grain shape,high surface density and good uniformity.It is found that Mn³⁺/Mn⁴⁺valence state ratio and oxygen content in the lattice also change with the change of O₂/Ar flux ratio,which will directly affect the ferromagnetic interaction and ferromagnetic/antiferromagnetic competition in the system,and ultimately lead to the difference in the macroscopic magnetism of the thin films.In addition,the surface morphology of the films also has a certain effect on the magnetic properties.（2）LMO polycrystalline thin films were prepared on quartz glass by magnetron sputtering technology.The effects of O₂/Ar flux ratio on the deposition quality and microstructure of thin films were analyzed.It is found that the change of O₂/Ar flux ratio can significantly change the Mn³⁺/Mn⁴⁺valence state ratio in the thin film,thus effectively regulating the magnetic structure and magnetic properties of the thin film.With the change of O₂/Ar flow ratio,the magnetic structure of the thin film has undergone the evolution from being dominated by antiferromagnetic order,and the coexistence of ferromagnetic and antiferromagnetic to being dominated by ferromagnetic order.The coexistence and competition of ferromagnetic and antiferromagnetic in the inner film also change,which finally leads to the macroscopic magnetic characteristics of the thin film.Such as cluster glass state,exchange bias phenomenon,Curie temperature,freezing temperature,irreversible temperature,saturation magnetization and coercivity field strength,etc.,also have corresponding changes.（3）LSMO epitaxial thin films with different thickness were prepared on（001）SrTiO₃ substrate by magnetron sputtering technology.The effects of post-annealing temperature and sputtering pressure on the crystallization quality,crystal orientation and surface morphology of the thin films were studied,and the optimal preparation process of LSMO epitaxial thin films was obtained.The prepared LSMO films grow epitaxial along the C-axis on（001）SrTiO₃ substrate and are subjected to substrate tensile strain.The film has high crystal quality,regular surface grains,fewer holes,high density and good uniformity.It is found that with the decrease of film thickness,the residual tensile strain increases,lattice distortion intensifies,ferromagnetic double exchange is weakened,and the Curie temperature,metal insulator transition temperature and saturation magnetization of the films decrease.At the same time,the resistance of the film and the resistance at room temperature increase.