Study On Modulation Of Poisson's Ratio And Correlated Physical Properties In Perovskite Manganite Oxide Film

The perovskite manganite oxide films are widely used in magnetic storage,sensors and spintronic devices due to their novel magnetic and transport properties.Therefore,it has attracted extensive attention in the fields of physics,materials science and engineering.The effect of misfit strain at the interface between films and substrates has been widely employed to modify the microstructure and improve the electronic properties of perovskite manganese oxide thin films,which can lead to plenty of emergent physical phenomena that do not exist in their bulk counterpart.However,this method is limited by the finite commercial single crystal substrates.Moreover,it is taken for granted that the Poisson's ratio of an oxide film is a positive constant.Those restrictions remarkably impede the development of misfit strain driven novel structure and functional properties for epitaxial oxide hetero-structure systems.In this thesis,the modulations of Poisson's ratio and associated magnetic,electrical transport and mechanical properties are systematically studied in La_0.7Sr_0.3MnO₃ films.The main contents of this study are listed as follows:First,pulsed laser deposition?PLD?was used for the preparation of La_0.7Sr_0.3MnO₃ films.High quality La_0.7Sr_0.3MnO₃ films with controllable Poisson's ratios from positive value to negative one were deposited on selecting substrates,with optimized oxygen partial pressure and film thickness.Secondly,the effect of Poisson's ratio on the magnetic and transport properties of La_0.7Sr_0.3MnO₃ films has been studied systematically.The results show that the saturation magnetization and Curie temperature can be well tuned by adjusting the Poisson's ratio of the La_0.7Sr_0.3MnO₃ films,which provides a new approach to the modulation of electronic properties of perovskite manganite oxide films.Finally,the correlations among the Poisson's ratio,Young's modulus and the hardness of La_0.7Sr_0.3MnO₃ films were investigated.The results show that the Young's modulus and the hardness are obviously strengthened for La_0.7Sr_0.3MnO₃ films with negative or zero Poisson's ratio.This result possibly offers new insights into the improvement of the mechanical properties for perovskite manganite oxide films.