Quantum Control And Photoelectric Response Of Epitaxial Thin Films Of Perovskite Oxides

Due to the strong coupling between the charge,spin,orbital and the lattice degree of freedom,perovskite manganites exhibit a variety of physical properties.For the closely energy states of these quantum states,the competition between these states can be feasibly controlled by the external fields,such as light,magnetic field,electrical field,strain and so on,yielding various novel physical properties.The studies of perovskite oxides may lead to an exploration of new photoelectric materials and devices based on strongly corrected electron systems.In this work,the magnetic and electron transport properties of La_0.8Ba_0.2MnO₃?LBMO?films were tuned by light and strain.The main results are listed as following:1.Epitaxial LBMO films have been grown on Sr TiO₃?STO?substrate by pulsed laser deposition,and their oxygen content was tuned by controlling the in-situ annealing time.The effects of oxygen content on the photo-induced effect,electrical and magnetic properties in the LBMO/STO films have been studied.It was found the oxygen content plays an important role in the physical properties of LBMO films.With increasing the oxygen content,the metal-insulator?ferromagnetic-paramagnetic?transition temperature and saturation magnetization increase while resistivity and magnetoresistance decrease.The oxygen-stoichiometric film exhibits the large photoconductivity and the maximum of photo-induced resistivity change reaches PR=73% under the excitation laser of 650 nm.2.The strain effect was realized by growing the different-thickness epitaxial LBMO films on La AlO₃?LAO?substrate.The thickness dependence of electrical and magnetic transport properties with different strain has been investigated.The compressive strain relaxes with increasing the thickness,resulting in a slightly enhancement of the metal-insulator transition temperature.In addition,the LBMO films can obtain the relatively large magnetization and small coercive field under appropriate compressive strain.3.High-quality LBMO films have been grown on LAO,?La,Sr??Al,Ta?O₃?LSAT?and STO substrates.The effects of strain and light field on the electrical and magnetotransport properties have been investigated.The photoconductivity in both insulator and metal states decrease with increasing strain.The films display the remarkable photoinduced relaxation,which can be well described by a double-exponent model.