Case Study Of Some Dynamical Problems In Perovskite Oxide Thin Films And Heterostructures

Due to the rich physical properties and the great potential applications,perovskite oxides received tremendous attention.In this thesis,by using epitaxial perovskite oxide thin film and heterostructures,oxygen-vacancy dynamics in resistive switching,lattice dynamics in multiferroics and spin dynamics in exchange bias training effect have been investigated.The main research results are as follows:By using 90° off-axis rf magnetron sputtering,La0.7Sr0.3MnO3(LSMO)thin films were grown on flat and vicinal LaAlO3(LAO)(001)single crystal substrates.The crosshatch topographies were observed in 80 nm LSMO thin films by atomic force microscopy(AFM).By using conductive atomic force microscopy(CAFM),crosshatch show in both AFM and CAFM,but they are not all necessarily in a oneto-one mapping relation.In local current-voltage measurements,threshold and bipolar switchings were observed.The analysis of current-voltage behavior demonstrated that the resistive switching relies on the local profile and concentration of oxygen vacancies,which are modulated by both the misfit and threading dislocations.By using 90° off-axis rf magnetron sputtering,280 nm BiFeO3(BFO)thin films were grown on flat and vicinal LAO(001)single crystal substrates.It is found that the film grown on flat LAO is mixed-phase while the film grown on vicinal LAO is rhombohedral(R)phase.By analying the polarized Raman spectra,the vibration modes of mixed-phase BFO assigned to the modes of the tetragonal(T)like phase,the R-like phase and the bridging phase.The temperature-dependent Raman spectrum unravels multiple anomalies in the phonon behavior of the T-like phase at its multiferroic transition(～370 K),the Polomska transition(～450 K)and the antiferromagnetic transition of the R-like phase(～640 K).The unusual phonon behavior indicates the presence of spin-phonon coupling and long-ranged strain coupling between the T-like and R-like phase.By using magnetron sputtering,La0.7Sr0.3FeO3/Ni79Fe21 thin films were grown on flat SrTiO3(001)and LAO(001)single crystal substrates.The samples show clear exchange bias training behaviour in major magnetization hysteresis loops(MHLs).The exchange bias field and the coercive field were analyzed by using different models.It is found that the model based on the relaxation of the frozen and rotatable spin components at the interface gives the best description.By using the first-order reversal curves(FORCs),the FORC diagrams corresponding to the first MHL,the second MHL and the quasiequilibrium stage were collected respectively.The FORC diagrams unraveled that the magnetization reversal evolves in the training process.