Abstract:
Perovskite-type complex oxides exhibit various intriguing and perplexing properties. Heterostructures integrating different perovskite oxides may have potential for various applications. Among the perovskite oxides, manganites are well known for the colossal magnetoresistance effects. Besides magnetic fields, they are also susceptible to other stimuli, e.g. electric fields/currents, lights, strain and pressure. In this thesis, the field modulation on the transport properties in heterostructures combining manganites with other perovskite oxides was investigated.
The electric currents can dramatically alter the properties of manganites. In thin films of La0.8Ca0.2MnO3, asymmetric conduction was induced by currents of very high densities. Current processing yielded low-temperature persistent conductivity in Pr0.7Sr0.3MnO3 films. Current-excited metastable states in Nd0.7Sr0.3MnO3 exhibited emergent properties, including metal-insulator transition, resistance steps and negative differential resistance.
The effects of tunable strain in thin films of Pr0.7Sr0.3MnO3 and La0.7Ba0.3MnO3 grown on 0.7PbMg1/3Nb2/3O3–0.3PbTiO3 (PMN-PT) were explored. Voltage controlled lattice deformation in PMN-PT were effectively transferred to Pr0.7Sr0.3MnO3 and La0.7Ba0.3MnO3. Large modulations of resistance in manganite films were observed. The resistance does not always change linearly with applied voltages. There are strong correlation between the nonlinearity and magnitude of resistance modulation.
Excellent rectifying properties, sizeable magnetic responses and strong photoelectric effects were observed in heterojunctions composed of manganites and Nb-SrTiO3. Doping levels in Nb-SrTiO3 have great influences on the transport processes and photoelectric effects. The impacts of small excess currents differ significantly with different bias voltages.
The results obtained suggest that field modulation in heterostructures should be an effective way to explore the physics of the manganites. The fabricated all-oxides heterostructures would be of great potential for various electronic applications.