Growth and Electric Field Control of Phase Separated Manganites

Perovskite Manganites have received numerous attentions due to exotic behaviors such as colossal magnetoreistance (CMR) and electronic phase separation (EPS). The purpose of my research is to answer fundamental questions about the growth properties of manganites and electric field control of the EPS properties.

Experimental study was conducted on controlling the growth mode of La_0.7Sr_0.3MnO₃[Lanthanum Strontium Manganese Oxide] thin films using pulsed laser deposition. Different thin film morphology, crystallinity and stoichiometry have been observed depending on growth parameters. To understand the microscopic origin, the thermodynamic processes were theoretically analyzed and a growth diagram was constructed. Three boundaries between highly and poorly crystallized, layer-by-layer and 3D, stoichiometric and non-stoichiometric growth were identified in the growth diagram. A good fit of our experimental observation with the growth diagram was found. This case study demonstrates that a more comprehensive understanding and the predicting of the growth mode in PLD is possible.

Behaviors such as high Tc superconductivity, CMR, and the metal-insulator transition, have been tied to inherent electronic phases coexisting in a single crystal material. These phases offer the potential for creating new types of electronic devices based on tuning the finely balanced energetics stabilizing emergent phase domains. Here we demonstrate novel approaches to induce resistive electric field effect transitions based on the modification of the inherent electronic domain structures in single crystal materials. A phase separated manganite system confined to a scale which isolates a few electronic domains is controlled using laterally gated electrodes to tune percolative conduction channels which give repeatable resistive changes. This technique also makes it possible to create multistate switching devices from a single confined transport channel. Electro-resistance up to 400% is observed during the cooling process under static electric field. These findings provide an avenue to control inherent electronic phases as a means of creating novel nano-electronic devices.

While manganites are the primary focus throughout this dissertation, both the growth diagram and spatially confined E-field techniques can be extended to understand fundamental growth phases in other epitaxial oxides materials and exploring the electric field effect on different oxides system.