Simulating the formation of electron tunnel junctions in manganite thin films

Certain hole-doped manganese oxides (manganites), such as (La_1−yPr_y)_1−xCa_xMnO₃, are charge-ordered insulators at low temperatures (~100 K). They undergo a first-order phase transition to a ferromagnetic metallic (FMM) state upon further cooling, during which FMM domains grow and coalesce. It has been shown experimentally that an electric field applied to this mixed-phase state leads to a rearrangement of the FMM regions, a process driven by dielectrophoresis. We have developed a C++ program which simulates the migration of FMM domains in the presence of a non-uniform electric field. Using the relaxation method, the program models the electric potential on a grid containing two electrodes and a few FMM domains. As the FMM regions percolate onto the electrodes, a metal-insulator-metal junction forms which may promote spin-dependent electron tunneling. The tunneling current can be calculated using a simple barrier penetration model. The resistance vs. time behavior was modeled and used to reproduce our experimental measurements. Independent of the simulations, we also fit our experimental current vs. voltage data using the simple barrier penetration model and the Simmons model, taking the separation and work function as free parameters. Understanding the behavior of these manganite microstructures is important for spintronics applications, which can be used in highly efficient computing technologies such as neuromorphic computing.