Simulation and experimental evidence of dielectrophoresis in manganite thin films*

Manganite thin films of (La_1-yPr_y)_1-xCa_xMnO₃ (LPCMO) which have been grown on NdGaO₃ (NGO) substrates exhibit a state where fluid-like ferromagnetic metallic (FMM) regions can coexist with a charge-order insulating background. It has been shown experimentally that these regions can be realigned using electric fields; a process which could be used in practice to effectively manipulate extremely small ferromagnetic regions. One of the main physical principles which can explain this phenomenon is dielectrophoresis, that is when neutral particles in a fluid experience a net-force due to a locally non-uniform electric field. A C++ code was written to simulate the time dependent dynamics of the FMM regions. Electrodes and circular FMM regions are generated on a grid and the relaxation method is used to find the potentials of the configuration statically. Using the fact that force on the regions is proportional to the gradient of the squared electric field, the regions can be repositioned and their movement over time can be observed. Our simulations support the effects we have observed experimentally, which show electric field induced percolation giving rise to the conditions for electron tunnelling through the insulating regions separating neighboring FMM regions.