Dynamic in-plane magnetic tunnel junctions formed in manganites using non-uniform-electric-fields*

 (La_1-yPr_y)_1-xCa_xMnO₃ (LPCMO) thin films grown on (110) NdGaO₃ (NGO) substrates exhibit electronic phase separation between ferromagnetic metallic (FMM) and insulating regions. The FMM regions are of micrometer scale, dynamic, and can be controllable using external electric fields. We have fabricated micrometer-sized gold contact patterns on LPCMO thin films to apply in-plane non-uniform electric fields. We observed that the non-uniform electric fields reorganize the FMM and insulating regions to form in-plane tunnel junctions. At higher temperatures close to the insulator-metal (IM) transition, the dI/dV-V curves show a zero-bias anomaly typically observed in the tunneling spectra of disordered metals. At temperatures about 10 K below the IM transition, a hard gap is observed in the dI/dV-V spectra with a gap value close to the charge-ordering gap in manganites. However, at higher voltages, the conductance shows a sharp and irreversible increase, and subsequent dI/dV-V spectra show quadratic behavior expected from metal-insulator-metal junctions. These electric field-induced tunnel junctions show clear signatures of tunneling magnetoresistance. Our data show that in-plane magnetic anisotropy plays an important role in the formation of these intrinsic tunnel junctions.