Characterization of Anisotropy in Manganite (LPCMO) Thin Films

Resistance measurements on thin films of strongly correlated electronic materials that have anisotropic properties due to atomic layering and/or substrate induced strain are primarily sensitive to in-plane conduction paths and therefore fail to capture any information about perpendicular transport. We present an experimental technique in which the films under investigation, pulse laser deposited (La$_{1-y}$Pr$_{y})_{5/8}$Ca$_{3/8}$MnO$_{3}$ (LPCMO) with thicknesses in the range 300-900 {\AA}, comprise the base electrodes of trilayer capacitor structures, thus allowing the simultaneous characterization of dc transport (resistance) in the parallel direction and ac transport (capacitance) in the perpendicular direction. For a given film, we find two distinct direction-dependent insulator-metal percolation transitions reflecting the competition between insulating and ferromagnetic metallic phases. With increasing thickness, the temperature difference between these transitions decreases. This decrease occurs because the presence of a strain-stabilized ferromagnetic metal phase at the LPCMO/substrate (NdGaO$_{3})$ has less of an effect on transport as the thickness increases and the LPCMO manifests isotropic bulk behavior.