Response of the capacitance of a planar La$_{0.67}$Ca$_{0.33}$MnO$_3$/SrTiO$_3$/La$_{0.67}$Ca$_{0.33}$MnO$_3$ heterostructure to an electric field

Manganite film electrodes were integrated with a spacer layer of strontium titanate to produce an epitaxial La$_{0.67}$Ca$_{0.33}$MnO$_3$/(1000 nm)SrTiO$_3$/La$_{0.67}$Ca$_{0.33}$MnO$_3$ (LCMO/STO/LCMO) heterostructure by laser ablation. At $T$ = 300 K, the mechanical stresses in the STO layer relaxed to a considerable extent, while the LCMO electrodes were found to be under biaxial lateral tensile strain, with the lattice unit cell of the top electrode distorted considerably stronger ($a\parallel/a\perp$ $\approx$ 1.026) than that of the bottom electrode ($\approx$ 1.008) ($a\parallel$ and $a\perp$ are the unit cell parameters in the substrate plane and along the normal to its surface, respectively). The reciprocal of the capacitance $C$ of the plane-parallel LCMO/STO/LCMO film capacitors thus formed increased almost linearly with increasing temperature $T$ in the range 50–250 K. At $T <$ 100 K, the capacitance $C$ decreased by approximately 50% in an electric field $E$ = 40 kV/cm. After the electric field E was varied as 0 $\to$ +100 kV/cm $\to$ 0, the capacitance $C$ decreased by approximately 3% and the maximum in the $C$ ($E$, $T >$ 200 K) dependence shifted by approximately 9 kV/cm with respect to the point $E$ = 0.