Intrinsic and extrinsic pressure effects in La0.7Ca0.3MnO3 thin films

The influence of quasihydrostatic pressure on the electrical transport in epitaxial ${\mathrm{La}}_{\mathrm{0.7}}{\mathrm{Ca}}_{\mathrm{0.3}}{\mathrm{MnO}}_{\mathrm{3}}\mathrm{/MgO(100)}$ thin films prepared by pulsed laser deposition (PLD) and metalorganic aerosol deposition (MAD) was studied for temperatures $\text{T=4.2–300\hspace{0.05em}}\mathrm{K}$ and magnetic fields $\text{B=0–12\hspace{0.05em}}\mathrm{T}.$ Usual or “intrinsic” pressure effect, characterized by a decrease of the resistance in the region of the metal–insulator transition $T_{\mathrm{MI}}$ was observed in PLD film for $\text{p=0–16\hspace{0.05em}}\mathrm{kbar}$ and also in MAD films for $\text{p⩽8\hspace{0.05em}}\mathrm{kbar}.$ An anomalous, or “extrinsic” pressure effect, characterized by a 2–3 order of magnitude increase of the resistance at low temperatures, persisting after the pressure release, was found for $\text{p>8\hspace{0.05em}}\mathrm{kbar}$ in films with extraordinarily high values of the pressure coefficient ${\mathrm{d(T}}_{\mathrm{MI}}\text{)/dp=2.70–3.85\hspace{0.05em}}\mathrm{K/kbar}.$ The lattice strain originated from the substrate due to epitaxy was found to control the $T_{\mathrm{MI}}$ values and intrinsic pressure behavior in the films. The extrinsic pressure effect in MAD films is caused by a plastic deformation of the film, yielding irreversible changes of the microstructure accompanied by a magnetoresistance, $\mathrm{\Delta R(B)/R(B),}$ more than ${10}^3\%$ at $\text{4.2\hspace{0.05em}}\mathrm{K}{\mathrm{<T<T}}_{\mathrm{MI}}.$