Response of the electrical resistance of La$_{0.67}$Ca$_{0.33}$MnO$_3$(40 nm) films mechanically compressed by the substrate in the course of their formation to electric and magnetic fields

The structure and electrical resistance of La$_{0.67}$Ca$_{0.33}$MnO$_3$(40 nm) epitaxial films grown quasicoherently on the surface of LaAlO$_3$(001) substrates are investigated. Compressive mechanical stresses that are active in the substrate plane during nucleation and growth encourage a decrease in the effective unit cell volume and an increase in the relative concentration of tetravalent manganese ions in the manganite layers. This leads to a decrease in the temperature of the maximum in the temperature dependence of the electrical resistivity of the films by approximately 90 K compared to the Curie temperature for the corresponding stoichiometric bulk crystals. It is found that, at $T <$ 120 K and $\mu_0H$ = 0 (where $H$ is the magnetic field strength), the measuring current depends nonlinearly on the voltage $V_b$ applied to the contacts. An increase in the applied voltage $V_b$ and in the magnetic field strength $H$ favors linearization of the current-voltage characteristics of the films.