Inelastic Relaxation of Oxygen and Low-Field Magnetoresistance in La$\text{}_{0.65}$Ca$\text{}_{0.35}$MnO$\text{}_{3}$ Films on Ferroelectric Ceramics Substrates

Galvanomagnetic properties of polycrystalline La$\text{}_{0.65}$Ca$\text{}_{0.35}$MnO$\text{}_{3}$ films with a thickness of 0.2~μm deposited onto Pb$\text{}_{2.9}$Ba$\text{}_{0.05}$Sr$\text{}_{0.05}$(Zr$\text{}_{0.4}$Ti$\text{}_{0.6}$)O$\text{}_{3}$ ferroelectric ceramics substrates were investigated. We discovered an irreversible increase in film resistance after numerous inversions of substrate polarization. This phenomenon was investigated several times for three film structures. The typical duration of the process of a monotonic 3-5 times increase in film resistance was 3-6 hours. The long-time relaxation of macroscopic film resistance is explained by dielectrization of film intercrystallite boundaries. The typical size of crystallites of both the film and the substrate is 3-10μm. Such small size explains the fact of macroscopic homogeneity of film conductivity, when the specific resistance increases from 1.8×10$\text{}^{-2}$ to 1.8Ω cm. A growth in resistance of narrow (10 nm) regions of film is explained by the redistribution of oxygen anions under the action of inhomogeneous mechanical stress. The stress between crystallites appears due to inverse piezoelectric effect of ferroelectric substrate. The magnitude of diffusion coefficient of oxygen is estimated to be D≥10$\text{}^{-20}$ m$\text{}^{2}$ s$\text{}^{-1}$.