(La1−xPrx)0.7Ca0.3MnO3 colossal magnetoresistive thin films on yttria stabilized zirconia

Thin epitaxial films of (La1−xPrx)0.7Ca0.3MnO3 (x=0,0.25,0.5,0.75,1) were grown on (001) ZrO2(Y2O3) substrates by aerosol MOCVD at 750°C. The structure and electronic properties of the films were compared with those of the films on perovskite substrates and with ceramics of the same composition. The films on ZrO2(Y2O3) are (110) oriented and possess a varying in-plane orientation microstructure giving rise to an extremely high density of the large-angle boundaries (∼1011 cm−2). Above the maximum resistivity temperature Tp, the microstructure results in a ∼30 meV increase of the hopping energy of small polarons (∼130 meV) and suppression of the maximum of d(log ρ/T)/d(1/T) at the transition from Arrhenius like (log ρ∝T−1) to Mott like (log ρ∝T−1/4) temperature dependence of resistivity (ρ). Below Tp an empirical law log ρ=αT 2+log ρ′ was derived indicating a thermally activated trapping of the itinerant charge carriers. Large-angle boundaries in the films on ZrO2(Y2O3) destabilize the ferromagnetic state and cause residual resistivity (ρ′) higher by a factor of 100 compared to the films on the perovskite substrates. They provide a reservoir for the tunnel magnetoresistance owing to the spin-polarized tunneling.