Colossal Magnetoresistive thin films of (La1-xPrx)0.7Ca0.3MnO3 prepared by aerosol MOCVD

O.Yu. Gorbenko, A.A. Bosak, A.R. Kaul, N.A. Babushkina, L.M. Belova

submitted (1998) to Journal of Physics D: Applied Physics

ABSTRACT. Thin epitaxial films of (La1-xPrx)0.7Ca0.3MnO3 (x=0,0.25,0.5,0.75,1) were grown on LaAlO3, SrTiO3 and ZrO2(Y2O3) by aerosol MOCVD at 750oC. The structure and electronic properties of the films were analyzed in relation to the properties of the ceramic materials of the same composition. Above Tp the VRH of small polarons was identified as the electrical conductivity mechanism. The charge ordering starting in (La1-xPrx)0.7Ca0.3MnO3 at 160-200 K leads to the drastic variation of the localization radius of the small polaron resulting in the switching from Arrhenius law (lgr ~ T-1 )to Mott law (lgr ~ T-1/4) of the conductivity. Below Tp the thermally activated trapping with the temperature dependent activation energy leads to the lgr~Tn law found experimentally. The value of Tp is controlled by tolerance factor t, which determines the mean bending of Mn-O-Mn chains. In the thin epitaxial films on perovskite substrates the tensile strain at the film-substrate interface results in the different bending of such chains in and out of the film plane producing the effect on Tp comparable with the effect of chemical pressure nearby critical value t ~ 0.91. By variation of x the colossal magnetoresistance in the very low magnetic field was achieved in the thin films: the field of 0.3 T was enough for 32 times decrease of the resistivity of La0.35Pr0.35Ca0.3MnO3 film on LaAlO3 at 155 K. Coherent large-angle boundaries in the structure of (110) oriented R1- yMyMnO3 films on ZrO2(Y2O3) strongly increase the resistivity both above and below Tp but the character of its temperature dependence and the mechanism of conductivity are still retained.

Coordination Chemistry Laboratory