Charge-ordering in thin films of bilayered rare earth manganates

Thin films of bilayered manganates of the formula LnSr2Mn2O7 (Ln=rare-earth), deposited on LaAlO3(100) substrates by nebulized spray pyrolysis, show charge-ordering transitions in the resistivity data. The transition temperatures decrease from 205 K to 185 K as the rare-earth ionic radii decrease from Ln=La to Gd. While magnetic-fields up to 6 tesla have little effect on the charge-ordering transition, small electric currents prevent the onset of the charge-ordered state. Furthermore, the resistance decreases markedly with increasing current, with nonlinear behavior, in polycrystalline films deposited on Si(100) substrates.