Influence ofCodoping on the charge-ordering state of the bilayered manganiteLaSr2Mn2O7

Abstract

The effect of $\mathrm{Co}$ doping on transport and magnetic properties of bilayered manganite ${\mathrm{LaSr}}_{2}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ charge ordering (CO) state is first investigated. With $\mathrm{Co}$ doping, CO and metal-insulator transition disappear and the resistivity behaves as semiconducting behavior throughout the measured temperature region when $x\ensuremath{\geqslant}0.08$. The antiferromagnetic (AFM) transition temperature shifts to lower temperatures and spin-glass state appears with increasing $\mathrm{Co}$ doping level. The decrease of magnetization magnitude and Weiss temperature with the $\mathrm{Co}$ doping indicate the dilution of the magnetically active $\mathrm{Mn}\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}\mathrm{Mn}$ network. No saturation of the magnetization at low temperatures and the increase of the coercive force with increasing $\mathrm{Co}$ doping level imply the appearance of the phase separation [the coexistence of AFM and ferromagnetic (FM)] ground state. The observed doping effect may originate from the weakening of the double exchange within FM layers of A-type antiferromagnet and the carrier localization caused by the disorder due to $\mathrm{Co}$ doping at $\mathrm{Mn}$ sites. The difference of the effect of $\mathrm{Mn}$-site doping on the CO state between perovskite and layered manganites is discussed.