The effect of oxygen stoichiometry on electrical transport and magnetic properties of La0.9Te0.1MnOy

The effect of the variation of oxygen content on structural, magnetic and transport properties in the electron-doped manganites La0.9Te0.1MnOy has been investigated. All samples show a rhombohedral structure with the space group R3C. The Curie temperature T-C decreases and the paramagnetic-ferromagnetic (PM-FM) transition becomes broader with the reduction of oxygen content. The resistivity of the annealed samples increases slightly with a small reduction of oxygen content. Further reduction in the oxygen content, the resistivity maximum increases by six orders of magnitude compared with that of the as-prepared sample, and the p(T) curves of samples with y = 2.86 and y = 2.83 display the semiconducting behavior (dp/dT < 0) in both high-temperature PM phase and low-temperature FM phase, which is considered to be related to the appearance of superexchange ferromagnetism and the localization of carriers. The results are discussed in terms of the combined effects of the increase in the Mn2+/(Mn2+ + Mn3+) ratio, the partial destruction of double exchange interaction, and the localization of carriers due to the introduction of oxygen vacancies in the Mn-O-Mn network. (C) 2004 Elsevier Ltd. All rights reserved.