Influence of annealing atmosphere on the properties of La0.5Sr0.5MnO3

The structure, magnetic and electrical transport properties of La0.5Sr0.5MnO3 annealed in different atmosphere have been investigated. No evident change of structural symmetry and the Curie temperature is observed for the samples. The resistivity at zero magnetic field of the samples annealed in air and nitrogen exhibits a metal–insulator transition, while no metal–insulator transition is observed for the sample annealed in oxygen, and for which the resistivity decreases monotonously with increasing temperature. Surprisingly, when an external magnetic field is applied, a metal–insulator transition appears for the sample annealed in oxygen. It is suggested that the annealing atmosphere affects the competition between FM and AFM phases due to the change of Mn4+/Mn3+ ratio and the oxygen/cation vacancies, and has a great influence on the electrical transport properties of La0.5Sr0.5MnO3.