Enhancement of the magneto resistance due to structural transition in Mg-doped perovskite Mn oxides

Substitution of magnesium for manganese in mixed perovskite La1-xSrxMnO3 was found to reduce the electrical conductivity and the Curie temerature T-c. A remarkable jump in the resistivity rho was observed in the 6% Mg-doped crystal with x = 0.175. This sample remains semiconducting at low temperatures, contrary to the Mg-free crystal. The abrupt change of rho reflects a first-order structural transition at a temperature T-s just below T-c. An applied magnetic field decreased T-s, leading to an enhancement of the magnetoresistance between T-s (0) and T-s (H). The microscopic properties of Mn3+ and Mn4+ ions due to Sr2+ and Mg2+ substitutions were illustrated by Mn-55 nuclear magnetic resonance study. (C) 1996 American Institute of Physics.