ENHANCEMENT OF THE MAGNETO RESISTANCE DUE TO STRUCTURAL TRANSITION INMG-DOPED PEROVSKITE MN OXIDES

Substitution of magnesium for manganese in mixed perovskite La1-xSrxMn O3 was found to reduce the electrical conductivity and the Curie temer ature T-c. A remarkable jump in the resistivity rho was observed in th e 6% Mg-doped crystal with x = 0.175. This sample remains semiconducti ng at low temperatures, contrary to the Mg-free crystal. The abrupt ch ange of rho reflects a first-order structural transition at a temperat ure T-s just below T-c. An applied magnetic field decreased T-s, leadi ng 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 resonanc e study. (C) 1996 American Institute of Physics.