TRANSPORT-PROPERTIES AND MAGNETIC-BEHAVIOR OF LA1-XSRXMNO3 SINGLE-CRYSTALS

A semiconductor-metal transition occuring just below the Curie tempera ture T-C was observed in single crystals of perovskite La1-xSrxMnO3 fo r x greater than or equal to 0.175. For x less than or equal to 0.15 t he crystals exhibit only semiconducting behaviour. These transport pro perties are closely connected with the electron transfer mediated by t he double exchange interaction between Mn3+ and Mn4+ ions. The electro nic state of manganese in these mixed systems is well illustrated by M n-55 nuclear magnetic resonance study. A maximum in the magnetoresista nce (MR) was observed near T-C for the crystals with x greater than or equal to 0.13 whereas huge MR persists well below T-C for the x = 0.1 0 sample, which is probably due to a non-collinear spin configuration.