Transport properties and magnetic behaviour of La_1-xSr_xMnO₃ single crystals

A semiconductor-metal transition occurring just below the Curie temperature T_C was observed in single crystals of perovskite La_1-xSr_xMnO₃ for x>or=0.175. For x<or=0.15 the crystals exhibit only semiconducting behaviour. These transport properties are closely connected with the electron transfer mediated by the double exchange interaction between Mn³⁺ and Mn⁴⁺ ions. The electronic state of manganese in these mixed systems is well illustrated by ⁵⁵Mn nuclear magnetic resonance study. A maximum in the magnetoresistance (MR) was observed near T_C for the crystals with x>or=0.13 whereas huge MR persists well below T_C for the x=0.10 sample, which is probably due to a non-collinear spin configuration.