F. Millot

Transport properties and magnetic behaviour of La1-xSrxMnO3 single crystals

A semiconductor-metal transition occurring just below the Curie temperature TC was observed in single crystals of perovskite La1-xSrxMnO3 for x>or=0.175. For x or=0.13 whereas huge MR persists well below TC for the x=0.10 sample, which is probably due to a non-collinear spin configuration.

Controlled reduction and oxidation of La0.85Sr0.15MnO3 single crystals

Abstract La 0.85 Sr 0.15 MnO 3 single crystals were grown by the floating zone method. They can be reversibly reduced under controlled oxygen partial pressure. Their defect chemistry is investigated together with the evolution of their cell parameters and that of their electric conductivity which is very sensitive to their oxygen content. On the other hand, stoichiometric crystals can be oxidized with a slow kinetics making possible the preparation of diphasic materials.

Transport properties and magnetic behavior of La1−xSrxMnO3 single crystals (abstract)

Single crystals of La1−xSrxMnO3 with x ranging from 0.06 to 0.42 have been investigated by various techniques: resistivity and magnetoresistance, superconducting quantum interference device magnetometry, and 55Mn nuclear magnetic resonance. In addition, for two Sr concentrations, x=0.13 and 0.25, the I(V) characteristic of the oxide‐metal junction has been measured versus temperature. Semiconductor‐metal transition occurring just below the Curie temperature Tc was observed for x≥0.175 whereas, for x≤0.15, the crystals exhibits only semiconducting behavior, in agreement in the previous studies. These transport properties are closely connected with the electron transfer mediated by the double exchange interaction between Mn3+ and Mn4+, as revealed by 55Mn spin‐echo experiments. A cusp in the magnetoresistance (MR) was observed near Tc for the crystals with x≥0.13 with typical maximum resistivity ratio R(0)/R(10 T)≊10; for the sample with x=0.1, the huge MR persists well below Tc≊140 K, which is probably due...