Positive magnetoresistance in low-doped La1-xSrxMnO3 (x <= 0.14) perovskites

The magnetic and transport properties, under magnetic field and hydrostatic pressure, in a series of single crystalline samples of low-doped La1-xSrxM nO3 (0.1 less than or equal to x less than or equal to 0.14) manganites are studied. A region with positive magnetic resonance around T-FI is detected in samples with x = 0.1 and 0.125. At this temperature the transition from the ferromagnetic-metallic (FM-M) phase to the ferromagnetic orbital order ed-insulating (FI) low-temperature phase occurs. This transition is accompa nied by a substantial upward jump in resistance that appears on entering th e FI phase. A jump in the magnetization, on crossing T-FI downward, with re spect to that measured in the FM-M phase is also detected. (C) 2000 America n Institute of Physics. [S0021-8979(00)42008-6].