Magnetoresistance of the spin-state-transition compound La1-xSrxCoO3

We have investigated the magnetoresistance (MR) of the perovskite oxide La1-xSrxCoO3 for 0 less than or equal to x less than or equal to 0.4 which shows a spin-state transition from low-spin Co-III to high-spin Co3+ as a function of temperature. In the metallic compositions (x greater than or equal to 0.25) appreciable MR occurs only near the ferromagnetic Curie temperature. For the most metallic composition x=0.4, there is a small positive contribution to the MR near the T-c. In the insulating samples (x less than or equal to 0.2) the MR shows a large hysteresis which depends on the temperature. The value of the MR is negative and large in the insulating compositions and shows a maximum near the temperature when magnetic studies showed a spin-glass-like transition. We also find a strong role of the spin-state transition of the Co3+ ions in the electronic transport leading to a characteristic behavior of the MR in the Co3+-rich insulating samples.