Magnetoresistance of the spin-state-transition compound ${\mathrm{La}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CoO}}_3$

We have investigated the magnetoresistance (MR) of the perovskite oxide ${\mathrm{La}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{CoO}}_3$ for 0 ⩽x⩽0.4 which shows a spin-state transition from low-spin ${\mathrm{Co}}^{\mathrm{III}}$ to high-spin ${\mathrm{Co}}^{3+}$ as a function of temperature. In the metallic compositions (x⩾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 ${\mathit{T}}_{\mathit{c}}$. In the insulating samples (x⩽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 where magnetic studies showed a spin-glass-like transition. We also find a strong role of the spin-state transition of the ${\mathrm{Co}}^{3+}$ ions in the electronic transport leading to a characteristic behavior of the MR in the ${\mathrm{Co}}^{3+}$-rich insulating samples. © 1996 The American Physical Society.