Spin-state-driven metal-insulator transition in (La,Sr)CoO3 under high-pressure

Using Co K beta x-ray emission spectroscopy (XES) we have investigated the effect of pressure on the Co spin state of a single crystal of metallic, ferromagnetic La0.82Sr0.18CoO3. The analysis of the XES spectra up to 14.4 GPa at 300 and 34 K clearly shows a gradual pressure-induced spin-state transition from a high- or intermediate-spin to a low-spin state. These results provide microscopic evidence that the recently observed pressure-induced metal-insulator transition in (La,Sr)CoO3 is driven by a simultaneous spin-state transition. We further show that under high pressures the low-spin state is relatively stable against temperature, in contrast to that in the LaCoO3 case. This is attributed to an enhancement of the crystal field splitting at high pressures.