Pressure-induced insulating state in (La,Sr)CoO₃

We have investigated the effect of pressure on the electronic, magnetic, and structural properties on a single crystal of conducting, ferromagnet (T$_{C}$=157K) La$_{0.82}$Sr$_{0.18}$CoO$_{3}$ located near the boundary of the metal-insulator transition. Contrary to the results reported on related systems, we find a transition from the conducting state to an insulating state and a decrease of T$_{C}$ with increasing pressure while the lattice structure remains unchanged. We show that this unusual behavior is driven by a gradual change of the spin state of Co$^{3+}$ ions from magnetic intermediate-spin (t$_{2g}^5$e$_{g}^{1}$; S=1) to a nonmagnetic low-spin (t$_{2g}^6$e$_{g}^{0}$; S=0) state.