Evolution of the spin-state transition with doping in La1−xSrxCoO3

Abstract

The thermally induced spin-state transition of Co${}^{3+}$ ions in the cobaltite LaCoO${}_{3}$, found at temperatures in the range 40 to 120 K, has been the subject of extensive experimental and theoretical investigation. Much less is known about what happens to the spin-state transition in hole-doped La${}_{1\ensuremath{-}x}$Sr${}_{x}$CoO${}_{3}$ (LSCO). The present ${}^{139}$La NMR experiments show that spin-state transitions persist in nanoscale hole-poor regions of the inhomogeneous doped material. In fact, thermally induced spin-state transitions remain important for doping levels close to the metal-insulator critical concentration of ${x}_{C}=0.17$. This finding suggests that the unusual glassy behavior seen in doped LSCO for $x<0.18$ results from the interplay of spin-state transitions in hole-poor regions and ferromagnetism in hole-rich regions.