Evolution of the spin-state transition with doping in La_(1-x)Sr_xCoO_3

摘要

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-x)Sr_xCoO_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.