Phase separation and inhomogeneity in La$_{1-x}$Sr$_{x}$CoO$_{3}$ single crystals

Nanoscale inhomogeneity in La$_{1-x}$ Sr$_{x}$CoO$_{3}$ has been studied in single crystal samples for 0.05$\le $ x $\le $0.3 using $^{139}$La NMR as a probe of the internal magnetic field distribution. The results show that phase separation occurs for x near the metal-insulator critical concentration x$_{C }$=0.17. The phase separation is confined to a much smaller range of x than that previously found in polycrystalline samples even though the bulk magnetic properties are similar. In single crystals with increasing x large, spin polarized (FM) regions merge into networks while smaller regions, identified as spin polarons, coexist with the larger regions. Insight into phase separation has been obtained by simulating the spectra with statistical model A phase diagram summarizing the evolution of the inhomogeneous internal field distribution with x and T will be presented.