Magnetic Phase Separation in La$_{1-x}$Sr$_{x}$CoO$_{3}$ Single Crystals using $^{139}$La NMR.

Nano-scale phase separation appears to occur in a number of doped transition metal oxides and has been shown to be important in the cobaltites. LSCO is a mixed valence (Co$^{3+}$, Co$^{4+})$ near-cubic perovskite. We report $^{139}$La NMR experiments on nanoscale phase separation in single crystals complementing earlier work on sintered powders$^{1}$. Concentrations in the range x=0.05 to 0.30, spanning the metal-insulator transition at x=0.18, were used. Spectra for x=0.30 reveal a single peak showing long-range FM order with an internal transferred hyperfine field of 2.5T, at the La site. NMR spectra for samples with x$<$0.30 show asymmetric peaks that can be well fitted with two Gaussian's, evidence of FM and spin/cluster-glass magnetic phases. A droplet model has been proposed in the literature, where Co neighbors interact via double exchange in hole-rich regions to form the FM phase. We find magnetic phase separation persists over a narrower x range in the single crystals than in previously studied sintered samples$^{1}$. 1) M.J.R Hoch et al. PRB 70, 174443 (2004)