Hole-Doping Effect on the Spin State and Microscopic Magnetic Properties of La_1-xSr_xCoO₃ (0\lex\le0.5): ⁵⁹Co and ¹³⁹La NMR Measurements

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^59Co and ^139La NMR measurements have been made to reveal microscopically the hole-doping effect on the spin state and magnetic properties of La_1-xSr_xCoO₃ (0{\le}x{\le}0.5). The signal from the Co atoms with no Sr nearest neighbors was observed in the spin-glass region below x_c--0.18. From the analysis of the temperature dependence of the Knight shift, the ground state of such Co atoms was found to be the trivalent low-spin state ¹A_1g. Above x_c, we observed at 4.2, K the ^59Co and ^139La signals which come from the cluster-glass region with a finite ferromagnetic correlation. Thus, it was microscopically confirmed that the boundary between the two regions is located at x_c--0.18.