${}^{59}\mathrm{Co}$ nuclear magnetic resonance (NMR) studies have been made to clarify the spin-state and local magnetic properties of ${\mathrm{Nd}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CoO}}_3$ $(0\mathrm{}<~x<~0.5).$ Three different types of Co NMR spectra are obtained. The parent ${\mathrm{NdCoO}}_3$ exhibits only one type of a resonance line associated with the low spin state of ${\mathrm{Co}}^{3+}$ ion. The temperature dependence of spectra indicates gradual transition from low spin $(T=0\mathrm{}\mathrm{K})$ to intermediate spin state. A similar feature has been observed in sample with $x=\mathrm{0.05.}\mathrm{}$ In the range $0.1<~x<~0.2,$ the spectra consist of two components of resonance lines. The first component is similar to that obtained in ${\mathrm{NdCoO}}_3,$ while the second one (much weaker) has been attributed to ${\mathrm{Co}}^{3+}$ ions (also having low spin) surrounded by few ${\mathrm{Co}}^{4+}$ ions among its LS/IS ${\mathrm{Co}}^{3+}$ neighbors. For the samples $0.3<~x<~0.5,$ only the signal of the second type is observed; the first type becomes too broadened to be detected. This signal remains almost unchanged down to 1.5 K, as has been observed in ${\mathrm{Nd}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{CoO}}_3.$ Also in the above sample, a very broad signal from Co ions with average internal field of 13 T appears at 1.5 K. This signal is ascribed to the ferromagnetic metalliclike parts of the sample. These data are consistent with the possible phase separation scenario in doped cobaltites.

• Received 15 September 2003

DOI:https://doi.org/10.1103/PhysRevB.69.064424