Phase separation in Nd1-xSrxCoO3 using Co-59 NMR

Abstract

Co-59 nuclear magnetic resonance (NMR) studies have been made to clarify the spin-state and local magnetic properties of Nd1-xSrxCoO3 (0less than or equal toxless than or equal to0.5). Three different types of Co NMR spectra are obtained. The parent NdCoO3 exhibits only one type of a resonance line associated with the low spin state of Co3+ ion. The temperature dependence of spectra indicates gradual transition from low spin (T=0 K) to intermediate spin state. A similar feature has been observed in sample with x=0.05. In the range 0.1less than or equal toxless than or equal to0.2, the spectra consist of two components of resonance lines. The first component is similar to that obtained in NdCoO3, while the second one (much weaker) has been attributed to Co3+ ions (also having low spin) surrounded by few Co4+ ions among its LS/IS Co3+ neighbors. For the samples 0.3less than or equal toxless than or equal to0.5, 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 Nd0.7Sr0.3CoO3. 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.