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The charge ordered state in half-doped Bi-based manganites studied by $^{17}$O and $^{209}$Bi NMR

A. Trokiner·S. Verkhovskii·A. Yakubovskii·K. Kumagai·S-W. Cheong·D. Khomskii·Y. Furukawa·J. S. Ahn·A. Pogudin·V. Ogloblichev·A. Gerashenko·K. Mikhalev·Yu. Piskunov
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Abstract

We present a $^{209}$Bi and $^{17}$O NMR study of the Mn electron spin correlations developed in the charge ordered state of Bi$_{0.5}$Sr$_{0.5}$MnO$_{3}$ and Bi$_{0.5}$Ca$_{0.5}$MnO$_{3}$. The unusually large local magnetic field $^{209}H_{loc}$ indicates the dominant $6s^{2}$ character of the lone electron pair of Bi$^{3+}$-ions in both compounds. The mechanism connecting the $s$ character of the lone pairs to the high temperature of charge ordering $T_{CO}$ is still not clarified. The observed difference in $^{209}H_{loc}$ for Bi$_{0.5}$Sr$_{0.5}$MnO$_{3}$ to Bi$_{0.5}$Ca$_{0.5}$MnO$_{3}$ is probably due to a decrease in the canting of the staggered magnetic moments of Mn$^{3+}$-ions from. The modification of the $^{17}$O spectra below $T_{CO}$ demonstrates that the line due to the apical oxygens is a unique local tool to study the development of the Mn spin correlations. In the AF state the analysis of the $^{17}$O spectrum of Pr$_{0.5}$Ca$_{0.5}$MnO$_{3}$ and Bi$_{0.5}$Sr$_{0.5}$MnO$_{3}$ prompts us to try two different theoretical descriptions of the charge-ordered state, a site-centered model for the first manganite and a bond-centered model for the second one.

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A. Trokiner, S. Verkhovskii, A. Yakubovskii, K. Kumagai, S-W. Cheong, D. Khomskii, Y. Furukawa, J. S. Ahn, A. Pogudin, V. Ogloblichev, A. Gerashenko, K. Mikhalev, Yu. Piskunov. 2005-04-26. The charge ordered state in half-doped Bi-based manganites studied by $^{17}$O and $^{209}$Bi NMR. https://doi.org/10.1103/physrevb.72.054442

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