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Magnetic Fluctuations in the Metallic State of Na$_{0.7}$CoO$_2$ Revealed by $^{23}$Na NMR

Y. Ihara·K. Ishida·C. Michioka·M. Kato·K. Yoshimura·H. Sakurai·E. Takayama-Muromachi
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Abstract

Nuclear-magnetic-resonance (NMR) studies were performed in Na$_{0.7}$CoO$_2$ to investigate its magnetic properties from the microscopic point of view. Na$_{0.7}$CoO$_2$ is a starting compound of the recently discovered superconductor Na$_{0.35}$CoO$_2$$\cdot 1.3$H$_2$O, in which Co atoms form a triangular structure. Although $^{23}$Na-NMR results show no magnetic anomaly down to 1.5 K, Knight shift ($^{23}K$) and $^{23}(1/T_1T)$ of $^{23}$Na continue to increase, suggestive of the vicinity of the magnetic phase. From the relation between $^{23}K$ and $^{23}(1/T_1T)$, it is shown that ferromagnetic fluctuations are dominant below 100 K. In addition to the ferromagnetic correlations, antiferromagnetic fluctuations are also developed in a low temperature region below 4 K. Magnetic fluctuations suggested by our experiment are discussed.

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Y. Ihara, K. Ishida, C. Michioka, M. Kato, K. Yoshimura, H. Sakurai, E. Takayama-Muromachi. 2004-07-08. Magnetic Fluctuations in the Metallic State of Na$_{0.7}$CoO$_2$ Revealed by $^{23}$Na NMR. https://doi.org/10.1143/jpsj.73.2963

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