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Magnetic ordering and spin waves in $\bf Na_{0.82}CoO_2$

S. P. Bayrakci·I. Mirebeau·P. Bourges·Y. Sidis·M. Enderle·J. Mesot·D. P. Chen·C. T. Lin·B. Keimer
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Abstract

Na$_x$CoO$_2$, the parent compound of the recently synthesized superconductor Na$_x$CoO$_2$:$y$H$_2$O, exhibits bulk antiferromagnetic order below $\sim20$ K for 0.75 $\leq x \leq$ 0.9. We have performed neutron scattering experiments in which we observed Bragg reflections corresponding to A-type antiferromagnetic order in a Na$_{0.82}$CoO$_2$ single crystal and characterized the corresponding spin-wave dispersions. The spin waves exhibit a strongly energy-dependent linewidth. The in-plane and out-of-plane exchange constants resulting from a fit to a nearest-neighbor Heisenberg model are similar in magnitude, which is unexpected in view of the layered crystal structure of Na$_{x}$CoO$_2$. Possible implications of these observations are discussed.

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S. P. Bayrakci, I. Mirebeau, P. Bourges, Y. Sidis, M. Enderle, J. Mesot, D. P. Chen, C. T. Lin, B. Keimer. 2005-03-29. Magnetic ordering and spin waves in $\bf Na_{0.82}CoO_2$. https://doi.org/10.1103/physrevlett.94.157205

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