We present the results of measurements of the dc-magnetic susceptibility chi(T) and the 23Na-NMR response of Na_{0.70}CoO_{2} at temperatures between 50 and 340 K. The chi(T) data suggest that for T > 75 K, the Co ions adopt an effective configuration of Co^{3.4+}. The 23Na-NMR response reveals pronounced anomalies near 250 and 295 K, but no evidence for magnetic phase transitions is found in chi(T). Our data suggest the onset of a dramatic change in the Co 3d-electron spin dynamics at 295 K. This process is completed at 230 K. Our results maybe interpreted as evidence for either a tendency to electron localization or an unconventional charge-density wave phenomenon within the cobalt oxide layer, CoO_2, 3d electron system near room temperature.
@article{arxiv.cond-mat/0308383,
title = {Unconventional Charge Ordering in Na0.70CoO2 below 300 K},
author = {J. L. Gavilano and D. Rau and B. Pedrini and J. Hinderer and H. R. Ott and S. M. Kazakov and J. Karpinski},
journal= {arXiv preprint arXiv:cond-mat/0308383},
year = {2009}
}
Comments
4 pages, 4 figures, re-submitted to Physical Review Letters. The manuscript has been revised following the recommendations of the referees. The discussion section contains substantial changes