In-plane Anisotropy of the Magnetic Fluctuations in NaxCoO2-yH2O

C. Michioka; Y. Itoh; H. Ohta; M. Kato; K. Yoshimura

doi:10.1016/j.jpcs.2007.08.035

paper

In-plane Anisotropy of the Magnetic Fluctuations in NaxCoO2-yH2O

arXiv:cond-mat/0607368 · doi:10.1016/j.jpcs.2007.08.035

Abstract

We report the $^{59}$ Co NMR studies of the in-plane anisotropy of bilayer hydrated Na $_{x} Co O_{2} \cdot$ $y H_{2} O$ using a oriented powder sample by a magnetic field in Fluorinert FC70. We found for the first time the $ab$ -plane anisotropy of the $^{59}$ Co NMR Knight shift $K$ , the nuclear spin-lattice relaxation rate 1/ $T_{1}$ and the nuclear spin-spin relaxation rate 1/ $T_{2}$ at a magnetic field $H \sim$ 7.5 T up to 200K. Below 75 K, the anisotropy of $K$ is large compared with that at high temperatures. The hyperfine coupling constants seem to change around the temperature 150 K, in which the bulk susceptibility $χ$ shows broad minimum, suggesting a change of the electronic state of CoO $_{2}$ plane. 1/ $T_{1}$ also shows a significant anisotropy, which cannot be explained only by the anisotropy of the hyperfine coupling constants nor the anisotropic uniform spin susceptibility. The difference in the in-plane anisotropy of $T_{1}$ from that of $K$ indicates that the magnetic fluctuation at a finite wave vector $q \neq = 0$ is also anisotropic and the anisotropy is different from that at $q = 0$ .

arXiv comment4 pages, 5 figures

In-plane Anisotropy of the Magnetic Fluctuations in NaxCoO2-yH2O

Abstract

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