Weak Magnetic Order in the Bilayered-hydrate Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O Structure Probed by Co Nuclear Quadrupole Resonance - Proposed Phase Diagram in Superconducting Na$_x$CoO$_{2} \cdot$ $y$H$_2$O

Y. Ihara; K. Ishida; C. Michioka; M. Kato; K. Yoshimura; K. Takada; T. Sasaki; H. Sakurai; E. Takayama-Muromachi

doi:10.1143/JPSJ.74.867

paper

Weak Magnetic Order in the Bilayered-hydrate Na $_{x}$ CoO $_{2} \cdot y$ H $_{2}$ O Structure Probed by Co Nuclear Quadrupole Resonance - Proposed Phase Diagram in Superconducting Na $_{x}$ CoO $_{2} \cdot$ $y$ H $_{2}$ O

arXiv:cond-mat/0410478 · doi:10.1143/JPSJ.74.867

Abstract

A weak magnetic order was found in a non-superconducting bilayered-hydrate Na $_{x}$ CoO $_{2} \cdot y$ H $_{2}$ O sample by a Co Nuclear Quadrupole Resonance (NQR) measurement. The nuclear spin-lattice relaxation rate divided by temperature $1/ T_{1} T$ shows a prominent peak at 5.5 K, below which a Co-NQR peak splits due to an internal field at the Co site. From analyses of the Co NQR spectrum at 1.5 K, the internal field is evaluated to be $\sim$ 300 Oe and is in the $ab$ -plane. The magnitude of the internal field suggests that the ordered moment is as small as $\sim 0.015$ $μ_{B}$ using the hyperfine coupling constant reported previously. It is shown that the NQR frequency $ν_{Q}$ correlates with magnetic fluctuations from measurements of NQR spectra and $1/ T_{1} T$ in various samples. The higher- $ν_{Q}$ sample has the stronger magnetic fluctuations. A possible phase diagram in Na $_{x}$ CoO $_{2} \cdot y$ H $_{2}$ O is depicted using $T_{c}$ and $ν_{Q}$ , in which the crystal distortion along the c-axis of the tilted CoO $_{2}$ octahedron is considered to be a physical parameter. Superconductivity with the highest $T_{c}$ is seemingly observed in the vicinity of the magnetic phase, suggesting strongly that the magnetic fluctuations play an important role for the occurrence of the superconductivity.

5 pages, 6 figures, submitted to J. Phys. Soc. Jpn

Weak Magnetic Order in the Bilayered-hydrate Na $_{x}$ CoO $_{2} \cdot y$ H $_{2}$ O Structure Probed by Co Nuclear Quadrupole Resonance - Proposed Phase Diagram in Superconducting Na $_{x}$ CoO $_{2} \cdot$ $y$ H $_{2}$ O

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Weak Magnetic Order in the Bilayered-hydrate Nax​CoO2​⋅yH2​O Structure Probed by Co Nuclear Quadrupole Resonance - Proposed Phase Diagram in Superconducting Nax​CoO2​⋅ yH2​O

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Cited by in corpus (23)

Weak Magnetic Order in the Bilayered-hydrate Na $_{x}$ CoO $_{2} \cdot y$ H $_{2}$ O Structure Probed by Co Nuclear Quadrupole Resonance - Proposed Phase Diagram in Superconducting Na $_{x}$ CoO $_{2} \cdot$ $y$ H $_{2}$ O