Anisotropic magnetization and charge density wave in a Na0.78CoO2 single crystal

作者：Rhyee Jong Soo^*; Peng J B; Lin C T

来源：Journal of the Korean Physical Society, 2008, 52(2): 391-395.

• magnetic anisotropy
• crystal growth
• electron-phonon interactions
• valence fluctuations

Single crystals of gamma-Na0.78CoO2 were grown using the floating zone method. The static magnetic susceptibility M/H(T) of Na0.78CoO2 showed significant anisotropic behavior for different crystal orientations of H parallel to (ab) and H parallel to (c). While (M/H)(ab)(T) for a magnetic field H = 1 T in an ab-plane followed the Curie-Weiss law at high temperatures (T >= 100 K), (M/H)(c)(T) for H parallel to c-axis deviated from Curie-Weiss behavior, which may be understood by using phonon localization from strong electron-phonon coupling. The impurity spin-1/2 effect, dressed by spin fluctuation, was significant at low temperatures (T <= 30 K) for both field orientations of H parallel to (ab) and H parallel to (c). The electrical resistivity rho(T) of Na0.78CoO2 showed a clear metallic character down to 16 K, with a weak increase in the resistivity rho(T) at low temperatures (T <= 16 K). The gap-like behavior of rho(T) was insensitive to applied magnetic fields up to 7 T, which indicates a non-degenerate charge gap. The electrical conductivity sigma(T) followed the density wave behavior with a small energy gap (0.64 meV) at low temperatures. We discussed the electrical resistivity rho(T) and the anisotropic M/H(T) behavior of Na0.78CoO2 in terms of the charge density wave and a strong electron-phonon interaction.

• 出版日期2008-2