Magnetic ordering in hydrated cobaltate [formula omitted

Abstract

We performed Co nuclear quadrupole resonance (NQR) measurements on bilayered hydrate cobaltate Na x ( H 3 O ) z CoO 2 · y H 2 O . The sample we used demonstrates a magnetic transition at T M ∼ 6 K , which is observed from susceptibility, nuclear spin-lattice relaxation rate, and NQR spectrum measurements. We observed inhomogeneous broadening of the NQR spectrum below T M . In order to interpret the internal field distribution, we numerically solved a nuclear-spin Hamiltonian including the nuclear quadrupole interaction and the Zeeman interaction, and estimated the internal fields from the observed Co-NQR spectrum. It is considered that the internal fields possess weak modulation. The obtained internal-field distribution suggests the occurrence of the spin-density-wave ordering.