Search for Magnetic Excitation Spectra of NaxCoO2.yD2O -Neutron Scattering-

TL;DR

This study used neutron scattering to investigate magnetic and phononic excitations in NaxCoO2.yD2O, finding strong phonon signals from D2O molecules but weak magnetic fluctuations, especially ferromagnetic, in the deuterated system.

Contribution

It provides the first detailed neutron scattering analysis of magnetic and phononic excitations in NaxCoO2.yD2O, highlighting the weak magnetic fluctuations in the deuterated compound.

Findings

Significant phonon scattering from D2O molecules.

No strong evidence of magnetic fluctuations in the deuterated system.

Weak antiferromagnetic fluctuations in non-deuterated parts.

Abstract

Neutron inelastic scattering studies on aligned crystals of NaxCoO2.yD2O have been carried out. Significant scattering has been observed for phonons originating from the vibrations of the short-range ordered D2O molecules. No firm evidence for the magnetic fluctuations has been found for the NaxCoO2.yD2O, while the very weak intensity modulation observed in the j scans along (1/2, 1/2, j) suggests the existence of the antiferromagnetic fluctuations in the non-deuterated parts of the sample, the volume fraction of which is estimated to be about 26 %. The present results indicate that magnetic fluctuations, especially ferromagnetic ones are rather weak, in the deuterated system, which is consistent with the results of the NMR Knight shift reported by the present authors' group. We discuss the short-range ordered state of D2O, too by analyzing the observed diffuse scattering.