The nature of the magnetic transition of the Na-rich thermoelectric Na0.75CoO2 at 22 K was studied by positive muon-spin-rotation and relaxation (μ+SR) spectroscopy, using a polycrystalline sample in the temperature range between 300 and 2.5 K. Zero-field μSR measurements indicated the existence of a static internal magnetic field at temperatures below 22 K (= Tm). The observed muon-spin precession signal below Tm consisted of three components with different precession frequencies, corresponding to three inequivalent μ+ sites in the Na0.75CoO2 lattice. The total volume fraction of the three components was estimated as 21% at 2.5 K; thus, this magnetic transition was not induced by impurities but is an intrinsic change in the magnetism of the sample, although the sample was magnetically inhomogeneous otherwise. On the other hand, a similar experiment on a Na0.65CoO2 sample exhibited no magnetic transition down to 2.5 K; which indicates that the average valence of the Co ions is responsible for inducing the magnetic transition at 22 K.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 17 Jun 2003|
|MoE publication type||A1 Journal article-refereed|