Interplay between mesoscopic phase separation and bulk magnetism in the layered NaxCoO2

Abstract

Specific heat of layered NaxCoO2 (x=0.65, 0.70, and 0.75) oxides has been measured in the temperature range of 3-360 K and magnetic fields of 0 and 9 T. The analysis of data, assuming the combined effect of interlayer superexchange and the phase separation into mesoscopic magnetic domains with localized spins embedded in a matrix with an itinerant electronic character, suggests that the dominant contribution to the specific heat in the region of short-range ordering is mediated by quasi-two-dimensional antiferromagnetic clusters, perpendicular to the CoO2 layers.