Bulk antiferromagnetism inNa0.82CoO2single crystals

Abstract

Susceptibility, specific heat, and muon spin rotation measurements on high-quality single crystals of ${\mathrm{Na}}_{0.82}{\mathrm{CoO}}_2$ have revealed bulk antiferromagnetism with Néel temperature $T_{\mathrm{N}}=19.8\mathrm{}\pm 0.1\mathrm{K}$ and an ordered moment perpendicular to the ${\mathrm{CoO}}_2$ layers. The magnetic order encompasses nearly 100% of the crystal volume. The susceptibility exhibits a broad peak around 30 K, characteristic of two-dimensional antiferromagnetic fluctuations. The in-plane resistivity is metallic at high temperatures and exhibits a minimum at $T_{\mathrm{N}}.$