Bulk antiferromagnetism in Na0.82CoO2 single crystals

Susceptibility, specific heat, and muon spin rotation measurements on high-quality single crystals of Na 0 . 8 2 CoO 2 have revealed bulk antiferromagnetism with Neel temperature T N =19.8′0.1 K and an ordered moment perpendicular to the 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 N .