Bulk antiferromagnetism in $\bf Na_{0.82}CoO_2$ single crystals

TL;DR

This study demonstrates bulk antiferromagnetism in Na_{0.82}CoO_2 single crystals with a Neel temperature near 20 K, characterized by susceptibility, specific heat, and muon spin rotation measurements, revealing nearly full-volume magnetic order.

Contribution

First comprehensive evidence of bulk antiferromagnetism in Na_{0.82}CoO_2 using multiple measurement techniques.

Findings

Neel temperature T_N ≈ 19.8 K

Magnetic order involves nearly 100% of the crystal volume

Susceptibility shows broad peak around 30 K indicating 2D antiferromagnetic fluctuations

Abstract

Susceptibility, specific heat, and muon spin rotation measurements on high-quality single crystals of $\rm Na_{0.82}CoO_2$ have revealed bulk antiferromagnetism with N\'{e}el temperature $\rm T_N = 19.8 \pm 0.1$ K and an ordered moment perpendicular to the $\rm CoO_2$ 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 $\rm T_N$.