Crystal growth and magnetic anisotropy in the spin-chain ruthenate Na 2 RuO 4

Abstract

We report single-crystal growth, electrical resistivity ρ, anisotropic magnetic susceptibility χ, and heat capacity Cp measurements on the one-dimensional spin-chain ruthenate Na2RuO4. We observe variable range hopping (VRH) behavior in ρ(T). The magnetic susceptibility with magnetic field perpendicular (χ¥) and parallel (χ¥) to the spin chains is reported. The magnetic properties are anisotropic with χ¥>χ¥ in the temperature range of measurements T≈2-305 K with χ¥/χ¥≈1.4 at 305 K. From an analysis of the χ(T) data we attempt to estimate the anisotropy in the g factor and Van Vleck paramagnetic contribution. An anomaly in χ(T) and a corresponding step-like anomaly in Cp at TN=37 K confirms long-range antiferromagnetic ordering. This temperature is an order of magnitude smaller than the Weiss temperature θ≈-250 K and points to suppression of long-range magnetic order due to low dimensionality. A fit of the experimental χ(T) by a one-dimensional spin-chain model gave an estimate of the intrachain exchange interaction 2J≈-85 K and the magnitude of the interchain coupling |2J¥|≈3 K.