Synthesis, crystal and magnetic structure of the spin-chain compound Ag2RuO4

Abstract

We report synthesis and crystal structure refinement of $\mathrm{A}{\mathrm{g}}_{2}\mathrm{Ru}{\mathrm{O}}_{4}$, followed by combined analysis of its physical properties through bulk experimental tools (magnetic susceptibility, electron transport, and heat capacity measurements), a microscopic experimental tool (temperature dependent neutron diffraction), and ab initio first-principles calculations. We observe a rather unique ${(\mathrm{Ru}{\mathrm{O}}_{3/1}{\mathrm{O}}_{2/2})}_{\mathrm{n}}$ polyoxoanion, where Ru is in a distorted trigonal bipyramidal coordination by oxygen. The $\mathrm{Ru}{\mathrm{O}}_{5}$ polyhedra are linked via the apical oxygen atoms to form chains extending along the crystallographic $a$ axis. Crystal structure, magnetization, and ab initio calculations indicate that Ru is in the $+6$ oxidation state with a nominal valence electron configuration of $4{d}^{2}$. Bulk magnetization, specific-heat, and neutron-diffraction measurements provide clear indication of an antiferromagnetic transition around 75 K with moderate spin canting in the order of ${30}^{\ensuremath{\circ}}$ with respect to the $c$ axis. The neutron-diffraction results as well as the density functional theory based first-principles calculations of exchange interactions revealed that the strong intrachain interaction is predominantly of ferromagnetic (FM) type, and that this spin order along the chains couples with the neighboring chains through comparatively weak FM and antiferromagnetic interactions. Notably, the Land\'e $g$ factor is found to be 1.8 (with an infinite chain model and even a simple Curie-Weiss approach), away from the ideal value of 2, due to the low dimensionality of the Ru/O substructure.