We study the high-temperature magnetic order in a quasi-two-dimensional honeycomb compound ${\mathrm{SrRu}}_2{\mathrm{O}}_6$ by measuring magnetization and neutron powder diffraction with both polarized and unpolarized neutrons. ${\mathrm{SrRu}}_2{\mathrm{O}}_6$ crystallizes into the hexagonal lead antimonate (${\mathrm{PbSb}}_2{\mathrm{O}}_6$, space group $P\overline{3}1m$) structure with layers of edge-sharing ${\mathrm{RuO}}_6$ octahedra separated by ${\mathrm{Sr}}^{2+}$ ions. ${\mathrm{SrRu}}_2{\mathrm{O}}_6$ is found to order at $T_N=565$ K with Ru moments coupled antiferromagnetically both in plane and out of plane. The magnetic moment is 1.30(2) ${\mu }_{\mathrm{B}}$/Ru at room temperature and is along the crystallographic $c$ axis in the G-type magnetic structure. We perform density functional calculations with constrained random-phase approximation (RPA) to obtain the electronic structure and effective intra- and interorbital interaction parameters. The projected density of states shows strong hybridization between Ru $4d$ and O $2p$. By downfolding to the target $t_{2g}$ bands we extract the effective magnetic Hamiltonian and perform Monte Carlo simulations to determine the transition temperature as a function of inter- and intraplane couplings. We find a weak interplane coupling, 3% of the strong intraplane coupling, permits three-dimensional magnetic order at the observed $T_N$.

• Received 14 April 2015

DOI:https://doi.org/10.1103/PhysRevB.92.100404