High antiferromagnetic transition temperature of a honeycomb compound SrRu$_2$O$_6$

TL;DR

This study reveals that SrRu$_2$O$_6$ exhibits a remarkably high antiferromagnetic transition temperature of 565 K, with detailed experimental and theoretical analysis showing strong intra-plane magnetic interactions and weak inter-plane coupling.

Contribution

The paper combines neutron diffraction, magnetization measurements, and density functional calculations to elucidate the magnetic structure and high transition temperature of SrRu$_2$O$_6$, highlighting the role of intra-plane interactions.

Findings

SrRu$_2$O$_6$ orders antiferromagnetically at 565 K.

Magnetic moments are aligned along the c-axis with a magnitude of 1.30 μ_B.

Weak inter-plane coupling (~3%) allows three-dimensional magnetic order.

Abstract

The high temperature magnetic order in SrRu$_2$O$_6$ was studied by measuring magnetization and neutron powder diffraction with both polarized and unpolarized neutrons. SrRu$_2$O$_6$ crystallizes into the hexagonal lead antimonate (PbSb$_2$O$_6$, space group \textit{P}$\overline{3}$1\textit{m}) structure with layers of edge-sharing RuO$_6$ octahedra separated by Sr$^{2+}$ ions. SrRu$_2$O$_6$ orders 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 \textit{c}-axis in the G-type magnetic structure. We performed density functional calculations with constrained RPA to obtain the electronic structure and effective intra- and inter-orbital interaction parameters. The projected density of states show strong hybridization between Ru 4$d$ and O 2$p$. By downfolding to the target $t_{2g}$ bands we extracted the effective magnetic Hamiltonian. We performed Monte Carlo simulations to determine the transition temperature as a function of inter- and intra-plane couplings and find weak inter plane coupling, 3\% of the intra-plane coupling, permits three dimensional magnetic order at $T_N$. As suggested by the magnetic susceptibility, two-dimensional correlations persist above $T_N$ due to the strong intra-plane coupling.