Abstract
The magnetic ground state of ${\mathrm{Sr}}_{3}A{\mathrm{RuO}}_{6}$, with $A=\phantom{\rule{0.28em}{0ex}}(\mathrm{Li},\mathrm{Na})$, is studied using neutron diffraction, resonant x-ray scattering, and laboratory characterization measurements of high-quality crystals. Combining these results allows us to observe the onset of long-range magnetic order and distinguish the symmetrically allowed magnetic models, identifying in-plane antiferromagnetic moments and a small ferromagnetic component along the $c$ axis. While the existence of magnetic domains masks the particular in-plane direction of the moments, it has been possible to elucidate the ground state using symmetry considerations. We find that due to the lack of local anisotropy, antisymmetric exchange interactions control the magnetic order, first through structural distortions that couple to in-plane antiferromagnetic moments and second through a high-order magnetoelastic coupling that lifts the degeneracy of the in-plane moments. The symmetry considerations used to rationalize the magnetic ground state are very general and will apply to many systems in this family, such as ${\mathrm{Ca}}_{3}A{\mathrm{RuO}}_{6}$, with $A=\phantom{\rule{0.28em}{0ex}}(\mathrm{Li},\mathrm{Na})$, and ${\mathrm{Ca}}_{3}{\mathrm{LiOsO}}_{6}$ whose magnetic ground states are still not completely understood.
Highlights
The variant of the hexagonal (2H) perovskite structure of general formula A3n+3mAnB3m+nO9m+6n has recently been the subject of extensive investigations
We find that due to the lack of local anisotropy, antisymmetric exchange interactions control the magnetic order, first through structural distortions that couple to in-plane antiferromagnetic moments and second through a high-order magnetoelastic coupling that lifts the degeneracy of the in-plane moments
Our results prove that antisymmetric exchange is crucial in establishing the ground state of this family of compounds
Summary
The variant of the hexagonal (2H) perovskite structure of general formula A3n+3mAnB3m+nO9m+6n has recently been the subject of extensive investigations. The Co3+ in the trigonal prismatic coordination has a strong spin-orbit interaction and the coupling with the triangular lattice leads to the realization of a frustrated Ising state with only partial magnetic order [3,4]. The investigation of this family of compounds has been extended to ions belonging to the 5d family, mostly to understand the changes induced by the presence of an even larger spin-orbit coupling; one of the most interesting systems reported is Sr3NiIrO6 [7] This compound, where Ni and Ir are magnetically active, presents many similarities with Ca3Co2O6, with the spin-orbit anisotropy and the triangular arrangement in antiferromagnetically coupled chains, possibly at the origin of a loss of long-range ordering with decreasing temperature [8]. + 1 or IRs, respectively, as secondary order parameters, potentially allowing small moments along the c axis
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