Magnetic ordering of the buckled honeycomb lattice antiferromagnetBa2NiTeO6

Abstract

We investigate the magnetic order of the buckled honeycomb lattice antiferromagnet ${\mathrm{Ba}}_{2}{\mathrm{NiTeO}}_{6}$ and its related antiferromagnet ${\mathrm{Ba}}_{3}{\mathrm{NiTa}}_{2}{\mathrm{O}}_{9}$ by neutron diffraction measurements. We observe magnetic Bragg peaks below the transition temperatures, and identify propagation vectors for these oxides. A combination of representation analysis and Rietveld refinement leads to a collinear magnetic order for ${\mathrm{Ba}}_{2}{\mathrm{NiTeO}}_{6}$ and a ${120}^{\ensuremath{\circ}}$ structure for ${\mathrm{Ba}}_{3}{\mathrm{NiTa}}_{2}{\mathrm{O}}_{9}$. We find that the spin model of the bilayer triangular lattice is equivalent to that of the two-dimensional buckled honeycomb lattice having magnetic frustration. We discuss the magnetic interactions and single-ion anisotropy of $\mathrm{Ni}^{2+}$ ions for ${\mathrm{Ba}}_{2}{\mathrm{NiTeO}}_{6}$ in order to clarify the origin of the collinear magnetic structures. Our calculation suggests that the collinear magnetic order of ${\mathrm{Ba}}_{2}{\mathrm{NiTeO}}_{6}$ is induced by the magnetic frustration and easy-axis anisotropy.