Zigzag spin structure in layered honeycomb Li3Ni2SbO6 : A combined diffraction and antiferromagnetic resonance study

The magnetic structure of $\mathrm{L}{\mathrm{i}}_{3}\mathrm{N}{\mathrm{i}}_{2}\mathrm{Sb}{\mathrm{O}}_{6}$ has been determined by low-temperature neutron diffraction, and the crystal structure has been refined by a combination of synchrotron and neutron powder diffraction. The monoclinic ($C2/m$) symmetry, assigned previously to this pseudohexagonal layered structure, has been unambiguously proven by peak splitting in the synchrotron diffraction pattern. The structure is based on essentially hexagonal honeycomb-ordered $\mathrm{N}{\mathrm{i}}_{2}\mathrm{Sb}{\mathrm{O}}_{6}$ layers alternating with $\mathrm{L}{\mathrm{i}}_{3}$ layers, all cations and anions being in an octahedral environment. The compound orders antiferromagnetically below ${T}_{\mathrm{N}}=15\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, with the magnetic supercell being a $2a\ifmmode\times\else\texttimes\fi{}2b$ multiple of the crystal cell. The magnetic structure within the honeycomb layer consists of zigzag ferromagnetic spin chains coupled antiferromagnetically. The ordered magnetic moment amounts to $1.62(2)\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{Ni}$, which is slightly lower than the full theoretical value. Upon cooling below ${T}_{\mathrm{N}}$, the spins tilt from the $c$ axis, with a maximum tilting angle of $15.{6}^{\ensuremath{\circ}}$ at $T=1.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Our data imply non-negligible ferromagnetic interactions between the honeycomb layers. The observed antiferromagnetic resonance modes are in agreement with the two-sublattice model derived from the neutron data. Orthorhombic anisotropy shows up in zero-field splitting of $\mathrm{\ensuremath{\Delta}}=198\ifmmode\pm\else\textpm\fi{}4$ and $218\ifmmode\pm\else\textpm\fi{}4\phantom{\rule{0.16em}{0ex}}\mathrm{GHz}$. Above ${T}_{\mathrm{N}}$, the electron spin resonance data imply short-range antiferromagnetic order up to about 80 K.