Zig-zag magnetic ordering in honeycomb-layered Na3Co2SbO6

Na3Co2SbO6 is a layered oxide with a hexagonal O3-type structure, in which CdI2-type edge-sharing MO6 octahedral layers are intercalated by Na. The MO6 octahedral layer in turn adopts a honeycomb ordering pattern of magnetic (S=3/2) Co2+ sites surrounding isolated non-magnetic Sb5+ sites. Magnetic susceptibility measurements show that Na3Co2SbO6 orders antiferromagnetically below TN=8.3 K, with an effective magnetic moment of 5.22 μB (indicating a strong orbital contribution above the expected spin-only value of 3.87μB). While a honeycomb arrangement of magnetic cations could, in principle, support a co-operative long-range-ordered magnetic structure in which all nearest neighbors are antiferromagnetic with respect to one another, symmetry analysis of low-temperature neutron powder diffraction data shows that it instead adopts a partially frustrated ‘zig-zag’ ordering in which 2/3 of nearest-neighbor interactions are ferromagnetic and 1/3 are antiferromagnetic. The low Néel temperature and Weiss constant of θ=2.2K underlines the presence of significant frustration of the expected strong superexchange interactions among Co2+.

‘Zig-zag’ magnetic structure of a honeycomb layer of Na3Co2SbO6.CoO6 octahedra are blue, Sb atoms are gray, red and green arrows are equal and opposite magnetic moments on Co(II) sites.Figure optionsDownload as PowerPoint slide