Zig-zag magnetic ordering in honeycomb-layered Na3Co2SbO6

Abstract

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 effec- tive magnetic moment of 5.22 μB (indicating a strong orbital contribution above the expected spin-only value of 3.87 μB). While a honeycomb arrangement of magnetic cations could, in principle, support a co-operative long-range-ordered magnetic struc- ture 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 N ́eel tempera- ture and Weiss constant of θ = 2.2 K underlines the presence of significant frustration of the expected strong superexchange interactions among Co2+.