Structure and Magnetic Properties of Cu₃Ni₂SbO₆ and Cu₃Co₂SbO₆ Delafossites with Honeycomb Lattices

Abstract

The crystal structures of two Delafossites, Cu3Ni2SbO6 and Cu3Co2SbO6, are determined by high-resolution synchrotron powder X-ray diffraction. The Ni and Co are ordered with respect to Sb in the layer of edge sharing octahedra, forming magnetic layers with honeycomb geometry. High-resolution electron microscopy confirms ordering, and selected-area electron diffraction patterns identify examples of the stacking polytypes. Low temperature synthetic treatments result in disordered stacking of the layers, but heating just below their melting points results in nearly fully ordered stacking variants. The major variant in both cases is a monoclinic distortion of a 6-layer Delafossite polytype, but a significant amount of a 2-layer polytype is also present for the Ni case. The antiferromagnetic ordering with transitions, at 22.3 and 18.5 K for Ni and Co variants, respectively, is investigated by temperature and field dependent magnetization, as well as specific heat. The sharp magnetic transitions support the presence of well developed 2:1 ordering of the Co:Sb or Ni:Sb ions in the honeycomb layers. Neutron diffraction measurements at 4 K are used to determine the magnetic structures. For both the Ni and Co phases, the propagation vector is k = [100], and can be described as alternating ferromagnetic chains in the metal-oxide plane giving an overall antiferromagntic "zigzag" alignment. While orientation of the magnetic moments of the Co is along the b-axis, the Ni moments are in the ac plane, approximately parallel to the stacking direction. Bulk magnetization properties are discussed in terms of their magnetic structures.

Zigzag antiferromagnetic quantum ground state in monoclinic honeycomb lattice antimonatesA3Ni2SbO6(A=<

“…For example, a spin-gap behavior was found for O3-derived Cu 2+ honeycomb compounds Na 2 Cu 2 TeO 6 [10,11], Na 3 Cu 2 SbO 6 [11][12][13][14][15]35] [30]. Antiferromagnetic zigzag ordering in the honeycomb plane was observed recently for the structurally related honeycomb-lattice delafossites Cu 3 Ni 2 SbO 6 and Cu 3 Co 2 SbO 6 [31]. No long-range magnetic order was found for honeycomb Na 3 LiFeSbO 6 and Na 4 FeSbO 6 and Li 4 MnSbO 6 probably due to disorder and frustration effects [34,36].…”

“…The similar behavior was reported for several other structurally related honeycomb compounds recently. In particular two spin-reorientation transitions below Neel temperature were revealed for Na 3 Ni 2 BiO 6 [33] and for both 2H and 3R polytypes of Cu 3 Co 2 SbO 6 [31,66]. Remarkably, the magnetic structure as refined experimentally from low temperature neutron diffraction studies was described as alternating ferromagnetic chains coupled antiferromagnetically giving overall antiferromagnetic zigzag alignment for both Na 3 …”

“…No long-range magnetic order was found for honeycomb Na 3 LiFeSbO 6 and Na 4 FeSbO 6 and Li 4 MnSbO 6 probably due to disorder and frustration effects [34,36]. At the same time, honeycomb-ordered O3-derived phases Na 3 M 2 SbO 6 (M=Cu, Ni, Co) [17,19,31], Li 3 Ni 2 SbO 6 [20], Li 3 Ni 2 BiO 6 [21], Na 3 Ni 2 BiO 6 [33], as well as P2-derived Na 2 M 2 TeO 6 (M=Co, Ni) [18,19], were found to order antiferromagnetically at low temperatures but their real quantum ground state remains unknown and requires joint experimental and theoretical efforts to be determined. The influence of the interlayer coupling and of the anisotropy on the ground state in such systems is largely unexplored at present.…”

Zigzag antiferromagnetic ground state with anisotropic correlation lengths in the quasi-two-dimensional honeycomb lattice compoundNa2Co2TeO6Bera1, Yusuf2, Kumar3 et al. 2017Phys. Rev. B10614873View full textAdd to dashboardCite

“…Recently, density functional theory (DFT) calculations proposed a long-range zigzag AFM ordering for the compounds Li 3 Ni 2 SbO 6 and Na 3 Ni 2 SbO. An AFM ordering at low temperatures was also reported for the O3 type honeycomb compounds Na 3 M 2 SbO 6 (M = Cu, Ni, and Co) [16,31,32], A 3 Ni 2 BiO 6 with A = Na and Li [25,33] and Li 3 Ni 2 SbO 6 [24], as well as for the P2 type compounds Na 2 M 2 TeO 6 (M = Co and Ni) [31,32,34], however, their real quantum ground states remain unknown and await for an experimental investigation. The influence of the intermediate soft Na/Li layers on the magnetic correlations remains as well unexplored in these systems.…”

Ground-state phases of the spin-1J1−J2Heisenberg antiferromagnet on the honeycomb lattice

“…Also, the iridates A 2 IrO 3 (A = Na, Li) [40][41][42][43] are believed to be magnetically ordered Mott insulator materials in which the Ir 4+ ions, which are disposed in weakly coupled honeycomb-lattice layers, have effective s = 1 2 moments. The two families of compounds BaM 2 (XO 4 ) 2 (M = Co, Ni; X = P, As) [44] and Cu 3 M 2 SbO 6 (M = Co, Ni) [45] also comprise similar quasi-2D materials, in each of which the magnetic M 2+ ions occupy the sites of weakly coupled honeycomb-lattice layers. In both of these families, the magnetic Ni 2+ ions are believed to take the high-spin value s = 1.…”