1202.3995 (Feng Ye et al.)

Direct evidence of a zigzag spin chain structure in the honeycomb
lattice: A neutron and x-ray diffraction investigation on single crystal $\rm
Na_2IrO_3$    [PDF]

Feng Ye, Songxue Chi, Huibo Cao, Bryan C. Chakoumakos, Jaime A. Fernandez-Baca, Radu Custelcean, Tongfei Qi, O. B. Korneta, G. Cao

We have combined single crystal neutron and x-ray diffractions to investigate
the magnetic and crystal structures of the honeycomb lattice $\rm Na_2IrO_3$.
The system orders magnetically below $18.1(2)$ K with Ir$^{4+}$ ions forming
zigzag spin chains within the layered honeycomb network with ordered moment of
$\rm 0.22(1) \mu_B$/Ir site. Such a configuration sharply contrasts the
N{\'{e}}el or stripe states proposed in the Kitaev-Heisenberg model. The
structure refinement reveals that the Ir atoms form nearly ideal 2D honeycomb
lattice while the $\rm IrO_6$ octahedra experience a trigonal distortion that
is critical to the ground state. The results of this study provide much-needed
experimental insights into the magnetic and crystal structure crucial to the
understanding of the exotic magnetic order and possible topological
characteristics in the 5$d$-electron based honeycomb lattice.

View original: http://arxiv.org/abs/1202.3995