periodic Néel state. This
is a two-dimensional non-collinear 120° structure of co-planar
spins forming 
angles between nearest neighbors.
A unit cell shown in red contains 3 atoms. The total magnetization M
in the unit cell is zero. In this picture, the spins are oriented in the
surface plane. The orientation of the spin with respect to the lattice
is determined by the spin-orbit interaction.