Figure 2:
Spin-Spiral State: (or spin-density wave)
Shown are several spin-spiral states 
as
function of the wave-vector 
pointing from left
to right. The upper two spin-configurations show transversal spin-spiral
states (the spin-rotation axis 
is normal to
wave vector
, 
, and the lower two spin-configurations show a longitudinal spin-spiral
state (the spin-rotation axis is parallel to
the wave vector , 
.
, 
defines the tild-angle 
of 
with respect to the rotation axis . The second
spin-configurations of the transversal and longitudinal spin-spiral state
show the special case of 
.