, that characterizes
the magnitude and/or orientation of the magnetic moment, 
, of the n-th atom as a function of its position, 
:
In general, an antiferromagnetic structure can be described by a
modulation wave vector, , that characterizes
the magnitude and/or orientation of the magnetic moment, , of the n-th atom as a function of its position, :
A spin wave can be described by a real 
, a
spiral structure requires a complex . For a
ferromagnet, the modulation wave vector vanishes.
The scattering amplitude for spin scattering, for example, may then be written as:
Bragg's law for magnetic scattering is then written as:
where G is a reciprocal lattice vector of the non-magnetic structure. We see that magnetic scattering appears in the form of satellites of charge peaks. These magnetic Bragg peaks can be observed with neutron and x-ray scattering. Notice that for antiferromagnets the charge and magnetic reflections are usually well separated, so that there are no interference effects between them.
