We now consider the same crystal as above, but in an antiferromagnetic state. If the magnetic moments of two adjacent layers are oriented antiparallely, the magnetic unit cell is twice the size of the "normal" chemical unti cell, and the distance between two identical magnetic layers, dmag, is twice the distance between lattice planes in the normal case:
Applying Bragg's law using this magnetic distance,
= 2 dmag
sin(
mag)
= 4 d
sin()
we see that now additional Bragg reflections are allowed, so-called superstructure peaks.
This is obviously a oversimplified picture, but you get the idea.
