  A canonical band theory of non-collinear magnetism is developed and applied
to the close packed fcc and bcc crystal structures. Several examples of
non-collinear magnetism in the periodic table are seen to be canonical in
origin. This is a parameter free theory where the crystal and magnetic
symmetry, and exchange splitting, uniquely determine the electronic bands. The
only contribution to the determination of magnetic stability is the change in
band energy due to hybridisation resulting from spin mixing, and on this basis
we are able to analyse the origin of the stability of non-collinear magnetic
structures, and the instability of the FM state towards non-collinear ordering.
