EXTINCTIONS IN SCATTERING FROM MAGNETICALLY ORDERED QUASIPERIODIC CRYSTALS

I shall discuss here the relation between the symmetry of a magnetic crystal and ex-tinctions in its neutron diffraction diagram. In doing so I shall provide an outline of a symmetry classification scheme for magnetically ordered crystals: A scheme which is in-spired by the spin-group classification of Litvin and Opechowski [1] in which the magnetic crystal is described by a spin density field S(r), left invariant by a set of rigid motions in physical space combined with primed or unprimed 1 proper rotations in spin space. Two aspects of my presentation should be emphasized from the start: (i) I have extended Litvin and Opechowski’s original scheme to deal with quasiperi-odic as well as periodic crystals. This includes any spin density field whose Fourier expansion requires only a discrete set L of wave vectors S(r) = k∈