Indétermination sur les dimensions de la maille magnétique dans l'étude par diffraction neutronique sur poudres de corps cubiques ou uniaxes

An ambiguity arises in the study by powder neutron diffraction of compounds where the magnetic atoms lie on a uniaxial or cubic Bravais lattice, when the magnetic lines are indexed {kl} or {l}. Many multiaxial configurations, all having the same isotropic coupling energy, are compatible with a given set of lines. For a simple cubic lattice it is shown that every multiaxial configuration is indistinguishable, using powder intensities, from a particular uniaxial one, and that both have the same dipolar energy.