MAGNETIC SYMMETRY AND FERROELECTRICITY INDUCED BY ANTIFERROMAGNETIC TRANSITIONS

Ferroelectricity is forbidden in centrosymmetric crystals. An antiferromagnetic transition in such crystals which results in a magnetic cell different from the chemical one may lead to noncentrosymmetric magnetic symmetry. It is therefore expected that ferroelectricity may be induced by such a transition. Neutron-diffraction experiments in CaMn2O4, TbCrO3, BiMn2O5 show that the magnetic transitions in these compounds belong to this category. To illustrate this effect from a symmetry point of view an antiferromagnetic transition in a structure belonging to the space group Pmma is considered. © 1969 The American Institute of Physics.