Phenomenological Landau analysis of predicted magnetoelectric fluorides:: KMnFeF6 and Ba2Ni7F18

Recently, on the basis of symmetry considerations, we predicted that KMnFeF6 and Ba2Ni7F18 are likely magnetoelectric multiferroic materials. In this contribution, we investigate using Landau theory and crystal structure considerations the polarization and the linear magnetoelectric effect in these materials. Based on these two examples, we show that any magnetoferroelectric will display additional electrical polarization below its magnetic ordering temperature. This additional electrical polarization is not related to the linear magnetoelectric effect. Its magnitude depends on the dielectric susceptibility.