Exchange interaction and conductivity in ferroelectric hexaferrite

Abstract

Ba 0.5Sr 1.5Zn 2Fe 12O 22 is a new promising multiferroic compound in which the existence of electric polarization is conditioned by the noncollinear arrangement of the iron spins. In principle, ferroelectricity might be present above the room temperature, but electrical conductivity prevents its observation at temperatures higher than ≈130 K. Our recent calculations showed that the electronic structure and in particular the conductivity is strongly influenced by relative fractions of iron and zinc in the tetrahedral sublattice of the spinel block in corresponding Y hexaferrite structure. In this paper, we show that the same holds for the exchange interactions. Dependence of the exchange integrals on the distribution of iron and zinc in the tetrahedral sublattice of the spinel block and on the content of Sr in Ba 2− x Sr x Zn 2Fe 12O 22 system is calculated using the ab initio approach with an improved treatment of strongly correlated 3d electrons of iron ions. The interaction between the two magnetic blocks that is decisive for the phase diagram is analysed in details.