Exchange integrals in magnetoelectric hexagonal ferrite (SrCo2Ti2Fe8O19): A density functional study

The exchange integrals in magnetoelectric hexagonal ferrite SrCo2Ti2Fe8O19 have been calculated by using density functional theory. To get 10 inter-sublattice and 3 intra-sublattice exchange integrals, the electronic structures and total energies of 20 spin arrangements have been calculated with General Gradient Approximation (GGA) + U method. The dependence of exchange integrals on U has been studied. The comparison between the exchange integrals in SrFe12O19 and those in SrCo2Ti2Fe8O19 shows that substitution of Co and Ti decreases the most interactions involving the 12 k sites. The investigation based on our exchange integrals indicates that magnetic interaction between R and S blocks reduces significantly in SrCo2Ti2Fe8O19