Synthesis and Magnetic Properties of M 2+ Ti 4+ Substituted Ba 12 Fe 28 Ti 15 O 84

We investigated the synthesis conditions and magnetic properties of M-Ti substituted Ba12Fe28Ti15O84 with initial compositions of Ba12Fe28-2xTi15+xMxO84 (M = Zn, Mg, Ni, Cu, and Co) sintered at 1100-1300°C. The highest substitution amounts of M-Ti for Fe were consistent with the Ti-ion preference of each transition metal site reported before, suggesting that substituted Ti ions also preferred the sites with high Ti-ion occupancies. The spontaneous magnetizations and Curie temperatures were decreased as the substitution amount x was increased, which means that the substitution weakened the super-exchange interactions between Fe-O-Fe. The highest Zn-Ti substitution rate was lower than the other M-Ti substitution rates, which implies that Zn ions tend to enter specific M(2) and M(14) sites in Ba12Fe28Ti15O84. The sweep of the magnetic field from 0 to 80 kOe changed the relative dielectric constant of Ba12Fe28Ti15O84 by 0.283%. This variation of the dielectric constant caused by the application of magnetic fields is not negligible, showing that this compound should be categorized as a multiferroic material.