Barium ferrite, abbreviated BaFe, is the chemical compound with the formula BaFe2O4. This and related ferrite materials are components in magnetic stripe cards. BaFe is described as Ba2+(Fe3+)2(O2-)4. The Fe3+ centers, with a high-spin d5 configuration, are ferromagnetically coupled. This area of technology is usually considered to be an application of the related fields of materials science and solid state chemistry. It is also used in subwoofer magnets to provide power.
A related family of industrially useful "hexagonal ferrites" are known, also containing barium. In contrast to the usual spinel structure, these materials feature hexagonally close-packed framework of oxides. Furthermore some the oxygen centers are replaced by Ba2+ ions. Formulas for these species include BaFe12O19, BaFe15O23, and BaFe18O27. Thus, BaFe12O19 is related to Fe12O20, with the empirical formula Fe3O4, i.e. magnetite.
Barium ferrites are robust ceramics that are generally stable to moisture and corrosion-resistant.