Crystal Structure and Magnetic Interactions of Ferrites

Systematic study on chemical compositions and magnetic properties of various ferrites were reported by Hilpert in 1909. He successfully prepared spinel ferrites using manganese, copper, cobalt, magnesium and zinc. Ferrites can be divided into three groups based on their crystal structures spinel ferrites, garnet ferrites and hexagonal ferrites. An ideal spinel structure consists of a cubic close-packed (fcc) array of oxygen anions, where one eighth of the tetrahedral (A) sites and one half of the octahedral (B) sites are filled with cations. Fundamental crystal structure of garnet is derived from the garnet mineral, Mn3Al2Si3O12, in which Si and Mn are substituted by Y and Al to form Y3Al5O12. Hexagonal ferrites are a family of inter-related compounds with hexagonal and rhombohedral symmetries. Due to the specific electronic configurations of cations and the types of superexchange interactions among them, the magnetic properties of ferrites are strongly dependent on the occupancy and exchange of cations in the two sites.