**2.2 Hexagonal ferrites**

Hexagonal ferrites are widely used as permanent magnets and are characterized by possesing a high coercivity [4].Their general formula is MeO·6Fe2O3 where Me can be Ba, Sr, or Pb. The hexagonal ferrite lattice is similar to the spinel structure, with the oxygen ions closely packed, but some layers include metal ions, which have practically the same ionic radii as the oxygen ions. This lattice has three different sites occupied by metals: tetrahedral, octahedral, and trigonal bi pyramid (surrounded by five oxygen ions).
