Coercivity enhancement of hexagonal ferrites

S. E. JACOBO; P. G. BERCOFF

Solid State Phenomena

Trans Tech Publications

Año: 2013 vol. 202 p. 113 - 125

1662-9779

Hexagonal ferrites have been widely used as permanent magnets since their discovery in the 1950s. In spite of their relatively modest magnetic properties, ferrite magnets still show the best performance to cost ratio and big efforts are being made in improving their magnetic capabilities by using different synthesis methods and compositions. Different scientific investigations and techniques (Mössbauer spectrometry, X-ray diffraction, magnetic measurements) have allowed to optimize the permanent magnet properties of rare earth substituted hexagonal ferrite magnets such as La-Co and  Nd-Co Sr and Ba ferrites. However, the solubility of rare earth ions in M-type hexaferrite is very low and their introduction leads to the formation of secondary phases, which must be avoided in order to obtain permanent magnets with optimal properties. We report results on enhanced coercivity of hexagonal ferrites with Nd-Co substitution. The synthesis of this kind of ferrite is performed with a defficient, non-stoichiometric iron content (ratio Fe/ Sr1?xRx of 11 instead of 12) in order to diminish secondary phases.  Comparison with samples of the same composition and stoichiometric formulation is made. A further improvement of both intrinsic and magnetic properties of the Nd-Co substituted ferrite can be obtained by adjusting the chemical composition.