Phase analysis and single domain detection in hexaferrite powders for magnetic recording

SrFe/sub 12/O/sub 19/, SrInFe/sub 11/O/sub 19/, and SrCo/sub 0.9/Ti/sub 0.9/Fe/sub 10.2/O/sub 19/ hexagonal ferrites were prepared by the metallorganic precursor method to test their characteristics as particulate media for magnetic recording applications. The chemical reactivity and the magnetic characteristics were analyzed as a function of thermal treatment. Reversible transverse susceptibility curves were used to verify the single- or polydomain state of the particles. All the magnetic data are explained on the basis of the phase diagram. It is concluded that the substitution of iron in hexaferrite results in a decreased reactivity and that the more drastic thermal treatment required for optimizing the magnetic properties deteriorates the morphological characteristics of the powders. It is possible, however, to define for each compound a suitable thermal treatment allowing single-domain particles with good magnetic properties.<>