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Hexagonal hard ferrites like SrFe12O19 are technically interesting materials not only because they are the traditional permanent magnets but also as emerging magnetic recording media and as potential magneto-optic devices. For these reasons the study of dislocations in these samples is quite significant. Flux grown single crystals of SrFe12O19 are etched in 37% HNO3 at 100 °C and 85% H3P4 at 120 °C. These two etchants produce hexagonal pits on (001) planes that are established as dislocation etchants by performing the following experiments: (1) successive etching for prolonged periods resulting in persistent point bottomed etch pits at all the stages; (2) etching of matched (0001) cleavages in similar, as well as dissimilar, etchants which produce 1:1 corresponding point bottomed etch pits on a pair of the matched cleavages; (3) etching of low angle grain boundaries which consist of a grid of equally spaced edge dislocations. An equally spaced row of etch pits is obtained along the grain boundaries. Hexagonal etch pits with smooth sloping planes are normally produced. Among such pits, unusual etch pattern features including pits with rythmically and irrythmically spaced terracings, eccentric pits, small point bottomed pits within a large flat bottomed pit with differing geometrical centers, and flat bottomed pits with beaked centers, are obtained. Unusual deviations from the perfect match of etch patterns on certain matched (0001) cleavages are examined critically. It is thought that these unusual etch patterns are due to bending, branching, and stepping of dislocations. The terracing of pits is attributed to the segregation of impurities along dislocation lines.

Results of X-ray diffraction topography, in reflection and transmission scanning geometry, of flux grown single crystals of substituted and unsubstituted hexaferrites bearing composition SrGa&,Fel~-(,,,~019 (where z = 0, 5, 7, 9; y = 0, 0.8, 1.3, 1.0) are presented. Diffraction topographs reveal defects like misoriented grains, dislocations, cavities, inclusions, and the strain patterns in these crystals. The unsubstituted hexaferrites exhibit better perfection when compared to the substituted ones. The study is reported to support the results obtained by chemical etching and fractography, besides yielding additional information covering defects.