Defects and Phase Transformations in Cobalt Ferrites

Defects and phase transformations in ferrimagnetic cobalt ferrites, with a Co/Fe ratio between 0.5^ and 0.76' have been, studied by means of high voltage transmission electron microscopy. The origin and characterization of ion radiation damage, ferrimagnetic domains, dislocations, and phase transformations in tdr and in the electron microscope are discussed. Chemicil polishing and subsequent irradiation of specimens in the 650 kV microscope produces defects in the crystal surface facing the gun. These defects are mainly spherical oxygen vacancy clusters, but occasionally small prismatic vacancy loops are formed. The projected
o 2 saturation defect concentration is about 2^10 per cm. Existing multiple beam dynamical theory has been used to quantitatively compare computed and actual dislocation images. It has been found
that under the proper diffracting couditions, dislocation can be characterized by the spacing of the subsidiary image fringes parallel to the dislocation line, so that the magnitude of the Burgers vector can 0 be determined directly, 'fhe dislocation partials are at most 50A apart. The usefulness of the transmitted beam image, with systematic higher order reflections operating is shown. This method appears to be preferable
over the kinematical weak beam method, when the foil is of normal thickness.

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