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...