Structural and Mössbauer Studies of Ball Milled Co-Zn Y-type Hexaferrites

Y-type hexaferrite samples Ba2ZnxCo2-xFe12O22 with x = 0, 1 and 2 were prepared from precursors synthesized by the citrate sol-gel auto combustion method. The powders were sintered at 1100° C for four hours. X-ray diffraction, scanning electron microscopy and Mössbauer spectroscopy were used to investigate the effect of ball milling on the structure, microstructure and on the hyperfine parameters. X-ray diffraction revealed the presence of a single Y-type hexaferrite in all sintered samples. This phase persisted in samples milled for periods up to four hours. Scanning electron microscopy images indicated that the particles changed shape, and their sizes reduced by a factor of 10 for milling times of four hours. Room temperature Mössbauer spectra of the hexaferrites elucidated the distribution of the various cations at the various sites of the hexaferrite lattice. The hyperfine field (Bhf) associated with each component was found to decrease almost exponentially with increasing milling time. The reduction in hyperfine field was associated with the weakening of the superexchange interactions between the spin-up and spin-down sublattices as a consequence of replacing Co^2+ magnetic ions by non-magnetic Zn^2+ ions and with the microstructure in the milled samples.