Magnetic properties of Ba hexaferrite and Fe compounds produced by millingand annealing in air

The structure and magnetic properties of different magnetic compounds are s tudied. The compounds are produced by first milling 80% Ba hexaferrite and 20% Fe for 40 h (giving severely deformed hexaferrite plus Fe), and for 60 h (giving magnetite plus Ba carbonate). These two precursors are annealed a t 850, 900 and 1000 degrees C in air and characterized by their structure a nd magnetic properties. When the precursor consists of deformed hexaferrite and Fe, the thermal treatment promotes the elimination of defects in the h exaferrite and the oxidation of Fe to hematite and some magnetite. In the o ther case, that is, when the precursor is magnetite and Ba carbonate the an nealing produces the re-transformation to the original hexaferrite and the excess of magnetite transforms to hematite. In this situation the annealing at 1000 degrees C produces a compound with a coercivity of 4.4 kOe and a m aximum magnetization at 15 kOe of over 51 emu/g, values which are comparabl e to the ones in the literature for this material considering that the frac tion of hexaferrite in the samples is 80%. (C) 1999 Elsevier Science B.V. A ll rights reserved.