Abstract
Hydrogen reduction process has been used to enhance the magnetic properties of barium hexaferrite synthesized through the ceramic processing route. Compacts of synthesized single-phase hexafeffite powder with crystalline size of the order of 221.4 nm, saturation magnetization of 46.4 emu/g and coercivity of 1954 Oe, were subjected to an isothermal hydrogenation treatment in the temperature range from 600 to 900 degrees C for complete and partial reduction. The isothermal hydrogen reduction of barium hexaferrite was the highest at the early stages and decreases as reduction proceeds till the end of reduction and the rate of reduction increases with the increase of reduction temperature. Based on XRD analysis, the hydrogen reduction treatment converted the barium hexaferrite into ultrafine composite of alpha-Fe, Ba2Fe2O5 and BaO. The crystallite sizes of the formed composite were between 160 and 112.5 nm depends on the reduction temperature. Magnetic measurements showed that the coercivity values for the reduced compacts in the range 15-56 Oe and saturation magnetization varying from 103 to 107 emu/g. These values were ascribed to the formation and growth of nanosized alpha-Fe. By re-calcination of the reduced samples at a temperature of 1200 degrees C for 1 h in air, they were converted to the barium hexaferrite phase with crystalline size varying from 204 to 154 nm. Magnetic measurements for the reformed barium hexaferrite showed enhancement coercivity values for the in the range 2156-2821 Oe and saturation magnetization varying from 55.59 to 63-27 emu/g. (c) 2006 Elsevier B.V. All rights reserved.