Study of the synthesis mechanism and magnetic properties of quasi-nano-sized Ba-Mg ferrite powders formed by self-propagating high-temperature synthesis

Quasi-nano-sized BaxMg1-xFe2O4 ferrite powders were prepared by using self-propagating high-temperature synthesis (SHS) combined with mechanical milling. The combustion temperature and the propagating rate of the SHS reaction were in the range of 930-1115 K and about 4.5-6.4 mm/s, respectively. X-ray and neutron-beam analysis showed that the SHS products were Ba0.38Mg0.62Fe2O4 and Ba0.42Mg0.58Fe2O4, respectively. The final ferrite powder size after mechanical milling was less than about 150 nm. The maximum magnetization (Ms), the residual magnetization (Mr) and the coercive force (iHc) of quasi-nano-sized BaxMg1-xFe2O4 significantly depend on the initial molar ratio of BaO to MgO of the reactant powder mixture and the oxygen partial pressure during the SHS reaction. The complex permeability decreased with the increase of the frequency, and its real value (mu(r)') reached the peak value at about 0.6 GHz. The SHS mechanism includes the competitive reduction reaction between barium and magnesium oxides, which influences the non-stoichiometric numbers and the magnetic properties of the ferrites. (C) 2008 Published by Elsevier B.V.