Effect of Organic Fuel on High-Frequency Magnetic Properties of Fe–Al2O3 Composite Powders Synthesized by a Combustion Method

Nanocrystalline Fe-Al
₂
O
₃
soft-magnetic composite powders were synthesized by a conventional combustion method followed by a H
₂
reduction process. In this paper, we analyzed the effect of the types and compositions of organic fuel on the dispersive magnetic properties of the composite powders for improving the soft-magnetic properties. To understand the properties, the microstructural and thermal characterization of as-synthesized oxide powders and their reduced powders were analyzed by an X-ray diffractor, a scanning electron microscope, and a thermogravimetric and differential thermal analyzer. In addition, the high-frequency dispersive magnetic simulation using the Landau-Lifshitz-Gilbert (LLG) equation and extended Maxwell-Garnet effective medium theory mixing rule was carried out. As a result, the microstructural and thermal analyses showed that the high-frequency dispersive magnetic behaviors of nanocrystalline Fe-Al
₂
O
₃
composite powders were dependent on the types and the compositions of fuel by controlling the released heat amount during the combustion redox reaction. In particular, a relative real permeability (u'
_y
) of 3.6 at 1 GHz was obtained in Fe-Al
₂
O
₃
(Fe:Al = 95:5, wt%) composite powders combusted by a mixed fuel composed of a 50 mol% glycine and a 50 mol% urea.