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

Abstract

Nanocrystalline Fe–Al2O3 soft-magnetic composite powders were synthesized by a conventional combustion method followed by a H2 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–Al2O3 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 ( $\text{u}^{\prime }_{r}$ ) of 3.6 at 1 GHz was obtained in Fe–Al2O3 (Fe: ${\rm{ Al}}=95$ :5, wt%) composite powders combusted by a mixed fuel composed of a 50 mol% glycine and a 50 mol% urea.