Structural and Magnetic Characteristics of Composite Compacts of ${\rm Fe}/{\rm Fe}_{3}{\rm O}_{4}$ Type Obtained by Sintering

Soft magnetic composite of ${\rm Fe}/{\rm Fe}_{3}{\rm O}_{4}$ type was synthesized by mechanical milling and reactive sintering starting from a mixture of Fe and ${\rm Fe}_{2}{\rm O}_{3}$ commercial powders. During mechanical milling, the Fe and ${\rm Fe}_{2}{\rm O}_{3}$ phases start to react after 120 min. A composite powder of ${\rm Fe}/{\rm Fe}_{2}{\rm O}_{3}$ type results after 60 and 120 min of milling. The composite powder obtained by milling was pressed in toroidal shape at 100 up to 300 MPa. The green composite compacts $({\rm Fe}/{\rm Fe}_{2}{\rm O}_{3})$ were sintered at 1100 $^{\circ}{\rm C}$ for 6 h, resulting in ${\rm Fe}/{\rm Fe}_{3}{\rm O}_{4}$ like sintered composite compacts having an amount of FeO phase. The microstructure analysis shows an iron matrix that embeds iron oxide clusters. The magnetic measurements in dc current indicate the positive influence of the increased applied pressure on the magnetic permeability and saturation induction characteristics. The investigations in dc revealed that the milling time has almost no influence on the magnetic characteristics of the sintered composite compacts. ac investigations showed that the magnetic permeability decreases upon increasing the testing frequency. The total losses increase significantly by increasing the frequency due to the excessive increase in eddy currents at higher frequencies.