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Fe/SiO2 Nanocomposite Soft Magnetic Materials S. Hui1, Y. D. Zhang1, T. D. Xiao1, Mingzhong Wu2, Shihui Ge2, W. A. Hines2, J. I. Budnick2, M. J. Yacaman3, and H. E. Troiani4 1 Inframat Corporation, 74 Batterson Park Road, Farmington, CT 06032 2 Physics Department and Institute of Materials Science, University of Connecticut, Storrs, CT 06269 3 Department of Chemical Engineering, University of Texas, Austin, TX 78712 4 CNM and Texas Materials Institute, University of Texas, Austin, TX 78712 ABSTRACT In an effort to explore new highly resistive soft magnetic materials, Fe/SiO2 nanocomposite materials have been synthesized using a wet chemical reaction approach in which the precursor complex was annealed at various temperatures. The crystallographic structure, nanostructure, morphology, and magnetic properties of the synthetic Fe/SiO2 particles were studied by x-ray diffraction, transmission electron microscopy, and magnetic measurements. The experimental results show that for this approach, the α-Fe particles are coated with amorphous silica. The progress of the reaction, the purity of Fe/SiO2 in the synthetic powder, and the Fe particle size are highly dependent on the annealing temperature. By adjusting the annealing temperature, the particle size can be controlled from approximately 20 nm to 70 nm. For the synthetic nanopowder obtained by H2 reduction at 400 oC, there exists a superparamagnetic behavior below room temperature; while for the nanopowders obtained by reduction at higher temperatures, the ferromagnetic behavior is dominant. Based on these studies, optimum synthesis conditions for Fe/SiO2 nanocomposites is determined. INTRODUCTION The application of soft magnetic materials in AC electrical and electronic devices can be divided into two categories. One is the low power application, such as magnetic cores in inductors. In this case, the material works in its initial (linear) magnetization region; the frequency range can be from 100 Hz to 10 GHz. The other is the high power application, such as magnetic cores of transformers or chokes. In this case, the material works in a high magnetization region (over 50% of its saturation magnetization). Both applications require soft magnetic core materials which possess high resistivity, high saturation magnetization, high Curie temperature, high initial permeability, low eddy current loss, low hysteresis loss, low residual loss, and low dielectric loss. The advances in electronic equipment technology are in the direction of increasing the operating frequency, which creates a large demand for high frequency magnetic core materials. Originally, metallic alloys possessed the best soft magnetic properties among all of the soft magnetic materials, but their extremely low resistivity (10-6 Ω cm) make them inapplicable for slightly elevated frequency (> 50 kHz), even in thin ribbon form. To overcome this problem, two types of highly resistive magnetic materials have been developed: ferrites and powder materials. However, ferrites possess low saturation magnetization and lo