Structure and magnetic properties of NiFe/SiO2 and Co/SiO2 nanocomposites consolidated by detonation compaction

In this article, the structural and magnetic properties of NiFe/SiO2 and Co/SiO2 nanocomposites fabricated via powder processing are presented. The NiFe/SiO2 and Co/SiO2 nanoparticles were both synthesized by a wet chemistry approach. The as-synthesized nanoparticles were characterized by scanning electron microscopy, x-ray diffraction, and superconducting quantum interference device magnetometer, yielding detailed information concerning the structure and size of NiFe or Co particles, coating, and composition purification. The nanoparticles were then consolidated into solid components via detonation compaction. Depending on the powder morphology and detonation conditions, the density of the consolidated sample can reach over 91% of the theoretical density of the conventional materials. X-ray diffraction experiments on the samples both before and after consolidation indicate that the crystal structure of the nanocomposites remains unchanged during detonation consolidations; however, a rather large increase in particle size for the magnetic constituent was observed. Static magnetic property studies carried out on the samples both before and after detonation showed no change in the saturation magnetization after consolidation, indicating that the detonation consolidation does not cause oxidation of the nanopowders. Initial complex permeability measurements on the consolidated samples showed an essentially flat mu' versus frequency response over a wide frequency range between 5 kHz and 13 MHz, implying a high resistivity of the consolidated sample. These experiments show that detonation compaction is a promising approach for consolidating magnetic nanoparticles, and NiFe/SiO2 and Co/SiO2 are good candidates for high frequency soft magnetic materials. (C) 2003 American Institute of Physics.