Microwave complex permeability of Fe3O4 nanoflake composites with and without magnetic field-induced rotational orientation

Magnetite (Fe3O4) nanoflakes with widths of 100-200 nm and thicknesses of 10-80nm were prepared by a hydrothermal synthesis method. Fe3O4 nanoflake composites with and without magnetic field-induced rotational orientation of flake planes of Fe3O4 nanoflakes in paraffin binder were fabricated using 35 wt. % Fe3O4 nanoflakes. The rotationally oriented composite showed higher permeability and resonance frequency than the nonoriented one, and its value of (mu(0) - 1)f(r) reached 214.8GHz and exceeded the Snoek's limit. Considering a uniform and a random distribution of flake planes of Fe3O4 nanoflakes in the oriented and nonoriented composites, respectively, the complex permeability of both composites was calculated using the Landau-Lifshitz-Gilbert equation and the Bruggeman's effective medium theory in the 2-18GHz microwave frequency range. (C) 2013 American Institute of Physics.