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 10-80 nm were prepared by a hydrothermal synthesis method. Fe3O4nanoflake composites with and without magnetic field-induced rotational orientation of flake planes of Fe3O4nanoflakes in paraffin binder were fabricated using 35 wt. Fe3O4nanoflakes. The rotationally oriented composite showed higher permeability and resonance frequency than the nonoriented one, and its value of (μ 0 - 1) f r reached 214.8 GHz and exceeded the Snoeks limit. Considering a uniform and a random distribution of flake planes of Fe3O4nanoflakes in the oriented and nonoriented composites, respectively, the complex permeability of both composites was calculated using the Landau-Lifshitz-Gilbert equation and the Bruggemans effective medium theory in the 2-18 GHz microwave frequency range.