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

Abstract

Magnetite (Fe₃O₄) nanoflakes with widths of 100–200 nm and thicknesses of 10–80 nm 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 (μ₀−1)fr reached 214.8 GHz 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 2–18 GHz microwave frequency range.