NiZn ferrite/Fe hybrid epoxy-based composites: extending magnetic properties to high frequency

Hybrid ferromagnetic composites composed of Ni_0.4Zn_0.6Fe₂O₄ ferrite powder and Fe particles in an epoxy matrix with various composition ratios were prepared by a simple mould casting route. Planetary ball milling was then introduced to pre-grind Fe and NiZn ferrite filler mixtures before casting, which resulted in fragmentation of the NiZn ferrites and modification of the Fe morphology from spherical particles to sub-micron flakes. Composites containing the ball-milled fillers exhibited a remarkable improvement in electromagnetic properties over the as-supplied materials, especially in the suppression of dielectric and magnetic loss. By combining the characteristics of high resonant frequency of the Fe and low energy losses of the ferrite, an optimum mixture of ball-milled 15 vol% NiZn ferrite and 38 vol% Fe in a hybrid epoxy-based composite gave an approximately one order of magnitude higher extended operating bandwidth over a ferrite-only containing composite, suppressing dielectric and magnetic loss tangents to approximately 10^?2 up to 150 MHz without significant deterioration of permeability. This approach of manipulating multi-phase ferromagnetic material fractions and their structure provide for flexibility in the development of bespoke electromagnetic materials for applications in electrically small antenna and metamaterials.