Size-dependent microwave absorption properties of Fe3O4 nanodiscs

Fabrication of uniform magnetic nanodiscs with tunable size is of great importance for the study of their size dependent microwave properties. In this work, uniform Fe3O4 nanodiscs with different sizes are successfully synthesized by hydrogen-wet reduction of α-Fe2O3 nanodisc templates. The thickness of the Fe3O4 discs are around 30 nm and the diameters could be adjusted between 80–500 nm by controlling the amount of water in the reaction. The dynamic permittivity and permeability of Fe3O4 nanodisc/paraffin composite (20 vol%) were measured in the frequency range of 0.1–18 GHz. It is found that a larger diameter leads to a higher permittivity, lower permeability and higher resonance frequency as a consequence of stronger shape anisotropy. Moreover, excellent microwave absorption performances are achieved by these nanodiscs, which exhibit wide effective absorption (RL < −10 dB) with wide frequency bandwidth. Furthermore, small nanodiscs show superior microwave absorption properties over large nanodiscs because of lower permittivity which results in a better impedance match. The study not only presents an effective method to fabricate high quality Fe3O4 nanodiscs with tunable sizes, but also could be of great help for designing magnetic nanodisc based microwave absorbers.