The Role of Stoichiometry in Mn_1-xZn_xFe₂O₄ Ferrite Microwave Absorbers

As 5G technology moves higher into the microwave frequency regime the risk of coupling EM energy into susceptible electronic circuits grows. Minimizing this interference is driving the need for compact, lightweight broadband absorbers to protect sensitive and high precision electronics. Manganese zinc ferrite (Mn_1-xZn_xFe₂O₄) microparticles have previously been demonstrated to be magnetically lossy up to 10 GHz, the desired frequency regime, and have the potential to meet the energy density and attenuation performance needs. However, optimizing the shielding effectiveness requires improved understanding of Mn_1-xZn_x stoichiometry and the dominant dielectric and magnetic absorption mechanisms for each stoichiometry. This presentation discusses results, up to 10 GHz, from experimentally investigating the shielding effectiveness and TE₀₁₁ loss attenuation of Mn_1-xZn_xFe₂O₄ with a mean particle size of 30 microns, loaded to 50 volume percent in epoxy, and variation in x values from 0 to 1 in intervals of 0.1. Complex permeability and permittivity measurements were conducted to identify the peaks in the dielectric and magnetic loss tangents. An increase in absorption was observed in Mn_1-xZn_xFe₂O₄ for x=0.4, 0.5, 0.6, and 0.7 compared with other stoichiometries at 2 and 5 GHz TE₀₁₁ modes, and we discuss possible explanations based on resonance behavior indicated by the dielectric and magnetic the loss tangents.