Low Loss Z-Type $\hbox {Ba}_{3}\hbox {Co}_{2}\hbox {Fe}_{24}\hbox {O}_{41}$ Hexaferrites for Antennas and RF Devices

Z-type hexaferrites are considered for applications in the 10 MHz to 1 GHz band due to their potential to overcome Snoek´s limit. However, state-of-art hexaferrites have high magnetic loss, related to substantial micro-structural inhomogeneity and processing details. The dependence of magnetic properties on the ceramic processing route is demonstrated in this paper for Ba₃Co₂Fe₂₄O₄₁ (Co₂Z) compositions. Fine Co₂Z powders prepared by wet-chemical synthesis were used to obtain different microstructures through dry or colloidal compaction, followed by sintering with different temperature programs. Large variations in permeability and loss behavior were found between samples with different processing histories and hence microstructures. The best results obtained were μ_r^´ ~ 2.5 and μ_r^´´ <; 0.2 (tanδ ≤ 0.1) for the 10 to 930 MHz band. This is a significant improvement w.r.t. previously reported values.