Low loss Co2Z hexaferrite with matched permeability and permittivity in HF and VHF bands

• Moderate SnO2 addition contributed to the grain densification and uniformity in (Ba0.5Sr0.5)3Co2Fe24O41+xSnO2 series.
• Co2Z hexaferrites obtained the matched permeability and permittivity with proper SnO2 addition.
• Co2Z hexaferrites gave a high refractive index (n=μ′ε′~14.2) over 3 to 300 MHz with 0.1 wt% SnO2.
• Co2Z hexaferrites presented low magnetic and dielectric losses over 3 to 300 MHz with 0.1 wt% SnO2.
• This low loss magneto-dielectric Z-type hexaferrite could be a good candidate for miniaturization of HF and VHF antennas.

Magneto-dielectric materials with matched permeability and permittivity have significant advantages for miniaturization and efficiency improvement of antennas. In this study, we adopted the Z-type hexaferrites in series (Ba0.5Sr0.5)3Co2Fe24O41+xSnO2 (where x=0, 0.1, 0.2, 0.4, and 0.6 wt%) to produce the magneto-dielectric material. It was found that moderate SnO2 could obviously enhance mass transfer and densification of the ferrites, while there was no significant increase in grain size, which favored to obtain low magnetic and dielectric losses. However, excessive SnO2 led to the appearance of Co2W phase and slight decrease of sintered density. The samples with 0.1 and 0.2 wt% SnO2 could obtain relatively high refractive index with real permeability and permittivity around 15. And the former presented the lowest magnetic and dielectric losses; the latter presented the best matched permeability and permittivity. Both of them are suitable for applications of antenna miniaturization between 3 and 300 MHz (HF and VHF bands).