Yu, ChuyingZeng, YangYang, BinWylde, RichardDonnan, Robert S.Wu, JiyueXu, JieGao, FengAbrahams, IsaacReece, Michael J.Yan, Haixue2018-04-032018-04-032018-04-02Yu, C., Zeng, Y., Yang, B., Wylde, R., Donnan, R., Wu, J., ... & Yan, H. (2018). SrFe12O19 based ceramics with ultra-low dielectric loss in the millimetre-wave band. Applied Physics Letters, 112(14), 143501.10.1063/1.5022271http://hdl.handle.net/10034/621059The following article appeared in Applied Physics Letters, 112,143501 and may be found at https://doi.org/10.1063/1.5022271. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing.Non-reciprocal devices such as isolators and circulators, based mainly on ferromagnetic materials, require extremely low dielectric loss in order for strict power-link budgets to be met for millimetre (mm)-wave and terahertz (THz) systems. The dielectric loss of commercial SrFe12O19 hexaferrite was significantly reduced to below 0.002 in the 75 - 170 GHz band by thermal annealing. While the overall concentration of Fe2+ and oxygen vacancy defects is relatively low in the solid, their concentration at the surface is significantly higher, allowing for a surface sensitive technique such as XPS to monitor the Fe3+/Fe2+ redox reaction. Oxidation of Fe2+ and a decrease in oxygen vacancies is found at the surface on annealing, which is reflected in the bulk sample by a small change in unit cell volume. The significant decrease in dielectric loss property can be attributed to the decreased concentration of charged defects such as Fe2+ and oxygen vacancies through annealing process, which demonstrated that thermal annealing could be effective in improving the dielectric performance of ferromagnetic materials for various applications.enhttp://creativecommons.org/licenses/by-nc-nd/4.0/Hexaferritelow lossTerahertzdielectric lossArticle1077-3118Applied Physics Letters