Effects of La substitution on micromorphology, static magnetic properties and low ferromagnetic resonance linewidth of self-biased M-type Sr hexaferrites for high frequency application. Issue 7 (1st April 2021) - Dai, Yue
Abstract: M-type Sr (SrM) hexaferrites have been widely applied in millimetre/microwave ferrite devices such as circulators and isolators. SrM hexaferrites must exhibit a high remanence ratio M r / M s, a high anisotropy field H a, and a low ferromagnetic resonance (FMR) linewidth Δ H to further develop millimetre/microwave equipment and devices with high frequencies, miniaturisation, and planarisation. However, it is difficult for M-type hexaferrite to simultaneously meet the requirements of high M r / M s, high H a, and low Δ H, which are key to realising high-frequency self-biased ferrite devices. In this work, Ca–La–Co-substituted SrM ferrite was prepared, and the influence of La substitution on the micromorphology, static magnetic properties, and Δ H values of SrM hexaferrites is discussed in detail. The results demonstrated that as the La substitution content x increased from 0.0 to 0.5, the saturation magnetisation 4π M s and coercivity H c initially increased, and then decreased. The H a values of all samples were higher than 18 kOe. The FMR linewidth Δ H initially increases, and then decreased after reaching a maximum value at x = 0.2. The independent grain approximation theory was used to analyse the changing trend of the FMR linewidth. The results showed that the crystalline anisotropy linewidth Δ H a accounted for a larger proportion of the FMR linewidth than the porosity linewidth Δ H p . The sample with a La substitution content x of 0.3, exhibited the best performance (4π M s = 3915 Gs, 4π M r = 3387 Gs, H c = 1818 Oe, M r / M s = 0.865, large H a = 23.99 kOe, and Δ H = 1548 Oe at 58.8 GHz). The materials prepared in this research have significant potential for application in high-frequency self-biased devices and microwave engineering.