Lanthanum substitution enhanced M-type strontium ferrite absorbing performance based on the substitution amount and iron strontium molar ratio

The development of high-performance microwave absorption materials with low reflection loss (RL) and broad effective absorption bandwidth (EAB) is crucial for advanced electromagnetic applications. In this study, La³⁺-doped M-type hexagonal strontium ferrites with tailored chemical compositions were synthesized via sol–gel auto-combustion. Four series of compounds were systematically investigated: Sr_(1−x)Fe₁₂La_xO₁₉ (x = 0.05, 0.1, 0.15, 0.2, and 0.3), SrFe_(12−y)La_yO₁₉ (y = 0.05, 0.1, 0.15, 0.2, and 0.3), SrFe₁₂La_mO₁₉ (m = 0.05, 0.1, and 0.2), and SrFe_nLa_0.05O₁₉ (n = 11.5, 12, 12.5, and 13). These results reveal that La³⁺ doping concentration and Sr/Fe ratio critically influence the morphology and grain size, which in turn govern microwave absorption performance. In particular, lamellar grains exhibit superior absorption properties compared to granular structures, while smaller grain sizes enhance electromagnetic attenuation. The optimized composition, SrFe_12.5La_0.05O₁₉, featuring a sharp lamellar morphology, achieves exceptional performance: a minimum RL of −56.51 dB at 1.49 mm thickness and an EAB expected to exceed 5.05 GHz. Notably, specific compositions exhibit distinct advantages: SrFe₁₃La_0.05O₁₉ exhibits the deepest RL (−65.14 dB) with a unique low-frequency matching point at 5.25 GHz, while SrFe_11.5La_0.05O₁₉ demonstrates the broadest full-spectrum EAB (5.05 GHz). These results validate microstructure engineering as a dominant strategy for designing GHz-range microwave absorbers, where coupled chemical substitution and morphological control enabled tailored electromagnetic functionality.