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

Abstract

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 were systematically investigated: Sr(1-x)Fe12LaxO19 (x = 0.05, 0.1, 0.15, 0.2, 0.3), SrFe(12-y)LayO19 (y = 0.05, 0.1, 0.15, 0.2, 0.3), SrFe12LamO19 (m = 0.05, 0.1, 0.2), and SrFenLa0.05O19 (n = 11.5, 12, 12.5, 13). The results reveal that La3+ doping concentration and Sr/Fe ratio critically influence morphology and grain size, which in turn govern microwave absorption performance. Specifically, lamellar grains exhibit superior absorption properties compared to granular structures, while smaller grain sizes enhance electromagnetic attenuation. The optimized composition, SrFe12.5La0.05O19, 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: SrFe13La0.05O19 exhibits the deepest RL (-65.14 dB) with a unique low-frequency matching point at 5.25 GHz, while SrFe11.5La0.05O19 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.