Molekul, Vol. 18. No. 2, July 2023: 266 – 272 266 MOLEKUL eISSN: 2503-0310 Articles https://doi.org/10.20884/1.jm.2023.18.2.7326 Enhanced Microwave Absorption Quality of Bio-Silica-Barium-Ferrite Composites: Interplay of Fe 3+ and Si 4+ Wahyu Widanarto 1 *, Mukhtar Effendi 1 , Wahyu Tri Cahyanto 1 , Sib Krishna Ghoshal 2 , Candra Kurniawan 3 , Erfan Handoko 4 , Mudrik Alaydrus 5 1 Department of Physics, Universitas Jenderal Soedirman, Purwokerto 53123, Indonesia 2 Department of Physics and Laser Centre, AMORG, Faculty of Science, Universiti Teknologi Malaysia, Johor Bahru, Skudai 81310, Malaysia 3 Research Center for Advanced Materials, BRIN, Bld. 224 Puspiptek Office Area, South Tangerang 15314, Indonesia 4 Department of Physics, Universitas Negeri Jakarta, Jakarta 13220, Indonesia 5 Department of Electrical Engineering, Universitas Mercu Buana, Jakarta 11650, Indonesia *Corresponding author email: wahyu.widanarto@unsoed.ac.id Received December 14, 2022; Accepted May 05, 2023; Available online July 20, 2023 ABSTRACT. This paper reports the improved microwave (MW) absorption characteristics of some newly prepared bio-silica- barium-ferrite composites (SBFCs) of the form ( x)Bio-SiO2:(80-x)Fe2O3:(20) BaO (where x = 0, 2, and 4 wt.%). These composites were prepared using the modified solid-state reaction method with simultaneous sintering at 800 and 1100 C. SBFCs were studied to determine the impact of various bio-silica concentrations on their morphology, structure, magnetic properties, permittivity, permeability, and X-band reflection loss. Various SBFC thicknesses were simulated to determine the reflection loss curves. It has been established that the MW absorption capacity of the examined SBFCs may be altered by adjusting the bio-silica concentration and sample thickness. Keywords: Bio-silica, Magnetic Properties, Permeability, Permittivity, Reflection Loss INTRODUCTION Compared to other ferrites with spinel and garnet structures, the barium ferrite magnetic material (BaFe12O19) with a wide crystalline anisotropic magnetic field was shown to be superior for applications in the gigahertz frequency range (Li et al., 2012; Li et al., 2013). A powerful uniaxial anisotropic magnetic field in BaFe12O19 makes it beneficial as a microwave (MW) absorbing material (Bierlich et al., 2017; Dong et al., 2014; Liu et al., 2012; Salman et al., 2016; Sun et al., 2012). Barium ferrite has outstanding MW absorption capacity due to its significant magnetic loss at the natural resonance frequency, wherein the magnetic loss is proportional to the quantity of Fe 3+ present. Thus, the MW absorption properties can be adjusted by exchanging Fe 3+ ions with other trivalent ions or a mix of divalent and tetravalent ions (Shi et al., 2019). One strategy to modify the anisotropic field and resonance frequency (fr) is to replace Fe 3+ with rare earth elements (Li et al., 2012; Sun et al., 2012). Such a strategy was very useful in improving the MW absorption capacity of various magnetic materials (Effendi et al., 2019; Widanarto et al., 2017, 2018). It also suggests that changing the dopants concentration makes it possible to modify the absorption characteristics of ferrites. However, the ever-increasing price of rare earth materials limits their broad applications. Based on these factors, we attempted to use some effective doping agent alternatives to the rare earth. A previous study revealed that rice husk could be a valuable source of high-quality bio-silica after full burning at temperatures 800 to 1000 C (Widanarto et al., 2020). Bio-silica derived from rice husk has various advantages over mineral silica (Malahayati et al., 2021). This silica is fine-grained, highly reactive, has cheap extraction costs because of its wide availability as raw materials, and may be used as a heavy metal binder. Considering these interesting attributes of bio-silica, the modified solid-state reaction approach was used to substitute Fe 3+ ions in barium ferrite with Si 4+ ions (bio-silica). The role of different bio-silica doping concentrations in improving the surface morphology, structure, composition, magnetic properties, permeability, and permittivity of the prepared bio-silica-barium-ferrite composites (SBFCs) was examined. By estimating the reflection loss (RL) based on the transmission/reflection line theory, the MW absorption parameters of the SBFCs were determined (Kumar & Chatterjee, 2018; Meng et