## 3 Results and Discussion
Meanwhile, Figure 7h-j show RL maps for \(x=0.75\), 1.0, and 1.25 samples synthesized using the M-S process. As the \(x\) value increases, the RL\({}_{\rm min}\) position shifts progressively to higher frequencies due to the rise in \(f_{FMR}\). These RL maps can be compared with those of the conventionally synthesized samples shown just above (Figure 7d-f). Overall, the RL map patterns appear similar; however, the RL\({}_{\rm min}\) points are slightly shifted to the left, indicating lower frequencies. This shift occurs because the samples synthesized using the M-S process exhibit significantly larger grain sizes and lower \(f_{FMR}\) values. The RL\({}_{\rm min}\) and corresponding frequency (\(f_{RLmin}\)) values for these samples are presented in Table 2.  
To elucidate the EM wave absorption mechanism, a simplified approach was applied to the \(x=1.0\) sample, which exhibited the broadest EM wave absorption performance across the measured frequency range. In Figure 7k, the reflection loss (RL) map was generated under the assumption of \(\varepsilon^{\prime\prime}=0\) across the entire measured frequency range, while the remaining spectra (\(\varepsilon^{\prime}\), \(\mu^{\prime\prime}\), \(\mu^{\prime\prime}\)) were kept unchanged. Similarly, in Figure 7l, the RL map was derived by assuming \(\mu^{\prime\prime}=0\), with the other spectra (\(\varepsilon^{\prime}\), \(\varepsilon^{\prime\prime}\), \(\mu^{\prime}\)) held constant. A comparison with the original RL map in Figure 7e reveals that Figure 7k shows minimal alteration in the RL pattern, indicating only a shift in the absorption profile. In contrast, setting \(\mu^{\prime\prime}=0\) results in the complete disappearance of the primary absorption features in Figure 7l. These findings suggest that the EM wave absorption in the W-type hexaferrite composites studied here is predominantly influenced by \(\mu^{\prime\prime}\), which is closely associated with the FMR phenomenon. Figure 8a-d presents the RL spectra for BaZn\({}_{2-x}\)Co\({}_{x}\)W powder-epoxy (10 wt%) composites of each composition at specific thicknesses, prepared by the conventional solid-state method and the M-S method. Figure 8a,c show the spectra at the RL\({}_{\rm min}\) point, where maximum absorption occurs, while Figure 8b,d depict the RL spectra at the thicknesses that provide the broadest frequency width (\(\Delta f_{wb}\)) satisfying RL \(<-10\) dB. All samples demonstrated excellent EM wave absorption performance with RL\({}_{\rm min}\leq-30\) dB near the \(f_{FMR}\). As shown in Figure 8a, the \(x=1.25\) sample exhibited outstanding absorption characteristics with RL\({}_{\rm min}=-69\) dB at \(f=\)7.89 GHz, while Figure 8b indicates that the \(x=1.0\) sample showed the best broadband absorption properties, with \(\Delta f_{wb}=12.52\) GHz. Among the samples prepared using the M-S method in Figure 7d, the \(x=1.25\) sample demonstrated excellent broadband absorption characteristics, with \(\Delta f_{wb}=12.37\) GHz. For samples with \(x<0.75\) and \(x>1.25\), it was difficult to obtain precise \(\Delta f_{wb}\) values because their absorption bandwidth exceeded the measurement range over 18 GHz. Table 2 presents the \(\Delta f_{wb}\) and corresponding thicknesses (\(d_{wb}\)). Frequencies exceeding 18 GHz are indicated as 18(+) in the Table. The EM wave absorption properties observed in this study are compared with those of recently reported materials [26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38] in Table 3, focusing on the RL\({}_{\rm min}\) and \(\Delta f_{wb}\) values. The results of this study demonstrate superior absorption characteristics compared to other materials. Figure 8: RL spectra at a specific thickness of (**a**,**b**) BaZn\({}_{2-x}\)Co\({}_{x}\)Fe\({}_{16}\)O\({}_{27}\) (\(x\) = 0.5, 0.6, 0.75, 1.0, 1.25, 1.5) powder–epoxy (10 wt%) composites and (**c**,**d**) BaZn\({}_{2-x}\)Co\({}_{x}\)Fe\({}_{16}\)O\({}_{27}\) (\(x\) = 0.75, 1.0, 1.25) powder–epoxy (10 wt%) composites processed using the M-S method.