## 3 Results and Discussion
If the \(\mu_{S}\prime\) value is estimated from the \(\upmu^{\prime}\) value at 100 MHz in Figure 5c, it can be observed that the sample with \(x=0.75\), which exhibits the lowest \(f_{FMR}\), also has the highest \(\mu_{S}\prime\) value. Furthermore, as the \(f_{FMR}\) increases with changes in the \(x\) value, the \(\mu_{S}\prime\) value declines accordingly. Given that the sample with \(x=0.4\) shows the lowest \(\mu_{S}\prime\) value, it is expected that it will have the highest \(f_{FMR}\), even though \(FMR\) is not observed within the measurement range. Figure 6a-d presents the \(\varepsilon^{\prime}\), \(\varepsilon^{\prime\prime}\), \(\upmu^{\prime}\), and \(\upmu^{\prime\prime}\) spectra for BaZn\({}_{2-x}\)Co\({}_{x}\)W-epoxy (10 wt%) composites (\(x=0.75\), 1.0, 1.25) synthesized via the M-S method. The \(\varepsilon^{\prime}\) and \(\varepsilon^{\prime\prime}\) spectra show no significant differences compared to the corresponding spectra for the same compositions in Figure 5a,b. However, the \(\upmu^{\prime}\) and \(\upmu^{\prime\prime}\) spectra display a noticeable shift towards lower frequencies compared to Figure 5c,d. The \(f_{FMR}\) values for each composition are listed in Table 2. A comparison indicates that samples prepared using the M-S method exhibit lower \(f_{FMR}\) values than those synthesized by the conventional solid-state method. This discrepancy is attributed to the influence of the average grain size. In structures where magnetic particles are dispersed in a non-magnetic binder, smaller grain sizes lead to an increase in internal magnetic fields, causing the \(f_{FMR}\) to shift to higher values. calculations are based on the following two Equations (5) and (6), derived from transmission line theory [25]:  
\[\frac{Z_{in}}{Z_{0}}=\sqrt{\frac{\mu_{r}}{\epsilon_{r}}}\text{tanh}(j\frac{2\pi fd} {c}\sqrt{\mu_{r}\epsilon_{r}}) \tag{5}\]  
\[\text{RL}(\text{dB})=20\text{log}\Big{|}\frac{Z_{in}-Z_{0}}{Z_{in}+Z_{0}}\Big{|} \tag{6}\]  
In this context, \(Z_{in}\) represents the impedance of the incident material, while \(Z_{0}\) denotes the impedance of free space. The complex permittivity \(\epsilon_{r}\) is expressed as \(\epsilon^{\prime}-\text{j}\epsilon^{\prime\prime}\), and the complex permeability \(\mu_{r}\) is expressed as \(\text{u}^{\prime}-\text{j}\text{u}^{\prime\prime}\). The frequency of the incident EM wave is indicated by \(f\), \(\epsilon\) represents the speed of light in a vacuum, and \(d\) is the thickness of the absorber. The RL values are calculated as a function of \(f\) and \(d\) over the range of \(0\text{ mm}\leq d\leq 10\text{ mm}\) and are displayed as 2D maps in Figure 7a-j. First, examining the RL map for the sample with the lowest \(f_{FMR}\), \(x=0.75\) (Figure 7d), the maximum EM wave absorption, indicated by the minimum RL value (RLmin), occurs at \(f_{RLmin}=3.4\) GHz, with a thickness of, \(d_{\text{RLmin}}=5.23\) mm, and RLmin \(=-50.3\) dB. The absorption region forms a diagonal pattern extending from the upper left to the lower right. As seen in Figure 7e-g, as the \(x\) value increases up to \(x=1.5\), the area of maximum absorption progressively shifts to higher frequencies and thinner thicknesses. All these samples demonstrate a broad EM wave absorption performance, with the shift in the strong absorption region corresponding to changes in \(f_{FMR}\). For samples with \(x\leq 0.6\), significant changes are observed due to the sharp increase in c-axis magnetic anisotropy as \(x\) decreases from \(x=0.75\). This causes the absorption region to rapidly move towards higher frequencies and thinner thicknesses (around 2 mm or less). In the \(x=0.6\) sample (Figure 7c), the absorption region spans horizontally above approximately 10 GHz, and as the \(x\) value decreases further to \(x=0.5\) and 0.4, this region shifts towards even higher frequencies. For the \(x=0.4\) sample, no strong absorption is observed below a 2 mm thickness, as the \(f_{FMR}\) exceeds 18 GHz, pushing the strong absorption region beyond the 18 GHz range.