## 3 Results and Discussion
### Characteristics of Randomly Oriented Polycrystalline Samples
#### 3.1.1 Lattice Parameters and Microstructures
Therefore, Equation (2) can be approximated by the following equation:  
\[M\ =\ M_{s}\bigg{(}1-\frac{A}{H}-\frac{B}{H^{2}}\bigg{)} \tag{3}\]  
Figure 1.0 The Sr\({}_{1-x}\)La\({}_{x}\)Fe\({}_{12-x}\)Co\({}_{x}\)O\({}_{19}\) (\(0.0\leq x\leq 0.3\)) samples sintered at 1230 \({}^{\circ}\)C for 2 h in air, presenting the initial magnetization curves (**a**) and \(M\)-\(H\) curves with the demagnetization curves in the inset (**b**). For a hexagonal crystal structure exhibiting uniaxial anisotropy, \(B\) can be expressed as follows:  
Figure 1.1  
The determination of \(M_{S}\) involves analyzing the linear portion of the \(M\) vs. \(1/H^{2}\) curves, with the condition that R\({}^{2}\) is greater than or equal to 0.999. The values for \(A\) and \(H_{a}\) can be calculated by fitting Equation (3) to the measured initial magnetization curves. It is important to note that R\({}^{2}\) is a statistical parameter reflecting the quality of the curve fit, and for reliable results, it should be at least 0.99. The \(A\), \(M_{S}\), and \(H_{a}\) values, along with their R\({}^{2}\) values calculated from Figure 5a and the intrinsic coercivity, \(H_{ci}\), values from Figure 5b, for all samples are listed in Figure 1.2  
Figure 6 shows the dependencies of \(M_{S}\), \(H_{ci}\), and \(H_{a}\) on \(x\) from the data in Figure 1.3 The \(M_{S}\) values increase from 70.90 to 72.40 emu/g as \(x\) increases from 0.0 to 0.15, and then they decrease to 71.38 emu/g up to \(x\) = 0.3. On the other hand, the \(H_{a}\) values increase from 17.7 to 25.9 kOe as \(x\) increases from 0.0 to 0.3. The \(H_{ci}\) values increase from 3.517 to 4.294 kOe as \(x\) increases from 0.0 to 0.15. The \(H_{ci}\) values increase slightly to 4.385 kOe at \(x\) = 0.2 and then increase to 5.001 kOe at \(x\) = 0.3. In order to understand the effect of sintering additives on the intrinsic magnetic properties of \(M_{s}\) and \(H_{a}\), we also evaluated those of La-Co-co-substituted SrM bulk samples without additives [37] and post-annealed at the same sintering conditions of 1230 \({}^{\circ}\)C for 2 h. Though not presented here, \(M_{s}\) values for present samples with additives are lower, i.e., below \(x\) = 0.15, but the difference in \(M_{s}\) becomes insignificant above \(x\) = 0.15. In the case of \(H_{a}\), for the present samples with additives, it is lower only at \(x\) = 0.0, but the difference in \(H_{a}\) becomes negligible above \(x\) = 0.10. The conspicuous difference in both \(M_{s}\) and \(H_{a}\) at \(x\) = 0 most likely originates from the substitution of Ca and Si additive cations for the Sr and Fe sites, respectively. As \(x\) increases, the influence of sintering additives on \(M_{s}\) and \(H_{a}\) seems to become smaller because La-Co substituents affect them dominantly. The \(M_{s}\) and \(H_{a}\) values evaluated using LAS have been reported for Sr\({}_{1-x}\)La\({}_{x}\)Fe\({}_{12-x}\)Co\({}_{x}\)O\({}_{19}\) samples by a few research groups [16; 19]. Unfortunately, it is difficult to compare our \(M_{s}\) values with their values because detailed \(M_{s}\) evaluation procedures are not described in their papers. Nevertheless, our \(M_{s}\) values from \(x\) = 0.0 to 3.0, in Table 2, are in good agreement with those reported by [PERSON] et al. [19], who employed the sintering additives of 0.4 wt% SiO\({}_{2}\) and 1.4 wt% CaCO\({}_{3}\). However, our \(M_{s}\) values were higher than those of Sr\({}_{1-x}\)La\({}_{x}\)Fe\({}_{12-x}\)Co\({}_{x}\)O\({}_{19}\) samples reported by [PERSON] et al. [16], who employed SiO\({}_{2}\), CaCO\({}_{3}\), and Al\({}_{2}\)O\({}_{3}\) (unknown wt%) as the sintering additives below \(x\) = 0.1; the difference becomes negligible above \(x\) = 0.1. On the other hand, our \(H_{a}\) values coincide with those reported only by [PERSON] et al. [19] for the \(x\) values ranging from 0.10 to 0.25. Our \(H_{a}\) value is smaller for \(x\) = 0.0 but it becomes larger for \(x\) = 0.30, which may be due to the difference in the amounts of sintering additives.