# Development of Multi-Cation-Doped M-Type Hexaferrite Permanent Magnets
## 3 Results and Discussion
### Magnetic Properties and Magnet Performances
Finally, anisotropic sintered magnets with the optimal multi-cation composition, Sr\({}_{0.4}\)Ca\({}_{0.3}\)La\({}_{0.3}\)Fe\({}_{10.2}\)Co\({}_{0.1}\)Mn\({}_{0.1}\)Si\({}_{0.05}\)Mg\({}_{0.05}\), were fabricated at a commercial ferrite magnet manufacturing site with pilot-level processing machines. Here, the differences from fabricating isotropic magnets on a laboratory scale were that the amount of raw material powder used was scaled up by 100 times, the fine milling process was improved, and a wet magnetic-field molding method was applied during the pressing process. The magnetic hysteresis curves, 4\(\pi\)_M_-_H_ and _B_-_H_, for the anisotropic magnets of Sr\({}_{0.4}\)Ca\({}_{0.3}\)La\({}_{0.3}\)Fe\({}_{10.2}\)Co\({}_{0.1}\)Mn\({}_{0.1}\)Si\({}_{0.05}\)Mg\({}_{0.05}\)Mg\({}_{0.05}\)TiO\({}_{9}\) sintered at 1200 \({}^{\circ}\)C and 1220 \({}^{\circ}\)C with and without sintering additives are presented in Figure 7b-e, along with those of a non-substituted SrFe\({}_{12}\)O\({}_{19}\) (SFO) magnet, shown in Figure 7a, for comparison. The SFO sample was a general-grade commercial ferrite magnet manufactured under optimal process conditions. The sintering conditions, sintered sample density, and magnet parameters including 4\(\pi\)M\({}_{\rm S}\), i\(H_{\rm C}\), b\(H_{\rm C}\), \(B_{\rm r}\), and \(BH_{\rm max}\) are listed in Table 3, where i\(H_{\rm C}\) and b\(H_{\rm C}\) are the absolute values of \(H\) when 4\(\pi\)_M_ = 0 and \(B\) = 0, respectively, in the 4\(\pi\)_M_-_H_ and _B_-_H_ curves. Refer to Table 3 for process conditions, such as sintering additives and sintering temperature, for each sample ID. The demagnetization curves of all the samples are plotted in Figure 7f. First, when comparing the overall demagnetization curve of the isotropic magnet without the magnetic-field molding process, as shown in Figure 4d, the squareness and \(B_{\rm r}\) values increased significantly. It can also be seen that the performance of the Sr\({}_{0.4}\)Ca\({}_{0.3}\)La\({}_{0.3}\)Fe\({}_{10.2}\)Co\({}_{0.1}\)Mn\({}_{0.1}\)Si\({}_{0.05}\)Mg\({}_{0.05}\)O\({}_{19}\) magnets significantly improved compared to the SFO magnets. The best performance of \(BH_{\rm max}\) = 4.70 M\(\cdot\)G\(\cdot\)Oe was obtained when the Sr\({}_{0.4}\)Ca\({}_{0.3}\)La\({}_{0.3}\)Fe\({}_{10.2}\)Co\({}_{0.1}\)Mn\({}_{0.1}\)Si\({}_{0.05}\)Mg\({}_{0.05}\)O\({}_{19}\) sample was sintered at 1200 \({}^{\circ}\)C using sintering additives of 0.4 wt.% SiO\({}_{2}\) + 0.8 wt.% CaCO\({}_{3}\). It is very promising that high magnet performance can be achieved even at a significantly lower sintering temperature, and that Co can be partly replaced with the much less expensive Mn. Figure 6: (**a–f**) SEM micrographs of Sr\({}_{0.4}\)Ca\({}_{0.3}\)La\({}_{0.3}\)Fe\({}_{10.2}\)Co\({}_{0.1}\)Mn\({}_{0.1}\)Si\({}_{0.05}\)Mg\({}_{0.05}\)O\({}_{19}\) (_y_ = 1.0) sintered samples: (**a,d**) after an additional 6 h of ball-milling and after subsequent sintering at (**b,e**) 1200 \({}^{\circ}\)C and (**c,f**) 1220 \({}^{\circ}\)C at low and high magnification.