## 3 Results
### Mossbauer Results
\begin{table}
\begin{tabular}{c c c c c} \hline
**\% at Co** & **Phase** & **Site** & **[\%]Area \(\pm\) 0.1** & **H\({}_{\rm hf}\)[T] \(\pm\) 0.1** \\ \hline \multirow{6}{*}{\(\mathbf{X=0}\) (\(N_{16}\)Fe\({}_{76}\)\(B_{8}\))} & \multirow{6}{*}{\(\mathbf{Nd_{2}Fe_{14}B_{4}}\)} & d & 8.4 & 0 \\ \cline{2-4}  & & \(\alpha\)Fe & s\({}^{\rm b}\) & 4.0 & 330 \\ \cline{2-4}  & & \(16\)k\({}_{1}\) & 14.3 & 292.4 \\  & & \(16\)k\({}_{2}\) & 15.7 & 310.5 \\  & & \(8\)j\({}_{1}\) & 13.2 & 274.7 \\  & & \(8\)j\({}_{2}\) & 11.0 & 344.9 \\  & & 4c & 23.9 & 283.7 \\  & & 4e & 9.4 & 242.3 \\ \hline \multirow{6}{*}{\(\mathbf{X=10}\) (\(N_{16}\)Fe\({}_{66}\)Co\({}_{10}\)\(B_{8}\))} & \multirow{6}{*}{\(\mathbf{Nd_{2}Fe_{14}B_{4}}\)} & d & 6.4 & 0 \\ \cline{2-4}  & & \(\alpha\)Fe & s\({}^{\rm b}\) & 5.0 & 330 \\ \cline{2-4}  & & \(16\)k\({}_{1}\) & 20.9 & 296.8 \\  & & \(16\)k\({}_{2}\) & 7.9 & 327.,1 \\  & & \(8\)j\({}_{1}\) & 16.7 & 268.7 \\  & & \(8\)j\({}_{2}\) & 10.8 & 350.5 \\  & & 4c & 22.5 & 296.4 \\  & & 4e & 9.7 & 242.8 \\ \hline \multirow{6}{*}{\(\mathbf{Nd_{1.1}Fe_{4}B_{4}}\)} & \multirow{6}{*}{\(\mathbf{Nd_{1.1}Fe_{4}B_{4}}\)} & d & 6.7 & 0 \\ \cline{2-4}  & & \(\alpha\)Fe & s\({}^{\rm b}\) & 3.5 & 330 \\ \cline{1-1} \cline{2-4}  & & \(16\)k\({}_{1}\) & 16.1 & 291.1 \\ \cline{1-1} \cline{2-4}  & & \(16\)k\({}_{2}\) & 17.6 & 305.2 \\ \cline{1-1}  & & \(8\)j\({}_{1}\) & 16.7 & 264.5 \\ \cline{1-1}  & & \(8\)j\({}_{2}\) & 11.9 & 330.6 \\ \cline{1-1}  & & \(4\)c & 16.8 & 280.1 \\ \cline{1-1}  & & \(4\)e & 10.7 & 242.5 \\ \hline \multirow{6}{*}{\(\mathbf{X=20}\) (\(N_{16}\)Fe\({}_{56}\)Co\({}_{20}\)\(B_{8}\))} & \multirow{6}{*}{\(\mathbf{Nd_{2}Fe_{14}B_{4}}\)} & d & 6.9 & 0 \\ \cline{2-4}  & & \(\alpha\)Fe & s\({}^{\rm b}\) & 3.1 & 330 \\ \cline{1-1} \cline{2-4}  & & \(16\)k\({}_{1}\) & 21.3 & 292.5 \\ \cline{1-1}  & & \(16\)k\({}_{2}\) & 15.7 & 294.6 \\ \cline{1-1}  & & \(8\)j\({}_{1}\) & 14.4 & 261.8 \\ \cline{1-1}  & & \(8\)j\({}_{2}\) & 11.4 & 329.6 \\ \cline{1-1}  & & \(4\)c & 19.0 & 265.7 \\ \cline{1-1}  & & \(4\)e & 8.3 & 229.9 \\ \hline \end{tabular}
\end{table} 
Table 2: Hyperfine parameters: hyperfine field H\({}_{\rm hf}\), relative area and sites of the Mössbauer spectra of the Nd\({}_{16}\)Fe\({}_{76-\times}\)Co\({}_{\rm x}\)B\({}_{8}\) samples with x = 0, 10, 20 and 25. Figure 4a shows the variation of the hyperfine field, H\({}_{\rm{hf}}\), of the different inequivalent Fe sites in the Nd\({}_{2}\)Fe\({}_{14}\)B hard magnetic phase as a function of Co content. It can be noted that the hyperfine field of the different sites has a tendency to decrease. This decrease is mainly due to the cobalt having a magnetic moment (1.71 uB/atom) lower than the magnetic moment of iron (2.22 uB/atom), and this result suggests that cobalt atoms enter within the lattice of Nd\({}_{2}\)Fe\({}_{14}\)B. However, for site 4c and 16k2 a higher rate of decrease of the hyperfine field with the cobalt concentration occurs; only for the 10% increase of cobalt does this result indicate that the cobalt atoms have a preference for substituting iron atoms at those sites. However, for 10% of cobalt, a higher rate of increase of the hyperfine field can occur because, in these sites, there is a higher presence of Fe neighbors than in the other sites for the different concentrations of doping with cobalt. These results agree with those of [PERSON] et al. [52]. Figure 4: (a) Hyperfine field of Fe sites (16k1, 16k2, §j1, §j2, 4c and 4e) of the hard magnetic phase Nd\({}_{2}\)Fe\({}_{14}\)B as a function of Co content. (b) Relative area of Fe sites (16k1, 16k2, §j1, §j2, 4c and 4e) of the hard magnetic phase Nd\({}_{2}\)Fe\({}_{14}\)B as a function of Co content. Figure 3: Mössbauer spectra of the Nd\({}_{16}\)Fe\({}_{76\rm{x}}\)Co\({}_{\rm{x}}\)B\({}_{\rm{8}}\) samples with x = 0, 10, 20 and 25 at room temperature.