# Local Phase Segregation Induced by Ion Milling in 2:17-Type Sm-Co Based Magnets
## 3 Results
### Atomic-Scale Structure Identification of the CBs in Both TEM Specimens  
To further identify the structure of different cell boundaries, HR-TEM characterizations for both TEM specimens were performed, as shown in Figures 5 and 6. As shown in the HR-TEM image of the cell boundary region of S1 (Figure 5a), a homogeneous and continuous cell boundary is observed along the {011} pyramidal plane, having a \(\sim\)60\({}^{\circ}\) angle to the {001} basal plane. The corresponding enlarged view and fast Fourier transformation (FFT) pattern taken from the white dashed square region in Figure 5a is performed to justify the atomic structure. The enlarged view shows that the Sm atoms with bright contrasts have assembled the 1:5H lattice, which is consistent with the [210]-1:5H projection shown in Figure 5c. The FFT pattern indexed by red dashed lines in Figure 5d contains only fundamental reflections, which is also consistent with the simulated electron diffraction pattern for SmCo\({}_{5}\) phase (Figure 5e). The measured lattice spacings based on the HR-TEM image are \(d\) (001) \(\approx\) 0.403 nm and \(d\) (120) \(\approx\) 0.250 nm. Then, the calculated lattice parameters are \(a\)\(\approx\) 0.500 nm and \(c\)\(\approx\) 0.403 nm. The difference between the calculated lattice parameters and the lattice parameter of binary SmCo\({}_{5}\) can be attributed to the combined effect of the substitution of Gd to Sm and the substitution of Cu to Co. The above analysis in both reciprocal and real spaces demonstrates that the cell boundaries in the TEM specimen S1 are the 1:5H phase.  
In contrast, the detailed atomic-scale structure of the cell boundary in the TEM specimen S2 is performed in Figure 6. The segregated cell boundaries in Figure 6a also occupy the {011} pyramidal plane. The structure of the 2:17R cell interiors phase is unchanged. The enlarged views of these two lamellar structures and corresponding FFT patterns are shown in Figure 6b,c,e,f, respectively. Both structures exhibit an FCC structure judged by atom stacking sequence in real space and FFT pattern in reciprocal space. According to the above STEM-HAADF images and elemental mapping images (Figures 3 and 4), the lamella with bright contrast is enriched with Gd and Sm elements, while the other with dark contrast is enriched with Co, Fe, and Cu elements. Consequently, the former can be deemed as an FCC-Sm(Gd) structure, whose lattice parameter is \(\sim\)0.514 nm (calculated  
Figure 5: HR-TEM image near the cell boundary region for the specimen 1 (**a**), enlarged view (**b**) of the white dashed square region in (**a**), and FFT pattern (**d**) taken from the dashed square region in (**a**). [210]-SmCo\({}_{5}\) projection (**c**) and simulated electron diffraction pattern (**e**) for SmCo\({}_{5}\) phase.  
from the measured lattice spacing value in Figure 6b, \(d\) (001)/2 \(\approx\) 0.257 nm), and this value is smaller than that for the FCC-Gd structure (0.532 nm) and slightly larger than that for the FCC-Sm structure (0.512 nm) [30]. The latter can also be identified as an FCC-Co (Fe, Cu) structure with a lattice parameter of 0.362 nm, which is also nearly equal to that for the \(\gamma\)-Fe (0.361 nm) [31], FCC-Co (0.355 nm) [32], or FCC-Cu (0.362 nm) [33] structures.