Figure 1 shows bright-field transmission electron microscopy (TEM) images and selected area electron diffraction (SAED) patterns of two different samples. Figure 1a is a bright-field TEM image of sample 1 (lower iron content, see Table 1) oriented close to the  pole in two-beam condition. The diamond-shaped cellular structure of the 1:5 boundary phase and the Z-phase, therefore show strong diffraction contrast. A detailed energy-dispersive X-ray microanalysis (EDX) of the single phases is presented in Supplementary Fig. 1 and Supplementary Table 1. The diamond-shaped cellular structure has a uniform size ~200 nm and is very well aligned. The Z-phase platelets are ~4 nm in height and are densely distributed. They intersect the 10-nm-thick diamond-shaped 1:5 boundary phase. Figure 1b shows a SAED pattern along the  zone-axis (red part) with a  oriented twin (blue part). The inset shows a line profile along the [00l] direction. The additional reflections marked by the triangles as well as the slight streaking originate from the Z-phase platelets forming an ordered superstructure along the c-axis direction (see the {0,0,3/2} type of reflections revealed by the line profile). Figure 1c is a bright-field TEM image of sample 2 (higher iron content, see Table 1) oriented close to the  pole in two-beam condition. The Z-phase shows here diffraction contrast, however, the striking difference compared to sample 1 is that there is no diamond-shaped cellular structure in the 1:5 boundary phase present. Only single, isolated facets of 1:5 cells are found. Figure 1d shows a SAED along the  zone-axis. The different zone-axis orientation makes no difference to the visibility of the 1:5 cellular structure in the two-beam condition obtained bright-field TEM images. The strong streaking being present in the SAED along the [00l] direction originates from the presence of the Z-phase platelets. The inset shows a line profile along the [00l] direction with additional reflections marked by triangles. These additional reflections do not lie on the center between two regular spots of the Sm2Co17 (2:17) phase as it is the case for sample 1 indicating together with the stronger streaking a larger Z-phase disorder for sample 2 as compared to sample 1. Therefore, it is obvious that the structure of sample 2 strongly deviates from that of sample 1: There is no diamond-shaped cellular structure of the 1:5 phase visible at all. However, still isolated unequally distributed 1:5-type lamellas occur. Some of them seem to act as bridges perpendicularly connecting to the Z-phase platelets. Those bridges may be boundaries between two phases, as the Z-phase platelets should only grow in one direction. A few of the Z-phase platelets also suddenly end somewhere in the 2:17 matrix, especially in sample 2.Fig. 1Nanoscale phase distribution. a Bright-field TEM image of sample 1. b Corresponding selected area electron diffraction pattern along the  zone axis (red text labels) with additional reflections from a  oriented twin (blue text labels). The superstructure reflections of type {0,0,3/2} along the hexagonal c-axis are denoted in the line profile shown in the inset of b. c Bright-field TEM image of sample 2. d Corresponding selected area diffraction pattern along the  zone-axis. Note the difference in ordering in the line profile inset in d compared to the line profile shown in the inset in b. The scales bars in the TEM images correspond to 50 nm. The scale bars in the electron diffraction patterns correspond to 5 nm−1 Table 1Iron content and magnetic properties of the samplesSampleNominal Fe content (wt%) B r (T) H cB (kA m−1) H cJ (kA m−1)(BH)max (kJ m−3)1191.28702,3802622230.9250280100The data were extracted from demagnetization curves obtained at T = 20 °C. The determined quantities are remanence (Br), coercive field strength at polarization equals zero (H cB), coercive field strength at flux density equals zero (H cJ) and energy density ((BH)max). These values can be compared to the values provided by Maybury et al.15