Fig. 3: Magnetic phase diagrams for different field-temperature protocols.

The magnetic field-temperature phase diagrams show the scattered peak intensity for the helical/conical phase in a and b. For the skyrmion phase, the maps for the (ordinary) first-order peaks are shown in c and d and those for the higher-order peaks in e and f. Both phase diagrams differ notably. The measurements were carried out using a, c, e a field-cooling and b, d, f zero-field-cooling protocol, as illustrated by white arrows in the insert (starting from the high-temperature, low-field point shown in yellow). The white dotted and dashed lines in the plots provide a guide to the eye for comparing the position of the two skyrmion pockets between the panels. Note that the higher-order skyrmion peaks become much more intense when the helical/conical and skyrmion reflections coexist, indicating a transformation of the magnetic structure. The circles show the data extracted from the example images in Fig. 2.