Supplementary Materials

Blowing magnetic skyrmion bubbles

Wanjun Jiang, Pramey Upadhyaya, Wei Zhang, Guoqiang Yu, M. Benjamin Jungfleisch, Frank Y. Fradin, John E. Pearson, Yaroslav Tserkovnyak, Kang L. Wang, Olle Heinonen, Suzanne G. E. te Velthuis, Axel Hoffmann

Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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  • Materials and Methods
  • Supplementary Text
  • Figs. S1 to S7
  • Captions for Movies S1 to S5
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Images, Video, and Other Other Media

Movie S1
MOKE movie of the transformation from stripe domains into skyrmion
This movie is the full version of the differential polar-MOKE imaging data presented in Figs. 3 (A) – (D). It was acquired while applying a continuous current density of je= +6.4×104 A/cm2 across the device, with B= +0.46 mT. The temporal resolution of the movie is 0.13 s. Generation of individual skyrmions can be observed.
Movie S2
MOKE movie for the persistent generation of skyrmions
This movie consists of differential polar-MOKE images and was acquired with a continuous current density of je= +6.8×104 A/cm2, with B= +0.46 mT, and a temporal resolution of 0.08 s. This current density is slightly larger than for the data presented in Figs. 3 (A) – (D) and the previous movie, which results in transformational dynamics at a higher rate. It shows that a large population of skyrmions are continuously generated and subsequently move along the current direction. The generation of skyrmions occurs close to the constriction where the y-component of the current is the largest. Furthermore, the continuous skrymion production results in a lateral distribution of the skyrmions.
Movie S3
MOKE movie of skyrmion generation under large pulsed current
This movie is the full version of the differential polar-MOKE imaging data presented in Fig. 2 in the main text and in Fig. S5. This MOKE movie was acquired in the presence of pulsed current je= +5×105 A/cm2 with B +0.5 mT. The duration of pulse is 1 s. Upon passing the current, it is observed that the images are getting blurry at the right side of the constriction, which can be attributed to the fast transformation dynamics that is beyond the temporal resolution of the imaging camera. It is also observed that the left side of stripe domains are compressed. Immediately after the pulse current, some stripe domains are present on both sides and eventually evolving into skyrmion bubbles on the right side.
Movie S4
MOKE movie of the motion of synthetic skyrmions
This movie is the full version of the differential polar-MOKE imaging data presented in Figs. 3(F)–(G). With external magnetic field of B= -0.5 mT, skyrmions are first initialized by passing current density of je= +5×105 A/cm2. These synthetic skyrmions are stable at room temperature after switching off the large current density. After that, small pulse currents of various amplitudes and duration of 1 s were applied to avoid more skyrmions being generated for which would complicate the data analysis. This procedure enables the current-velocity characteristics of synthetic skyrmions to be investigated. By looking at the movie frame by frame (of time period 0.16 s) acquired at the current density je= +3×104 A/cm2, stochastic motion of these synthetic skyrmion under current stimulation can be resolved. By counting the number of skyrmions that moved out from the frame and their average time spent during travelling, the average velocity can be determined.
Movie S5
MOKE movie of the current response of the domains stabilized by in-plane field
This movie consists of differential polar-MOKE images and was acquired by starting from zero field and ramping the field to B = 5 mT, with the magnetic field applied in the sample plane and parallel to the long axis of the device, and a temporal resolution of 0.15 s. Note that, while a small in-plane magnetic field is present, we still image the polar-MOKE contrast to visualize the out-of-plane component of the magnetization. By applying a pulse current of width 1s of amplitude je= +7×105 A/cm2 (which is higher than the threshold current that required to dynamically generated skyrmion for the out-of-plane magnetic fields), the migration of stripe domains through geometrical constriction, instead of transforming into skyrmion bubbles were observed.