Physics & Astronomy Associate Professor Xuemei Cheng, Bryn Mawr

"Room-temperature magnetic skyrmions in multilayers with perpendicular magnetic anisotropy"

Magnetic skyrmions, topologically protected spin textures characterized by a topological integer, have an exceptional stability against transitions into trivial spin textures, such as the ferromagnetic state. Compared to the domain walls in racetrack memory devices, magnetic skyrmions not only exhibit high mobility driven at much lower current densities but also can navigate around pinning centers. Therefore, magnetic skyrmions are promising candidates for current-driven memory devices. In magnetic multilayers, the interplay of various interactions, including the Heisenberg exchange, dipolar interactions, magnetic anisotropy, and interfacial Dzyaloshinskii-Moriya interactions enables forming and stabilizing magnetic skyrmions at room temperature. A full understanding of the motion of magnetic skyrmions in fields is key to their applications in memory devices. It is also intriguing to examine whether magnetic skyrmions, quasi-particles without an electric charge but with a topological charge, show a transverse motion in magnetic and electric fields, as the electric charges in the ordinary Hall effect.

In this work, we report the formation of robust nanoscale skyrmion phase at room temperature in [Pt/Co/Heavy Metal]n multilayers with perpendicular magnetic anisotropy. We also experimentally demonstrate the skyrmion Hall effect, and the resultant skyrmion accumulation, by driving skyrmions from the creep-motion regime (where their dynamics are influenced by pinning defects) into the steady-flow-motion regime. The experimental observation of transverse transport of skyrmions due to topological charge may potentially create many exciting opportunities, such as topological selection.

Work at Bryn Mawr College was supported by NSF CAREER award (No. 1053854). Work at the Argonne National Laboratory was supported the DOE, Office of Science, Basic Energy Sciences under Contract No. DE-AC02-06CH11357. Work at UCLA was supported by TANMS.

Reference:
[1] W. Jiang, et al., Science, 349, 283 (2015).
[2] W. Jiang, et al., Nature Physics (2016) doi: 10.1038/nphys3883