In the quest for higher-density information storage, some scientists have turned their attention to magnetic skyrmions—stable nanometer-sized swirls of spin. Initially restricted to the ultracold regime (see Physics Today, April 2009, page 12), skyrmions are now routinely studied in various layered magnetic materials at room temperature. Researchers can generate and eliminate skyrmions en masse via magnetic fields (see Physics Today, April 2016, page 22). But that’s not good enough for a future skyrmion hard drive, which would have to be able to manipulate the magnetic vortices one by one.
Now, for the first time, researchers have created and then destroyed a single magnetic skyrmion at room temperature—and they did so using electric currents rather than magnetic fields. Seonghoon Woo at the Korea Institute of Science and Technology and his colleagues accomplished the feat using a stacked device composed of gadolinium, iron, and cobalt sandwiched between platinum and magnesium oxide. The Gd-Fe-Co layer is ferrimagnetic—the magnetic moments of the Fe and Gd atoms point in opposite directions, and their magnitudes are unequal. Current passing through the magnetized layer generates spin torques, which provide the force needed to create skyrmions. Using x-ray flashes repeated every 2 ns, Woo and colleagues imaged several skyrmions that emerged as a result of the electric pulse, as shown in the figure (the colored dots in the panels to the right represent moments in time from the graph on the left). One vortex, Sk2, persisted after the pulse ceased. The researchers then applied a reversed pulse, and Sk2 disappeared. Woo and colleagues laid out the mechanism behind their observations and demonstrated control over how many skyrmions are written and destroyed. Although the technique will have to be scaled up to manipulate multiple skyrmions in rapid succession, researchers have cleared a crucial hurdle toward building a practical device. (S. Woo et al., Nat. Electr. 1, 288, 2018.)