Skyrmions are atypical (chiral) magnetic bubbles. The magnetization inside a skyrmion is uniform, as in a ferromagnetic field, while outside it points in the opposite direction. In contrast, the wall delimiting a skyrmion has a unique magnetic "texture". Imagine for a moment that we can pass through a skyrmion: the magnetization rotates progressively 180° inside the nanoscale wall (20 to 30 nm), points in the prevailing direction inside the skyrmion, and then turns 180° again in the same direction when crossing through the second wall. Thus, in the end, the magnetization rotated 360°, whereas in a non-chiral magnetic bubble, the two 180° rotations would have counterbalanced each other. It is precisely this characteristic that gives skyrmions their interesting capacity to store and manipulate information more easily.

In the case studied, this magnetic topology is explained by an interface interaction (known as Dzyaloskinskii-Moriya) within an asymmetric stacking of ultra-thin platinum-cobalt-alumina films. This configuration favors the creation of stable skyrmions that are not very sensitive to defects, and that are mobile under the influence of an electric current.

Using a grid voltage, the researchers were able to modulate the size and density of magnetic skyrmions in these stacks composed of a heavy metal (platinum), a very thin ferromagnetic metal (cobalt), and an insulating oxide (alumina). In this manner, they could completely erase the skyrmions and then make them reappear.

While the movement of skyrmions by an electric current had already been sufficiently mastered, their creation and annihilation under voltage is a first at room temperature. This switch, which uses materials that are compatible with classical electronics, is an essential building block for producing future spintronic devices based on skyrmions.

These measurements were carried out on microscale skyrmions. The next step will consist in studying smaller skyrmions that are more interesting for applications. However, these smaller skyrmions will be much more difficult to observe.