Atomic Magnet Curve Balls

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Saving data to your computer’s memory takes energy. The magnetic textures of skyrmions could lead to power-saving options. Skyrmions are uncharged circular structures with a spiraling magnetic texture.

For the first time, scientists have experimentally validated a theoretical prediction that magnetic skyrmions will move intact in a direction perpendicular to the electric current (Nature Physics, "Direct observation of the skyrmion Hall effect"). An analogy to electrons with similar behavior is called the Hall effect. Thus, this phenomenon is called the skyrmion Hall effect.

The motion of a magnetic skyrmion—stable magnetic island with a core surrounded by a symmetric arrangement of twisting magnetic spins

The motion of a magnetic skyrmion – stable magnetic island with a core surrounded by a symmetric arrangement of twisting magnetic spins (top) – was controlled by using short pulses of electric current. Its trajectory (blue arrow at the bottom) along a thin flat wire (black) was measured by taking an image of the wire after each pulse. The skyrmion, which shows up as a white dot in the images, moves diagonally from one edge of the flat wire (top) to the other edge (bottom). (Image: Argonne National Laboratory)

The high stability and easy manipulation of skyrmions could revolutionize energy-efficient information technologies including memory and logic devices.

Magnetic skyrmions are stable magnetic objects that are a few nanometers to microns in size with an atom-sized core surrounded by an axially symmetric arrangement of twisting magnetic spins. The specific manner in which the spins rotate makes each skyrmion distinct and hard to transform as a group into a uniform magnetic state, as in conventional magnets.

Just like a baseball’s trajectory can be controlled by the spin applied by a pitcher, the trajectory of the skyrmions can be controlled by applying a magnetic field in a direction perpendicular to the electric current used to move the skyrmions.

Although scientists predicted the skyrmion Hall effect some time ago, an experimental demonstration had not been achieved. A team led by researchers at Argonne National Laboratory experimentally demonstrated the skyrmion Hall effect.

First, they created skyrmions in a micron-sized wire consisting of ultra-thin layers of tantalum, a compound of cobalt-iron and boron with ferromagnetic properties, and tantalum oxide. The coupling between the ferromagnet and tantalum provides the twisting force required to assemble the spins into a particular configuration.

In the experiments performed at room temperature, scientists passed an electric current along the wire and used a technique known as magneto-optical imaging to follow the motion of the skyrmions within the magnetic layer.

They observed that skyrmions move in a curved trajectory at a well-defined angle with respect to the applied electric current direction. Further, the angle of the skyrmion’s trajectory can be controlled by changing the strength of the electric current and by the sign of the applied magnetic field.

When scientists discovered the conventional Hall effect exhibited by electrons decades ago, they considered it a minor effect that might not be significant for any applications. However, numerous semiconductor-based applications including switches in portable electronics and sensors currently use this effect.

Based on this experimental demonstration of the ability to control the motion of skyrmions at will, it has been envisioned that in the future magnetic skyrmions can be the information carriers within memory and logic devices that are low-power alternatives to current technologies.