Magnetic Curve Balls

A twisted array of atomic magnets were driven to move in a curved path, a needed level of control for use in future memory devices.

Image courtesy of Argonne National Laboratory

The Science

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. An analogy to electrons with similar behavior is called the Hall effect. Thus, this phenomenon is called the skyrmion Hall effect.

The Impact

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

Summary

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.

Contact

Axel Hoffmann and Suzanne G. E. te Velthuis
Argonne National Laboratory
[email protected]; [email protected]

Funding

U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (work at Argonne National Laboratory including magneto-optic Kerr effect imaging) including the Center for Nanoscale Materials (lithography), a DOE Office of Science user facility and National Science Foundation (NSF) Nanosystems Engineering Research Center for Translational Applications of Nanoscale Multiferroic Systems (thin film growth, University of California, Los Angeles). Support for individuals was provided by other agencies: W. Jiang by the 1000-Youth Talent Program of China and National Key Research Plan of China; Y. Zhou by the National Natural Science Foundation of China and Shenzhen Fundamental Research Fund; X. Zhang by Japan Society for the Promotion of Science RONPAKU (Ph.D. dissertation); and X. Wang and X. Cheng (Bryn Mawr College) by an NSF CAREER award.

Publications

W. Jiang, X. Zhang, G. Yu, W. Zhang, X. Wang, M.B. Jungfleisch, J.E. Pearson, X. Cheng, O. Heinonen, K.L. Wang, Y. Zhou, A. Hoffmann, and S.G.E. te Velthuis, “Direct observation of the skyrmion Hall effect.” Nature Physics 13, 162 (2017). [DOI: 10.1038/nphys3883]