The checklist of desirable characteristics for any physical carrier of digital information contains a bit of a paradox: it should be stable enough to store data over time yet capable of being erased and overwritten on demand. Magnetic skyrmions—nano-sized swirls of electron spin—fit the bill in terms of stability. However, existing methods for skyrmion creation and annihilation require complex fabrication techniques or precisely tailored electrical inputs that limit their scalability to real-world applications.
Recently, an international team of researchers developed an approach to writing and deleting skyrmions using conventional current pulses in a simple, two-terminal nanowire device. Their report, published in the journal Nano Letters, describes the observation of small magnetic skyrmions and their current-driven behaviors, using full-field x-ray microscopy at Advanced Light Source (ALS) Beamline 6.1.2.
“Skyrmion-based devices that are operated electrically would be affected by resistive heating and magnetic fields generated by the electrical current flowing through the device,” said the paper’s first author Soong-Geun Je, a former postdoc at the Center for X-Ray Optics (CXRO) in Berkeley Lab’s Materials Sciences Division, and currently an assistant professor of physics at Chonnam National University, South Korea. “These two by-products have been considered undesirable because electrical devices have not been designed to exploit them.”
The researchers focused on the fact that skyrmions can be created by thermal fluctuations, at a rate dependent on an external magnetic field. The x-ray microscopy experiments at the ALS, combined with micromagnetic simulations, established that the skyrmion creation and annihilation that the researchers observed in their setup arose from current-generated heating (Joule heating) and current-generated magnetic fields (Oersted fields).
“Many fantastic but complicated skyrmion writing and deleting mechanisms have been found,” said Mi-Young Im, a CXRO staff scientist and the last author of the paper. “It was very surprising to find that things such as Joule heating and Oersted fields—which we have been trying to avoid—can sometimes provide a solution to overcome a barrier that we face in a different direction.”
S.-G. Je, D. Thian, X. Chen, L. Huang, D.-H. Jung, W. Chao, K.-S. Lee, J.-I. Hong, A. Soumyanarayanan, and M.-Y. Im, “Targeted Writing and Deleting of Magnetic Skyrmions in Two-Terminal Nanowire Devices,” Nano Lett. 21, 1253 (2021), doi;10.1021/acs.nanolett.0c03686.