Those zippy skyrmions

Faster information processing at low current densities is a desirable trait for future computing applications. Magnetic nanobubbles or 'skyrmions' that can be moved by tiny electrical currents were, thus, touted as promising candidates as nanoscale bits in logic-in-memory devices used in next-gen electronics, particularly spintronics.

Skyrmions are small, swirling topological magnetic excitations with particle-like properties. Their tiny size provides great computing and information storage capacities as well as low power consumption. But currently, skyrmions are marred by very low speeds, which impact their performance.

Now, an international team of researchers led by French scientist Olivier Boulle at the Grenoble Alps University has been able to break this speed barrier and produced skyrmions that move at incredible speeds of up to 1,000 metres per second.

The way these skyrmions are organised can be exploited to represent future bits in computer memory – the presence of skyrmions can be thought of as 1 and absence as 0, says Naveen Sisodia, currently an Assistant Professor at the Indian Institute of Technology Gandhinagar and the co-first author of the study published in Science (bit.ly/skyrmions-2024).

However, skyrmions suffer a problem: these nanobubbles move no faster than 100 metres per second, which is too slow for computing applications. The current team of researchers overcame this hurdle upon discovering faster skyrmion movement in a specially designed synthetic antiferromagnetic material through simulations and, later, using experiments.

Skyrmions are better than today's storage devices, which store data in magnetic domains. Magnetic storage devices, such as the hard discs currently used, entail mechanical movement of the head that reads and writes information stored magnetically.

"Skyrmions are just a magnetic state and can move data without having any moving part. Think of a wave in the sea. In an ideal situation, an object located at a certain point in the sea remains where it is even after a wave (has) passed by. When skyrmions move, magnetic spins or atoms remain wherever they are," explains Sisodia, who was a postdoc in Boulle's lab.

The synthetic antiferromagnetic material that they designed is composed of two platinum-cobalt layers separated by a thin layer of ruthenium, which acts as a non-magnetic spacer.

This seems to be a significant experiment and the strategy may become important for fast manipulation of skyrmions in near-term devices, says Awadhesh Narayan, Assistant Professor at the Indian Institute of Science, Bengaluru, who works on magnetic materials.

"One significant challenge of skyrmions has been their sluggish motion, which can arise due to 'deflections' (called the 'skyrmion Hall effect'). The authors have overcome this challenge by a clever choice of antiferromagnetic materials, which suppress these deflections. As a result, they are able to reach very high skyrmion velocities," says Narayan, who was not associated with the study.