Reconstructed vortex rings in a magnetic micropillary. Photo credit: Claire Donnelly
The first experimental observation of three-dimensional magnetic “vortex rings” provides fundamental insights into complicated nanoscale structures in volume magnets and offers new perspectives for magnetic devices.
Magnets often hold hidden beauty. Take a simple fridge magnet: intuitively it is “sticky” on the one hand, but not on the other. The secret lies in the way in which the magnetization is arranged in a precisely defined pattern within the material. More complicated magnetization textures are at the heart of many modern technologies, such as: B. Hard drives. An international team of scientists from the Paul Scherrer Institute PSI, the ETH Zurich, the University of Cambridge, the Donetsk Institute for Physics and Engineering and the Institute for Numerical Mathematics RAS in Moscow are now reporting on the discovery of unexpected magnetic structures in a tiny column of magnetic Materials Gadolinium Cobalt.
As they write in an article published in the magazine on November 30, 2020 Natural physics,[1] The researchers observed submicron loop-shaped configurations that they identified as magnetic vortex rings. Far beyond their aesthetic appeal, these textures could point the way to further complex three-dimensional structures that arise in the mass of magnets and one day form the basis for new types of technological applications.
Fascinating insights
Determining the magnetization arrangement within a magnet is extremely difficult, especially for micro- and nano-scale structures, for which studies have typically limited themselves to looking at a flat layer just below the surface. This changed in 2017 when researchers at PSI and ETH Zurich introduced a new type of X-ray method for nanotomography of mass magnets, which they demonstrated in experiments on the Swiss light source SLS.[2] This advance opened a unique window into the inner workings of magnets and provided a tool for determining three-dimensional magnetic configurations on the nanoscale in micrometer-sized samples.
Reconstructed vortex rings in a magnetic micropillary. Photo credit: Claire Donnelly
With these skills, members of the original team ventured into new territory together with international employees. The stunning loop shapes they observed appear in the same gadolinium-cobalt micropillar samples in which they had previously discovered complex magnetic configurations made up of eddies – the kind of structures observed when the water rises from a sink winds down – and their topological counterparts, antivortices. That was a first, but the presence of these textures was not in itself surprising. Unexpectedly, however, the scientists also found loops made up of pairs of vertebrae and antivortices. This observation initially turned out to be puzzling. Eventually, with the implementation of novel sophisticated data analysis techniques, they discovered that these structures are what are known as vortex rings – essentially donut-shaped vortices.
A new twist on an old story
Vortex rings are known to anyone who has seen smoke rings blown or who has watched dolphins create loop-shaped air bubbles for their own entertainment as well as that of their audience. The newly discovered magnetic vortex rings are fascinating in themselves. Their observation not only confirms predictions made about two decades ago and clarifies the question of whether such structures can exist. They also offered surprises. In particular, magnetic vortex rings have been predicted to be a transient phenomenon, but in the experiments now reported, these structures turned out to be remarkably stable.
The stability of magnetic vortex rings should have important practical implications. For one, they could potentially move through magnetic materials, as rings of smoke move stably through air or rings of air bubbles move through water. Learning how to control the rings within the magnet volume can open up interesting perspectives for energy-efficient storage and processing of 3D data. There is also interest in the physics of these new structures, as magnetic vortex rings can take shapes that are impossible for their smoke and bubble counterparts. The team has already observed some unique configurations, and exploring them further promises to bring even more magnetic beauty to light in the future.
References:
- “Experimental observation of vortex rings in a mass magnet” by Claire Donnelly, Konstantin L. Metlov, Valerio Scagnoli, Manuel Guizar-Sicairos, Mirko Holler, Nicholas S. Bingham, Jörg Raabe, Laura J. Heyderman, Nigel R. Cooper and Sebastian Gliga, November 30, 2020, Natural physics.
DOI: 10.1038 / s41567-020-01057-3 - “Three-dimensional magnetization structures with X-ray vector nanotomography” by Claire Donnelly, Manuel Guizar-Sicairos, Valerio Scagnoli, Sebastian Gliga, Mirko Holler, Jörg Raabe and Laura J. Heyderman, July 20, 2017, nature.
DOI: 10.1038 / nature23006
