Nanoscale magnetic double helices (top) have been found to host highly coupled textures, observed both experimentally and with simulations (bottom). Image: Claire Donnelly.
Nanoscale magnetic double helices (top) have been found to host highly coupled textures, observed both experimentally and with simulations (bottom). Image: Claire Donnelly.

Scientists have used state-of-the-art 3D printing and microscopy to provide a new glimpse of what happens when taking magnets into three-dimensions at the nanoscale.

The international team, led by researchers at Cambridge University’s Cavendish Laboratory in the UK, used an advanced 3D printing technique they developed to create magnetic double helices made of cobalt. Like the double helix of DNA, these magnetic double helices twist around one another, combining curvature, chirality and strong magnetic field interactions between the helices.

In doing this, the scientists discovered that the magnetic double helices produce nanoscale topological textures in the magnetic field, something that had never been seen before, opening the door to the next generation of magnetic devices. The scientists report their findings in a paper in Nature Nanotechnology.

Magnetic devices impact many different parts of our societies: magnets are used for the generation of energy, data storage and computing. But magnetic computing devices are fast approaching their shrinking limit in two-dimensional systems. For the next generation of computing, there is growing interest in moving to three dimensions. Not only can higher densities be achieved with 3D nanowire architectures, but three-dimensional geometries can change the magnetic properties and offer new functionalities.

“There has been a lot of work around a yet-to-be-established technology called racetrack memory, first proposed by Stuart Parkin,” explained Claire Donnelly from Cambridge’s Cavendish Laboratory, who is the paper's first author and has recently moved to the Max Planck Institute for Chemical Physics of Solids in Germany. “The idea is to store digital data in the magnetic domain walls of nanowires to produce information storage devices with high reliability, performance and capacity.

“But until now, this idea has always been very difficult to realise, because we need to be able to make three-dimensional magnetic systems and we also need to understand the effect of going to three dimensions on both the magnetization and the magnetic field.

“So, over the last few years our research has focused on developing new methods to visualize three dimensional magnetic structures – think about a CT scan in a hospital, but for magnets. We also developed a 3D printing technique for magnetic materials.”

The 3D measurements were performed at the PolLux beamline of the Swiss Light Source at the Paul Scherrer Institute, currently the only beamline able to offer soft X-ray laminography. Using these advanced X-ray imaging techniques, the researchers observed that the 3D double helix structure leads to a different texture in the magnetization compared to what is seen in 2D.

Pairs of walls between magnetic domains (regions where the magnetization points in the same direction) in neighbouring helices are highly coupled. As a consequence, they deform: the walls attract one another, causing the helices, because of their 3D structure, to rotate, 'locking' them into place and forming strong, regular bonds, similar to the base pairs in DNA.

“Not only did we find that the 3D structure leads to interesting topological nanotextures in the magnetization, where we are relatively used to seeing such textures, but also in the magnetic stray field, which revealed exciting new nanoscale field configurations!” said Donnelly.

“This new ability to pattern the magnetic field at this length scale allows us to define what forces will be applied to magnetic materials and to understand how far we can go with patterning these magnetic fields. If we can control those magnetic forces on the nanoscale, we get closer to reaching the same degree of control as we have in two dimensions.”

“The result is fascinating – the textures in the DNA-like double helix form strong bonds between the helices, deforming their shape as a result,” explained lead author Amalio Fernandez-Pacheco, a former Cavendish researcher who is now working at the Institute of Nanoscience & Materials of Aragón in Spain. “But what is more exciting is that around these bonds form swirls in the magnetic field – topological textures!”

Having gone from two to three dimensions in terms of the magnetization, now Donnelly and her collaborators want to explore the full potential of going from two to three dimensions in terms of the magnetic field.

“The prospects of this work are many-fold: these strongly bonded textures in the magnetic helices promise highly robust motion and could be a potential carrier of information,” said Fernandez-Pacheco. “Even more exciting is this new potential to pattern the magnetic field at the nanoscale. This could offer new possibilities for particle trapping, imaging techniques as well as smart materials.”

This story is adapted from material from the University of Cambridge, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.