Scientists have used state-of-the-art 3D printing and microscopy to provide
a new glimpse of what happens when taking magnets to three-dimensions on the
nanoscale—1000 times smaller than a human hair.
The international team led by Cambridge University's Cavendish Laboratory
used an advanced 3D printing technique they developed to create magnetic
double helices—like the double helix of DNA—which twist around one another,
combining curvature, chirality, and strong magnetic field interactions
between the helices. Doing so, the scientists discovered that these 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 results are published in Nature
Nanotechnology.
Magnetic devices impact many different parts of our societies, magnets are
used for the generation of energy, for 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, where 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. 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," said Claire Donnelly, the study's first author from Cambridge's
Cavendish Laboratory, who has recently moved to the Max Planck Institute for
Chemical Physics of Solids.
"But until now, this idea has always been very difficult to realize, 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
magnetisation 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 DNA structure leads to a
different texture in the magnetisation compared to what is seen in 2D. Pairs
of walls between magnetic domains (regions where the magnetisation all
points in the same direction) in neighboring helices are highly coupled—and
as a result, deform. These walls attract one another and, because of the 3D
structure, rotate, "locking" 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 magnetisation, 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, former Cavendish Researcher,
now working at the Institute of Nanoscience & Materials of Aragón. "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 magnetisation, now
Donnelly and her collaborators from the Paul Scherrer Institute and the
Universities of Glasgow, Zaragoza, Oviedo, and Vienna will explore the full
potential of going from two to three dimensions in terms of the magnetic
field.
"The prospects of this work are manyfold: 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."
Reference:
Claire Donnelly, Complex free-space magnetic field textures induced by
three-dimensional magnetic nanostructures, Nature Nanotechnology (2021).
DOI: 10.1038/s41565-021-01027-7.