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| A vertical slice of the internal magnetic structure of a sample section. The sample is 0.005 millimetres (5 microns) in diameter and the section shown here is 0.0036 millimetres (3.6 microns) high. The internal magnetic structure is represented by arrows for a vertical slice within it. In addition, the colour of the arrows indicates whether they are pointing towards (orange) or away from the viewer (purple). Graphics and text: Paul Scherrer Institute/Claire Donnelly |
Thanks to a technique called hard X-ray magnetic tomography, researchers at the Paul Scherrer Institute (PSI) in Switzerland, the ETH Zurich and the University of Glasgow have succeeded in imaging the magnetization in 3D bulk-like magnets and observe features down to just 100 nm. In particular, they have observed structures known as Bloch points, which were predicted theoretically more than 50 years ago but never actually seen in an experiment until now. The new work could help us better understand the relationship between the magnetic structure and the behaviour and performance of bulk magnets, and so improve the everyday applications in which they are employed.
“Although it was possible to image the arrangement of magnetic moments in 3D before now in films of up to around 200 nm thick using soft X-rays and electrons, it was not possible to study the internal micromagnetic structure of larger, bulk, systems,” explains team member Claire Donnelly of the PSI. “In general, it is not possible to slice down a magnet to investigate its structure because the magnetic configuration will change accordingly. Scientists have tried to overcome this problem in the past using neutron magnetic imaging, but they were only able to achieve a spatial resolution of tens to hundreds of microns using this approach.
“In our new work, we are able to study the internal magnetization within a micron-sized system with 100 nm spatial resolution and observe micromagnetic details within the bulk for the first time.”
The researchers, led by Laura Heyderman, imaged the internal magnetic structure of a micron-sized pillar made of the magnetic material gadolinium-cobalt using hard X-ray magnetic tomography, a technique developed at PSI during the course of this study. “We had to make a number of advances in developing this method,” explains Donnelly. ‘First, we developed hard X-ray magnetic imaging with nanoscale magnetic resolution (this work was published last year). Hard X-rays have a much higher energy than soft X-rays and thus a much larger penetration depth, which allows us to study thicker samples with high spatial resolution.
X-ray nanotomography reveals 3D magnetization structures, Belle Dumé, Nanotechweb.org
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