Magnets often harbour hidden beauty. Take a simple fridge magnet: somewhat counterintuitively, it is ‘sticky’ on one side but not the other. The secret lies in the way the magnetisation is arranged in a well-defined pattern within the material. More intricate magnetisation textures are at the heart of many modern technologies, such as hard drives.
Now, an international team of scientists from the University of Cambridge, the Paul Scherrer Institute (PSI), ETH Zurich, the Donetsk Institute for Physics and Engineering in Ukraine and the Institute for Numerical Mathematics RAS in Moscow have discovered unexpected magnetic structures inside a tiny pillar made of the magnetic material GdCo2.
The researchers observed sub-micrometre loop-shaped configurations, which they identified as magnetic vortex rings. Far beyond their aesthetic appeal, these textures might point the way to further complex three-dimensional structures arising in the bulk of magnets and could one day form the basis for new technological applications. Their results are reported in the journal Nature Physics.
Determining the magnetisation arrangement within a magnet is highly challenging, in particular for structures at the micro- and nanoscale, for which studies have been typically limited to looking at a shallow layer just below the surface. That changed in 2017 when researchers at PSI and ETH Zurich introduced a new X‑ray method for the nanotomography of bulk magnets, which they demonstrated in experiments at the Swiss Light Source. That advance opened up a window into the inner life of magnets, providing a tool for determining three-dimensional magnetic configurations at the nanoscale within micrometre-sized samples.
Image: Reconstructed vortex rings inside a magnetic micropillar
Credit: Claire Donnelly
Reproduced courtesy of the University of Cambridge