Magnetic vortices come full circle

The first experimental observation of three-dimensional magnetic ‘vortex rings’ provides fundamental insight into intricate nanoscale structures inside bulk magnets, and offers fresh perspectives for magnetic devices.

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 magnetization textures are at the heart of many modern technologies, such as hard disk drives. Now, an international team of scientists at PSI, ETH Zurich, the University of Cambridge (UK), the Donetsk Institute for Physics and Engineering (Ukraine) and the Institute for Numerical Mathematics RAS in Moscow (Russia) report the discovery of unexpected magnetic structures inside a tiny pillar made of the magnetic material GdCo2. As they write in a paper published today in the journal Nature Physics [1], 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 novel technological applications.

Mesmerising insights

Determining the magnetisation arrangement within a magnet is extraordinarily 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 novel X‑ray method for the nanotomography of bulk magnets, which they demonstrated in experiments at the Swiss Light Source SLS [2]. That advance opened up a unique window into the inner life of magnets, providing a tool for determining three-dimensional magnetic configurations at the nanoscale within micrometre-sized samples.

Utilizing these capabilities, members of the original team, together with international collaborators, now ventured into new territory. The stunning loop shapes they observed appear in the same GdComicropillar samples in which they had before detected complex magnetic configurations consisting of vortices — the sort of structures seen when water spirals down from a sink — and their topological counterparts, antivortices. That was a first, but the presence of these textures has not been surprising in itself. Unexpectedly, however, the scientists also found loops that consist of pairs of vortices and antivortices. That observation proved to be puzzling initially. With the implementation of novel sophisticated data-analysis techniques they eventually established that these structures are so-called vortex rings — in essence, doughnut-shaped vortices.

Read more on the PSI website

Image: Magnetic beauty within. Reconstructed vortex rings inside a magnetic micropillar.

Credit: Claire Donnelly

Bone breakages and hip fracture risk is linked to nanoscale bone inflexibility

Experiments carried out at Diamond using high energy intense beams of X-rays examined bone flexibility at the nanoscale. This allowed scientists to assess how collagen and minerals within bone flex and then break apart under load – in the nanostructure of hip bone samples.  

The report’s findings suggest that doctors should look not only at bone density, but also bone flexibility, when deciding how to prevent bone breakages. 

New research undertaken at Diamond’s Small Angle X-ray Scattering beamline (I22) has highlighted a gap in preventative treatment in patients prone to bone fractures.  The study, published in Scientific Reports and led by Imperial College London, found that flexibility as well as density in the bone nanostructure is an important factor in assessing how likely someone is to suffer fractures. 

Read more on the Diamond website

Image: Nanostructure: Collagen and mineral strain under load. Image: Shaocheng Ma, Imperial College London.