Tag: magnetic devices

Researchers observe topological magnetic monopoles and dipoles in a ferromagnetic material

Researchers observe topological magnetic monopoles and dipoles in a ferromagnetic material

A scientific collaboration between scientists from Universidad de Oviedo and ALBA Synchrotron has achieved a detailed description of magnetic singularities and their interactions from the analysis of data acquired at MISTRAL beamline with the magnetic vector tomography technique. The results of the study, fully experimental not involving simulations and published at Communications Physics, provide a solid ground to understand fundamental knowledge about these singularities, what may have future applications on the design of magnetic devices.

Cerdanyola del Vallès, 31st March 2023 A non-saturated ferromagnetic material exhibits a non-uniform magnetization, forming a mosaic of magnetic domains with different magnetizations. The separation between these domains, domain walls, often intersect which results in exotic magnetization distributions called magnetic singularities. A particular type of magnetic singularities, Bloch points, are the focus of the study performed by researchers from Oviedo University and ALBA Synchrotron, and can be visualized in figure panels b and c.

The work, published at Communications Physics, described how the magnetization behaves around these Bloch points. At their location, the magnetization vectors cancel one another since they point oppositely (-> <- or <- ->), but around them they form complex patterns as the ones shown in figure at panels b and c, with vortex distribution.

A further description of the Bloch singularities is based on analogies with classical electrostatics. The converging and diverging magnetizations remind the electric fields of negative and positive point charges and lead to the concept of emergent magnetic field that, in complete analogy to electric field and electrical charge, allows to define a magnetic charge Q. Within this vision, Bloch points are described as magnetic monopoles of topological magnetic charges Q that create the emergent field Be.

Read more on the ALBA webiste

Image: Scientist at work on the MISTRAL beamline

Magnetic vortices come full circle

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 GdCo2 micropillar 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