Skyrmions, discovered in 2009, are tiny magnetic vortices found in certain materials. Their potential for revolutionary data storage has piqued the interest of researchers. Subsequently, antiskyrmions were predicted by theorists and finally observed a decade after the discovery of skyrmions.
Scientists from HZDR, MPI CPfS, IFW Dresden, and the University of South Florida have delved into this intricate phenomenon using advanced measurement techniques and an ion beam saw. Their findings have been published in the journal Communications Materials.
Dr. Toni Helm, from the Dresden High Magnetic Field Laboratory (HLD) at HZDR, explains that an antiskyrmion can be considered as the antiparticle of a skyrmion. Both are classified as quasiparticles, deriving their properties from the collective interaction of numerous particles in solid matter. Notably, their properties differ significantly from those of their underlying elementary particles.
To illustrate the behavior of these quasiparticles, Helm employs a metaphor: Imagine special materials as a magnetic sea where microscopic skyrmion vortices form. Approaching them, a “magnetic” observer would either be attracted or repelled due to their peculiar characteristics. In contrast, finding antiskyrmions would be extremely challenging, as these “anti” vortices combine the diverse behaviors of skyrmions within themselves.
A characteristic footprint hidden in electrical signals
Helm’s team was faced with the challenge of detecting the elusive antiskyrmions, but they followed a theoretical prediction that offered a potential solution. They discovered that antiskyrmions possess unique geometric properties known as topology, which give rise to a distinct electrical signature in the material.
To uncover this signature, the researchers employed a combination of electrical measurement techniques and magneto-optical microscopy, allowing them to observe the electrical conduction of the material and reveal the presence of antiskyrmions for the first time.
The key to detecting antiskyrmions lies in the Hall effect, which involves applying an external magnetic field perpendicular to the current’s direction. When topological vortices like antiskyrmions are present, they generate a local magnetic field that leads to an additional voltage in the material, distinct from other effects. The theory indicates that this signal is directly connected to the topology of the vortices, enabling the differentiation between skyrmions and antiskyrmions.
Through their study, Helm’s team found that the contribution of the Hall effect from antiskyrmions is remarkably small. Instead, the measured signature predominantly arises from the magnetic properties of the antiskyrmions. This newfound understanding aids in better discerning the genuine Hall signature from other influences and provides an initial estimation of its magnitude, thereby refuting previous research results.
Scalable: The smaller, the more structured
In their study, Helm’s team focused on investigating a specific magnetic compound belonging to the class of Heusler compounds. This compound was composed of platinum, manganese, and tin. Interestingly, these crystalline materials exhibited unique behavior that defied expectations based on their elemental composition. Despite none of the constituent building blocks being ferromagnetic on their own, the compound itself displayed ferromagnetic properties.
The researchers explored the material under certain conditions and observed the emergence of various intriguing topological structures, such as skyrmions and antiskyrmions. A particularly fascinating finding was that the size of the antiskyrmions was directly influenced and controllable by adjusting the thickness of the sample.
While these antiskyrmions remained undetectable in larger chunks of the initial material, they manifested when the material was thinly sliced into pieces less than 10 micrometers thick. To achieve this, the scientists utilized an ion beam gun to carefully cut the crystal into tiny slices, enabling the detection and examination of these elusive quasiparticles.
The aspect of scalability proved to be of great importance for potential technological applications. Creating nanoscale devices is essential to leverage the unique properties of quasiparticles for novel magnetic storage and data transmission systems.
In their research journey, Helm’s team collaborated with colleagues from the HZDR Ion Beam Center. This collaboration enabled the investigation of additional material properties, which were then incorporated into supplementary theoretical calculations and simulations. As a result, the team not only substantiated the existence of antiskyrmions but also provided a comprehensive understanding of how these quasiparticles can form in the complex magnetic environment of the studied material. This newfound knowledge opens doors to exciting possibilities for harnessing antiskyrmions and advancing the field of magnetic research.