New research published in Nature Communications reports on development in skyrmion stability, brought to us from scientists at the Institute of Theoretical Physics and Astrophysics of Kiel University. Skyrmions are minuscule, magnetic whirls that are used as bits to store information in electronic devices. While the potential applications for for skyrmions are high, until now researchers have struggled with maintaining their stability, which affects their lifetime. The Kiel University researchers suggest that previously overlooked magnetic interactions may affect skyrmion stability.
Skyrmions are sometimes called magnetic knots because their magnetic structure helps keep them from collapsing. The issue, say the researchers, is keeping that structure and stability. Skyrmions with diameters of less than 10 nanometers have only been seen at extremely low temperatures. This is a problem because these smaller skyrmions are what scientists need to develop spin-electronic devices but the applications of the devices are usually conducted at room temperature.
"The situation is comparable to a marble lying in a trough which thus needs a certain impetus, energy, to escape from it. The larger the energy barrier, the higher is the temperature at which the skyrmion is stable", explains Professor Stefan Heinze from Kiel University. That’s why researchers are focusing on improving the energy barrier of skyrmions.
In order to do so, the Kiel University team reconsidered the magnetic interactions of skyrmions from the angle of the Heisenberg theory, which could potentially explain the occurrence of ferromagnetism by the quantum mechanical exchange interaction stemming from the spin dependent "hopping" of electrons between two atoms. First author Dr. Souvik Pau comments, "If one considers the electron hopping between more atoms, higher-order exchange interactions occur." Yet unfortunately, the team determined that because skyrmion interactions are much weaker than the pair-wise exchange proposed by Heisenberg, they could ultimately not explain this behavior.
Nevertheless, the scientists were able to use atomistic simulations and quantum mechanical calculations from super computers to show that the weak interactions can nonetheless significantly explain skyrmion stability. In particular, according to Eureka Alert, they showed how cyclic hopping over four atomic sites influences the energy of the transition state extraordinarily strongly where only a few atomic bar magnets are tilted against each other. In other words, even the weaker interactions help skyrmion stability.
The researchers say these findings will be helpful in developing new electronic devices and they encourage the continued investigation of this fascinating little magnetic knots.