Ultrafast Demagnetization between Rare Earth Atoms
Researchers at Uppsala University have discovered how conduction electrons mediate the exchange between rare earth atoms to allow a very fast demagnetization.
The researchers have come one step further to understanding the nature of magnetism and its dynamics in rare-earth compounds with chemical formula ReRh2Si2 where they have looked at seven different rare earths Re=Pr, Nd etc.
They used modern electronic structure theory and the so-called magnetic force theorem to describe the properties of conduction and localized electrons in ReRh2Si2 and to calculate the magnetic interactions between the rare-earth atoms. This is a well-established technique which provides a reliable description of magnetic systems where the interactions between electrons are not too strong.
The researchers also consider the effect of magnetic interactions on the ultrafast dynamics based on the Landau-Lifshitz-Gilbert equation which connects their calculations with previous experimental observations.
— Our theoretical calculations and analysis are focused on magnetic interactions between the rare earth atoms and how they contribute to the experimentally observed ultrafast demagnetization induced by external pulse, as found by our collaborators. The trends revealed by the theoretical calculations suggest that the conduction electrons, that move freely in these systems, mediate the exchange between the rare earth atoms and allow a very fast demagnetization, says Vladislav Borisov, researcher at the Division of Materials Theory at the Department of Physics and Astronomy.
The particular case of ReRh2Si2 is interesting, because these compounds are antiferromagnetic, in contrast to many other systems studied previously in the context of ultrafast magnetic dynamics. Furthermore, similar crystal and magnetic structure of all ReRh2Si2 compounds allows to see more clearly the trends across the rare-earth series, which is not possible for pure Re elements, since they have very different magnetic and crystal structures. In this sense, ReRh2Si2 systems are ideal test beds for studying how the number of localized 4f electrons influences the ultrafast magnetism.
Understanding the mechanism of the ultrafast magnetic dynamics is important, because its realization can lead to important applications, such as ultrafast magnetic devices for computer logic.
The conclusions of the study can be applied to design magnetic devices with a large and tunable speed. Such devices can find applications in memory and logic architectures and can offer competitive performance compared to known systems.
The researchers that were part of the study from Uppsala University were researcher Vladislav Borisov, visiting researcher Danny Thonig and Professor Olle Eriksson. The research was done together with several experimental and theoretical groups, including Laurenz Rettig’s research group at Fritz Haber Institute in Berlin, Örebro University, Goethe University Frankfurt in Germany, Johannes Kepler University in Austria, Max Planck Institute for Microstructure Physics in Halle (Germany), Helmholtz Center for Materials and Energy in Berlin (Germany), Swiss Light Source in Switzerland and Donostia International Physics Center and Ikerbasque, the Basque Foundation for Science, in Spain.
Windsor, Y.W., Lee, SE., Zahn, D. et al. Exchange scaling of ultrafast angular momentum transfer in 4f antiferromagnets. Nat. Mater. (2022). https://doi.org/10.1038/s41563-022-01206-4 Published: 24 February 2022.