Future IT: Antiferromagnetic dysprosium reveals magnetic switching with less energy
A short laser pulse pertubates magnetic order in dysprosium. This happens much faster if the sample had a antiferromagnetic order (left) compared to ferromagnetic order (right). © HZB
The cover of the 10. november issue of PRL highlights the work done by Nele Thielemann-Kühn and colleagues: The study was selected as well for a Focus story in Physics and an Editors’ Suggestion.
HZB scientists have identified a mechanism with which it may be possible to develop a form of magnetic storage that is faster and more energy-efficient. They compared how different forms of magnetic ordering in the rare-earth metal named dysprosium react to a short laser pulse. They discovered that the magnetic orientation can be altered much faster and with considerably less energy if the magnetic moments of the individual atoms do not all point in the same direction (ferromagnetism), but instead point are rotated against each other (anti-ferromagnetism). The study was published in Physical Review letters on 6. November 2017 and on the cover of the print edition.
Dysprosium is not only the atomic element with the strongest magnetic moments, but it also possesses another interesting property: its magnetic moments point either all the same direction (ferromagnetism) or are tilted against each other, depending on the temperature. This makes it possible to investigate in the very same sample how differently oriented magnetic moments behave when they are excited by an external energy pulse.
Magnetic-order perturbation examined at BESSY II
Physicist Dr. Nele Thielemann-Kühn and her colleagues have now investigated this problem at BESSY II. The BESSY II X-ray source is one of the few facilities worldwide that enables processes as fast as magnetic-order perturbations to be observed. Her finding: the magnetic orientation in antiferromagnetic dysprosium can be much more easily toggled using a short laser pulse than in ferromagnetic dysprosium.
“This is because the magnetic moments at the atomic level are coupled to angular momenta like that of a gyroscope”, explains Thielemann-Kühn. Tipping a rotating gyroscope requires force because its angular momentum must be transferred to another body. “Albert Einstein and Wander Johannes de Haas showed in a famous experiment back in 1915 that when the magnetisation of a suspended bar of iron changes, the bar begins to rotate because the angular momenta of the atomic-level magnets in the suspended bar are transferred to it as a whole. If the atomic-level magnetic momenta are already pointing in different directions initially, their angular momenta can interact with one another and cancel each other out, just as if you were to combine two gyroscopes rotating in opposite directions”, clarifies Dr. Christian Schüssler-Langeheine, head of the group.
Antiferromagnetic order is perturbed faster
The transfer of angular momentum takes time, though. Antiferromagnetic order, for which this transfer is not required, should therefore be able to be perturbed faster than ferromagnetic order. The empirical evidence for this conjecture has now been delivered in this study by Thielemann-Kühn and her colleagues. Moreover, the team also discovered that the energy needed in the case of the antiferromagnetic momenta is considerably lower than in the case of ferromagnetic order.
From this observation, the scientists have been able to suggest how materials could be developed with a combination of ferromagnetic and antiferromagnetic aligned spins that are suitable as magnetic storage media and might be switched with considerably lower energy expenditure than material made from conventional magnets.
Physical Review Letters (06 November 2017): Ultrafast and energy-efficient quenching of spin order: Antiferromagnetism beats ferromagnetism; Nele Thielemann-Kühn, Daniel Schick, Niko Pontius, Christoph Trabant, Rolf Mitzner, Karsten Holldack, Hartmut Zabel, Alexander Föhlisch, Christian Schüßler-Langeheine
DOI: 10.1103/PhysRevLett.119.197202
Highlighted as Focus story in "Physics": Quick Changes in Magnetic Materials
- Ultrafast dissociation of molecules studied at BESSY IIFor the first time, an international team has tracked at BESSY II how heavy molecules – in this case bromochloromethane – disintegrate into smaller fragments when they absorb X-ray light. Using a newly developed analytical method, they were able to visualise the ultrafast dynamics of this process. In this process, the X-ray photons trigger a "molecular catapult effect": light atomic groups are ejected first, similar to projectiles fired from a catapult, while the heavier atoms - bromine and chlorine - separate more slowly.
- Battery research with the HZB X-ray microscopeNew cathode materials are being developed to further increase the capacity of lithium batteries. Multilayer lithium-rich transition metal oxides (LRTMOs) offer particularly high energy density. However, their capacity decreases with each charging cycle due to structural and chemical changes. Using X-ray methods at BESSY II, teams from several Chinese research institutions have now investigated these changes for the first time with highest precision: at the unique X-ray microscope, they were able to observe morphological and structural developments on the nanometre scale and also clarify chemical changes.
- BESSY II: New procedure for better thermoplasticsBio-based thermoplastics are produced from renewable organic materials and can be recycled after use. Their resilience can be improved by blending bio-based thermoplastics with other thermoplastics. However, the interface between the materials in these blends sometimes requires enhancement to achieve optimal properties. A team from the Eindhoven University of Technology in the Netherlands has now investigated at BESSY II how a new process enables thermoplastic blends with a high interfacial strength to be made from two base materials: Images taken at the new nano station of the IRIS beamline showed that nanocrystalline layers form during the process, which increase material performance.