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
- Catherine Dubourdieu receives ERC Advanced GrantProf. Dr. Catherine Dubourdieu heads the Institute “Functional Oxides for Energy-Efficient Information Technology” at HZB and is Professor at the Physical and Theoretical Chemistry division at Freie Universität Berlin. The physicist and materials scientist specialises in nanometre-sized functional oxides and their applications in information technologies. She has now been awarded a prestigious ERC Advanced Grant for her research project “LUCIOLE”, which aims at combining ferroelectric polar textures with conventional silicon technologies.
- Green hydrogen: How photoelectrochemical water splitting may become competitiveSunlight can be used to produce green hydrogen directly from water in photoelectrochemical (PEC) cells. So far, systems based on this "direct approach" have not been energetically competitive. However, the balance changes as soon as some of the hydrogen in such PEC cells is used in-situ for a catalytic hydrogenation reaction, resulting in the co-production of chemicals used in the chemical and pharmaceutical industries. The energy payback time of photoelectrochemical "green" hydrogen production can be reduced dramatically, the study shows.
- Perovskite solar cells from the slot die coater - a step towards industrial productionSolar cells made from metal halide perovskites achieve high efficiencies and their production from liquid inks requires only a small amount of energy. A team led by Prof. Dr. Eva Unger at Helmholtz-Zentrum Berlin is investigating the production process. At the X-ray source BESSY II, the group has analyzed the optimal composition of precursor inks for the production of high-quality FAPbI3 perovskite thin films by slot-die coating. The solar cells produced with these inks were tested under real life conditions in the field for a year and scaled up to mini-module size.