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Forschungszentrum Jülich - Annual Report 2012

Creatingknowledge Annual Report 2012 | Forschungszentrum Jülich 33 ‘sandwich’ together with the cobalt surface. The sandwich can be switched back and forth as desired between two magnetic states using magnetic fields. In this process, the electrical resistance of the layer system changes by more than 20%. Such ‘magnetoresistive effects’ can be used to store, process and measure data. However, to generate them in molecular systems, researchers previously required temperatures well below -200 °C. The new layer system, by contrast, is highly magnetoresistive even at a com- paratively high temperature of -20 °C. “This is a considerable step forward on the way to developing molecular data storage and logic elements that work at room temperature,” says Dr. Nicolae Atodiresei from Forschungszentrum Jülich. Together with the team from Forschungszentrum Jülich’s Peter Grünberg Institute and the Institute for Advanced Simulation, he developed a physical model that explains the proper- ties of the material. The scientists per- formed the sophisticated calculations required for this on the Jülich supercom- puter JUGENE. Although the researchers used up to 8,000 processors, the calcu- lations still took a total of around three months. The result: the key requirement is that the molecule must be practically flat. Two molecules each then form a stack and attach themselves closely to the cobalt surface. The cobalt and the bottom molecule form the magnetic sandwich, while the upper molecule acts as a ‘spin filter’. Its primary task is to allow electrons with spins of a certain orientation to pass through. This orien- tation can be controlled with a magnetic field, for example. Experienced and successful The Jülich physicists’ simulations bene- fited from the fact that they had suc- cessfully been working on deriving the properties and functions of organic molecules on surfaces from the laws of quantum mechanics alone for some time. Earlier publications and confer- ence papers on this field of research prompted the cooperation of this suc- cessful international team. They aroused the interest of scientists from India and the USA, who work experimentally and analytically, in the theorists from Jülich. The scientists are now planning to further optimize their material based on their findings. Nicolae Atodiresei is daring in his optimism: “I think I know how to develop sandwich systems that are magnetoresistive even at room temperature.” The researchers are also planning to modify their system in such a way that the spin filter effect can be controlled by electrical fields and light pulses as well. Nature (doi:10.1038/nature11719) Above: One ZMP molecule attaches itself directly to the cobalt surface (gold), and a second one above it at a greater distance. Right: The layer system formed can be used to store magnetic informa- tion, depicted here as ones and zeros. The green and red arrows show the orientation of the magnetic moments (spins). Institute