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DESY News: X-ray analysis points way to flexible and transparent magnets
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X-ray analysis points way to flexible and transparent magnets
Magnets from organic materials can enable new applications and offer a sustainable alternative to metal magnets containing rare earths. With a worldwide unique experimental setup at DESY's X-ray source PETRA III, scientists from Tübingen, Hamburg, Berlin, Nebraska und Italy have demonstrated magnetism in completely organic thin films for the first time. “These results open the way to the advent of flexible, light and transparent magnets and, thus, to a variety of new futuristic applications,” explains Maria Benedetta Casu from the University of Tübingen who led the research. The team reports its comprehensive analysis in the journal Chem.
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These radicals are organic molecules that carry an unpaired electron, resulting in a permanent magnetic moment that is not due to the effect of an external magnetic field. “Organic radicals are very promising materials for electronics and quantum technology,” says Tobias Junghöfer from the University of Tübingen, one of the main authors of the study. However, to use these radicals in a device, they usually need to be fabricated as a thin film, 1000 times thinner than a human hair, coating a substrate such as silicon dioxide (SiO2). “In the past, magnetism in purely organic radicals was known only for crystals and it was completely unknown in thin films. It was never studied before because this was a huge challenge,” explains Casu.
A decade ago, such experiments were not yet technically possible. “Then, our colleagues at the University of Hamburg developed a high magnetic field machine for ultracold measurements down to 0.1 Kelvin, very close to absolute zero, and much colder than the temperature of outer space,” reports Casu. “However, it was necessary to work with synchrotron light from an advanced source such as PETRA III. The combination of the beamline P04 at PETRA III and our machine is unique and it is the only facility in the world where it is possible to obtain these results.”
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The unique setup at beamline P04 of DESY's X-ray source PETRA III. Credit: Universität Hamburg, Ivan Baev
“We applied a strong magnetic field at very low temperature to align the single magnetic moments in each molecule of our radical films along the direction of the field,” explains Ivan Baev from the University of Hamburg, also one of the main authors of the study. “The absorption spectra were measured once with left circularly polarized light and once with right circularly polarized light.” Analysing the measurements was not easy. “It took a long time to interpret the data, as this is the first experiment of its kind, but it was very rewarding,” reports Casu. “We have shown that completely organic, light and transparent radical thin films have long-range magnetism, and their magnetic behaviour can be changed depending on the film production, for example by changing the temperature of the coated substrates during coating. This renders organic radicals promising candidates for novel and sustainable magnetic materials.”
Scientists from the Universities of Tübingen, Hamburg and Nebraska, from the Italian Istituto Nanoscienze in Modena and from Helmholtz-Zentrum Berlin contributed to this research.
Reference
Magnetic behaviour in metal-free radical thin films; Tobias Junghoefer, Arrigo Calzolari, Ivan Baev, Mathias Glaser, Francesca Ciccullo, Erika Giangrisostomi, Ruslan Ovsyannikov, Fridtjof Kielgast, Matz Nissen, Julius Schwarz, Nolan M. Gallagher, Andrzej Rajca, Michael Martins, Maria Benedetta Casu; Chem, 2021; DOI: 10.1016/j.chempr.2021.11.021