Success in future data storage

Physicist Eric Ludwig examines switchable molecular complexes at the
ASPHERE photoelectron spectrometer, which was built by a team of scientists led by Lutz Kipp at the Deutschen Elektronen-Synchrotron (DESY) in Hamburg.
Photo/Copyright: Holger Naggert

Scientists at Kiel University have achieved another breakthrough on the way towards data storage on a molecular level. They have managed to switch the magnetic state of an ultrathin film of molecules on and off with the aid of light. The Collaborative Research Centre 677 "Function by Switching", funded by the German Research Foundation (DFG), recently published this result in the renowned scientific journal “Angewandte Chemie”.

Thin layers of magnetically switchable compounds play an important role in data storage and in electronic devices in general. Normally these layers consist of crystalline materials, which are evaporated onto ever-smaller devices at high temperatures in ultra-high vacuum environments. Until now it had not been possible to use magnetic molecules for these purposes, since they usually disintegrate under those conditions.

The team of scientists working at the Collaborative Research Centre 677 "Function by Switching" has discovered that a particular class of molecules – so-called spin crossover complexes – can be evaporated and vacuum-deposited as thin films retaining their characteristic properties. Through external stimuli such as pressure and temperature the magnetism of these molecules, which contain an iron atom, can be switched on and off. A major advantage of this molecular film compared to crystalline solids lies in the fact that it may be applied to flexible materials and could lead to storage units with a higher storage capacity.

Felix Tuczek, Professor at the Institute of Inorganic Chemistry, and Lutz Kipp, Professor at the Institute of Experimental and Applied Physics, along with their team, proved that the magnetism of a seven nanometre thin film – which contains about six layers of these molecular complexes – could be switched by exposure to light. For this experiment, they used an ultraviolet photoelectron spectrometer by which the electronic structure of these compounds can directly be investigated under ultra-high vacuum conditions. Prior to this, scientists from Kiel had already succeeded in controlling the magnetic state of single molecules in a single layer by injecting electrons.

“Our progress in making this class of molecules act as tiny magnetic memories opens up opportunities for new technical applications”, says Tuczek. At this stage, the magnetic state can be controlled only in an environment of about minus 170 degree Celsius. The next goal would be to realize a switchable film of molecules at room temperature, he adds.

The Collaborative Research Centre 677 has already produced a series of spectacular findings in the past. One of them was the synthesis of a molecular machine that works in a way similar to a record player and whose magnetic state can be switched in liquids at room temperature. Novel applications such as a switchable contrast agent in MRT (magnetic resonance tomography) may thus become possible. The common denominator in these research activities is the goal to transfer magnetic features of crystalline solids to single molecules and ultrathin molecular films. In this research area, the Collaborative Research Centre 677 at Kiel University is now an international leader.

Original publication:

E. Ludwig, H. Naggert, M. Kalläne, S. Rohlf, E. Kröger, A. Bannwarth, A. Quer, K. Rossnagel,L. Kipp und F. Tuczek (2014): Fe(II) spin-crossover complexes in ultrathin films: Electronic structure and spin-state switching by visible and vacuum-UV light

Angew. Chem. Int. Ed. 2014, in press. DOI: 10.1002/ange.201307968

Further information on the Collaboration Research Centre 677: www.sfb677.uni-kiel.de

Contact

Prof. Dr. Felix Tuczek

Institute of Inorganic Chemistry

Phone: +49 (431) 880 1410

Email: sekretariat-tu@ac.uni-kiel.de

Prof. Dr. Lutz Kipp

Institute of Experimental and Applied Physics

Phone: +49 (431) 880 3875

Email: kipp@physik.uni-kiel.de