Making a switchable magnet from a biomolecule


A molecule is magnetic (more precisely: paramagnetic) when its number of electrons is odd or when it contains transition metal ions like iron. Sujoy Karan from the group of Prof. Berndt investigated all-trans-retinoic acid, a non-magnetic bio-molecule with an even number of electrons, on an inert gold surface and observed that, surprisingly, the molecule may be made magnetic by passing current through it. Once it is magnetic, it may be switched back to non-magnetic. This process may be repeated and does not affect neighboring molecules. 

Currently, these observations are a serious challenge to state-of-the-art theory. From a broader perspective, they suggest that it may be possible to custom-make arbitrary arrays of ultrasmall magnets on surfaces using an unforeseen class of molecules. In addition, living organisms utilize retinoic acid for signal transduction. Whether effects related to the new observation may play a role in organisms is yet unknown. 

The experimental results from Kiel and Beijing along with theory from Munich recently appeared in Physical Review Letters.