Magnet molecules are magnetic memories expected to be used for storing information at the nanoscale and for quantum technologies. Reading this magnetic information is complex because it requires polarized light.
Scientists have managed to overcome this constraint by introducing chirality within a magnet molecule. Results to be found in the Journal of the American Chemical Society.
As its name suggests, a molecule magnet is a magnet made up of a single molecule. It has a non-zero magnetic moment, often linked to the presence of unpaired electrons coming from the metal ions of the structure.
Applying an external magnetic field to these objects orients the magnetic moments of each molecule in a particular direction. This magnetic state is preserved when the magnetic field is cut, which gives each molecule the memory of the magnetic field that was applied to it.
And memory at such a small size means potential applications for high-density information storage, quantum computing or spintronics. We still need to be able to read the magnetic information carried by each molecule.
It is possible to obtain this magnetically stored information, without physical contact, by optical reading. Until now, it required a bundle of light polarized (often laser) and analyzes the modification of the polarisation circular* by interaction with local magnetic moments, a phenomenon called “magneto-optical Faraday effect”. This mode of reading, briefly commercialized, was quickly abandoned because of the complexity linked to the polarized nature of light.
Such an obstacle can be circumvented by combining chirality** and magnetism. Indeed, chiral magnetic materials exhibit a property called magneto-chiral dichroism (MChD), which means that their absorption of unpolarized light depends on their magnetic state. Introducing chirality into a magnet molecule should allow the optical reading of their magnetic state with non-polarized light.
Using the principles of molecular chemistry, a team of chemists from the National Laboratory for Intense Magnetic Fields (CNRS/ Université Grenoble Alpes/INSA Toulouse/Université Toulouse III Paul Sabatier) managed to introduce this chirality into a magnet molecule containing an ion dysprosium(III). The scientists then developed a specific measurement protocol for magnetochiral dichroism. It consists of varying the magnetic field applied to the molecules, and therefore their magnetism, by continuously recording the optical response of the system for all field values.
The magneto-chiral optical data they obtain perfectly follows the magnetization curves obtained by magnetometry. These results, published in the J. Am. Chem. Soc., show that by introducing chirality into the magnet molecules, unpolarized light is able to probe their magnetic state via the MChD, even at zero field.
It is a paradigm shift in the field of optical data reading which opens the way to the development of new optical reading technologies by freeing ourselves from the polarization of light.
Notes:
* Circular polarization of light is a type of polarization where the electric field of the light wave rotates helically around the direction of propagation.
** Chirality is a geometric property of certain objects or molecules which cannot be superimposed on their mirror image.
Editor: CCdM
Reference:
Optical Readout of Single-Molecule Magnets: Magnetic Memories with Unpolarized Light.
J. Am. Chem. Soc.2024, 14623616−23624.
https://pubs.acs.org/doi/10.1021/jacs.4c08684
