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Scientists have managed to overcome this constraint by introducing chirality into a magnet molecule. The results can be found in the Journal of the American Chemical Society.
As the name suggests, a magnet molecule is a magnet composed of a single molecule. It has a non-zero magnetic moment, often linked to the presence of unpaired electrons from the metallic ions in its structure.
When an external magnetic field is applied to these objects, the magnetic moments of each molecule are oriented in a particular direction. This magnetic state is preserved when the magnetic field is turned off, giving each molecule the memory of the magnetic field it has been exposed to.
And memory at such a small scale means potential applications for high-density information storage, quantum computing, or spintronics. However, the real challenge lies in the ability to read the magnetic information carried by each molecule.
It is possible to retrieve this magnetically stored information, without physical contact, through optical reading. Until now, this required a beam of polarized light (often a laser) and analyzing the modification of circular polarization* through interaction with local magnetic moments, a phenomenon known as the "Faraday magneto-optical effect." This method of reading, briefly commercialized, was quickly abandoned due to the complexity associated with polarized light.
Such an obstacle can be bypassed by combining chirality** and magnetism. Indeed, chiral magnetic materials exhibit a property called magneto-chiral dichroism (MChD), which means their absorption of unpolarized light depends on their magnetic state. Introducing chirality into a magnet molecule should enable optical reading of their magnetic state using unpolarized light.
Using molecular chemistry principles, a team of chemists from the Laboratoire national des champs magnétiques intenses (CNRS/Université Grenoble Alpes/INSA Toulouse/Université Toulouse III Paul Sabatier) succeeded in introducing chirality into a magnet molecule containing a dysprosium(III) ion. The scientists then developed a specific measurement protocol for magneto-chiral dichroism. It involves varying the magnetic field applied to the molecules, and therefore their magnetism, while continuously recording the system's optical response for all field values.
The magneto-chiral optical data they obtained perfectly matches the magnetization curves obtained through magnetometry. These results, published in J. Am. Chem. Soc., demonstrate that by introducing chirality into magnet molecules, unpolarized light can probe their magnetic state via MChD, even at zero field.
This is a paradigm shift in the field of optical data reading, paving the way for the development of new optical reading technologies that do not require polarized 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 that are not superimposable on their mirror image.
Editor: CCdM
Reference:
Optical Readout of Single-Molecule Magnets: Magnetic Memories with Unpolarized Light.
J. Am. Chem. Soc., 2024, 146, 23616−23624.
https://pubs.acs.org/doi/10.1021/jacs.4c08684