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A research group at The University of Tokyo has discovered a new principle by which helical chiral molecules acquire spin through molecular vibrations, enabling them to adhere to magnets. Until now, it was believed that chiral molecules could only exhibit magnetic properties when an electric current was applied. This discovery overturns that conventional understanding.

Chiral molecules, which have a helical structure, are known to interact with magnets in a phenomenon known as chirality-induced spin selectivity (CISS). For instance, when a chiral molecule is connected to a magnet and an electric current is applied, magnetoresistance effects can be observed. It has also been reported that magnets can be used to separate right-handed and left-handed chiral molecules.

The prevailing explanation is that the flow of current through a chiral molecule induces magnetic properties, similar to an electromagnet. However, this explanation has limitations, as it does not fully account for the large magnetoresistance effects or CISS phenomena observed even in the absence of an electric current.

Professor Shinji Miwa of the Institute for Solid State ÌÇÐÄÊÓƵics of the University of Tokyo, Professor Tastuhiko Ohto of Nagoya University and a collaborative research team have developed a specialized electrochemical cell using spintronics technology for this study.

By varying the thickness of a gold film and analyzing the current change, oscillatory changes in magnitude and sign were observed (fig. 2c). These results indicate the presence of interlayer exchange coupling between the chiral molecules and the magnet.

To understand the mechanism behind the coupling, it is necessary to determine how chiral molecules acquire magnetic properties in the absence of an electric current. Researchers found that vibrational motion in chiral molecules leads to the emergence of spin that depends solely on chirality, regardless of the direction of the magnetic field. Fig 2d shows theoretical results of first-principles calculations.

This study experimentally demonstrates that the CISS phenomenon arises from interlayer exchange coupling. Furthermore, it reveals that chiral molecules can acquire spin and exhibit magnetic properties through molecular vibrations, without the need for an applied current. Since this mechanism does not rely on electric current, it may occur universally in diverse environments, including chemical reactions and biological processes.

This new insight is expected to lead to future research and applications across a wide range of fields, including chemistry and life sciences.