Long-Timescale Magnetization Ordering Induced by an Adsorbed Chiral Monolayer on Ferromagnets

TL;DR

This study demonstrates that a chiral monolayer can induce long-timescale magnetization reorientation in ferromagnets, revealing exchange interactions as a key factor, with implications for spintronics and magnetic memory technologies.

Contribution

It provides experimental evidence linking molecular tilt angle changes to magnetization reorientation, indicating a long-timescale effect stabilized by exchange interactions in CISS.

Findings

Magnetization reorientation correlates with molecular tilt angle changes.

The effect persists over long timescales, suggesting exchange interactions.

CISS influences magnetization without external magnetic fields or currents.

Abstract

When an electron passes through a chiral molecule there is a high probability for a correlation between the momentum and spin of the charge, thus leading to spin polarized current. This phenomenon is known as the chiral induced spin selectivity (CISS) effect. One of the most surprising experimental results recently demonstrated is that magnetization reversal in a ferromagnet (FM) with perpendicular anisotropy can be realized solely by chemisorbing a chiral molecular monolayer without applying any current or external magnetic field. This result raises the currently open question of whether this effect is due to the bonding event, held by the ferromagnet, or a long timescale effect stabilized by exchange interactions. In this work we have performed vectorial magnetic field measurements of the magnetization reorientation of a ferromagnetic layer exhibiting perpendicular anisotropy due to CISS using nitrogen-vacancy centers in diamond, and followed the time dynamics of this effect. In parallel, we have measured the molecular monolayer tilt angle in order to find a correlation between the time dependence of the magnetization re-orientation and the change of the tilt angle of the molecular monolayer. We have identified that changes in the magnetization direction correspond to changes of the molecular monolayer tilt angle, providing evidence for a long-timescale characteristic of the induced magnetization reorientation. This suggests that the CISS effect has an effect over long-timescales which we attribute to exchange interactions. These results offer significant insights into the fundamental processes underlying the CISS effect, contributing to the implementation of CISS in state-of-the-art applications such as spintronic and magnetic memory devices.