Chiral molecule-induced contributions to ferromagnetic resonance

TL;DR

This study investigates the impact of chiral molecular interfaces on the magnetization dynamics of thin ferromagnetic multilayers, finding no measurable static effects but clarifying how equilibrium and non-equilibrium effects influence resonance behavior.

Contribution

It introduces a macrospin model to distinguish between equilibrium energy landscape modifications and non-equilibrium spin torques induced by chirality in ferromagnetic resonance.

Findings

No measurable changes in resonance field or linewidth due to chirality.

Equilibrium effects shift resonance conditions via free energy landscape modifications.

Non-equilibrium spin torques can alter the effective damping rate.

Abstract

Despite extensive research on chirality-driven spin selectivity, most studies have focused on static magnetic properties, while the influence of chirality on the dynamic magnetic response remains largely unexplored. Here, we investigate how chiral molecular interfaces affect magnetization dynamics in thin Co/Ni multilayers with perpendicular magnetic anisotropy using broadband ferromagnetic resonance spectroscopy. A comparison between bare (reference) films and molecule-functionalized (hybrid) samples reveals no measurable changes in either the resonance field or the linewidth that could be attributed to the presence of the chiral environment. Motivated by our findings we develop a macrospin description that distinguishes equilibrium modifications of the magnetic free-energy landscape (MIPAC-type effects) from non-equilibrium, CISS-induced spin torques. Our analysis shows that equilibrium modifications primarily shift the resonance condition via changes to the free energy landscape and thereby the effective field, whereas damping-like non-equilibrium torques provide a distinct channel for varying the effective damping rate. This approach establishes clear criteria for disentangling chiral-interface-induced energy modifications from torque-driven dynamical effects in ferromagnetic resonance experiments.