Dynamical Configurations and Bistability of Helical Nanostructures under External Torque

TL;DR

This study investigates the complex motion and bistability of ferromagnetic helical nanostructures under rotating magnetic fields, revealing new dynamical behaviors influenced by geometry and magnetization, with implications for nanoscale control.

Contribution

It introduces a theoretical model and experimental observations of bistable dynamics in helical nanostructures under external torque, highlighting the role of geometry and thermal fluctuations.

Findings

Observation of various dynamical configurations depending on magnetization and geometry.

Identification of bistable behavior with random switching between configurations.

Theoretical model confirming experimental results and applicable to ellipsoidal systems.

Abstract

We study the motion of a ferromagnetic helical nanostructure under the action of a rotating magnetic field. A variety of dynamical configurations were observed that depended strongly on the direction of magnetization and the geometrical parameters, which were also confirmed by a theoretical model, based on the dynamics of a rigid body under Stokes flow. Although motion at low Reynolds numbers is typically deterministic, under certain experimental conditions, the nanostructures showed a surprising bistable behavior, such that the dynamics switched randomly between two configurations, possibly induced by thermal fluctuations. The experimental observations and the theoretical results presented in this letter are general enough to be applicable to any system of ellipsoidal symmetry under external force or torque.