Rotational ratchets with dipolar interactions

TL;DR

This study uses Brownian dynamics simulations to explore how dipolar interactions influence the rotational ratchet effect in magnetic particle systems, revealing both enhancement and suppression mechanisms.

Contribution

It demonstrates how dipolar interactions can both enhance and dampen the ratchet effect, depending on the coupling strength, which was not previously understood.

Findings

Dipolar interactions can enhance the ratchet effect via increased effective fields.

Dipolar interactions can dampen the ratchet effect by restricting rotational motion.

Short-range repulsive interactions also influence the ratchet behavior.

Abstract

We report results from a computer simulation study on the rotational ratchet effect in systems of magnetic particles interacting via dipolar interactions. The ratchet effect consists of directed rotations of the particles in an oscillating magnetic field, which lacks a net rotating component. Our investigations are based on Brownian dynamics simulations of such many-particle systems. We investigate the influence of both, the random and deterministic contributions to the equations of motion on the ratchet effect. As a main result, we show that dipolar interactions can have an enhancing as well as a dampening effect on the ratchet behavior depending on the dipolar coupling strength of the system under consideration. The enhancement is shown to be caused by an increase in the effective field on a particle generated by neighboring magnetic particles, while the dampening is due to restricted rotational motion in the effective field. Moreover, we find a non-trivial influence of the short-range, repulsive interaction between the particles.