Nonmonotonic Magnetic Friction from Collective Rotor Dynamics

TL;DR

This paper reveals that magnetic interactions can cause nonmonotonic frictional behavior in a contactless magnetic rotor system, driven by collective magnetic reorientations and hysteresis, challenging traditional friction laws.

Contribution

It demonstrates that magnetic configurational dynamics can produce nonmonotonic friction dependence without physical contact, introducing a new mechanism for contactless friction control.

Findings

Friction peaks at intermediate interlayer distances due to magnetic frustration.

Energy dissipation is driven by collective magnetic reorientations.

The system exhibits hysteretic torque cycles during sliding.

Abstract

Amontons' law postulates a monotonic relationship between frictional force and the normal load applied to a sliding contact. This empirical rule, however, fails in systems where internal degrees of freedom - such as structural or electronic order - play a central role. Here, we demonstrate that friction can emerge entirely from magnetically driven configurational dynamics in the absence of physical contact. Using a two-dimensional array of rotatable magnetic dipoles sliding over a commensurate magnetic substrate, we observe a pronounced non-monotonic dependence of friction on the interlayer separation, and thus on the effective load. The friction peaks at an intermediate distance where competing ferromagnetic and antiferromagnetic interactions induce dynamical frustration and hysteretic torque cycles during sliding. Molecular dynamics simulations and a simplified two-sublattice model confirm that energy dissipation is governed by collective magnetic reorientations and their hysteresis. Our results establish the occurrence of sliding-induced changes in collective magnetic order, which has a strong impact on friction, and thus open new possibilities for contactless friction control, magnetic sensing, and the design of reconfigurable, wear-free frictional interfaces and metamaterials.