Challenging a 300-year-old law of friction

Researchers at the University of Konstanz have uncovered a new mechanism of sliding friction: resistance to motion that arises without any mechanical contact, driven purely by collective magnetic dynamics. The study shows that friction does not necessarily increase steadily with load, as postulated by Amontons’ law – one of the oldest and most fundamental empirical laws of physics – but can instead exhibit a pronounced maximum when internal magnetic ordering becomes frustrated.

For more than three centuries, Amontons’ law has linked friction directly to load, reflecting the everyday experience that heavier objects are harder to move; for example, pushing a heavy piece of furniture requires far more effort than sliding a light chair. This behaviour is commonly attributed to tiny deformations of the surfaces in contact under load, which increase the number of microscopic contact points and thereby enhance friction. In most classical situations, these deformations remain small and do not qualitatively change the internal structure of the materials during sliding. It is therefore not clear whether Amontons’ law will also hold when sliding induces much stronger internal reconfigurations, as can occur in magnetic materials where motion can modify the magnetic order.

To explore this regime, the team carried out a tabletop experiment using a two-dimensional array of freely rotating magnetic elements moving above a second magnetic layer. Although the two layers never come into physical contact, their magnetic coupling gives rise to a measurable friction force. By varying the separation between the layers, the researchers could continuously tune the effective load while directly observing how the internal magnetic configuration evolves during motion.

“By changing the distance between the magnetic layers, we could drive the system into a regime of competing interactions where the rotors constantly reorganize as they slide,” says Hongri Gu, who carried out the experiments.

Strikingly, friction is weakest at both small and large separations. At intermediate distances, however, competing interactions dominate: the top layer favours an antiparallel alignment of magnetic moments (parallel, but pointing in opposite directions), while the underlying layer favours a parallel arrangement. This incompatibility forces the system into a dynamically unstable configuration. As the layers slide past each other, the magnets are repeatedly driven to switch between these incompatible states in a hysteretic manner (that means the current state depends on its past history), strongly enhancing energy dissipation and producing a pronounced maximum in friction.

“From a theoretical perspective, this system is remarkable because friction does not originate from a physical surface contact, but from the collective dynamics of magnetic moments,” explains Anton Lüders, who developed the theoretical description. The competing magnetic interactions naturally lead to hysteretic reorientations during motion and, as a result, to a friction force that varies non monotonically with load. In this sense, the breakdown of Amontons’ law is not an anomaly but a direct consequence of magnetization dynamics during sliding.

“What is remarkable is that friction here arises entirely from internal reorganization,” adds Clemens Bechinger, who supervised the project. “There is no wear, no surface roughness and no direct contact. Dissipation is generated solely by collective magnetic rearrangements.”

Because the underlying physics is scale free, the results extend far beyond the macroscopic model system. Similar effects may arise in atomically thin magnetic materials, where even small mechanical displacements can switch magnetic order. The findings therefore open new avenues for probing and controlling magnetism through frictional measurements.

In the long term, this work points toward tunable frictional interfaces without wear. By exploiting magnetic hysteresis, friction could be adjusted remotely and reversibly, enabling concepts such as frictional metamaterials, adaptive dampers or contactless control elements. Potential applications range from micro and nanoelectromechanical systems, where wear limits device lifetime, to magnetic bearings, vibration isolation and atomically thin magnets, where mechanical motion is tightly coupled to internal magnetic order. More broadly, magnetic friction offers a new route to accessing collective spin dynamics through purely mechanical measurements, forging a novel link between tribology and magnetism.

 

Facts:

Embargoed until 18 March 2026, 06:00 US Eastern Time
(10:00 London Time, 11:00 CET)
  Original publication: Hongri Gu, Anton Lüders, and Clemens Bechinger, Nonmonotonic Magnetic Friction from Collective Rotor Dynamics (Nature Materials)
DOI: https://doi.org/10.1038/s41563-026-02538-1
  Press release: University of Konstanz, supported by AI  

Note to editors:
You can download an image here: https://www.uni-konstanz.de/fileadmin/pi/fileserver/2026/300_jahre_altes_reibungsgesetz.png

Caption: Schematic of two magnetic layers composed of permanent magnets. The magnets in the upper layer are free to rotate, while those in the lower layer are fixed. When the layers move relative to each other, the upper magnets periodically reorient, dissipating energy and giving rise to contactless friction. By decreasing the distance between the layers, which controls the effective load, the friction does not increase monotonically, in contrast to the prediction of Amontons’ law.
Copyright: Hongri Gu

Further images and videos of the experimental setup and magnetic rotor dynamics are available upon request.

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