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, published in Nature Materials, 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 behavior 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.
