A scanning tunneling microscope tip measures a magnetic atom’s contribution to sliding friction. A cobalt (Co) atom (blue) sits on top of a single layer of manganese (Mn) atoms supported on a tungsten surface (grey), and a spin-polarized STM tip slides the Co atom laterally. The Mn spins arrange in an antiferromagnetic pattern (red and green) and the Co atom’s spin prefers to align with the nearest Mn atom. (Left) A stable binding site is found at a tip position where the Co atom can satisfy a ferromagnetic interaction with the last atom in the tip, as well as with the nearest Mn atom. (Right) A less stable binding site occurs at a tip position where these magnetic interactions cannot both be fulfilled.