Runaway "fingerlike" instability of magnetic walls in ultrathin layers

Smooth domain walls in ultrathin ferromagnetic film were investigated. It was shown that the walls can develop jaggedness even in the absence of random defects. From the Kerr imaging of 0.7 nm thin Co films and from numerical simulations, a previously unseen runaway fingerlike instability in magnetic wall was reported. Results show that a threshold for the instability is controlled by ferromagnet's parameters.