Using a magnet to tune a magnet

Domain wall pattern for a ferromagnet. The technical use of the magnet is determined by the ease with which the walls can be moved, or equivalently, by the force with which they are pinned. Strong pinning gives a hard magnet, soft pinning a soft magnet. The distance between the walls is 100 nanometers or 10 millionths of a centimeter. Credit: Y-A. Soh and G. Aeppli