Making magnets speak: the Barkhausen effect

There are two important aspects to this “snapping” of a domain wall past a defect. First, it explains how iron can stay magnetized after the applied field is shut off: the domain walls try and return to their original position, but they routinely get “stuck” on a defect, leaving the metal partially magnetized. Second, this “snapping” results in a tiny spike in the magnetic field produced by the metal — and these tiny sharp changes in the magnetic field are what we are hearing in the Barkhausen effect!