Blog post: swansont: Master of My Domain

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!