Do magnets have aligned magnetic domains?
One theory of why a material, capable of being magnetised, becomes magnetic (i.e., attracts ferrous material), is that the individual, but randomly distributed 'domains' within are lined up (by some exterior force - e.g., magnetic field from a coil, 'stroking' with an already magnetised piece of iron/streel, etc.), so that the domains line up. The summation of their individual magnetic fields effectively produces one large magnetic field in the material and makes what we call a magnet! Some materials, after this process, retain their magnetism and are called permanent magnets, others, such as relay cores, once the external force is removed, exhibit very little residual magnetism.
