Magnetic domains Ferromagnetism

electromagnetic dynamic magnetic domain motion of grain oriented electrical silicon steel



kerr micrograph of metal surface showing magnetic domains, red , green stripes denoting opposite magnetization directions.

the above seem suggest every piece of ferromagnetic material should have strong magnetic field, since spins aligned, yet iron , other ferromagnets found in unmagnetized state. reason bulk piece of ferromagnetic material divided tiny regions called magnetic domains (also known weiss domains). within each domain, spins aligned, (if bulk material in lowest energy configuration, i.e. unmagnetized), spins of separate domains point in different directions , magnetic fields cancel out, object has no net large scale magnetic field.

ferromagnetic materials spontaneously divide magnetic domains because exchange interaction short-range force, on long distances of many atoms tendency of magnetic dipoles reduce energy orienting in opposite directions wins out. if dipoles in piece of ferromagnetic material aligned parallel, creates large magnetic field extending space around it. contains lot of magnetostatic energy. material can reduce energy splitting many domains pointing in different directions, magnetic field confined small local fields in material, reducing volume of field. domains separated thin domain walls number of molecules thick, in direction of magnetization of dipoles rotates smoothly 1 domain s direction other.