Editing Magnetism (section)

==== Magnetic domains ====

{{main|Magnetic domains}}

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The magnetic moments of atoms in a [[Ferromagnetism|ferromagnetic]] material cause them to behave something like tiny permanent magnets. They stick together and align themselves into small regions of more or less uniform alignment called [[magnetic domains]] or [[Weiss domains]]. Magnetic domains can be observed with a [[magnetic force microscope]] to reveal magnetic domain boundaries that resemble white lines in the sketch. There are many scientific experiments that can physically show magnetic fields.

When a domain contains too many molecules, it becomes unstable and divides into two domains aligned in opposite directions so that they stick together more stably.

When exposed to a magnetic field, the domain boundaries move, so that the domains aligned with the magnetic field grow and dominate the structure (dotted yellow area), as shown at the left. When the magnetizing field is removed, the domains may not return to an unmagnetized state. This results in the ferromagnetic material's being magnetized, forming a permanent magnet.

When magnetized strongly enough that the prevailing domain overruns all others to result in only one single domain, the material is [[Saturation (magnetic)|magnetically saturated]]. When a magnetized ferromagnetic material is heated to the [[Curie point]] temperature, the molecules are agitated to the point that the magnetic domains lose the organization, and the magnetic properties they cause cease. When the material is cooled, this domain alignment structure spontaneously returns, in a manner roughly analogous to how a liquid can [[freezing|freeze]] into a crystalline solid.