Editing Hysteresis (section)

====Physical origin====
{{Main|Ferromagnetism}}
The phenomenon of hysteresis in [[ferromagnetism|ferromagnetic]] materials is the result of two effects: rotation of [[magnetization]] and changes in size or number of [[magnetic domain]]s. In general, the magnetization varies (in direction but not magnitude) across a magnet, but in sufficiently small magnets, it does not. In these [[Single domain (magnetic)|single-domain]] magnets, the magnetization responds to a magnetic field by rotating. Single-domain magnets are used wherever a strong, stable magnetization is needed (for example, [[magnetic recording]]).

Larger magnets are divided into regions called ''domains''. Across each domain, the magnetization does not vary; but between domains are relatively thin ''domain walls'' in which the direction of magnetization rotates from the direction of one domain to another. If the magnetic field changes, the walls move, changing the relative sizes of the domains. Because the domains are not magnetized in the same direction, the [[magnetic moment]] per unit volume is smaller than it would be in a single-domain magnet; but domain walls involve rotation of only a small part of the magnetization, so it is much easier to change the magnetic moment. The magnetization can also change by addition or subtraction of domains (called ''nucleation'' and ''denucleation'').