 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").The most known empirical models in hysteresis are Preisach and Jiles-Atherton models.