Micromagnetics deals with the interactions between magnetic moments on sub-micrometre length scales. These are governed by several competing energy terms. Dipolar energy is the energy which causes magnets to align north to south pole. Exchange energy will attempt to make the magnetic moments in the immediately surrounding space lie parallel to one another (if the material is ferromagnetic) or antiparallel to one another (if antiferromagnetic). Anisotropic energy is low when the magnetic moments are aligned along a particular crystal direction. The Zeeman energy is at its lowest when magnetic moments lie parallel to an external magnetic field.