Exchange spring magnet
The magnetostatic energy is the energy stored in the field generated by a material's magnetic moments. The magnet's field reaches its maximum intensity if all the magnetic moments orient in one direction; this is what occurs in a hard magnet. In order to prevent building up the magnetic field, sometimes magnetic moments tend to form loops. That way, the energy stored in the magnetic field can be constrained; this is what occurs in a soft magnet. What determines whether a magnet is hard or soft is the dominant term of its magnetic energy. For hard magnets, the anisotropy constant is relatively large, making the magnetic moments align with easy axis. The opposite case applies to soft magnets, in which the magnetostatic energy is dominant.
Eddy current
A magnet induces circular electric currents in a metal sheet moving past it. See the diagram at right. It shows a metal sheet "(C)" moving to the right under a stationary magnet. The magnetic field "(B, green arrows)" of the magnet's north pole "N" passes down through the sheet. Since the metal is moving, the magnetic flux through the sheet is changing. At the part of the sheet under the leading edge of the magnet "(left side)" the magnetic field through the sheet is increasing as it gets nearer the magnet, formula_1. From Faraday's law of induction, this creates a circular electric field in the sheet in a counterclockwise direction around the magnetic field lines. This field induces a counterclockwise flow of electric current "(I, red)", in the sheet. This is the eddy current. At the trailing edge of the magnet "(right side)" the magnetic field through the sheet is decreasing, formula_2, inducing a second eddy current in a clockwise direction in the sheet.