Curie Temperature, Tc: The temperature at which the parallel alignment of elementary magnetic moment completely disappears, and the material is no longer able to hold magnetization.

Anisotropic Magnet: A magnet having a preferred direction of magnetic orientation, so that the magnetic characteristics are optimum in one preferred direction.

Coercive Force, Hc: The demagnetizing force, measured in Oersteds, necessary to reduce observed induction, B, to Zero after the magnet has previously been brought to saturation.

Air Gap: A low permeability gap in the flux path of a magnetic circuit. Often air, but inclusive of other materials such as paint, aluminum, etc.

Closed Circuit: This exists when the flux path external to a permanent magnet is confined within high permeability materials that compose the magnet circuit.