Glossary (Terms and Definitions)

Remanence

Br is the flux density in a magnetic material at zero air gap (H=0) which remains after the removal of the magnetising field. Measured in Gauss, Tesla or mT.

Flux Density

B describes the magnetic field strength under particular conditions, e.g. the actual flux density measured on the pole face of a magnet will depend on the material, the magnet shape and the associated ferrous circuit. Measured in Gauss, Tesla or mT. Also called the magnetic induction.

Coercive Force

Hc is the strength of the demagnetising field where B=0 (bHc) or J=0 (jHc), the latter known as the intrinsic coercive force. Measured in Oersted or kA/m.

Maximum Energy Product

BH max indicates the highest energy that a magnet can provide when operating at a working point on the demagnetisation curve where B x H is a maximum. Measured in Mega-Gauss-Oersteds or kJm³.

Demagnetisation Curve

This is the second quadrant of a major hysteresis loop for a magnetic material and defines the main magnetic properties of a permanent magnet.

Working Point

This is the point on the demagnetisation curve where the value of B & H correspond to the actual working conditions of the magnet. The load line for a particular shape of magnet and its associated circuitry, drawn from the origin, cuts the demagnetisation curve at the working point. For static applications there is one working point, several for a rotating or variable system.

L / D Ratio

This ratio of magnet length to diameter or (for rectangular magnets) is used to establish the load line angle and thus the working point (B/µoH) particularly for magnets used in an open circuit condition.

Isotropic

Capable of being magnetised in any direction.

Anisotropic

Indicates that a preferred magnetic axis has been fixed during manufacture in order to produce higher magnetic properties in that preferred direction. Anisotropic magnets can only be magnetised in the preferred direction.