Glossary   

Air Gap

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

Anisotropic Magnet

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

Closed Circuit

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

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.

Curie Temperature
(Tc)

The temperature at which the parallel alignement of elementary magnetic moments completely disappears, and the material is no longer able to hold magnetization.

Demagnetization Curve

The second quadrant of the hysteresis loop, generally describing the behavior of magnetic characteristics in actual use, also known as the B-H curve.

Eddy Currents

Circulating electrical currents that are induced in electrically conductive elements when exposed to changing magnetic fields, creating an opposing force to the magnetic flux. Eddy currents can be harnessed to perform useful work (such as damping of movement), or may be unwanted consequences of certain designs which should be accounted for or minimized.

Ferromagnetic Material

A material whose permeability is very much larger than 1 (from 60 to several thousand times), and which exhibits hysteresis phenomena.

Flux (Ø)

The condition existing in a medium subjected to a magnetizing force. This quantity is characterized by the fact that an electromotive force is induced in a conductor surrounding the flux at any time the flux changes in magnitude. The cgs unit of flux is the maxwell.

Fringing Fields

Leakage flux particularly associated with edge effects in a magnetic circuit.

Gauss

Lines of magnetic flux per square centimeter, cgs unit of flux density, equivalent to lines per square inch in the English system, and webers per square meter or Tesla in the SI system.

Hysteresis Loop

A closed curve obtained for a material by plotting corresponding values of magnetic induction, B, (on the abscissa) against magnetizing force, H (on the ordinate).

Induction (B)

The magnetic flux per unit area of a section normal to the direction of flux. Measured in Gauss, in the cgs system of units.

Intrinsic Coercive force
(Hci)

Measured in Oersteds in the cgs system, this is a measure of the material's inherent ability to resist demagnetization. It is the demagnetization force corresponding to zero intrinsic induction in the magnetic material after saturation. Practical consequences of high Hci values are seen in greater temperature stability for a given class of material, and greater stability in dynamic operating conditions.

Irreversible Loss

Defined as the partial demagnetization of a magnet caused by external fields or other factors. These losses are only recoverable by remagnetization. Magnets can be stabilized to prevent the variation performance caused by irreversible losses.

Isotropic magnet

A magnet material whose magnetic properties are the same in any direction.

Magnetic Field strength
(H)

A measurement of the magnetic ability to induce a magnetic field at a given point. This is measured in Oersteds.

Magnetic Flux

The total magnetic induction over a certain area.

Magnetizing Force
(H)

The magnetomotive force per unit length at any point in the magnetic circuit. this is measured in Oersteds.

Magnetomotive Force
(F)

The magnetic potential difference between any two points.

Maxwell

A unit of magnetic flux. One Maxwell is one line of magnetic flux.

Oersted, Oe

A unit of magnetic field strength or magnetizing force.

Orientation Direction

The direction in which an anisotropic magnet should be magnetized in order to optimize the magnetic properties.

Saturation

This is a condition where all magnetic moments have become oriented in one direction.

Stabilization

Exposing a magnet to demagnetizing influences which are expected in the application in order to prevent irreversible loss during the operation of the magnet.