Air Gap

A low permeability gap in the flux path of a magnetic circuit. Often applied to air but can also refer to other materials which reduce magnetic strength such as paint, aluminum, resins et.c.

Anisotropic Magnet

A magnet having a preferred direction of magnetic orientation, so that the magnetic characteristics and poles are prealigned accordingly.


Chemical element (Ba – element 56) used as an additive for ferrite production.

Ceramic magnet

A Ferrite magnet made from iron oxide with additions of Barium, Strontium or Lead. Nowadays, for health reasons, Strontium is the preferred choice.

Closed Circuit

This exists when the external flux path external of a permanent magnet is confined with high permeability material.

Coercive force

BHC is the demagnetizing force corresponding to zero magnetic induction, B, in a magnetic material after saturation.Old units: Oersted. New units: A/m or kA/m.l.

Curie Temperature, Tc

The transition temperature at which the material loses its magnetic properties.


Demagnetization results in a lessening of the magnetic properties of a permanent magnet. It occurs when the magnet is exposed to:

  1. high AC-field.
  2. reverse fields applied by electromagnets or other permanent magnets.
  3. exposure at an elevated temperature.

Demagnetization Curve

The second quadrant of the hysteresis loop. Working magnets’ characteristics are positioned in this quadrant having undergone a controlled de-magnetization from the maximum point. Also known as the B-H curve (usually designated Bd and Hd).


The ratio of mass to volume. Specific weight of material (gr/cm3). Relative density relates a given material to the density of water.

Eddy Currents

Circulating electrical currents that are induced in electrically conductive elements when exposed to changing magnetic fields and thus creating an opposing force to the magnetic flux (and generally heat). Eddy currents can be harnessed to perform useful work (such as damping of movement or in non-ferrous separators), or may be the unwanted consequence of a design which needs amending so

Ferromagnetic Material

Commonly a material which can exhibit a net magnetic moment in the absence of a magnetic field.


The condition existing in a medium subjected to a magnetizing force.  The CGS unit of flux is the Maxwell.


A galvanometer that measures the change of flux linkage with a search coil. Modern instruments use integrating circuits for measuring flux.

Fringing Fields

Leakage flux particularly associated with edge effects in a magnetic circuit


Lines of magnetic flux per square centimeter. Gauss is the CGS unit of flux density which is equivalent to lines per square inch in the English system, and Webers per square meter or Tesla in the SI system.


Instrument for measuring the instantaneous value of magnetic induction (B).


Barium-, Strontium-, or Lead-Ferrite All hard Ferrites have a hexagonal structure. Examples are BaOx6 Fe2O3 SrOx6 Fe2O3.

Hysteresis loop

Is a closed curve obtained for a material by plotting the relevant values of magnetic induction. B stands for the ordinates and magnetizing force (or field) and H for the abscissa when the material is subjected to a complete cycle of magnetization and de-magnetization. The dotted line shows the virgin curve for a magnet that has not been magnetized before.


Magnetic induction is the flux per unit area normal to the direction of the magnetic path.

Intrinsic coercive force

Denoted by Hc which indicates a magnet’s resistance to demagnetization. It is the demagnetizing force corresponding to zero intrinsic induction in a magnetic material after saturation.

Irreversible losses

Irreversible changes of magnetic properties can occur when magnets are exposed to excess temperature or reversing fields. Once a magnet suffers this loss it can only be recovered by remagnetizing.


A non-oriented magnetic material having equal physical and magnetic properties in all directions.


A piece of soft iron that is placed on or between the poles of a magnet, decreasing the ‘reluctance’ of an air gap and thereby reducing the flux leakage from the magnet.

Knee od demagnetization Curve

The second quadrant of the hysteresis loop. Working magnets’ characteristics are positioned in this quadrant having undergone a controlled de-magnetization from the maximum point. Also known as the B-H curve (usually designated Bd and Hd).

Leakage flux

Is the flux whose path is outside of the used or intended magnetic circuit. It is measured in Maxwell.

Length of Air-Gap, Lg

The length of the path of the central flux line in an air gap.

Magnetic Circuit

An assembly consisting of some or all of the following: permanent magnets, ferromagnetic conduction elements, air gaps, electrical currents.

Magnetic Flux

The total magnetic induction over a given area when the magnetic induction B is uniformly distributed over an area A giving BA. The general equation is BxdA.


An external field is applied to a magnet to charge it or magnetize it. For Ferrites, the field strength should be approximately three times the value of its coercive force.

Magnetizing Force, H

The magnetomotive force per unit length at any point in a magnetic circuit. Measured in Oersteds in the CGS system.

Magnetomotive Force, F

Analogous to voltage in electrical circuits, this is the magnetic potential difference between any two points.

Maximum Energy Product, BHmax

The point on the Demagnetization Curve where the product of B and H is at maximum and the required volume of magnet material required to project a given energy into its surroundings is at a minimum. Measured in MegaGauss Oersteds, MGOe.

North Pole

That pole of a magnet which, when freely suspended, would point to the north magnetic pole of the earth. The definition of polarity can be a confusing issue, and it is often best to define it as “north seeking pole” instead of “north pole” in specifications.


The old unit for the magnetic field strength, H.  The oersted is equal to a magneto motive of one Gilbert per centimeter of flux path. Conversion: 1 Oe = 0,796 A/cm.

Operating point

The location on a demagnetization curve with a specific B and H value (Bd, Hd). The operating point is the crossing between the load line and the demagnetization curve. The operating point is typically found in the 2nd quadrant. It can eventually move into the third quadrant in the case of electro-magnetic applications.

Orientation direction

A permanent magnet has its highest magnetic properties in direction of orientation. For ring- and disc-shape magnets the typical direction of orientation is axial. For rectangular and cubical shapes the orientation is through the height (h). Arc and segment magnets are oriented through the radius or through the diameter.

Oxide magnet

Parallel to a Ferrite magnet – made from Oxides and Carbonates of Iron, Barium or Strontium.

Paramagnetic Material

A material having a permeability slightly greater than 1.

Permanent magnet

Is a body capable of maintaining a magnetic field at other than cryogenic temperature with no expenditure of power.


Is the general term used to express the relationship between magnetic induction, B and the field strength, H


The inverse of reluctance, analogous to conductance in electrical circuits.

Permeance Coefficient, Pc

Ratio of the magnetic induction, Bd, to its self-demagnetizing force, Hd. Pc = Bd/Hd. This is also known as the “load line” or operating point of the magnet, and is useful in estimating the flux output of the magnet under various conditions.

Pole Pieces

Ferromagnetic materials placed on magnetic poles used to shape and alter the effect of flux ‘lines’

Ratio of dimension h:d

(Also named – ratio.) The ratio of the length of a magnet to its diameter, or to the diameter of a circle of equivalent cross sectional area.

Relative Permeability, µr

The ratio of permeability of a medium to that of a vacuum; µr = µ/µo. In the CGS system, µo = 1 in a vacuum by definition. The permeability of air is also, for all practical purposes, equal to 1 in the cgs system

Reluctance, R

R : Analogous to resistance in an electrical circuit, reluctance is related to the magnetomotive force. Magnetic flux will follow the path of least reluctance.

Remanence, Bd

The magnetic induction which remains in a magnetic circuit after the removal of an applied magnetizing force. If there is an air gap in the circuit, the remanence will be less than the residual induction, Br.

Residual Induction, Br

This is the point at which the hysteresis loop crosses the B axis at zero magnetizing force, and represents the maximum flux output from the given magnet material. By definition, this point occurs at a zero air gap, and therefore cannot be observed in the practical use of magnet materials

Remanent induction

BM is the magnetic induction that remains in a magnetic material after magnetizing and conditioning for final use

Return Path

Conduction elements in a magnetic circuit which provide a low reluctance path for the magnetic flux.

Reversible Temperature Coefficient

A measure of the reversible changes in flux caused by temperature variations.


The condition under which all elementary magnetic moments have become oriented in one direction. A ferromagnetic material is saturated when an increase in the applied magnetizing force produces no increase in induction. Saturation flux densities for steels are in the range of 16,000 to 20,000 Gauss.


Exposure of a magnet to demagnetizing influences expected to be encountered in use in order to prevent irreversible losses during actual operation. Demagnetizing influences can be caused by high or low temperatures, or by external magnetic fields.


Chemical element (Sr – atomic number 38) used as a component for ferrite magnet production

Temperature coefficient

Is a value that describes the change of a magnetic property with a change in temperature. It is usually expressed as a % change per unit of temperature


Induction, flux per unit area in the SI system. 1 Tesla = 1 Vs/m2 or 10.000 Gauss. The unit is named after Nicola Tesla.


SI unit for magnetic flux, notated as Wb. 1 Weber = 10-8 Maxwell = 1 Vs Unit Weber is named after Professor Wilhelm Weber.

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