Glossary Of Magnet Terminology

- Mar 30, 2018 -

Air Gap - The "external" distance from one pole of the magnet to the other though a non-magnetic material (usually air, but inclusive of other materials such as paint, aluminum, etc).

BH Curve - The result of plotting the value of the magnetic field (H) that is applied against the resultant flux density (B) achieved. This curve describes the qualities of any magnetic material.

BHmax (Maximum Energy Product) - The Maximum Energy Product at the point on the B/H Curve that has the most strength, expressed in MGOe (MegaGaussOersteds). When describing the grade of a neodymium magnet, this number is commonly referred to as the "N" number, as in Grade N52 magnets.

Brmax (Residual Induction) - Also called "Residual Flux Density".  The magnetic induction remaining in a saturated magnetic material after the magnetizing field has been removed.  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 zero air gap, and therefore cannot be seen in practical use of magnet materials.

Coercive Force (Hc) - The demagnetizing force, measured in Oersted, necessary to reduce observed induction, B, to zero after the magnet has previously been brought to saturation.

Curie Temperature (Tc) - The temperature at which a magnet loses all of its magnetic properties.

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.

Demagnetization Force - A magnetizing force, typically in the direction opposite to the force used to magnetize it in the first place. Shock, vibration and temperature can also be demagnetizing forces.

Dimensional Tolerance - An allowance, given as a permissible range, in the nominal dimensions of a finished magnet. The purpose of a tolerance is to specify the allowed leeway for variations in manufacturing.

Gauss - Unit of magnetic induction, B.  Lines of magnetic flux per square centimeter in the C.G.S. system of measurement.  Equivalent to lines per square inch in the English system, and Weber per square meter or tesla in the S.I. system. 10,000 gauss equals 1 tesla.

Gauss meter - An instrument used to measure the instantaneous value of magnetic induction, B, usually measured in Gauss (C.G.S.). Also called a DC magnetometer.

Gilbert - The unit of magneto motive force, F, in the C.G.S. system.

Hysteresis Loop - A plot of magnetizing force versus resultant magnetization (also called a B/H curve) of the material as it is successively magnetized to saturation, demagnetized, magnetized in the opposite direction and finally re-magnetized. With continued recycles, this plot will be a closed loop which completely describes the characteristics of the magnetic material. The size and shape of this "loop" is important for both hard and soft materials.
The first quadrant of the loop (that is +X and +Y) is called the magnetization curve. It is of interest because it shows how much magnetizing force must be applied to saturate a magnet. The second quadrant (-X and +Y) is called the Demagnetization Curve.
Induction, (B) - The magnetic flux per unit area of a section normal to the direction of flux. Measured in Gauss, in the C.G.S. system of units.

Intrinsic Coercive Force (Hci) - Indicates a materials resistance to demagnetization. It is equal to these demagnetizing force which reduces the intrinsic induction, Bi, in the material to zero after magnetizing to saturation; measured in oersted.

Isotropic Material - The material that can be magnetized along any axis or direction (a magnetically unoriented material). The opposite of Anisotropic Magnet.

Magnetic Circuit - Consists of all elements, including air gaps and non-magnetic materials that the magnetic flux from a magnet travels on, starting from the north pole of the magnet to the south pole.

Magnetic Flux - Is a contrived but measurable concept that has evolved in an attempt to describe the "flow" of a magnetic field.  When the magnetic induction, B, is uniformly distributed and is normal to the area, A, the flux, ? = BA.

Magnetic Flux Density - Lines of flux per unit area, usually measured in Gauss (C.G.S.). One line of flux per square centimeter is one Maxwell.

Magnetic Induction (B) - The magnetic field induced by a field strength, H, at a given point. It is the vector sum, at each point within the substance, of the magnetic field strength and the resultant intrinsic induction. Magnetic induction is the flux per unit area normal to the direction of the magnetic path.

Magnetic Line of Force - An imaginary line in a magnetic field, which, at every point, has the direction of the magnetic flux at that point.

Magnetic Pole - An area where the lines of flux are concentrated.

Maximum Operating Temperature (Tmax) - Also known as maximum service temperature, is the temperature at which the magnet may be exposed to continuously with no significant long-range instability or structural changes.

Maxwell - Unit of magnetic flux in the C.G.S. electromagnetic system. One Maxwell is one line of magnetic flux.

Surface Field (Surface Gauss) - The magnetic field strength at the surface of the magnet as measured by a Gauss meter. 

Temperature Coefficient - A factor that is used to calculate the decrease in magnetic flux corresponding to an increase in operating temperature. The loss in magnetic flux is recovered when the operating temperature is decreased.

Tesla - The S.I. unit for magnetic induction (flux density). One Tesla equals 10,000 Gauss.

Weber - is the practical unit of magnetic flux. It is the amount of magnetic flux which, when linked at a uniform rate with a single-turn electric current during an interval of 1 second, will induce in this circuit an electromotive of force of 1 volt.

µre recoil permeability is the average slope of the recoil hysteresis loop. Also be known as the minor loop.