Magnet Glossary

The distance between the working face of the magnet and the part with which it is interacting. Often air, but inclusive of other materials such as coating layer thickness on magnet. If the air gap is enlarged, the interacted strength will be weakened.

In manufacturing process, the molecule of magnetic material is aligned by an external magnetic field — this process is also called anisotropy or orientation — to obtain the higher magnetic value in the direction of anisotropic axis. Except AlNiCo magnet (oriented in heat treatment), all other magnets get anisotropy in the molding process. Magnetizing direction on an anisotropic magnet only could be along the anisotropic axis. Anisotropic magnet will output much stronger flux and remanence than isotropic magnet.

A closed curve obtained for a material by plotting (usually to rectangular coordinates) corresponding values of magnetic induction (B) for ordinates and magnetizing force (H) for abscissa when the material is passing through a complete cycle. In practice, if a magnet is operated in a static manner with no external fields present, the normal curve is sufficient for design purposes.

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

The demagnetizing force required to reduce residual induction (Br) to zero in a magnetic field after magnetizing to saturation.

A temperature point above which the magnet will completely lose its permanent magnet properties. The Curie temperature is dependent on magnet composition.

The second quadrant of the hysteresis loop — it completely characterizes the magnetic properties of the material at a specific temperature. To get correct demagnetization curve, a specific size sample in compliance with relevant standard must be used.

The ratio of a magnet length to its diameter, or the diameter of a circle of equivalent cross sectional area. For simple geometries such as bars and rods, the dimension ratio is related to the slope of the operating line of the magnet.

Indicates the energy that a magnetic material can supply to an external magnetic circuit when operating at any point on its demagnetization curve.

Expresses the concentration of lines of force per unit area passing from one pole to the other. Magnet material type, dimension ratio, air gap and position of probe determine the measured value.

That value of H corresponding to the remanent induction (Bd).

See B-H curve.

Indicates the material's resistance to demagnetization. Equal to the demagnetizing force which reduces the intrinsic induction in the material to zero after magnetizing to saturation. The higher the figure, the more stable the magnet.

Partial demagnetization caused by exposure to high or low temperatures, external fields or other factors — not recoverable when the magnet returns to original conditions. Occur when the operating point falls below the knee of the demagnetization curve.

A magnet not pre-oriented by an external magnetic field. Magnetic values measured in any direction or axis of an isotropic magnet show no difference. Can be magnetized with any preferred pattern determined by magnetizing yoke.

The point at which the B-H curve ceases to be linear and starts to drop. If the operating point falls below the knee, small changes in H result in large changes of B and the magnet will suffer irreversible flux loss (recoverable after re-magnetization).

One or several pieces of soft iron placed on or between pole faces of a permanent magnet to decrease the reluctance of the air gap and thereby reduce flux leakage. Also makes the magnet less susceptible to demagnetizing influences.

Permanent magnet families (except bonded and cast AlNiCo) are made by powder metallurgic process — they lack ductility and are very brittle. Not recommended as structural parts.

Consists of permanent magnets, pole tips, air gap and leakage fields.

The measure of the vector magnetic quantity that determines the ability of an electric current, or a magnetic body, to induce a magnetic field at a given point.

A contrived but measurable concept describing the "flow" of a magnetic field. Mathematically, it is the surface integral of the normal component of the magnetic induction over an area.

The magnetic field induced by a field strength at a given point. Also means flux per unit area normal to the direction of magnetic path.

The maximum product of (BdHd) obtainable on the demagnetization curve. Using magnet with greater (BH)max can reduce magnet volume for the same task and conditions. Unit: kJ/m³ or MGOe.

The maximum temperature to which the magnet may be exposed with no significant long-range instability or structural changes. Valid for magnets with sufficient h:D ratios.

Also called "axis", "easy axis" or "angle of inclination". The direction in which an anisotropic magnet should be magnetized to achieve optimum magnetic properties.

Exists when a magnetized magnet is by itself with no external flux path of high permeability material.

The location on a demagnetizing curve with specific flux density (B) and field strength (H). The longer the magnet in the anisotropic axis, the nearer the operating point is to remanence (Br).

Expresses the ability of induction to pass through a material and demonstrates various relationships between magnetic induction (B) and field strength (H). For some permanent magnets, permeability is only marginally better than air.

The reciprocal of the reluctance (R), measured in maxwells per gilbert.

The ratio of the remanent induction (Bd) to a demagnetizing force (Hd) — also referred to as operating slope, shear line, load line or B/H in open circuit condition. Important data for magnet material selection.

Elements used to construct an efficient holding magnet — both are mild steel or iron. Pole pieces collect flux from pole faces and concentrate it; counter-plate completes the magnetic circuit.

The average slope of the recoil hysteresis loop, also known as a minor loop.

The quantity that determines the magnetic flux resulting from a given magneto-motive force — somewhat analogous to electrical resistance.

Any magnetic induction that remains in a magnetic material after removal of an applied saturating magnetic field. Bd is the magnetic induction at any point on the demagnetization curve.

The magnetic induction corresponding to zero magnetizing force in a magnetic material after saturation in a closed circuit.

Steel or ferrous elements in a magnetic circuit which form a low reluctance path for the magnetic flux.

Partial demagnetization caused by exposure to high or low temperatures — recoverable when the magnet returns to its original temperature.

A factor describing the reversible change in a magnetic property with change in temperature. Usually expressed as percentage change per unit of temperature.

Restriction of the Use of Certain Hazardous Substances in Electrical & Electronic Equipment (EU directive 2002/95/EC). Pb, Cd, Hg, Cr6+, PBDEs and PBBs must be controlled within specified PPM.

See permeance coefficient.

Treatments on a magnet with defined temperature or intentional magnetic field exposure to prevent magnetic flux change caused by later external influences.