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Glossary of Magnet Science

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

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.

Gauss, Gs: A unit of magnetic flux density in the GCS system; the lines of magnetic flux per square inch. 1 Gauss equals 0.0001 Tesla in the SI system.

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

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 of performance caused by irreversible losses.

Isotropic Magnets: A magnet material whose magnetic properties are the same in any direction, and which can therefore be magnetized in any direction without loss of magnetic characteristics.

Magnetic Flex: The total magnetic induction over a given area.

Magnetizing Force: the magnetomotive force per unit length at any point in a magnetic circuit. The unit of the magnetizing force is Oersted in the GCS system

Maximum Energy Product, (BH)max.: There is a point at the Hysteresis Loop at which the product of magnetizing force H and induction B reaches a maximum. The maximum value is called the Maximum Energy Product. At this point, the volume of magnet material required to project a given energy into its surrounding is a minimum. This parameter is generally used to describe how "strong" this permanent magnet material is. Its unit is Gauss Oersted. One MGOe means 1,000,000 Gauss Oersted.

Rare Earths: A family of elements with an atomic number from 57 to 71 plus 21 and 39. They are lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, and yttrium.

Remenance, 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 remenance will be less than the residual induction, Br.

Reversible Temperature Coefficient: A measure of the reversible changes in flux caused by temperature variations.

Residual Induction, Br: A value of induction at the point at Hysteresis Loop, at which Hysteresis loop crosses the B axis at zero magnetizing force. The Br represents the maximum magnetic flux density output of this material without an external magnetic field.

Sintering: The bonding of powder compacts by the application of heat to enable one or more of several mechanisms of atom movement into the particle contact interfaces to occur; the mechanisms are: viscous flow, liquid phase solution-precipitation, surface diffusion, bulk diffusion, and evaporation-condensation. Densification is a usual result of sintering.

Surface Coatings: Unlike Samarium Cobalt, Alnico and ceramic materials, which are corrosion resistant, Neodymium Iron Boron magnets are susceptible to corrosion. Base upon of magnets' applications, following coatings can be chosen to apply on surfaces of Neodymium Iron Boron magnets.
 
Coating Performance Coating Thickness Corrosion-Resistant in Salt Fog (Hr) Color PCT (Hr) at 120 °C, 2 atm, 100% RH
Zn > 8 µm > 24 Silver -
Color Zn > 10 µm > 72 multicolor 12
Ni-Cu-Ni > 12 µm > 72 Silver, Lustrous 24
Epoxy 15 - 30 µm > 72 Black -
 
 
 
Information on Rare Earth Permanent Magnets
Further Information on Permanent Magnets
 


 


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