Neodymium Magnet Glossary

A

Air gap

Any space between a magnet and the steel or magnet it attracts, whether air, paint, plastic, fabric or wood. Pull force drops quickly as the gap grows. How air gaps affect strength.

Alnico

A magnet alloy of aluminum, nickel and cobalt with iron. Very temperature-stable but easily demagnetized.

Anisotropic

Having a preferred magnetic direction. Sintered neodymium magnets are anisotropic: their grains are aligned during pressing, so they can only be magnetized strongly along that one axis.

Anneal

A controlled heat treatment that relieves internal stresses and refines the microstructure of a magnet material after sintering.

Axially magnetized

Magnetized along the central axis of a disc, cylinder or ring, so the poles are on the flat faces. What axially magnetized means.

B

Bd/Hd, load line and permeance coefficient

The ratio Bd/Hd at a magnet's operating point, also called the permeance coefficient (Pc). Drawn on the B/H curve it's the load line. Long, thick magnets have a high Pc and resist demagnetization better than thin, flat ones.

Bd (induction at the operating point)

The flux density inside a magnet at its working point in a real circuit, which is always below Br because of the magnet's own demagnetizing field and any air gap.

Bg (air-gap induction)

The flux density in the air gap of a magnetic circuit, such as between a magnet and a steel pole piece. It's what does useful work in motors and sensors.

B/H curve (hysteresis loop)

A graph of flux density (B) against magnetizing field (H) as a material is magnetized, reversed and magnetized again. The area inside the loop is the energy lost each cycle (hysteresis loss). Permanent magnets have wide loops; soft steel has narrow ones.

BHmax (maximum energy product)

The most magnetic energy a material can deliver per unit volume, from the peak of B × H on its demagnetization curve. It's the number in a grade name: N52 is about 49 to 53 MGOe.

Bi or J (intrinsic induction)

The part of total flux density contributed by the magnet material itself: B minus the applied field H.

Bis or Js (saturation induction)

The highest intrinsic induction a material can reach when fully magnetized. Beyond it, a stronger field adds no more magnetization.

B (magnetic flux density, induction)

How concentrated a magnetic field is at a point, measured in tesla (T) or gauss (G); 1 T = 10,000 G. A gaussmeter measures B. Flux density explained.

Br (remanence, residual induction)

The flux density a magnet material keeps after being fully magnetized, with no external field and a closed magnetic path. N52 material has a Br of about 14,300 to 14,800 G (1.43 to 1.48 T).

C

CGS units

The centimeter-gram-second unit system that gives magnet data in gauss, oersteds and MGOe. The SI equivalents are tesla, A/m and kJ/m³.

Closed circuit

A magnetic path made entirely of magnet and steel with no air gap, such as a magnet bridged by a steel keeper. Magnets work hardest and are most stable in a closed circuit.

Countersunk magnet

A magnet with a cone-shaped hole so a flat-head screw sits flush with its face. Shop Countersunk Magnets.

Curie temperature (Tc)

The temperature at which a magnetic material loses all of its magnetism. About 310°C (590°F) for standard N-grade neodymium and up to about 350°C (662°F) for high-temperature grades.

D

Demagnetization

Loss of magnetization caused by heat, an opposing magnetic field, or physical damage. A demagnetizing force is the field (internal or external) that pushes a magnet toward demagnetization.

Demagnetization curve

The second-quadrant part of a magnet's B/H loop. It shows how flux density falls as an opposing field is applied, and it's where Br, Hc and BHmax are read.

Density

Mass per unit volume. Sintered neodymium magnets are about 7.4 to 7.6 g/cm³, close to steel.

Diamagnetic

Weakly repelled by magnetic fields. Water, copper, graphite and bismuth are diamagnetic; the effect is tiny compared with ferromagnetic attraction.

Diameter

The distance across a disc, ring, cylinder or sphere. For discs and rings we list it first, as diameter × thickness.

Diametrically magnetized

Magnetized across the diameter, so the poles are on opposite sides of the curved edge. Used for rotating shafts, sensors and couplings. See diagrams.

Dimensional tolerance

How far a magnet's actual size may vary from its nominal size. Standard neodymium magnets are typically held to about ±0.004 in (±0.1 mm).

Dimensions

A magnet's size. We list discs and rings as diameter × thickness (rings: outer diameter × inner diameter × thickness) and blocks as length × width × thickness, with the magnetized dimension last.

Direction of magnetization

The axis along which a magnet is magnetized, running from its south pole to its north pole inside the magnet. Magnetization directions.

Domains

Tiny regions inside a magnetic material where atomic magnetic moments point the same way. Magnetizing a material lines its domains up. How magnets work.

E

Eddy currents

Electric currents induced in a conductor, such as copper or aluminum, by a changing magnetic field. They create drag on a moving magnet, which is why a magnet falls slowly through a copper tube.

Electromagnet

A magnet made by passing electric current through a coil, usually around an iron core. Its field turns off when the current stops.

F

Ferrite (ceramic) magnet

A low-cost permanent magnet made from iron oxide with strontium or barium. It doesn't rust and handles heat well but is much weaker than neodymium. (Soft ferrites with nickel, zinc or manganese are used in transformer cores.)

Ferromagnetic

Strongly attracted to magnets and able to be magnetized. Iron, most steels, nickel and cobalt are ferromagnetic. What magnets attract.

Field gradient

How quickly a magnetic field changes with distance. Strong gradients pull hardest on steel particles, which is why separator magnets are designed for high gradients.

Field lines

Imaginary lines that show a field's direction and strength: out of the north pole, into the south pole, never crossing, closer together where the field is stronger. Field lines explained.

Fluxmeter

An instrument that measures total magnetic flux, usually with a search coil, often to check a magnet's moment in quality control. Compare with a gaussmeter, which measures flux density at a point.

G

Gauss (G)

A CGS unit of flux density. 10,000 G = 1 tesla; 10 G = 1 millitesla. Earth's field is about 0.25 to 0.65 G.

Gaussmeter

A meter with a Hall-effect probe that measures flux density at a point, in gauss or tesla. How surface field is measured.

Grade (N rating)

The code for a magnet material's strength and temperature class, such as N42 or N52SH. The number is BHmax in MGOe; letters after it set the temperature rating. What N ratings mean.

H

Hci or iHc (intrinsic coercivity)

The opposing field needed to fully demagnetize the magnet material itself. Higher Hci means better resistance to heat and opposing fields; high-temperature grades (H, SH, UH and up) have higher Hci. Grade data.

Hc or HcB (coercive force)

The opposing field needed to bring a magnet's flux density B to zero. Measured in oersteds (Oe) or kA/m.

Hd

The demagnetizing field inside a magnet at its operating point. Together with Bd, it defines where the magnet works on its curve.

Hm

The peak field applied when testing or magnetizing a material.

H (magnetic field strength)

The magnetizing or demagnetizing field applied to a material, measured in oersteds (Oe) or A/m.

Homogeneous field

A field with the same strength and direction throughout a region, such as inside a large MRI scanner.

Horseshoe magnet

A U-shaped magnet with both poles on the same side, which concentrates the field between the tips.

Hs (saturating field)

The magnetizing field needed to fully saturate a magnet material. Neodymium needs a very strong pulse field, which is why magnets are magnetized at the factory.

Hysteresisgraph

A lab instrument that traces a material's B/H curve, used to verify Br, Hc, Hci and BHmax.

I

ID (inner diameter)

The diameter of the hole in a ring magnet. Ring sizes are listed as outer diameter × inner diameter × thickness.

Irreversible losses

Strength a magnet loses permanently, for example from overheating or a strong opposing field, that doesn't return when conditions go back to normal. Re-magnetizing can restore it unless the material itself is damaged.

Isotropic

Having the same magnetic properties in every direction. Isotropic magnets can be magnetized in any direction but are weaker than anisotropic ones.

K

Keeper

A piece of soft steel placed across a magnet's poles to close the magnetic circuit. Mainly used with alnico magnets, which demagnetize easily.

Kilogauss (kG)

1,000 gauss, or 0.1 tesla. Grade data often lists Br in kG.

L

Lodestone

Naturally magnetized magnetite (Fe₃O₄), the first magnet people discovered and the basis of the earliest compasses.

M

Magnetic assembly

A magnet combined with steel parts or housings, such as a pot magnet or channel magnet, to shape and concentrate its field.

Magnetic circuit

The complete path flux follows, from a magnet's north pole through air and steel back to its south pole. Steel parts that guide flux back are the return path.

Magnetic flux (Φ)

The total amount of magnetic field passing through an area, measured in webers (Wb) or maxwells (Mx).

Magnetization

The process of aligning a material's domains with a strong field, or the resulting magnetic moment per unit volume.

Magnetomotive force (mmf)

The magnetic equivalent of voltage that drives flux around a magnetic circuit. Measured in gilberts (CGS) or ampere-turns (SI).

Maximum operating temperature

The highest temperature a magnet can reach without permanently losing strength: 80°C (176°F) for standard N grades, up to 230°C (446°F) for AH grades. Thin magnets in open circuits can lose strength below this.

Maxwell (Mx)

A CGS unit of magnetic flux. 100,000,000 Mx = 1 weber.

MGOe (mega-gauss-oersted)

The unit for energy product. 1 MGOe is about 7.96 kJ/m³.

Monopole

A hypothetical isolated north or south pole. None has ever been observed: every magnet has both poles.

N

NdFeB

Short for neodymium-iron-boron (Nd₂Fe₁₄B), the alloy in neodymium magnets.

North pole

The pole that turns toward Earth's geographic North Pole when a magnet swings freely. Field lines leave a magnet at its north pole.

O

Oersted (Oe)

The CGS unit of magnetic field strength (H), named for Hans Christian Ørsted. 1 kOe ≈ 79.6 kA/m.

Open circuit

A magnet with an air gap in its path, as when a magnet sits alone in air. Most real uses are open circuits.

P

Paramagnetic

Very weakly attracted to magnets. Aluminum, platinum and oxygen are paramagnetic, but the pull is far too small to notice with a hand magnet.

Permanent magnet

A material that stays magnetized and produces its own field without any power. Neodymium magnets are permanent magnets.

Permeability

How easily a material carries magnetic flux. Steel has a high relative permeability (hundreds to thousands of times air), which is why it attracts magnets and redirects fields.

Permeance and reluctance

Reluctance is a magnetic circuit's resistance to flux, the magnetic equivalent of electrical resistance; permeance is its inverse. Air gaps add reluctance.

Plating and coating

A protective layer that keeps neodymium magnets from rusting. Our standard is nickel-copper-nickel; epoxy, plastic and rubber are also available. Coating options.

Pole and polarity

A pole is a region where field lines leave (north) or enter (south) a magnet; polarity is which is which. Opposite poles attract, like poles repel.

Pot magnet

A magnet set in a steel cup that concentrates the pull on one face. What threaded pot magnets are used for.

Pull force

The force needed to pull a magnet straight off a thick, flat steel plate with no gap. Listed in pounds on our products. What pull force means.

R

Rare earth elements

Seventeen metals, including neodymium, praseodymium, dysprosium and samarium, used to make the strongest permanent magnets. Rare earth magnets.

Repelling

The push between like poles (north to north or south to south). Forcing strong magnets together this way can partly demagnetize thin ones.

S

Samarium cobalt (SmCo)

A rare earth magnet that handles high temperatures and resists corrosion, but is weaker and more expensive than neodymium.

Shear force

The force needed to slide a magnet along a steel surface. It's usually about 15 to 25% of the rated pull force, which is why magnets slip on vertical surfaces.

Sintering

Fusing pressed magnet powder into a solid, dense part by heating it below its melting point in a vacuum furnace. Most neodymium magnets are sintered. How magnets are made.

South pole

The pole that turns toward Earth's geographic South Pole when a magnet swings freely. Field lines enter a magnet at its south pole.

Stacking

Placing magnets north to south so they act as one thicker magnet. Gains shrink once the stack is as tall as it is wide. Stacking magnets.

Strike plate

A steel disc or plate used as a magnet's target in place of a second magnet. Using strike plates.

T

Tesla (T)

The SI unit of flux density, named for Nikola Tesla. 1 T = 10,000 G. Hospital MRI scanners use 1.5 to 3 T.

W

Weber (Wb)

The SI unit of magnetic flux, named for Wilhelm Weber. 1 Wb = 1 tesla × 1 square meter.

Weight

How much a single magnet weighs. A 1/2 × 1/8 Inch neodymium disc weighs about 3 grams.