Lexicon of knowledge and magnetic definitions
Knowledge compendium for engineers, hobbyists, and industry
Here is a comprehensive technical dictionary of magnetic terms. You will find here not only simple definitions but also physics formulas, material parameters, and explanations of phenomena such as hysteresis or coercivity. Learn more to precisely select products in our store.
A
Air gap is the space (e.g., air, paint, rust) separating the magnet from the ferromagnetic material. Its influence on induction is described by a simplified relationship:B_g ≈ B_r / (1 + (L_g/L_m))Where L_g is the gap length, and L_m is the magnet length. Even a 1 mm gap can reduce the force of a magnetic holder by 50-70%.
Metal mixture is a metallic material with properties different from its components. A neodymium magnet is an alloy of Nd2Fe14B (Neodymium-Iron-Boron) with a tetragonal structure. Changing proportions and adding Dysprosium (Dy) or Terbium (Tb) allows obtaining high-temperature grades (SH, UH, EH).
Annealing is a thermal process used in magnet metallurgy. The material is heated to high temperatures (often in a vacuum) and then slowly cooled to relieve internal lattice stresses and optimize grain microstructure, which translates into higher coercivity (HcJ) in sintered neodymium magnets.
The magnetization vector M is parallel to the rotational symmetry axis of the magnet (e.g., the height of a cylinder). This is the standard configuration for cylindrical magnets, ensuring the strongest field on the flat bases.
B
A vector quantity describing the flux density inside the material. Measured in Tesla (T) or Gauss (G). It is defined by the equation:B = μ₀(H + M)Where:
μ₀ – vacuum permeability,
H – field intensity,
M – magnetization. SI unit: Tesla (T).
μ₀ – vacuum permeability,
H – field intensity,
M – magnetization. SI unit: Tesla (T).
Remanent induction (Bd), is the point where the hysteresis curve intersects the vertical B axis (at H=0). It determines the magnetic flux density remaining in the material after saturation. For N52, this value is approx. 1.43 T (14.3 kG).
Permeance coefficient (Pc), determining the magnet's operating point on the demagnetization curve. It depends on the magnet's shape. Long magnets (high Pc) work higher on the curve and are more temperature-stable.
Symbol Bg denotes the working induction in the air gap. Calculated by the formula:Bg = Br × (Lm / (Lm + Lg))(For a closed circuit without losses). A key value when designing speakers and motors.
Hysteresis loop shows the non-linear B(H) relationship. The area of the loop represents energy lost as heat in one magnetization cycle (J/m³). For permanent magnets, we aim for the widest possible loop (high coercivity).
BHmax parameter is the point on the demagnetization curve (in the 2nd quadrant) where the product of B × H reaches a maximum. It corresponds to the volumetric "efficiency" of the magnet. (BH)max ≈ Br² / 4μ₀Unit: kJ/m³ or MGOe.
C
Centimeter-Gram-Second system. Still popular in magnetism due to convenience (μ₀ = 1).
Induction: Gauss (G)
Field H: Oersted (Oe)
Flux: Maxwell (Mx)
Energy: MGOe.
Induction: Gauss (G)
Field H: Oersted (Oe)
Flux: Maxwell (Mx)
Energy: MGOe.
A state where the circuit's reluctance (magnetic resistance) is minimal, and the flux closes inside a ferromagnetic material (keeper). In this state, the magnet performs no external work and is at its lowest potential energy state.
The value of the opposing magnetic field H at which induction B drops to zero. It determines resistance to demagnetization under normal operating conditions (e.g., in motors).
Phase transition temperature where domain alignment disappears due to thermal agitation. For NdFeB Tc ≈ 310-340°C. Above this temperature, the material becomes paramagnetic.
D
Loss of magnetization vector M. Causes:
1. Thermal: T > Tmax
2. Field: External field H > HcJ
3. Mechanical: Strong impacts (less relevant for neodymiums than for AlNiCo).
1. Thermal: T > Tmax
2. Field: External field H > HcJ
3. Mechanical: Strong impacts (less relevant for neodymiums than for AlNiCo).
2nd quadrant of the hysteresis loop. Crucial for engineers. Shows the dependence of B on negative field H. If the magnet's operating point (determined by its shape) falls below the "knee" of this curve, permanent damage to the magnet occurs.
Volumetric density. For sintered NdFeB magnets, it is:
ρ ≈ 7.4 - 7.6 g/cm³.
Formula for weight: m [g] = V [cm³] × 7.5. This value is close to the density of steel.
ρ ≈ 7.4 - 7.6 g/cm³.
Formula for weight: m [g] = V [cm³] × 7.5. This value is close to the density of steel.
Material with relative permeability μr < 1 (susceptibility χ < 0). It expels the magnetic field from its interior. Examples: water, pyrolytic graphite (levitating over neodymium), gold, bismuth.
Magnetization direction perpendicular to the cylinder's rotation axis. N and S poles are on the "round" sides. Used in magnetic couplings and rotation angle sensors.
Range of acceptable dimension deviations. Standard ±0.1 mm. Note that nickel layer adds approx. 0.02-0.04 mm to raw magnet dimensions.
For neodymium sinters, the standard production tolerance is ±0.1 mm. Dimensions are given in the format: Diameter x Height or Length x Width x Height (last dimension is the magnetization direction).
Every magnet is a dipole, which results from Gauss's law for magnetism (∇·B = 0) – field lines are always closed. Isolated magnetic charges (monopoles) do not exist, so every magnet has an N and S pole.
E
Currents induced in a conductive magnet by a changing B field (according to Faraday's law). They cause heat losses:
P_eddy ∝ f² × B².
To limit them, laminated magnets (sliced) are used in motors.
P_eddy ∝ f² × B².
To limit them, laminated magnets (sliced) are used in motors.
In air transport: weight including magnetic shielding. A package with magnets is treated as "Dangerous Goods" (UN 2807) if the field exceeds 0.00525 Gauss at a distance of 4.6m.
A solenoid with a ferromagnetic core. Field B depends on current I and number of turns N:
B ≈ μNI / L.
The advantage is field controllability; the disadvantage is the need for continuous power supply.
B ≈ μNI / L.
The advantage is field controllability; the disadvantage is the need for continuous power supply.
Measure of field energy density. Mathematically, it is the maximum area of a rectangle inscribed under the B(H) demagnetization curve. Determines device miniaturization.
F
Compound MFe12O19 (where M = Ba, Sr). Electrical insulator (no eddy currents). Cheap, corrosion-resistant, but weak (Br ≈ 0.4 T). Has a positive temperature coefficient of coercivity (harder to demagnetize when warm).
Material with very high magnetic susceptibility (μr >> 1), exhibiting hysteresis. Possesses spontaneous domain magnetization. Examples: Fe (Iron), Co (Cobalt), Ni (Nickel), Gd (Gadolinium).
Change in induction per unit distance. The force acting on a ferromagnet depends on the product of the field and its gradient:
F ∝ B · (dB/dx).
In a homogeneous field (gradient = 0), a magnet acts only with torque, but is not attracted!
F ∝ B · (dB/dx).
In a homogeneous field (gradient = 0), a magnet acts only with torque, but is not attracted!
Number of field lines per unit area. This is the most important parameter for the user, defining the force of interaction at a given point. On the surface of an N52 magnet, it can be approx. 5000-6000 Gauss.
Electronic integrating measuring device. Measures the change in flux associated with a measuring coil (Search Coil) during its movement in the field. Result in Wb or Vs (Volt-second).
Field lines that "bulge" outside the air gap or circuit. This effect increases the effective gap cross-section and must be considered in precise circuit calculations.
G
CGS unit of magnetic induction.
1 T = 10,000 G.
Earth's field is approx. 0.5 G. Neodymium magnet is approx. 13,000 G (inside material).
1 T = 10,000 G.
Earth's field is approx. 0.5 G. Neodymium magnet is approx. 13,000 G (inside material).
Meter using a Hall probe to measure B induction at a point. Allows checking polarity and measuring actual induction on the magnet surface.
CGS unit of magnetomotive force.
1 Gb = 10 / 4π Ampere-turn (At) ≈ 0.796 At.
Currently rarely used in favor of SI units.
1 Gb = 10 / 4π Ampere-turn (At) ≈ 0.796 At.
Currently rarely used in favor of SI units.
Material code designation. Example N42SH:
N - Neodymium,
42 - (BH)max in MGOe,
SH - Operating temp. up to 150°C (Super High).
No letter at the end means standard up to 80°C.
N - Neodymium,
42 - (BH)max in MGOe,
SH - Operating temp. up to 150°C (Super High).
No letter at the end means standard up to 80°C.
H
Special magnet arrangement (changing orientation by 90°), which amplifies the field on one side (even 1.4x) and cancels it on the other. Used in magnetic hangers and particle accelerators.
Generation of transverse voltage in a current-carrying conductor placed in a B field. Basis for most magnetic field sensors, teslameters, and rotary encoders.
Material with a wide hysteresis loop and high coercivity (HcJ > 10 kA/m). After magnetization, it becomes a permanent magnet. Examples: NdFeB, SmCo, Barium Ferrite.
Force value (in kg or N) with which a magnet holds onto a steel surface. Depends on the magnet grade, but also on steel thickness and roughness (substrate).
Space region where induction vector B is constant in magnitude and direction (field lines are parallel). Generated, e.g., inside a Helmholtz coil.
U-shaped magnet. This shape brings N and S poles closer, which increases attraction force on a small area. Rare for modern neodymiums (too hard to manufacture), common for AlNiCo casts.
B(H) graph for a full saturation -> demagnetization -> saturation cycle. Key points are: Remanence (+B), Coercivity (-H), and Saturation.
I
The value of field H at which the material's polarization J drops to zero. It is the true measure of the material's resistance to permanent magnetic destruction. For neodymiums, HcJ > HcB.
Ability of material to maintain its polarization J. It is a better measure of magnet stability than normal coercivity HcB. Neodymium magnets with high HcJ (UH, EH grades) can work in difficult conditions.
Flux drop after exceeding a certain temperature, which does not return after cooling. To recover original parameters, the magnet must be remagnetized in a pulse magnetizer.
Material property consisting of identical parameters in every direction (no preferred axis). Isotropic magnets are cheaper to produce but approx. 2-3 times weaker than anisotropic ones.
K
Steel element closing the magnetic circuit. In pot magnets, the steel cup acts as a keeper, redirecting the field to one side, increasing force.
Induction unit: 1 kG = 0.1 T. Often found in descriptions of older measuring devices.
L
Flux that does not perform useful work (e.g., escapes through the sides of the gap). Design aims to minimize leakage by using shields and keepers.
Straight line from the origin on the demagnetization graph. Its slope (Permeance Coefficient) depends solely on magnet geometry. Intersection with the BH curve determines the operating point.
Iron ore (Fe₃O₄), a natural permanent magnet. Used in antiquity as a primitive compass (magnetic needle).
M
Body generating a static magnetic field. Consists of magnetic domains aligned in one direction. See full definition in the guide.
Magnet Fishing is a hobby involving searching for ferromagnets in water using a strong neodymium magnet on a rope. Requires a holder with a top mount.
Physical mass. Magnets are heavy (like steel). Large magnet 50x50x25mm weighs almost half a kilogram (470g).
Anisotropic feature means that the magnet has a one fixed direction of easy magnetization (crystal c-axis). Anisotropic magnets achieve significantly higher (BH)max parameters than isotropic ones but must be magnetized according to the direction set during pressing in the field.
Path for magnetic flux. Governed by Hopkinson's law (equivalent to Ohm's law):MMF = Φ × R_m(Magnetomotive force = Flux × Reluctance).
Vacuum permeability. Physical constant amounting to:
μ₀ = 4π × 10⁻⁷ H/m.
μ₀ = 4π × 10⁻⁷ H/m.
Regions (micrometer size) where electron spins are aligned. In an unmagnetized state, domains are arranged chaotically (vector sum = 0). Magnetization is the process of aligning domains.
Vector field exerting force on moving electric charges and magnetic moments. Generated by permanent magnets or electric current.
Scalar product of induction vector B and area S.
Φ = B · S (for uniform field).
SI unit: Weber (Wb). Practically speaks about the "total amount of magnetism" flowing out of a pole.
Φ = B · S (for uniform field).
SI unit: Weber (Wb). Practically speaks about the "total amount of magnetism" flowing out of a pole.
Irreversibility of the magnetization process. To remove magnetization, turning off the external field is not enough – an opposing field (coercivity) must be applied. It is the "memory" of magnetic material.
Main field quantity describing the magnetic state of matter. In SI, measured in Tesla. In air B = μ₀H. Inside a magnet, B is the sum of contribution from currents (H) and spins (M).
Classified by magnetic susceptibility. Most important for us are ferromagnets (magnets, steel) and paramagnets (aluminum). The former amplify the field, the latter are indifferent.
Vector measure of field source strength. For a magnet, it is the product of magnetization and volume. Determines the torque acting on a magnet in an external field.
Hypothetical partial magnetic charge (isolated N or S). Despite searches, not found experimentally. B field lines are always closed (have no beginning or end).
Direction of easy magnetization given during production. A finished anisotropic cylindrical (axial) magnet cannot be remagnetized to diametrical.
Measure of material's ability to concentrate magnetic field. μ = B / H. Soft steel has μ of several thousands, making it ideal for keepers and housings.
State where all domains are aligned with the field direction. Steel saturates at approx. 2.0 Tesla. This means a "stronger" magnet won't attract a thin sheet that saturated any harder.
Separator is a set of strong magnetic rods or plates, mounted on production lines to protect machines and clean product from filings. Check DHIT separator offer.
Method of protection against field by "shunting" it. Magnetic field prefers flowing through steel than air. Thick-walled steel box is the best shield for strong magnets.
Artificial aging of magnet (thermal cycles or slight opposing field) so its parameters don't change during operation (important in meters).
Process of saturating material. Neodymium magnets require a powerful field pulse (order of 3-4 Tesla) to fully align domains and achieve full power.
Magnetic field intensity coming from free (external) currents. SI unit: A/m (Ampere per meter).
Line integral of field intensity. In a coil, it is the product of current and number of turns (Ampere-turns). Source of flux flow in a circuit.
For neodymiums depends on grade:
N: 80°C
M: 100°C
H: 120°C
SH: 150°C
UH: 180°C
EH: 200°C.
Exceeding causes irreversible power loss.
N: 80°C
M: 100°C
H: 120°C
SH: 150°C
UH: 180°C
EH: 200°C.
Exceeding causes irreversible power loss.
Flux unit in CGS system. 1 Mx = 10⁻⁸ Wb. Corresponds to one "line of force" in older textbooks.
Energy density unit. 1 MGOe ≈ 7.96 kJ/m³. The more MGOe, the smaller magnet needed to do the same work.
Creating multiple pole pairs (e.g., N-S-N-S-N-S) on one surface. Increases holding force at the surface itself but drastically reduces field range. Used in flexible magnets.
N
Neodymium magnet is a sinter based on the intermetallic phase Nd₂Fe₁₄B. Patented in 1982 by General Motors and Sumitomo. Strongest magnet at room temp.
Pole from which (conventionally) magnetic field lines exit. Attracts the south pole of another magnet.
O
CGS unit of field intensity. 1 Oe ≈ 79.58 A/m. Named after Hans Christian Ørsted, discoverer of electromagnetism.
Situation where magnet poles are not connected by a ferromagnet. The magnet then works at a point with low permeance coefficient (Pc), exposing it to temperature influence.
P
Material with susceptibility χ > 0 (slightly positive). Amplifies field minimally. Example: air, aluminum, platinum.
Reciprocal of reluctance in a magnetic circuit (equivalent to conductance in electricity).
P = 1/R_m = (μ S) / l.
P = 1/R_m = (μ S) / l.
Magnet shape factor, depends on L/D ratio. Determines load line slope. Pc = -Bd/Hd. Higher Pc (longer magnet) = greater resistance to demagnetization.
Anti-corrosion protection. Types:
1. Ni-Cu-Ni: Silver, standard.
2. Epoxy: Black, moisture resistant.
3. Gold: Decorative, medical.
4. Parylene: Thin, very tight.
1. Ni-Cu-Ni: Silver, standard.
2. Epoxy: Black, moisture resistant.
3. Gold: Decorative, medical.
4. Parylene: Thin, very tight.
A barrier layer 10-30 μm thick. Neodymium (Nd) forms hydroxides upon contact with moisture, destroying the structure. Standard Ni-Cu-Ni (approx. 15-20μm) protects against atmospheric corrosion. Tested in a salt spray chamber.
Pole arrangement. For two magnets to attract, they must face each other with opposite poles (N to S). In our self-adhesive magnets, we sell pairs with different polarity.
Soft steel shape (e.g., st3) placed on the magnet pole. Serves to concentrate flux (increase induction) in the working gap.
Breakaway force is measured perpendicularly to the surface, on a thick steel plate. Approximate Maxwell formula:F [N] ≈ B²A / 2μ₀Where A is the pole area.
R
Group of 17 elements (scandium, yttrium + lanthanides). Key for magnetism are: Neodymium (Nd), Praseodymium (Pr), Samarium (Sm), Dysprosium (Dy), and Terbium (Tb).
Ratio of material permeability to vacuum permeability. For neodymium magnets μr ≈ 1.05 (they are almost like air for external field). For steel μr ≈ 2000-5000.
Magnetic resistance. Air has huge reluctance, steel small. A magnet strives to minimize reluctance in its surroundings (that's why it attracts steel).
Remanence is the maximum induction a magnet can generate by itself in a closed circuit. Measure of magnet's strength potential.
Another name for Remanence (Bd or Br). Field value remaining in saturated ferromagnet after removing external field H.
Steel housing or plate closing the magnetic circuit. In pot magnets, the housing redirects the field from the "back" of the magnet to the front, increasing force.
S
Alternative to neodymiums. Weaker (20-30 MGOe), but very thermally stable (up to 350°C) and chemically (don't rust). Very expensive and brittle.
Inductive sensor for fluxmeter. Number of turns and coil area must be known to convert induced voltage to magnetic flux.
Sliding force is the force needed to move a magnet parallel to the surface. Depends on friction coefficient. For steel-nickel pair it is approx. 15-20% of pull force. Using rubber increases this force.
Unit system based on Meter, Kilogram, Second, and Ampere. In magnetism applies:
Tesla [T], Weber [Wb], Henry [H], Ampere per meter [A/m].
Tesla [T], Weber [Wb], Henry [H], Ampere per meter [A/m].
Powder metallurgy process. Pressed "green" block of neodymium dust is heated in a vacuum furnace, where grains fuse into solid ceramic of high density.
Displacement of fast-changing magnetic field (and current) to conductor surface. In high-speed motors causes losses and magnet heating.
Pole attracting geographic North of Earth. Field lines enter the S pole.
Connecting magnets increases induction, but non-linearly. Two 5mm thick magnets won't give 2x larger field than one, but will have field range similar to a 10mm magnet.
B value measured by gaussmeter at pole center. Always lower than Br. Depends on magnet thickness – thicker magnet (higher L/D) means higher surface field.
T
For neodymiums:
Br: approx. -0.11% / °C
HcJ: approx. -0.60% / °C
Means that upon heating, the magnet becomes temporarily weaker (reversible process up to Tmax).
Br: approx. -0.11% / °C
HcJ: approx. -0.60% / °C
Means that upon heating, the magnet becomes temporarily weaker (reversible process up to Tmax).
SI unit of induction.
1 T = 10,000 Gauss.
Neodymium magnets achieve induction order of 1.4 T.
1 T = 10,000 Gauss.
Neodymium magnets achieve induction order of 1.4 T.
W
SI unit of magnetic flux.
1 Wb = 1 V·s = 1 T·m².
1 Wb = 1 V·s = 1 T·m².
Y
Magnetic circuit element (usually steel frame) that isn't a field source but serves to guide and close it (e.g., in speakers).
Sources
The limit values given on this page are based on standards and technical literature. Below are the sources we rely on when establishing parameters.
- Arnold Magnetic Technologies — TECHNotes: właściwości materiałów NdFeB Manufacturer of magnetic materials. Temperature coefficients, the role of cobalt and dysprosium.
- Nd₂Fe₁₄B — the magnetic phase of neodymium (Wikipedia) Phase composition, Curie temperature, crystal structure.
- Rola dodatku kobaltu w spiekach Nd-Fe-B (ScienceDirect) Peer-reviewed paper. Why cobalt raises the Curie temperature and how it affects coercivity.
- IEC 60404 — materiały magnetyczne, terminologia i metody pomiaru International standard. Definitions of remanence, coercivity and energy density.