Air Gap
Air gap, also airgap or air-gap – is a non-magnetic part of a magnetic circuit. It is usually connected magnetically in series with the rest of the circuit so that a substantial portion of the magnetic flux flows through the gap.
Anisotropic
An anisotropic material has different properties in different directions. For example, wood that has a grain is more robust in some one direction than another. Like wood, neodymium magnets are also anisotropic. Even before it is magnetized, a neodymium magnet has a “preferred” magnetization direction.
Neodymium magnets are made with a preferred magnetization direction which can not be changed. These materials are either manufactured in the influence of strong magnetic fields or pressed a specific way and can only be magnetized through the preferred axis. Sintered Neodymium (Iron Boron) and Samarium Cobalt magnets are anisotropic.
B/H Curve
The result of plotting the value of the magnetic field (H) applied against the resultant flux density (B) was 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 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 is remaining in a saturated magnetic material after the magnetizing field has been removed. This is when 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 the practical use of magnet materials.
C.G.S.
Abbreviation for the “Centimeter, Grams, Second” system of measurement.
Coercive Force (Hc)
The demagnetizing force, measured in Oersteds, 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 power used to magnetize it in the first place. Shock, vibration, and temperature can also be demagnetizing forces.
Dimensions
The physical size of a magnet, including any plating or coating.
Dimensional Tolerance
An allowance, given as a permissible range, in the nominal dimensions of a finished magnet. The purpose of tolerance is to specify the allowed leeway for variations in manufacturing.
(Magnetic) Dipole Moment (m)
a quantity that describes the torque a given magnet will experience in an external magnetic field.
Some folks (like physicists) use a magnetic dipole model to simulate or mathematically model a magnet or group of magnets. Mathematically, it’s easier than considering the complexities of weird magnet shapes. It’s not theoretically perfect. Using it won’t always match measured field strengths near a neodymium magnet. It works great for a sphere but isn’t correct near other shapes like discs or blocks. It’s an excellent approximation when you measure far away from a magnet, but not so good close up, especially near the edges of a magnet.
Calculate the dipole moment using the formula m = dipole moment in A m2 = Br x V / μo, where:
Br is Br max, the Residual Flux Density, expressed in Tesla.
V is the volume of the magnet, expressed in cubic meters.
μo is the permeability of a vacuum, or 4 π x 10-7 N/A2.
Electromagnet
A magnet consists of a solenoid with an iron core, which has a magnetic field only during the time of current flow through the solenoid.
Ferromagnetic Material
A material that either is a source of magnetic flux or a conductor of magnetic flux. Most ferromagnetic materials have some component of iron, nickel, or cobalt.
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 webers 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, is usually measured in Gauss (C.G.S.). Also called a DC magnetometer.
Gilbert
The unit of magnetomotive 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 remagnetized. With continued recycles, this plot will be a closed-loop that completely describes the characteristics of the magnetic material. The size and shape of this “loop” are essential for both hard and soft materials.
With soft materials, which are generally used in alternating circuits, the area inside this “loop” should be as thin as possible (it is a measure of energy loss). But with rugged materials, the “fatter” the loop, the stronger the magnet will be.
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. It is 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 the demagnetizing force, which reduces the intrinsic induction, Bi, in the material to zero after magnetizing to saturation, measured in oersteds.
Irreversible Losses
Partial demagnetization of the magnet, caused by exposure to high or low temperatures, external fields, shock, vibration, or other factors. These losses are only recoverable by remagnetization. Magnets can be stabilized against irreversible losses by partial demagnetization induced by temperature cycles or external magnetic fields.
Isotropic Material
A material that can be magnetized along any axis or direction (a magnetically unoriented material). The opposite of Anisotropic Magnet.
Keeper
A soft iron piece is temporarily added between the poles of a magnetic circuit to protect it from demagnetizing influences. Also called a shunt. Keepers are generally not needed for Neodymium and other modern magnets. They are more commonly used with older Alnico Horseshoe Magnets.
Kilogauss
One Kilogauss = 1,000 Gauss = Maxwells per square centimeter.
Magnet
A magnet is an object made of certain materials which create a magnetic field. Every magnet has at least one north pole and one south pole. By convention, we say that the magnetic field lines leave the North end of a magnet and enter the South end of a magnet. This is an example of a magnetic dipole (“di” means two, thus two poles).
If you take a bar magnet and break it into two pieces, each piece will again have a North pole and a South pole. If you take one of those pieces and split it into two, each of the smaller pieces will have a North pole and a South pole. No matter how small the part of the magnet becomes, each piece will have a North pole and a South pole. It is impossible to end up with a single North pole or a single South pole which is a monopole (“mono” means one or single, thus one pole).
Magnetic Circuit
It 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 Field (B)
When specified on our site, the surface field or magnetic field refers to the strength in Gauss.
Magnetic Field Strength (H)
Magnetizing or demagnetizing force is the measure of the magnetic vector quantity that determines the ability of an electric current, or a magnetic body, to induce a magnetic field at a given point, measured in Oersteds.
Magnetic Flux
Is a contrived but measurable concept that has evolved to describe the “flow” of a magnetic field. When the magnetic induction, B, is uniformly distributed and is typical to the area, A, the flux, Φ = 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 is induced by field strength, H, at a given point. It is the vector sum, at each end 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.
Magnetomotive Force (F or mmf)
The magnetic potential difference between any two points. Analogous to voltage in electrical circuits. That which tends to produce a magnetic field. Commonly produced by a current flowing through a coil of wire and measured in Gilberts (C.G.S.) or Ampere Turns (S.I.).
Material Grade
Neodymium (NdFeB) magnets are graded by the magnetic material from which they are manufactured. Generally speaking, the higher the grade of material, the stronger the magnet. We find that the Pull Force of a magnet relates directly to the “N” number. Neodymium magnets currently range in grade from N35 to N52. The theoretical limit for Neodymium magnets is grade N64, though it isn’t presently feasible to manufacture magnets this strong. The grade of most of our stock magnets is N42 because we feel that N42 provides the optimal balance between strength and cost. We also stock a wide range of sizes in grade N52 for customers who need the strongest permanent magnets available.
Maximum Energy Product (BHmax)
The magnetic field strength at the point of maximum energy product of a magnetic material. The field strength of fully saturated magnetic material measured in Mega Gauss Oersteds, MGOe.
Maximum Operating Temperature (Tmax)
Also known as maximum service temperature, is the temperature at which the magnet may be exposed 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.
Magnetization Curve
The first quadrant portion of the hysteresis loop (B/H) Curve for a magnetic material.
Magnetizing Force (H)
The magnetomotive force per unit of magnet length, measured in Oersteds (C.G.S.) or ampere-turns per meter (S.I). Maxwell – The C.G.S. unit for total magnetic flux, measured in flux lines per square centimeter.
MGOe
Mega (million) Gauss Oersteds. Unit of measure typically used in stating the maximum energy product for a given material. See Maximum Energy Product.
North Pole
The north pole of a magnet is the one attracted to the magnetic north pole of the earth. This north-seeking pole is identified by the letter N. By accepted convention, the lines of flux travel from the north pole to the south pole.
Oersted (Oe)
The C.G.S. unit for magnetizing force. The English system equivalent is Ampere Turns per Inch (1 Oersted equals 79.58 A/m). The S.I. unit is Ampere Turns per Meter.
Orientation
Used to describe the direction of magnetization of a material. Orientation Direction – The direction in which an anisotropic magnet should be magnetized to achieve optimum magnetic properties.
Paramagnetic Materials
Materials that are not attracted to magnetic fields (wood, plastic, aluminum, etc.). A material is having a permeability slightly greater than 1.
Permanent Magnet
A magnet retains its magnetism after it is removed from a magnetic field. A permanent magnet is “always-on.” Neodymium magnets are permanent magnets.
Permeance (P)
A measure of the relative ease with which flux passes through a given material or space. It is calculated by dividing magnetic flux by magnetomotive force. Permeance is the reciprocal of reluctance.
Permeance Coefficient (Pc)
Also called the load-line, B/H, or “operating slope” of a magnet, this line is on the Demagnetization Curve where a given magnet operates. The value depends on both the shape of the magnet and the surrounding environment (some would say, how it’s used in a circuit). In practical terms, it’s a number that defines how hard it is for the field lines to go from the north pole to the south pole of a magnet. A tall cylindrical magnet will have a high Pc, while a short, thin disc will have a low Pc.
Permeability (μ)
The ratio of the magnetic induction of a material to the magnetizing force producing it (B/H).
It is a measure of how much a material becomes magnetized in the presence of a magnetic field.
The magnetic permeability of a vacuum (µo) is 4π×10-7 N/A2.
Plating/Coating
Most neodymium magnets are plated or coated in order to protect the magnet material from corrosion. Neodymium magnets are mainly composed of neodymium, iron and boron. The iron in the magnet will rust if it is not sealed from the environment by plating or coating. Most of the neodymium magnets that we stock are triple plated in nickel-copper-nickel, but some are plated in gold, silver, or black nickel, while others are coated in epoxy, plastic, or rubber.
Polarity
The characteristic of a particular pole in a specific location of a permanent magnet. Differentiates the North from the South Pole.
Pull Force
The force required to pull a magnet free from a flat steel plate using force perpendicular to the surface. The limit of the holding power of a magnet. The pull force listed is actual data acquired by testing using our state-of-the-art force test stand.
Rare Earth
Commonly used to describe high energy magnet material such as NdFeB (Neodymium-Iron-Boron) and SmCo (Samarium-Cobalt).
Relative Permeability
The ratio of permeability of a material to that of a vacuum. In the C.G.S. system, the permeability is equal to 1 in a vacuum by definition. The permeability of air is also for all practical purposes similar to 1 in the C.G.S. system.
Reluctance (R)
A measure of the relative resistance of a material to the passage of flux. It is calculated by dividing the magnetomotive force by magnetic flux. Reluctance is the reciprocal of permeance.
Remanence,(Bd)
The magnetic induction remains in a magnetic circuit after the removal of an applied magnetizing force.
Return Path
Conduction elements in a magnetic circuit provide a low reluctance path for the magnetic flux.
Reversible Temperature Coefficient
A measure of the reversible changes in flux caused by temperature variations.
Saturation
The state where an increase in magnetizing force produces no further increase in magnetic induction in a magnetic material.
South Pole
The south pole of a magnet is the one attracted to the south pole of the earth. This south-seeking pole is identified by the letter S. By accepted convention, the lines of flux travel from the north pole to the south pole.
Stabilization
The process of exposing a magnet or a magnetic assembly to elevated temperatures or external magnetic fields to demagnetize it to a predetermined level. Once done, the magnet will suffer no future degradation when exposed to that level of demagnetizing influence.
Surface Field (Surface Gauss)
The magnetic field strength at the surface of the magnet is measured by a Gauss meter.
Temperature Coefficient
A factor 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
The S.I. unit for total magnetic flux. The functional unit of magnetic flux. It is the amount of magnetic flux which, when linked at a uniform rate with a single-turn electric circuit for 1 second, will induce in this circuit an electromotive force of 1 volt.
Weight
The weight of a single magnet