# Glossary Below are the definitions of some of the most commoly used terms in Magnetism and when describing permanent magnets.

# A

• #### Air gap

It is the space between the magnetic poles of a magnet, which can be filled with any non-magnetic material, such as brass, wood or plastic.

• #### Anisotropic magnet

A magnet having a preferred direction of magnetic orientation, so that the magnetic characteristics are optimal in a preferred direction.

• #### Anisotropy

Anisotropy is the property of certain specific physical magnitudes which have different values in certain directions. Magnets are anisotropically manufactured at high magnetic field in a specific direction during the sintering process.

# B

• #### Bipolar magnet

Magnet having two poles on the same side.

# C

• #### Coercive field

With the value of the coercive field Hc, we can determine the intensity of the magnetic field opposed needed to completely demagnetize a magnet. In other words, the higher its value, the more the magnet will keep its magnetic capabilities when it will be subject to an opposite field.

• #### Coercive force, Hc

Also called coercivity. Hc is the magnetic field required to reduce the induction B and the magnetization M to zero. It is measured in oersteds or amps / meter is used to measure the resistance of a magnetic material to its demagnetization.

• #### Coercivity Hci Or Ihc

It is the resistance of a magnetic material to demagnetization. The value H cancels the magnetic induction and it is measured in oersteds or amps per meter A / m.

• #### Curie temperature, Tc

This is the temperature above which ferromagnetic materials become paramagnetic, while losing substantially all of its permanent magnetic properties. It usually depends on the chemical composition of the magnetic material.

# D

• #### Demagnetization curve

It corresponds to the second quadrant of the hysteresis loop, generally describing the behavior of the magnetic properties in actual use. Also known as B-H curve. This is the part of the curve of a full hysteresis loop in the second dial which defines the main magnetic properties of a magnet. It describes the change due to the magnetic induction or from the demagnetization remanence value to zero by applying a negative direction field.

• #### Diamagnetic

Magnetic properties of materials that have lower permeability values to 1 (eg. Silver, copper, water, gold, lead, zinc ...).

# E

• #### Energy product (Bh) max

This is the energy that a magnetic material can provide to an external magnetic circuit when it operates on an item of its demagnetization curve. It is measured in Megagauss-oersteds, MGOe, or kJ / m³. BHmax represents the maximum energy which can be stored in a magnet. The unit used is the kJ.m³ (kilo joule per cubic meter) or MGOe (Mega Gauss Oersted).

# F

• #### Ferromagnetic

Magnetic property of materials that exhibit superior permeability values of 60 to several thousand times μ0 and exhibits hysteresis phenomena. Ex. (Cobalt, iron, mu-metal, nickel ...).

• #### Flux

This is the number of “magnetic lines of force”, measured in Gauss or Tesla. These lines can be visualized using iron dust.

• #### Flux density

Magnetic flux per unit area of a section normal to the direction of flow. Also known as magnetic induction. Measured in Gauss, it is a way of defining the induction field as the force line number per unit area.

# G

• #### Gauss

Measurement unit of the induction, B, in the Gaussian system. 1 G = 10-4 T; 1 mT = 10 G magnetic flux lines per centimeter square cgs unit flux density equivalent lines per square inch in the English system and Weber per square meter or Tesla in the IS system.

# H

• #### Hysteresis

This is the ability of a magnetic material to keep the magnetic force at the time of being exposed to a demagnetizing force.

• #### Hysteresis curve

This is the closed curve obtained when measuring the induction B or the magnetization M when it is subjected to a magnetic field H which describes a complete circle between the limits defined by the induction or magnetization saturation in the first to the third quadrant.

# I

• #### Intrinsic coercivity

Value of the measured field in oersteds or A / m, which indicates the resistance of a material to demagnetization. The maximum value is obtained after leading the magnet towards saturation.

• #### Intrinsic induction, Bi

This is the magnetic material contribution to the total magnetic induction B. It is the vector difference between the magnetic induction in the material and the magnetic induction that would exist in a vacuum under the same force fields, H.

• #### Irreversible loss

This corresponds to the irreversible changes that take place when a magnet is demagnetized partially or completely because of exposure to high or low temperatures, or because of other factors such as external demagnetization fields. When the magnets are magnetized again, these losses are recovered. Defined as 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 change in performance caused by irreversible losses.

• #### Isotropic magnet

A magnet material whose magnetic properties are the same in any direction and can be magnetized in any direction without loss of magnetic characteristics.

• #### Isotropy

A magnet is considered isotropic when its properties are independent of its orientation. The particles are randomly oriented. They have no preferred magnetic orientation, which allows snap in any direction.

# M

• #### Magnetic constant

Also called vacuum permeability or magnetic vacuum permittivity, it is a physical constant. It is symbolized by μ0. μ0 can be seen as the intrinsic magnetic vacuum permeability.

• #### Magnetic Field Strength

It is the magnetization or demagnetization strength, measured in oersteds. It determines the ability of an electric current or a magnetic material to produce a magnetic field in a certain place.

• #### Magnet

Object made of a hard magnetic material, that is to say whose residual field and the coercive field are great. This gives it special properties like exercising an attractive force on any ferromagnetic material.

• #### Magnetic induction

It is the magnetization or demagnetization strength, measured in oersteds, which determines the capacity of an electric current or a magnetic material, to impose a magnetic field on a predetermined point.

• #### Magnetic induction B

Commonly called induction, it is a phenomenon which binds the electrical voltage in a conducting loop and the variation of a magnetic field therethrough. This voltage is commonly called electromotive force or EMF.

• #### Magnetic permeability

Is the ability of a material to produce a magnetic field, that is to concentrate the magnetic flux lines and thus to increase the value of magnetic induction. This value of the magnetic induction depends on the environment in which it is produced.

• #### Magneticsusceptibility

Magnetic susceptibility is the ability of a material to react to the action of a magnetic field. The reaction is of two types: the appearance of a mechanical force and magnetization of the material.

• #### Maximum temperature

This is the maximum exposure temperature that a magnet can withstand without structural changes or imbalances in its properties.

• #### Maxwell

Unit by magnetic flux in the Gaussian measurement system. A Maxwell is equivalent to a magnetic flux line.

# N

• #### North pole

Magnetic pole of a magnet which is attracted to the geographic South Pole of the Earth.

# O

• #### Oersted, Oe

CGS measurement unit used to describe the magnetizing force. The English system is Ampere / turn by inch and in the IS system, Ampere / turn per meter. The unit of magnetic field strength, H, in the GSM electromagnetic system.

• #### Orientation direction

The direction in which an anisotropic magnet should be magnetized to achieve optimal magnetic properties. Also referred to as “axis”, “easy axis”, or “tilt angle”.

# P

• #### Paramagnetic

Magnetic property of materials which exhibits permeability values close to 1. The absolute permeability μ of diamagnetic and paramagnetic materials is practically equal to that of vacuum (eg .: air, aluminum, magnesium, platinum ...).

• #### Permissiveness coefficient, Pc

This is a proportion of magnetic induction, Bd, at its demagnetization force, Hd. Also called “load line”, “the operating line slope”, or operating points of the magnet, which is useful in the evaluation of the production of the flux of the magnet in various conditions.

# R

• #### Remanence (Br)

This is the residual magnetization of the magnet which has been magnetized to saturation in a closed circuit. Br is calculated by Tesla (T) miniTeslas (mT) or Gauss (G), and corresponds to the magnetic induction in the material after being magnetized to saturation and prepared for its final use. The remanence Br is used to measure the induction or persistent flux density in a magnet after being magnetized. For simplicity, the higher the value, the stronger the magnet. The magnetic flux density is measured in Tesla (T). Gauss (G) is also used, 1Tesla = 10,000 Gauss.

• #### Remanent field

This is the magnetic field existing in the material in the absence of any current.

• #### Residual induction, Br

This is the point where the hysteresis loop crosses the B axis at zero magnetizing force and represents the output of the given magnetic material maximum flux. By definition, this point appears at zero air void and can not be used in magnetic materials.

# S

• #### South pole

Magnetic pole of a magnet which is attracted to the geographic North Pole of the Earth.

• #### Saturation

This is the maximum value of magnetization, which refers to the lowering of the permeability and the increasing magnetization force. This is the flux density with a maximum value of magnetization, the highest magnetic polarization that a magnet can get. In the case of an inductor, it corresponds to the lowering of the current by inductance. It is the condition in which all the elementary magnetic moments have become oriented in one direction. A ferromagnetic material is saturated when an increase in magnetization force applied produces no increase in induction. The flux density saturation for steels is in the range of 16000-20000 Gauss.

• #### Sintering

It is the heat treatment at high temperatures, so that the pressed parts have a lower volume and are more dense. For ferrites, the values are approximately 1200°C to 1250°C and rare earths, of 1050°C to 1200°C.

• #### Stabilization

It is the prior exposure of a magnet to demagnetization forces that may be encountered to prevent irreversible loss in actual use. The demagnetization influences can be caused by high or low temperatures, or by external magnetic fields.

# T

• #### Temperature Coefficient

This coefficient describes the changes in magnetic properties depending on temperature change. Usually this value is expressed in % of field change per degree of temperature.

• #### Tesla

Unit for the magnetic flux density of 1 Tesla = 10,000 Gauss..