Magnet Definitions & Glossary

Understanding the key terms in the magnet industry is crucial for professionals and hobbyists alike. This glossary presents an alphabetical list of common terms related to magnetism and magnetic products. Whether you're purchasing magnets or working on engineering projects, this guide will help you navigate through the terminology used in the industry.

 

Adsorption Strength

Adsorption force, also known as attraction, refers to the force that acts between two objects, such as a magnet and a magnetic body containing iron. The unit of measurement for adsorption force is the Newton (N). Other basic units of force, such as kilogram-force (kgf) and pound-force (lbf), can also be used to represent adsorption force.

Air Gap

The space between a magnet and the material it is attracting or repelling. The size of the air gap influences the overall strength of the magnetic circuit.

Alnico Magnet

A type of magnet made from aluminum (Al), nickel (Ni), and cobalt (Co) alloys. Alnico magnets have good temperature stability and are often used in applications such as electric motors, sensors, and guitar pickups.

Axial Magnetization

A magnetization method where the north and south poles are located on the flat faces of the magnet (along the axis). This is common for disk and cylinder-shaped magnets.

B-H Curve

Also known as a hysteresis loop, the B-H curve plots the relationship between magnetic flux density (B) and magnetic field strength (H). It shows the performance of a magnetic material.

Bonded Magnet

A type of magnet made by binding magnetic powders with plastic or resin. Bonded magnets can be formed into complex shapes and offer lower magnetic strength than sintered magnets but with greater flexibility in design.

Br (Residual Induction)

The measure of a magnet’s ability to retain its magnetic strength after being magnetized. A higher Br value indicates a stronger magnet.

Curie Temperature

The temperature at which a magnet loses its magnetic properties. Each magnetic material has a specific Curie temperature, beyond which the magnet becomes non-magnetic.

Coercivity (Hcb/Hcj)

Coercivity refers to the coercive magnetic force, which is the strength of an external magnetic field (H) required to return a magnetized material to a non-magnetized state by applying an opposing (-) magnetic field (H). A higher coercivity value indicates greater resistance to demagnetization, making it more difficult to reduce the magnetization. Coercivity is measured in amperes per meter (A/m) in the SI system of units and in Oersted (Oe) in the CGS system of units.

Diamagnetism

A weak form of magnetism where materials are repelled by magnetic fields. Diamagnetic materials include copper, silver, and gold.

Eddy Currents

Loops of electric current induced within conductors by a changing magnetic field. Eddy currents can cause energy loss in electrical systems and magnetic assemblies.

Electromagnet

A type of magnet where the magnetic field is produced by an electric current. Electromagnets are widely used in motors, transformers, and medical devices like MRI machines.

Ferrite Magnet

Also known as ceramic magnets, ferrite magnets are made from iron oxide and barium or strontium carbonate. They are inexpensive and resistant to corrosion, making them suitable for various industrial applications.

Flux

The magnetic field produced by a magnet, typically measured in Weber (Wb). Magnetic flux represents the strength and extent of a magnetic field.

Gauss

A unit of measurement for magnetic flux density. One gauss is equivalent to one line of flux per square centimeter. The gauss is named after German mathematician Carl Friedrich Gauss.

Halbach Array

A special arrangement of permanent magnets that enhances the magnetic field on one side while canceling it on the opposite side. Halbach arrays are used in applications like particle accelerators and maglev trains.

Hysteresis

The lag between the magnetization of a material and the external magnetic field applied to it. This effect is depicted by the B-H curve and influences how a material stores magnetic energy.

Induction

The process by which a material becomes magnetized when exposed to an external magnetic field. Magnetic induction plays a critical role in transformers, inductors, and other electronic components.

Isotropic Magnet

A magnet with no preferred direction of magnetization, meaning it can be magnetized in any direction. Isotropic magnets are usually weaker than anisotropic magnets.

Keeper

A piece of soft iron placed across the poles of a permanent magnet to protect it from demagnetization and maintain its strength.

Load

Load refers to the force exerted when two points are in contact, such as between a magnet and a steel plate. This force can vary based on factors like friction, surface condition, and impact. Slip load, which indicates whether a magnet and a steel plate (or similar surfaces) can stay in place without slipping while supporting a horizontally applied load, is measured in Newtons (N).

Method of measuring adsorption force and slip load

The numerical values obtained for adsorption force often fluctuate based on the usage environment and measurement method employed. Therefore, it is crucial to specify the environmental conditions and measurement method when referencing the adsorption force in the technical data of a magnet. At Magfine, these forces are defined based on standardized measurement methods and specified conditions of use.

Measurement method

1. Adsorption strength

The adsorption force is the force when a magnet is detached from a steel plate perpendicular to the vertical axis, and the magnet separates from the steel plate.

2. Slip load

A slip load is the force when a magnet is pulled parallel to the horizontal axis and the magnet moves away from the steel plate.

Environmental conditions

1. The thickness (T) of the steel plate and the thickness of the magnet (H) are as specified.
2. The magnet is positioned centrally on the steel plate.
3. The surface area of the steel plate is at least three times greater (300%) than the surface area of the magnet.
4. The steel plate material is pure iron (Fe).
5. The surface of the steel plate is flat and smooth, with no roughness, and the friction coefficient is disregarded.
6. The gap between the steel plate and the magnet is eliminated to ensure no spacing.

Magnetic Circuit

The path through which magnetic flux flows in a magnet system, similar to the flow of electric current in an electrical circuit. The efficiency of a magnetic circuit depends on the materials and geometry used.

Magnetic Field

An invisible field surrounding a magnet in which magnetic forces are exerted. Magnetic fields are represented by lines of flux and measured in teslas or gauss.

Magnetic Flux Density

Magnetic force is illustrated by a bundle of multiple lines of magnetic force emanating from a unit surface area. Remanence (Br) represents the amount of magnetic flux (B) that remains when a permanent magnet is magnetically saturated to point M by an external magnetic field (H) and then the external magnetic field (H) is reduced to zero. Surface magnetic flux density refers to the magnetic flux density at the outer surface of the magnet. In the SI system of units, magnetic flux density is measured in teslas (T) (Wb/m²), and in the CGS system, it is measured in gauss (G) (Mx/cm²).

Magnetic Moment

A vector quantity representing the strength and orientation of a magnet’s magnetic field. Magnetic moment determines the torque a magnet will experience in an external magnetic field.

Magnetism

The capacity of a permanent magnet is often referred to as "magnetic force." More specifically, the reactive property of a magnet is called "magnetism," the strength of this magnetism is known as "magnetic force," and the area where magnetism operates is termed the "magnetic field" or "magnetic flux." These properties are energy-dependent, and the N and S poles engage in a tug of war, repelling each other due to the bipolar characteristics of the magnet. This magnetic energy is not visible under normal conditions.

Magnetism flows out from the N pole and into the S pole, and this interaction between the poles is visually represented by lines known as "lines of magnetic force." Using a magnet and iron powder, these lines provide a visual representation of the magnetic energy.

While the performance of a magnet is often described abstractly as "weak" or "strong," such assessments are subjective and cannot be accurately measured by third parties. The true efficiency of a magnet is typically evaluated using a BH analyzer to create a hysteresis curve, known as the BH curve. This curve provides key indicators measured according to international standard units, including magnetic flux density (B), coercivity (HCB/Hcj), and maximum energy product (BH-max). For precise evaluation, refer to a magnetic drive converter for magnetic drives.

Magnetization

The process of making a material magnetic by aligning its internal magnetic domains. Magnetization can be permanent or temporary, depending on the material used.

Maximum Energy Product

The maximum energy product, denoted as BH-max, is the peak value of the magnetic field strength (H) multiplied by the magnetic flux density (B), represented as (Bd) * (Hd). This value serves as a benchmark for the maximum amount of magnetic flux that can be obtained from a unit volume of the magnet. A higher BH-max value indicates a better balance between magnetic flux density (B) and coercivity (HCB / Hcj), particularly when the line between point P and the origin (0) approaches a 45-degree angle. BH-max is measured in kilojoules per cubic meter (kJ/m³) in the SI system of units and in Megaoersteds (MOe) in the CGS system of units.

Neodymium Magnet (NdFeB)

The most powerful type of permanent magnet, made from an alloy of neodymium, iron, and boron. Neodymium magnets are used in various applications, including electronics, medical devices, and automotive industries.

Permeability

A measure of how easily a material can support the formation of a magnetic field within itself. Higher permeability materials allow magnetic lines of force to pass through more easily.

Permanent Magnets

A material that continuously generates its own magnetism is known as a "magnet." Artificially produced iron-based magnets consist primarily of iron (Fe), with about 1% carbon (C) and other elements. In these magnets, the atomic magnetism of iron aligns consistently with atoms such as carbon, resulting in a sustained external magnetic field. These magnets are referred to as permanent magnets.

    

Pole

The region at the end of a magnet where the magnetic field is strongest. Magnets have two poles: north and south, which exert attractive or repulsive forces depending on the interaction with other magnetic materials.

Reduced magnetization and demagnetization

The magnetization of magnets diminishes over time, but in normal temperature environments, this decrease is minimal and occurs over many years. As a result, most people believe that magnets never lose their magnetism, hence the term "permanent magnets." The magnetic strength of a permanent magnet is influenced by the ambient temperature and varies according to the temperature coefficient. Higher temperatures weaken the magnetic force, while lower temperatures enhance it.

However, permanent magnets cannot withstand prolonged exposure to high temperatures. Continuous heating causes the direction of the iron atoms to become disordered, leading to a gradual reduction in magnetism. Once a certain temperature is surpassed, the magnet becomes completely demagnetized. This critical temperature is known as the Curie point or Curie temperature, named after the French physicist Pierre Curie, who discovered it in 1895.

Additionally, a strong impact can cause the directions of the atoms to become disordered due to vibrations, which can also result in a reduction of magnetization.

Reluctance

The opposition a material presents to the flow of magnetic flux, similar to electrical resistance in a circuit. High reluctance materials reduce the efficiency of magnetic circuits.

Residual Magnetism

The amount of magnetism left in a material after an external magnetic field is removed. This is important for materials that need to retain magnetic properties in applications like data storage.

Samarium-Cobalt Magnet (SmCo)

A type of rare-earth magnet known for its high temperature stability and resistance to corrosion. Samarium-cobalt magnets are often used in high-performance applications such as aerospace and defense.

Saturation

The point at which a material can no longer be magnetized, no matter how strong the external magnetic field. Saturation represents the maximum magnetization of a material.

Sintered Magnet

A type of magnet made by pressing and heating magnetic powders until they fuse together. Sintered magnets, such as neodymium and samarium-cobalt, are stronger and more durable than bonded magnets.

Tesla

The SI unit of magnetic flux density. One tesla is equal to one weber per square meter. The tesla is commonly used to measure the strength of magnets used in MRI machines and other advanced technologies.

Temporary Magnet

A magnet that only exhibits magnetic properties when exposed to an external magnetic field. Temporary magnets lose their magnetism when the external field is removed.

Temperature Coefficient

The rate at which a magnet's performance degrades with increasing temperature. Materials with a low temperature coefficient are more stable at high temperatures.

Weber

The unit of magnetic flux in the International System of Units (SI). One weber is the magnetic flux that, passing through a one-turn loop, induces an electromotive force of one volt when reduced to zero at a uniform rate in one second.