Home >
Basic Knowledge >
Terms used in relation to permanent magnets
Terms used in relation to permanent magnets
| Term | Code | Unit | Explanation |
|---|---|---|---|
| Neodymium magnet | Nd-Fe-B | - | Neodymium magnets are one of the rare-earth permanent magnets. Neodymium magnets are the strongest permanent magnets that are mainly comprised of neodymium (Nd), which is a rare earth element, iron (Fe) and boron (B), and they have an anisotropic property. Neodymium magnets need to be rustproofed, as they tend to rust. Dysprosium-free neodymium magnets have also been available commercially in recent years. |
| Samarium-cobalt magnet |
Sm-Co | - | Samarium-cobalt magnets are one of the rare-earth permanent magnets. Samarium-cobalt magnets are permanent magnets containing intermetallic compounds of samarium (Sm) with cobalt (Co), and have an anisotropic property. Samarium-cobalt magnets do not need to be rustproofed in normal use, as they are difficult to rust. Samarium-cobalt magnets have excellent temperature characteristics. |
| Ferrite magnet | BaO-6Fe2O3 SrO-6Fe2O3 |
- | Ferrite magnets are highly versatile and the most widely used magnets. Ferrite magnets are mainly comprised of iron oxides, and have the advantage of being inexpensive, stable magnetic properties, and do not corrode. Barium (Ba) ferrite magnets are isotropic, while strontium (Sr) magnets are anisotropic. |
| Sintered magnet | - | - | Sintered magnets are made of powdered magnetic material shaped into magnets with a die and sintered at high temperature. Sintered magnets include ferrite magnets, samarium-cobalt magnets, neodymium magnets, and so on. Sintered magnets are suitable for forming standard shapes, such as circular, cylindrical and rectangular parallelepiped magnets. |
| Bonded magnet | - | - | Bonded magnets are magnets which are made by mixing magnetic powder with rubber and plastic and forming them into a magnet with a die or by extrusion. Bonded magnets are suitable for forming complex shapes. However, the magnetic force of bonded magnets is less than that of sintered magnets, because bonded magnets have less magnetic substance per volume. |
| Isotropy | - | - | Isotropy refers to a magnetic property with no particular direction. If magnetic powder is mixed with a base material and formed into bonded magnets etc., the easy magnetisation axis (the direction in which the crystalline structure of a magnetic material is easily magnetised) becomes misaligned. Such magnets are called "Isotropic magnets". Isotropic magnets can magnetise equally in any direction. |
| Anisotropy | - | - | Anisotropy refers to having a different magnetic property in a certain direction. Magnets formed from magnetic powder whose easy magnetisation axis is aligned in a certain direction are called "Anisotropic magnets". Anisotropic magnets become strongly magnetised by the process of magnetisation in the direction of the easy magnetisation axis. The easy magnetization axes are principally aligned by in-field forming method, and can be also lined up by applying mechanical pressure. |
| Orientation | - | - | "Orientation" is a technical term used in the manufacture of magnets. If magnetic powder is formed into magnets by compression in a magnetic field generator, the easy magnetisation axis of the crystalline structure will align in the same direction as the direction of the magnetic field formed by the magnetic field generator. Aligning the direction of the easy magnetization axes of crystalline structures in the direction of a magnetic field is called "magnetic field orientation", and the method for forming a magnetic field is called "magnetic field forming" or "in-field forming". Magnets generated by the above process are sintered to become anisotropic magnets. |
| Magnetic field | H | A/m (Oe) | A magnetic field is a vector field located around a magnet and current. A unit representing magnetic field strength (H) is "Ampere per meter [A/m]" in the SI system, and "Oersted [Oe]" in the CGS system. |
| Magnetisation | - | - | "Magnetisation" means that a substance becomes magnetised by the effect of a magnetic field or magnet. Magnetisation also refers to magnetising a magnetic material. |
| Demagnetisation | - | - | Removal of magnetism from a magnetised material is called "demagnetisation". Demagnetisation is based upon the principle that magnetism is reduced by applying an alternating magnetic field to a magnetised material, which causes the alternating magnetic field to decrease gradually. |
| Magnetic substance | - | - | A "Magnetic substance" means substances which can be magnetised by the effect of a magnetic field or magnet. Substances which magnetise strongly are called "Ferromagnetic substances", and are used as the material for permanent magnets, including iron and magnetite. However, substances which do not magnetise are called "Non-magnetic substances"; paper and plastic as typical examples, as well as metallic substances such as gold, silver, copper, aluminium, and magnesium. |
| Magnetic force line / magnetic flux |
- | - | Imaginary lines representing the orientation of a magnetic field are called "Magnetic force lines". Magnetic force lines are expressed by lines originating from the N-pole and returning to the S-pole, and never cross each other. A bundle of magnetic force lines are called a "Magnetic flux". |
| Magnetic flux density | B | T (G) | The magnetic flux per unit area is called the "Magnetic flux density". The magnetic flux density represents the magnetic force at a point where a magnetic field exists. The unit representing magnetic flux density (B) is Tesla [T] in the SI system, and Gauss [G] in the CGS system. |
| Magnetic hysteresis curve |
- | - | A magnetic hysteresis curve is a non-linear data aggregate or graph, which represents the tendency and distribution of magnetisation. The curve representing the relationship of an external magnetic field (H) with magnetisation (J) with the magnetic flux density (B) of a material is called the "Magnetic hysteresis curve (magnetisation curve)". Magnetic hysteresis curves may be classified into two types; a curve representing the relationship between the magnetisation of a material and the magnetic field (J-H curve), and the curve representing the relationship between the magnetic flux density and the magnetic field (B-H curve). The second quadrant in the graph of a magnetic hysteresis curve is called the "Demagnetisation curve", which is an important curve representing a material's characteristics. |
| Maximum energy product |
Bhmax | J/m3 (GOe) |
The maximum energy product is one of the characteristic values representing magnetic strength. The area of a rectangle (BxH) whose diagonals exist between the operating point and origin of the demagnetisation curve represented by the B-H curve is called the "Energy product", and the maximum value of an energy product is called the "Maximum energy product". |
| Remanent magnetic flux density |
Br | T (G) | "Remanent magnetic flux density" is the magnetic density at the intersection of the vertical axis with the demagnetisation curve. Remanent magnetic flux density represents the magnetic flux density that a material can retain, even under the condition that a magnetic field is applied to such material to saturation, and then its magnetic field reduces to zero. Remanent magnetic flux density (Br) is dependent on materials, and referred to as one of characteristic values for measuring strength of magnetic force proper to materials. |
| Surface magnetic flux density |
Bg | T (G) | "Surface magnetic flux density" is the magnetic flux density on the pole's surface of a magnet. For actual measurement, the surface magnetic flux density is determined as the value at a point which is slightly away from the pole's surface due to a mechanical reason of the measuring instrument. Surface magnetic flux density is useful for comparing different magnets, though it is difficult to determine a measurement point because surface magnetic flux density varies according to the magnet shape. |
| Coercive force | Hcb (bHc) Hc (j iHc) |
A/m (Oe) | "Coercive force" is the intersection point of the transverse axis with the demagnetisation curve. Coercive force means the external magnetic force under the condition that the magnetic force of a material magnetised by applying a magnetic field to saturation is reduced to zero by applying a magnetic field whose direction is opposite to the magnetisation direction. The intersection point of the J-H curve with the transverse axis is represented by Hc (j or iHc), and the intersection point of the B-H curve with the transverse axis is represented by Hcb (bHc). Coercive force literally means the strength to retain the magnetic force, and is expressed as the characteristic value representing the characteristics of a material, as with remanent magnetic flux density. It is necessary to design a magnet carefully, using a material with a high remanent magnetic flux density and low coercive force, as it is highly dependent on the shape and temperature. |
| Permeance coefficient | Pc | Dimensionless | "Permeance coefficient" is the parameter determining where a magnet operates, and depends on the magnet's shape. A magnet always generates a magnetic field outside itself, and also generates a magnetic field in the opposite direction (demagnetising field) inside itself. A demagnetising field is an element which reduces the magnetic force, and depends on the magnet's shape. A permeance coefficient is defined by magnetic flux density against demagnetizing force. The shorter (thinner) the magnet is shaped in the magnetization direction in comparison with the surface area of the pole, the higher the demagnetizing field will become and the lower the permeance coefficient and magnetic force will become. |
| Curie temperature | - | K、℃ | The "Curie temperature" or "Curie point", is the temperature at which a certain material completely loses its magnetic force due to the change of its crystalline structure due to an increase in temperature. Once a magnet reaches the Curie temperature, it cannot regain its magnetic force even if the temperature reduces to the ambient temperature. |
