Glossary of Magnet Terms

A

Aging demagnetization

This is a phenomenon in which the magnetic flux of a permanent magnet decreases with time. Even though we say "permanent magnets", they do not remain magnets permanently. Over a long period time, permanent magnets are gradually demagnetized by the impact of heat fluctuation. The degree of deterioration depends on the type and material of magnet and the magnetic characteristics. Even for the same type of magnet with the same characteristics, the degree of deterioration varies with the magnet shape, magnetic circuit configuration (permeance coefficient) and temperature. Generally, the lower the usage temperature and the higher the permeance coefficient and also the higher the Curie temperature and the higher the coercive force of the material, the less the change over time. You can obtain data on the amount of change over time for Shinetsu rare earth magnets from our download page.

Antiferromagnetism

A magnetic property in which the neighboring magnetic moments in the material are oriented in the opposite directions to each other so that the magnetization of the material as a whole is zero. A material that demonstrates this magnetic property is called an antiferromagnetic body. When such a body reaches the Neel temperature, it becomes paramagnet.

Axis of easy magnetization

For a magnetic body with crystal magnetic anisotropy, this is the crystal direction in which magnetization is difficult. See the item on crystal magnetic anisotropy.

Axis of hard magnetization

For a magnetic body with crystal magnetic anisotropy, this is the crystal direction in which magnetization is difficult. See the item on crystal magnetic anisotropy.
B

Bending strength

This is a characteristic value showing the strength against bending and is also called bend strength. When only a bending moment operates on material without shear force operating, compressive force works on the bend arc axis side and tensile force works on the outside with a boundary at the neutral surface, which neither expands nor contracts even when receiving a bend operation. Bending strength shows the maximum strength at which the test piece is broken by the bend load. The JIS prescribe two types of bend stress test methods, the 3-point bend test and the 4-point bend test, according to the load method. The units are [Pa]. This value is sometimes used to show the mechanical strength of a magnet.

Bonded magnets

Magnets manufactured by mixing fine magnet particles or fine powder with adhesive or other binder then molding it into a solid magnet. The magnet powder used is sometimes ferrite and sometimes rare earths. Because binder is used, the degree of freedom of the product shape and the dimensional precision are both high. However, bonded magnets contain a large non-magnetic section so compared to sintered magnets, the magnetic characteristic is lower and the heat resistance is less.
C

Coefficient of thermal expansion

The degree to which the size of an object changes with temperature. There are the coefficient of volumetric expansion for the change in the volume and the coefficient of linear expansion for the change in length. The unit is per kelvin [1/K]. For strongly magnetic bodies with crystalline magnetic anisotropy, the coefficient of linear expansion may vary with the crystal direction. Neodymium magnets have different coefficients of thermal expansion in the magnetized direction and the non-magnetized direction. In particular, heating produces contraction along the non-magnetized direction. When pasting together an iron yoke etc. with neodymium magnets, it is necessary to pay attention to the difference in the degree of thermal expansion for change in temperature.

Coercive force or coercivity

This means the value of the external magnetic field that brings to zero the magnetization or magnetic flux density of a magnetic body when that external magnetic field is caused to operate in the opposite direction from the orientation of the magnetization of the magnetic body. The value of the external magnetic field when the magnetic polarization (or magnetization) and magnetic flux density of the magnetic body come to zero are written as H_cJ and H_cB to distinguish them, but when evaluating magnetic characteristics, normally the coercive force means H_cJ. This means the stability of magnetization in the face of an external magnetic field or the capacity to resist an external magnetic field. Material with high coercive force is hard magnetic material and material with low coercive force is soft magnetic material. This is the most important characteristic for a permanent magnet material.

Cogging

A phenomenon in which the mechanical attractive force between the armature and the rotor in the motor pulse finely depending on the rotation angle. This is distinguished from rotation torque fluctuation. This occurs because the armature position and shape and the rotor magnetic flux influence each other. When the cogging torque is small, the motor rotates smoothly and highly precise control is possible. With permanent magnet synchronous motors, measures are taken to reduce cogging, such as using tile shaped magnets that are thin at both ends, using skew magnetization, and further skewing the field magnet.

Compressive strength

This is the maximum stress when a test piece breaks under a compressive load. The compressive pressure when a one-axis load is applied to round and square pillar shaped test pieces is expressed as the value divided by the cross-sectional area perpendicular to that axis. General, the value of compressive strength is larger than the value of tensile strength. The units are pascals [Pa]. Since rare earth magnets are severely brittle, their tensile strength can not be measured. Therefore, the compressive strength is substituted for the mechanical strength.

Curie temperature

The temperature at which a ferromagnetic body or ferrimagnetic body shifts to the paramagnetic state due to temperature rise. The magnetic moments lined up in the magnetic body are constantly vibrating due to heat fluctuation. As the temperature rises, the heat fluctuation becomes stronger and proportional to this, the magnetic moment alignment becomes disrupted. Finally, this order is completely lost. The temperature at which this happens is the Curie temperature. In order to show strong magnetism at normal temperatures, this Curie temperature must be adequately higher than room temperature. Curie temperatures higher than room temperature are attained in the transition elements of iron, cobalt, and nickel and in alloys of these metals and rare earth elements.
D

Demagnetization at high temperature

The phenomenon in which the magnetic flux decreases when a magnet magnetized at room temperature is exposed to high temperature caused by the shaking or flipping over of magnetic moments due to heat fluctuation is called demagnetization at high temperature. The demagnetization that occurs when the magnet is first raises to high temperature is called the initial demagnetization and the demagnetization that occurs over a certain period of time is called the change over time. Demagnetization for which the magnetic flux recovers when the magnet exposed to high temperature is returned to normal temperature is called reversible demagnetization. On the other hand, demagnetization for which the magnetic flux does not recover when the magnet is returned to normal temperature is called irreversible demagnetization. For details on the mechanisms behind these types of demagnetization, see "Magnet fundamentals" on our homepage.

Demagnetizing field

A magnetic field generated in a permanent magnet in the opposite direction of its magnetization. This is also called a demagnetizing field. The size of a demagnetizing field is proportional to the size of the magnetization and this proportionality coefficient is called the demagnetizing field coefficient. Like the permeance coefficient, the demagnetizing field coefficient is determined only by the shape of the magnet. With the magnetic field as positive, the larger the permeance coefficient, the smaller the demagnetizing field coefficient. Looking at the magnet shape, the more a magnet is shaped long and fine in the magnetization direction moving the magnetic poles farther from each other, the smaller the demagnetization coefficient.

Diamagnetism

A magnetic characteristic in which the magnetic moments in the material are oriented in various random directions in the absence of an external magnetic field such that the body as a whole is not magnetized, but that when an external magnetic field is applied, the body is magnetized in the opposite direction and proportional to the intensity of the magnetic field. A material that demonstrates this magnetic property is called a diamagnetic body. This property is seen in inert gases, such metals as copper, gold, silver, and zinc, and in organic compounds.

Dipole ring magnets

This is a magnetic circuit that generates a uniform strong magnetic field in a specific direction. This is an extraordinarily efficient magnetic circuit and looking at the ratio of the magnetic field generated to the weight of magnets used, this is the magnetic circuit that can be made most compact. The magnetic circuit is cylindrically shaped, with magnets placed along the circumference of the cylinder cross sections. The segment magnets are pasted into place in such a way that the magnetic orientation direction is continuous.
E

Eddy current

Induced eddy current generated in a conductor by the magnetic flux changing in that conductor (for example aluminum, copper, or other metal). It was discovered by the French physicist Léon Foucault. When an induced current is generated, this becomes an eddy current that generates a magnetic field that impedes change in the magnetic flux and ultimately kinetic energy is converted into heat, creating loss in various electromagnetic motion conversion devices. The amount of heat thus generated is called the Joule heat. The generation of Joule heat by eddy current is a cause of reduce efficiency for motors and other electromagnetic motion conversion devices. On the other hand, it is used as a heat source in electromagnetic cookers etc.

Electrical resistivity

Value expressing the difficulty with which electric current flows in the material. The current I in the material is proportional to the applied voltage V (by Ohm's Law) and this coefficient V/I is called the electrical resistance. On the other hand, the specific electric resistance per unit cross sectional area or per unit length is called the electrical resistivity. The larger a material's specific electrical resistance, the more difficultly current flow and the larger the amount of Joule heat generated for the same current flow. For magnetic circuits such as motors with fluctuating magnetic flux amount and direction, the eddy current generated in the magnet is smaller the larger the specific electric resistance.

EPS (Electric Power Steering)

EPS is the abbreviation for electric power steering. This is a mechanism that assists steering operations with electrical power. Because power steering until now has been hydraulic, it drained power from the engine even when no steering operation was underway, but by converting to electric, energy consumption when the power steering is not in operation can be cut, which improves the fuel economy. Differing according to the positioning of the electric power steering motor, there are the column type, the rack type, the pinion type, as well as electrical-hydraulic power steering (H-EPS), which retains the hydraulic system and drives the hydraulic pump with an electric motor. In compact cars, many electric power steering systems use ferrite magnets, but in medium- and large-size cars, the use of brushless motors with rare earth magnets is expanding.

EV (Electric Vehicles)

EV is the abbreviation for electric vehicle. An electric vehicle obtains its power by turning a motor with electricity rather than using an internal combustion engine burning gasoline or other fuel. As the source for the electricity, there are PEV, which use batteries, vehicles that drive while generating electricity from solar batteries, FCV that obtain the electricity for driving by generating it in a fuel cell, as well as HEV (Hybrid Electric Vehicles) that generate electricity with an engine and when the system is fully charged drive with both the electric motor and engine. Pure electric vehicles, which exclude hybrid electric vehicles, are still not common, but from the perspectives of energy problems and environmental protection, they are expected to develop significantly in the future. The drive motors and electric generation motors in these electric cars, including hybrid electric vehicles, mainly use rare earth magnets.

Exchange spring magnets

This is a new type of magnet comprising a fine sub-micron hard magnetic phase and soft magnetic phase that behaves like a homogenous and uniform magnet with magnetic exchange coupling operation working between the two phases. Because its magnetization behavior is as though the hard magnetic phase and soft magnetic phase are linked with a magnetic spring, this kind of magnet is called an exchange spring magnet. In the second quadrant of the magnetization curve, these magnets have a strong magnetization recovery capacity not found in normal magnets. They have a comparatively high magnetization, but the history curve square type is poor and the coercive force is small. It is said that if a high- coercivity exchange spring magnet with anisotropy could be developed, it would be the best magnet in the world, but this goal has not been attained at this time. Since the magnet organization above is a nano-scale complex organization, these magnets are also called nano-composite magnets.
F

Ferrimagnetism

A magnetic property in which magnetic moments of different size in the material are oriented in the opposite directions to each other so that the magnetization generated is just the difference between these magnetic moments. A material that demonstrates this magnetic property is called a ferrimagnetic body. A typical ferrimagnetic body is ferrite. Compared to ferromagnetism, in which all the magnetic moments are aligned in parallel, generally the magnetization is smaller. The same as for a ferromagnetic body, when a ferrimagnetic body reaches the Curie temperature, it becomes paramagnetic.

Ferrite magnets

A magnet made from magnetic oxides whose primary component is Fe₂O₃. In practical magnets, barium and strontium are included, so these magnets are also called barium ferrite magnets or strontium ferrite magnets. Features of these magnets include that the primary components are iron oxides, they are inexpensive, they have high corrosion resistance, they have high electrical resistivity, etc. However, their magnetic characteristics are lower than those of rare earth magnets and their maximum energy product is about 1/10 of that for a rare earth magnet.

Ferromagnetism

A magnetic property in which the magnetic moments in a material are oriented in parallel through exchange interaction. A material that demonstrates this magnetic property is called a ferromagnetic body. As a result of the magnetic moments being aligned in parallel, a ferromagnetic body has spontaneous magnetization, but because a magnetization domain structure is used, normally in the initial state, the magnetization is zero. In the narrow sense, strongly magnetic means ferromagnetic. When a ferromagnetic body reaches the Curie temperature, thermal vibration disrupts the alignment of the moments and the body becomes paramagnetic.
G

Gauss [G]

CGS unit expressing the magnetic flux density. It is named after the German physicist Johann Carl Friedrich Gauss. The magnetic flux density when 1 [Mx] of magnetic flux passes through a surface with an area of 1 [cm²] is 1 [G]. 1 [G] = 10^-4[T], the SI unit for magnetic flux density.
H

Hard disk drives (HDDs)

Magnetic recording devices mounted in computers and the like. A magnetic field is generated in the recording head, this generates magnetization in the magnetic bodies on the recording medium, and this records digital signals. Rare earth magnets are used in spindle motors for rotating the recording medium, voice coil motors (VCMs) for driving the magnetic head, etc.

Hard magnetic material

This means a magnetic material with a large coercive force and which is not easily demagnetized by external magnetic fields. This generally means a magnet or permanent magnet but magnetic recording materials can be called a type of hard magnetic material. Ferrite magnets, NdFeB family magnets, SmCo family magnets, and other rare earth magnets, platinum iron, platinum cobalt, FeCoCr alloys are among the representative magnetic material.

HEV (Hybrid Electric Vehicles)

HEV is the abbreviation for hybrid electric vehicle. These cars drive using either one or both of an electric motor and an internal combustion engine according to conditions. Hybrid electric vehicles, combining an electric motor and engine, are the parallel type, in which the motor assists the engine in starting off and acceleration and in which the motor generates power during breaking to recover electric power, the series type, in which the engine is used only for generating electricity, the vehicle is always driven by the electric motor, and electric power is recovered during braking, or the parallel-series type in which the use of the electric motor and engine is optimally controlled according to driving conditions. The series-parallel type primarily obtains its drive power from the electric motor during start-off and drives with both the engine and the motor when going at high speed. The engine always runs in the best state for fuel economy and generates electricity for storage as necessary. During deceleration, the braking energy is recovered and stored and serves as an energy source for starting off again. High-performance rare earth magnets are used for hybrid electric vehicle drive motors and electric generators and are spreading in markets around the world ahead of 100% motor-driven electric vehicles. There is a high probability of this type of vehicle developing a great deal in the future and new types, such as diesel hybrids and plug-in hybrids, are also under study.
I

Initial demagnetization

One definition of the drop in the amount of magnetic flux when a magnet is raised to high temperature. There is the reversible demagnetization portion, which is the amount the magnetization recovers if the magnet is remagnetized, and the permanent demagnetization portion, which is not recovered. In general, depending on the type of magnet and differences in the Curie temperature and even for the same type of magnet, the amount of demagnetization varies with the magnetic characteristics (primarily the coercive force) and magnet shape and magnetic circuit configuration (permeance coefficient) and the temperature the magnet is heated to. The higher the Curie temperature, the larger the coercive force, the larger the permeance coefficient, and the better the corrosion resistance of the magnet, the smaller the initial demagnetization. High-temperature demagnetization of a magnet is generated by a combination of initial demagnetization and change over time, as well as permanent demagnetization.

IPM motors (Interior Permanent Magnet Motors)

These are synchronous motors with rotating magnetic fields that have magnets embedded in the rotor. These motors can use both the torque due to magnet magnetization and the reluctance torque due to the rotor magnetization. Since the magnets are embedded in a rotor made from silicon steel plates or the like, the centrifugal force during motor rotation does not make the magnets fly out and the mechanical stability is high. It is possible to control the current phase to run with high torque or over a wide range of speeds, so these motors are energy saving, high efficiency, and high torque. In recent years, use has been expanding rapidly in electric vehicles, hybrid vehicles, high-performance air conditioners, large industrial motors, train motors, etc.

Isotropic magnets

This is a magnet whose crystal grains do not have their easy magnetization axis lined up in a specific direction and whose magnetic characteristic is isotropic. On the other hand, a magnet whose crystal grain directions are aligned and have their easy magnetization axis lined up is called an anisotropic magnet. Isotropic magnets include bond magnets using quick-cooled thin alloy as the raw material and isotropic ferrite magnets, but their magnetic characteristics are inferior to those of anisotropic magnets. Rare earth sintered magnets can not be made isotropic.
J

Jet mill

An air jet pulverizer. Such a machine pulverizes using the kinetic energy of a fluid without using a pulverizing medium such as balls. The raw material is caught up in the gas ejected from the nozzle at high pressure and the particles riding in the high-pressure gas collide with and pulverize each other due to the motion of the gas or the particles riding on the high-pressure gas collide with a collision plate and pulverized. Since rare earth alloys are generally active and react violently with oxygen, they are pulverized with a jet mill using high-pressure nitrogen gas with the oxygen removed.
L

Linear synchronous motors (LSMs)

A motor in which a needle having the secondary field magnet poles moves in a straight line state synchronized with the moving magnetic field generated on the primary side armature side. Since the needle is moved directly according to the signals input to the armature, the operation precision and capacity for high speed are superior. Linear synchronous motors using rare earth magnets provide large propulsion and quick response, so in recent years, their use has been greatly expanding.
M

Magnetic charge

The amount of magnetism at both ends of the magnetic dipoles. This corresponds to the electric charge for electricity. However, unlike electric load, magnetic charge does not exist independently and is always present in the state of magnetic dipoles. The units are the weber [Wb] for SI units and the electromagnetic unit [emu] for CGS units. A magnetic charge of 1 [Wb] in SI units generates 1 [Wb] of magnetic flux. In CGS units, the magnetic charge of 1 [emu] generates 1 dyne of force at a distance of 1 [cm]. 1 [Wb] = 10⁸/4π [emu]

Magnetic permeability

The value of the magnetic flux density B divided by the magnetic field H. The units are [H/m] for SI units and are an abstract number in the CGS units. The symbol is μ. The magnetic permeability in a vacuum is expressed as μ₀. In the SI unit system, μ₀ = 4π ×10^-7 [H/m] and in the CGS unit system, μ₀ = 1. On the other hand, the susceptibility is the magnetism polarization J divided by the magnetic field H and is written as χ[H/m]. (J = χH) Therefore, the magnetic flux density B = μ₀H+J = (μ₀+χ) H, so the magnetic permeability is the magnetic permeability in a vacuum and the magnetization ratio μ = (μ₀+χ). Also, the ratio of the magnetic permeability μ and the magnetic permeability in a vacuum μ₀ is called the specific magnetic permeability μ_r (=μ/μ₀).

Magnetization

This is the magnetic moment per unit volume. The units are the weber per meter squared [Wb/m²] or the tesla [T = Wb/m²] for SI units and the electromagnetic unit per square centimeter [emu/cm²] and the magnetization is expressed with the symbol I. 1 [Wb/m²] = 10⁴/4π [emu/cm²]. In the CGS units, the units of gauss [G] multiplied by 4π are often used and in this case, the magnetization is expressed with the symbols 4πI, giving 1 [T] = 10⁴ [G].

To Magnetize

The job of applying an adequate external magnetic field to a magnetic raw material that has not magnetization until the material is magnetically saturated. Even after the external magnetic field is removed, magnetization remains in the magnet raw materials. It is only at this point that the magnetic material is a permanent magnet. The strength of the external magnetic field required in order to obtain a magnetization state near saturation depends on the magnet type, coercive force (H_cJ), and shape. These conditions are called the magnetization characteristic of the magnet. Magnetization methods are the method using a static magnetic field and the method using a pulse magnetic field.

Magnetic domain

This is a small area in which the magnetic moment of a collection of magnetic dipoles are aligned. They exist within ferromagnetic bodies and ferrimagnetic bodies. In such magnetic bodies, if the spontaneous magnetization is all aligned in the same direction, this becomes an unstable state with extremely high magnetostatic energy. In order to avoid this, magnetic domains are finely divided into domains with appropriate size and direction. This is called a magnetic domain structure. The magnetic domains formed at this time create a structure in which the mutual magnetic moments cancel each other out or magnetic moments link with each other. As a result, the spontaneous magnetization of the overall magnetic body is reduced, giving the magnetic potential a more stable state.

Magnetic domain wall

This is a space in the magnetic domain structure of a magnetic body between magnetic domains and in which the magnetic moment of atoms invert continuously and little bit by little bit. When the magnetization directions of neighboring magnetic domains are 90° or 180°, they are called 90° magnetic domain walls and 180° magnetic domain walls. A domain wall at which the magnetic moments rotate around an axis in the direction perpendicular to the boundary surface is a Bloch domain wall and a domain wall at which the magnetic moments rotate around an axis in the surface inside (the thin film thickness direction) seen in a thin film is a Néel domain wall.

Magnetic dipole

Magnetic charge dipole. Unlike electricity, it is not possible to take out an independent magnetic pole (magnetic monopole), so the minimum unit for magnetism is not the magnetic pole, but rather the magnetic dipole.

Magnetic field

This is the field of force operating on the magnetic charge. It is also called the magnetic field. The units are the ampere/meter [A/m] for SI units and the oersted [Oe] for CGS units. The symbol for the magnetic field is H. 1 [A/m] = 4π·10^-3 [Oe]. On the Earth, there exists a magnetic field called geomagnetism.

Magnetic flux

This is the total quantity of magnetic force lines and corresponds in a magnetic circuit to the current in an electric circuit. This is obtained by integrating the flux density over the surface area. The symbol for the magnetic flux is φ. The units are the weber [Wb] for SI units and the Maxwell [Mx] for CGS units. 1 [Wb] = 10⁸ [Mx]

Magnetic flux density

This is the amount of magnetic flux per unit surface area. The units are the tesla [T] for SI units and the [G] for CGS units. The symbol for the magnetic flux density is B. The magnetic flux density within a magnetic body is the sum of the external magnetic field H and the magnetic body magnetic polarization J and in SI units is expressed as B=μ₀H+J. 1 [T] = 10⁴ [G]

Magnetic hysteresis loop

This is a loop showing the processing of magnetization of a magnetic body for an external magnetic field. Normally, this means the hysteresis loop of an adequately magnetized magnetic body. A curve plotting the magnetic polarization J change for an external magnetic field H is called the J-H curve and a curve plotting the change of the magnetic flux B for an external magnetic field H is called the B-H curve.

Magnetic moment

The strength of magnetic dipoles. The units are the weber meter [Wb·m] for SI units and the electromagnetic unit centimeter [emu·cm] for CGS units. The magnetic moment per unit volume is called the magnetization.

Magnetic resistance

This is the quantity in a magnetic circuit that corresponds to the resistance in an electric circuit. It is also called the reluctance. In a ring magnetic circuit with a magnetic permeability of μ, cross-section area S, and length L, if the current penetrating the ring is I and the magnetic flux within the ring body is φ, the relationship I=φL/μS is established. Comparing this to an electric circuit, the magnetomotive force I [A] corresponds to the electromotive force, the magnetic flux φ[Wb] passing through the magnetic circuit corresponds to the current, and Rm=L/μS corresponds to the electrical resistance and is called the magnetic resistance.

Magneto crystalline anisotropy

It is said that the magnetic characteristics of a material, in particular the stability of the magnetization of that material, depends on the crystalline anisotropy The reason for this is that the electron structure depends not only on the type of elements the magnet is composed of but also on its crystalline anisotropy. Fundamentally, this means that the ease of orientation for spontaneous magnetization depends on the crystalline anisotropy, but there are also cases in which it means that the secured coercive force, magnetization characteristics, etc. depend on the direction of the crystal. With iron single crystals, the [100] direction is easier to magnetize than the [110] and [111] directions and with nickel, the [111] direction is easier to magnetize than the [110] and [100] directions. The crystal direction that is easy to magnetize is called the easy magnetization axis (direction) and on the other hand the crystal direction that is difficult to magnetize is called the difficult magnetization axis (direction).

Magnetostriction

This is a slight deformation (warping) generated when a strongly magnetic body is magnetized. This is also called magnetic strain. The size depends on the intensity of spontaneous magnetization, the crystal axis directions, etc., but δL/L is a mere 10^-5 to 10^-6. Internal stress affects the magnetic domain structure and magnetization structure through magnetostriction and generates magnetic anisotropy. Magnetostriction is also one cause of strange noise in motors.

Magnetostatic energy

This is the magnetic potential energy generated when a magnetic body is present in a magnetic field. For a strongly magnetic body, even in the absence of an external magnetic field, magnetostatic energy is generated within the magnetic body by the internal magnetic field generated in the opposite direction from the magnetization (and called the diamagnetic field). The amount is the amount of work required for the magnetic poles to exist counter to the internal magnetic field at both ends of the magnetic body. A strongly magnetic body is given a magnetic domain structure in order to minimize this magnetostatic energy.

Maximum energy product

This is an index expressing the performance of a permanent magnet. The units are the joule per meter cubed [J/m³] for SI units and the gauss oersted [GOe] for CGS units and the maximum energy product is expressed as (BH)max. The product of H (taken as positive) and B at the point (H, B) on the B-H demagnetization curve is called the energy product and the maximum value of this product is the maximum energy product. This value shows a yardstick for the maximum amount of magnetic flux taken out from the magnet per unit volume. When a magnetic circuit is designed to come to the maximum energy product point, the magnet volume can be made smallest.

Maxwell [Mx]

CGS unit for magnetic flux. It is named after the British physicist James Clerk Maxwell. The maxwell has the relationship with the CGS unit for magnetic flux density, the gauss [G], of 1 [Mx] = 1 [G·cm²] and with the SI unit for magnetic flux, the weber [Wb], of 1 [Mx] = 10^-8 [Wb].

Minor loop

The working point of a magnet moves according to the usage conditions, but this movement generally is not along the demagnetization curve, but rather is a small loop within the hysteresis curves with the working point at the starting point. This curve is called a minor loop of the hysteresis curves and is a curve unique to the material. Also, see the section on recoil curves.

MRI (Magnetic Resonance Imaging)

MRI is the abbreviation for magnetic resonance imaging. It is a medical diagnostic device that captures cross-sectional images of the human body using nuclear magnetic resonance (NMR) of hydrogen atoms present within the body. For hydrogen atoms, the form of the electromagnetic signals generated by the nuclear magnetic resonance phenomenon differs according to the chemical and physical state of the body they are placed in. These signals are used to construct a k-space through 2-dimensional Fourier transformation and this information is presented as an image to obtain information about body tissue and lesions. Because MRIs can provide precise, detailed medical information, they have become an indispensable diagnostic technology for today's medicine. MRI devices require powerful spatial magnetic fields of 0.1T or more that are uniform to within 1/10^th of geomagnetism. In order to generate such uniform magnetic fields, large magnetic circuits with super-conducting magnets and rare earth magnets are used.
The term "nuclear magnetic resonance" includes the term "nuclear", but this has no connection whatsoever to nuclear fission or nuclear radiation. Unlike X-ray medical diagnostics, it is thought that the powerful external magnetic field used in NMR diagnostics has almost no affect on the human body and MRIs are safe and useful medical diagnostics devices.
N

Nanocomposite magnets

Magnets that have fine hard magnetic phases and soft magnetic phases, in which exchange bonding operation works between the phases and which behaves like one single-phase magnet. These magnets are called nanocomposite magnets because the size of the structure is on the nanometer (10^-9m) order. From this magnetic characteristic, they are also called exchange spring magnets. (See the item on exchange spring magnets.)

Neel temperature

Temperature at which an antiferromagnetic body transforms into a paramagnetic state. It is named after the French physicist Louis Neel.

Neutralization

Setting the magnetization of a magnetic body to 0. There are alternating neutralization that passes through a minor loop by alternatingly inverting the external magnetic field and thermal neutralization that erases the magnetization by raising a strongly magnetic body above its Curie point with no external magnetic field present, then cooling it. However, alternating neutralization can not bring the magnetization completely to zero. In particular, it is necessary to pay attention to the fact that when remagnetizing a neodymium sintered magnet after alternating neutralization, a strong magnetic field is necessary. Also, because the heating above the Curie temperature used in thermal neutralization affects the magnetic characteristics and surface treatment, in actual practice neutralization is often extremely difficult.
O

Oersted [Oe]

CGS unit for magnetic field strength. It was introduced by the Danish physicist and chemist Hans Christian φrsted. 1 oersted is the strength of the magnetic field when the force operating on a single magnetic pole is 1 [dyne]. 1[Oe]=(1/4π) x 10³ [A/m], SI magnetic field strength unit.
P

Parallel magnetic field press

A method of pressing a sintered magnet in which the direction of the magnetic field applied for orientation during the magnetic powder pressing is parallel to the molding press pressure direction. This is also called vertical magnetic field pressing. On the other hand, the pressing method in which the magnetic field direction and pressing direction are perpendicular is called perpendicular magnetic field pressing (horizontal magnetic field pressing). Because the orientation state of the magnetic particles is disrupted by the pressing punch pressure, the product's magnetic characteristic is lower than for perpendicular magnetic field pressing. However, in some cases the product shape and magnetization direction require the use of parallel magnetic field pressing.

Paramagnetism

A magnetic characteristic in which the magnetic moment in the material does not generate magnetization of the whole in various random directions in the absence of an external magnetic field, but when an external magnetic field is applied, the magnetic moments align in their own way according to the intensity of the magnetic field and generate magnetization. Such materials are called paramagnetic bodies.

Permanent magnet direct current motors

This is a synchronous magnetic motor that places permanent magnets on the stator and uses an electromagnet with its coil wound on a soft magnetic core as the rotor. The rotational force is obtained between the permanent magnets of the stator and the electromagnetic induction produced on the rotor by the current flowing while the brush magnet poles switch. This is the most popular type of motor using magnets and a large number are in use. The structure is simple and sturdy and the price is reasonable, so they are easy to use. In general, ferrite magnets are used for stator magnets, but in recent high-performance type motors, rare earth magnets have been coming into use.

Permanent magnet synchronous motors

This is a rotating magnetic field motor with a structure that combines permanent magnets with silicon steel sheets, iron, or the like as the rotor and on the other hand winds the armature on silicon steel sheets or iron as the stator. Since the motor rotation rate varies with the frequency of the field magnetic current flowing in the stator, the operation of the motor itself can be controlled with a DC inverter power supply. Because it is easy to electrically control the rotation rate, response speed, etc., this type of motor is used over a wide range as high-performance actuators for a variety of industrial motors. Two types can be roughly distinguished, the surface permanent magnet motor (SPM motor) that pastes permanent magnets on the rotor surface and the interior permanent magnet motor (IPM motor) that embeds permanent magnets within the rotor.

Permeance coefficient

A coefficient determined by the magnetic circuit and the shape of the magnet. If the permeance coefficient is p, the magnet's working point is the intersection of a straight line (the permeance line) drawn from the origin and having a slope of μ0p and the B-H demagnetization curve. The permeance coefficient is used in designing magnetic circuits. For a stand-alone magnet, if the magnet is shaped long and fine in the magnetization direction, the permeance coefficient found setting H positive is larger.

Perpendicular magnetic field pressing

A method of pressing a permanent magnet with single axis anisotropy in which the direction of the magnetic field applied in order to orient the magnetic powder within the magnetic field in the manufacturing process is perpendicular to the pressing pressure direction. This is also called horizontal magnetic field pressing. On the other hand, the pressing method in which the magnetic field direction and pressing direction are parallel is called parallel magnetic field pressing (vertical magnetic field pressing). Because the orientation state of the magnetic particles is not disrupted during pressing, the product's magnetic characteristic is higher than for parallel magnetic field pressing. However, in some cases the product shape and magnetization direction make perpendicular magnetic field pressing impossible.
R

Radial magnets

Cylinder anisotropic magnets whose easy magnetization axis direction is the radial direction. For radial anisotropy, the number of magnetic poles and the magnetization pattern of the magnet can be adjusted with the way the magnetization is performed and the cogging torque etc. can be adjusted through multi-pole and skew magnetization. Also, assembly in a motor rotor is generally easy, reducing motor manufacturing costs. However, from the perspective of magnet manufacture, the processes for manufacturing radial magnets are complex and the production efficiency and yield are poor, which raises costs. Also, in motor rotors, even at the changeover points between magnetic poles, in other words at the sections where magnetic flux is not generated, magnetic material is used, so compared to manufacture using segment magnets, the weight of magnets used is greater, which increases costs.

Rare earth elements

The general name for seventeen elements, the fifteen elements from lanthanum (atomic number 57) to lutetium (atomic number 71) and scandium (atomic number 21) and yttrium (atomic number 39). The rare earth elements have similar outer electron shell structures and ion radii, so they have similar chemical characteristics. They were first discovered in relatively rare minerals, so they are called the rare earth elements, but looking at the Earth's crust as a whole, the actual amount present is not that small. There is more cerium than copper and more yttrium, lanthanum, and neodymium than cobalt. They are contained in the carbonate mineral bastnaesite, the phosphate minerals xenotime and monazite, ion absorbing minerals, and other mineral ores, but currently, the majority of these minerals are produced in China. Rare earth elements are widely used in fluorescent bodies and media, magnetic materials, fine ceramics, semi-conductors, etc. and can be considered precious functional elements supporting contemporary civilization.

Rare earth magnets

The general name for permanent magnets whose main components are metal alloys of iron group transition elements and rare earth elements. These magnets can be roughly divided by manufacturing method into sintered magnets and bonded magnets. There are two types of typical magnetic alloys, the Sm-Co family and the Nd-Fe-B family. Compared to other permanent magnets, ferrite and alnico, rare earth magnets have clearly superior residual magnetic flux density B_r , coercive force H_cJ , maximum energy product (BH)_max , etc. They are used in many industrial products that are representative of contemporary society, from industrial motors to computers, appliances, cell phones, automobiles, etc. Rare earth magnets are becoming indispensable materials for smaller size and higher performance of such equipment and device.

Recoil curve

In a magnetic circuit, the B-H history curve when the working point of a magnet changes with change in the external magnetic field. This B-H history curve does not necessarily match the B-H demagnetization curve and can be a minor loop within the B-H demagnetization curves. For a permanent magnet, the loop is fine enough to approximate with a straight line and is also called the recoil line. Also, the specific magnetic permeability for the recoil line is called the recoil permeability.

Residual magnetic flux density (remanence)

In the magnetic hysteresis loops showing the magnetic characteristics of a material, the remanence is the value of the flux density remaining when the external field returns from the high value of saturation magnetization to 0. The remanence is also called the residual magnetization. The higher the value, the higher the useable magnetic flux density. The units are the tesla [T] for SI units and the gauss [G] for CGS units and the remanence is expressed as Br. For an isotropic material, the remanence is about 50% to 75% of the saturation magnetization, but for rare earth sintered magnet material, because the easy magnetization axis direction is oriented in the magnetization direction, the remanence is about 95% or more of the saturation magnetization.
S

Saturation magnetization

The saturation value of magnetization of a ferromagnetic body. The inside of the magnetic body is normally divided into any number of domains, but accompanying increase in the external magnetic field, domain walls may move and magnetization may rotate within domains, so ultimately the magnetic body becomes one domain (single-domain state). If the easy magnetization axis and the external magnetic field direction match, this state is called magnetization saturation and the value of the magnetization at this time is called the saturation magnetization.

Shear modulus

This is one type of modulus of elasticity and is also called the shearing modulus or shear modulus of elasticity. Thinking about an elastic square column, if a shear stress τ works on the bottom surface and surfaces parallel to it, the side surfaces of the square column deforms into a diamond shape with an apex of 90°±γ. At this time, in the range for which Hook's law is valid, there is the proportionality relationship τ=Gγ. This coefficient G is the shear modulus. The units are pascals [Pa]. This value is sometimes used to show the mechanical strength of a magnet.

Sintered magnet

A magnet produced with what is called a powder metallurgical process. Currently, a sintered magnet often means a rare earth sintered magnet. After the magnet alloy is finely pulverized, the easy magnetization axis is aligned in the magnetic field, the material is press molded, then it is sintered. Since the sintering contraction is large, the dimensional precision is poor and generally, processing is required after sintering. Compared to bond magnets produced by mixing in plastic, since there is no plastic or other non-magnetic section, the magnetic characteristics are high and the heat resistance is superior.

Soft magnetic material

Magnetic material whose magnetization and permeability are large and in which the magnetization varies with the external magnetic field direction and size Soft magnetic material is used to strengthen the magnetic field generated by the coil and permanent magnet and used as the path of the magnetic flux generated. Soft magnetic material is used in transformer and motor iron cores etc.

SPM motors (Surface Permanent Magnet Motors)

These are synchronous motors with rotating magnetic fields that have a shape formed by embedding magnets in the surface of the rotor. They use the strong magnetism of the magnets for good motor torque linearity and superior control. Optimizing the magnet shapes provides motors with low cogging torque. On the other hand, there are problem points, for example the brittleness of the glued structure. In recent years, because of their advantages for energy conservation, clean energy, etc., the application of surface permanent magnet motors is expanding. They are used in some electric cards and electric power steering and also in a variety of industrial motors.

Spontaneous magnetization

This is magnetization that occurs in the state in which a magnetic body has its atomic magnetic moments aligned without being affected by an external magnetic field. Normally, magnetic bodies have a magnetic domain structure and it is observed that spontaneous magnetization does not occur, but spontaneous magnetization is measured in single crystals and other single domain states. For a strongly magnetic body, spontaneous magnetization is maximum at absolute zero degrees. As the temperature rises, the magnetic moment of each atom decreases due to heat fluctuation and it disappears at the Curie temperature.

Stepping motors

A motor that is rotated in units of a certain step angle by pulse electrical power. The rotation angle varies with the number of input pulses and the rotation speed varies with the input frequency so operating of a stepping motor can be controlled without feedback. Stepping motors are widely used as drive sources for positioning control in factory automation and office automation related equipment.
T

Tesla [T]

The SI unit of magnetic flux density Named after the Croatian-born American electrical engineer Tesla. The magnetic flux density when 1 [Wb] of magnetic flux passes through a surface with an area of 1 [m²] is 1 [T]. 1 [T] = 10^-4[G], the CGS unit for magnetic flux density.

Thermal coefficient of coercive force (Hcj)

The coercive force Hcj of magnets varies with the temperature. The slope when this thermal change is approximated with a straight line is called the thermal coefficient of coercive force. The unit is per cent per kelvin [%/K]. Rare earth magnets generally have a negative value for this coefficient and the smaller the absolute value, the less the change of the coercive force H_cJ with temperature. For Nd-Fe-B family magnets, this coefficient has values about from -0.40 to -0.65 [%/K] and for SmCo family magnets, this coefficient has values about from -0.17 to -0.25 [%/K].

Thermal coefficient of remanence (Br)

Coefficient when the thermal change of the remanence is approximated with a straight line with the temperature as a variable. The unit is per cent per kelvin [%/K]. The thermal coefficient of remanence generally has a negative value and the smaller the absolute value, the less the change of the remanence with temperature. For SmCo family magnets, the change in remanence with temperature is about 0.03 to 0.04 [%/K] and for NdFeB family magnets, about 0.09 to 0.11 [%/K], which is smaller change with temperature than for ferrite magnets at 0.19 [%/K].

Thermal conductivity

Value indicating the ease with which heat is transmitted from the high-temperature section to the low-temperature section. The thermal conductivity is expressed as the amount of heat flowing perpendicularly across the unit equal-temperature surfaces in a unit time and the temperature difference per unit length in that direction. The unit is [W/m·K].
V

VCMs (Voice Coil Motors)

Original, voice coil motor referred to the linear actuators that drive the coils of speakers, but recently the motors for driving hard disk drive (HDD) heads are also called voice coil motors. Voice coil motors for hard disk drives usually have a structure that places a coil between two magnet sheets and drive the suspension arm with the force generated by the magnetic field and the current flowing in the coil. The detection head is mounted on the suspension arm. (See the page with the magnet application examples.) One or two neodymium rare earth magnet sheets are used in voice coil motors for various hard disk drives. With recent hard disk drive size reductions, voice coil motors themselves are becoming smaller, so stronger yet smaller rare earth magnets are required.

Vickers hardness

This is one scale expressing the hardness of a material. This hardness is defined from the ratio of the load when a diamond indenter with the shape of a square-based pyramid with an angle of 136° between opposite faces is pressed into the test piece as one term and the surface area of the indentation that results as the other term. Vickers hardness is widely used for metal materials, especially for hard materials such as magnets.
W

Weber [Wb]

This is the SI unit for the total amount of magnetic flux. It was named in honor of the German physicist Wilhelm Eduard Weber. 1 [Wb] is the amount of magnetic flux induced by electromagnetic inductance for a 1 electromotive force when the magnetic flux moves uniformly for 1 second in a coil with one winding. 1 [Wb] = 1 [V·s]. 1 [Wb] = 10⁸ [Mx], the CGS magnetic flux unit. The unit for the magnetic charge is also the weber.

Working point

This is a point on the magnet's B-H demagnetization loop and indicates the B and H state of the magnet in the magnetic circuit. By knowing the working point, it is possible to forecast the magnetic flux density B that can be taken out from the magnetic circuit and whether or not the magnet itself demagnetizes. Also, the straight line drawn from the origin to this point is called the permeance line and when the slope of this line is expressed as B/H = μ₀ p, p is called the permeance coefficient.
Y

Young's modulus

This is one type of modulus of elasticity and is also called the elongation elasticity modulus. If T is the stress working on the cross-section when a rod of uniform thickness is fastened at one end and the other end is pulled in the axial direction and ε is the elongation per unit length, then the proportional relationship T=Eε (Hook's law) holds within a certain range. The proportionality constant E in this equation is called Young's modulus. The units are pascals [Pa]. This value is used when thinking about the mechanical characteristics of a magnet.

For inquiries regarding rare earth magnets