magnetization

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WordNet

1. the extent or degree to which something is magnetized (同)magnetisation
2. the process that makes a substance magnetic (temporarily or permanently) (同)magnetisation, magnetic induction
3. the physical property of being magnetic (同)magnetisation
4. attract strongly, as if with a magnet; "She magnetized the audience with her tricks" (同)mesmerize, mesmerise, magnetise, bewitch, spellbind
5. make magnetic; "The strong magnet magnetized the iron shavings" (同)magnetise
6. the process of removing magnetization (同)demagnetisation

PrepTutorEJDIC

1. 磁気を除くこと,消磁

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/06/07 16:54:54」(JST)

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This article is about magnetization as it appears in Maxwell's equations of classical electrodynamics. For a microscopic description of how magnetic materials react to a magnetic field, see magnetism. For mathematical description of fields surrounding magnets and currents, see magnetic field.

Electromagnetism
Electricity Magnetism
Electrostatics Electric charge Static electricity Electric field Conductor Insulator Triboelectricity Electrostatic discharge Induction Coulomb's law Gauss's law Electric flux / potential energy Electric dipole moment Polarization density
Magnetostatics Ampère's law Magnetic field Magnetization Magnetic flux Biot–Savart law Magnetic dipole moment Gauss's law for magnetism
Electrodynamics Lorentz force law Electromagnetic induction Faraday's law Lenz's law Displacement current Maxwell's equations Electromagnetic field Electromagnetic radiation Maxwell tensor Poynting vector Liénard–Wiechert potential Jefimenko's equations Eddy current London equations
Electrical network Electric current Electric potential Voltage Resistance Ohm's law Series circuit Parallel circuit Direct current Alternating current Electromotive force Capacitance Inductance Impedance Resonant cavities Waveguides
Covariant formulation Electromagnetic tensor (stress–energy tensor) Four-current Electromagnetic four-potential
Scientists Ampère Coulomb Faraday Gauss Heaviside Henry Hertz Lorentz Maxwell Tesla Volta Weber Ørsted

In classical electromagnetism, magnetization or magnetic polarization is the vector field that expresses the density of permanent or induced magnetic dipole moments in a magnetic material. The origin of the magnetic moments responsible for magnetization can be either microscopic electric currents resulting from the motion of electrons in atoms, or the spin of the electrons or the nuclei. Net magnetization results from the response of a material to an external magnetic field, together with any unbalanced magnetic dipole moments that may be inherent in the material itself; for example, in ferromagnets. Magnetization is not always homogeneous within a body, but rather varies between different points. Magnetization also describes how a material responds to an applied magnetic field as well as the way the material changes the magnetic field, and can be used to calculate the forces that result from those interactions. It can be compared to electric polarization, which is the measure of the corresponding response of a material to an electric field in electrostatics. Physicists and engineers define magnetization as the quantity of magnetic moment per unit volume. It is represented by a vector M.

Definition

Magnetization can be defined according to the following equation:

Here, M represents magnetization; m is the vector that defines the magnetic moment; V represents volume; and N is the number of magnetic moments in the sample. The quantity N/V is usually written as n, the number density of magnetic moments. The M-field is measured in amperes per meter (A/m) in SI units.

Magnetization in Maxwell's equations

The behavior of magnetic fields (B, H), electric fields (E, D), charge density (ρ), and current density (J) is described by Maxwell's equations. The role of the magnetization is described below.

Relations between B, H, and M

Main article: Magnetic field

The magnetization defines the auxiliary magnetic field H as

(SI units)

(Gaussian units)

which is convenient for various calculations. The vacuum permeability μ₀ is, by definition, 4π×10⁻⁷ V·s/(A·m).

A relation between M and H exists in many materials. In diamagnets and paramagnets, the relation is usually linear:

where χ_m is called the volume magnetic susceptibility.

In ferromagnets there is no one-to-one correspondence between M and H because of Magnetic hysteresis.

Magnetization current

The magnetization M makes a contribution to the current density J, known as the magnetization current or bound (volumetric) current:

and for the bound surface current:

so that the total current density that enters Maxwell's equations is given by

where J_f is the electric current density of free charges (also called the free current), the second term is the contribution from the magnetization, and the last term is related to the electric polarization P.

Magnetostatics

Main article: Magnetostatics

In the absence of free electric currents and time-dependent effects, Maxwell's equations describing the magnetic quantities reduce to

$\begin{align} \mathbf{\nabla\cdot H} &= -\nabla\cdot\mathbf{M}\\ \mathbf{\nabla\times H} &= 0 \end{align}$

Where Magnetization is volume density of magnetic moment. That is: if a certain volume has magnetization then the volume element has a magnetic moment of

These equations can be solved in analogy with electrostatic problems where

$\begin{align} \mathbf{\nabla\cdot E} &= \frac{\rho}\epsilon_0\\ \mathbf{\nabla\times E} &= 0 \end{align}$

In this sense plays the role of a fictitious "magnetic charge density" analogous to the electric charge density (see also demagnetizing field).

It is important to note that there is no such thing as a "magnetic charge," but that issue was still debated through the whole 19th century. Other concepts, that went along with it, such as the auxiliary field H, also have no real physical meaning in their own right. However, they are convenient mathematical tools, and are therefore still used today for applications such as modeling the magnetic field of the Earth.

Magnetization dynamics

Main article: Magnetization dynamics

The time-dependent behavior of magnetization becomes important when considering nanoscale and nanosecond timescale magnetization. Rather than simply aligning with an applied field, the individual magnetic moments in a material begin to precess around the applied field and come into alignment through relaxation as energy is transferred into the lattice.

Demagnetization

In addition to magnetization, there is also demagnetization. Demagnetization is the process by which the magnetic field of an object is reduced or eliminated. The process of demagnetizing can be accomplished in many ways. One technique used for demagnetization is to heat the object above its Curie Temperature. The reason for this is that when a magnetic material is heated to its Curie Temperature, thermal fluctuations have enough energy to overcome the exchange interactions which cause ferromagnetism, and magnetic ordering is destroyed. One other way of achieving demagnetization is to use an electric coil. If the object is retracted out of a coil with alternating current running through it, the object's dipoles will become randomized and the object will be demagnetized.

Applications of Demagnetization

One application of demagnetization is to eliminate unwanted magnetic fields. The reason for doing this is that magnetic fields can have unwanted effects on different devices. In particular magnetic fields can affect electronic devices such as cell phones or computers. If such a device is going to be coming into contact with other possibly magnetic objects, the magnetic fields might need to be reduced in order to protect the electronic device. Therefore demagnetization is sometimes used to keep magnetic fields from damaging electrical devices.

See also

• Permeability (electromagnetism)
• Magnetic susceptibility
• Earth's magnetic field
• Geomagnetic reversal
• Geomagnetic excursion
• Orbital magnetization

The dictionary definition of magnetization at Wiktionary

Sources

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English Journal

• Effect of Annealing in Magnetic Field on Ferromagnetic Nanoparticle Formation in Cu-Al-Mn Alloy with Induced Martensite Transformation.

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• Magnetic-Field-Assisted Assembly of Anisotropic Superstructures by Iron Oxide Nanoparticles and Their Enhanced Magnetism.

• Jiang C1, Leung CW2, Pong PW3.
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• Nanometer Scale Hard/Soft Bilayer Magnetic Antidots.

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• Ji F1,2,3, Xu M4, Wang C5,6, Li X2, Gao W2, Zhang Y2, Wang B2,3, Tang G2, Yue X2.
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Japanese Journal

• Multifunctional Material: Bistable Metal-Cyanide Polymer of Rubidium Manganese Hexacyanoferrate

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• Magnetic and fluorescence properties of cerium-doped yttrium gadolinium aluminum iron garnet crystals

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• Jpn. J. Appl. Phys. 53(11), 113001, 2014-10-07
• … The saturation magnetization for the sample with x = 0 and y = 3.0 is 4.35 emu/g, while that with x = 2.5 and y = 3.0 is 87.5 emu/g. …
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• 磁化（Magnetization）｜マグネット用語集｜希土類磁石の基礎 ...

磁化（Magnetization） 単位体積あたり磁気モーメントのこと。単位はSI単位ではウェーバ毎平方メートル[Wb/m 2]あるいはテスラ[T = Wb/m 2]、CGS単位では電磁単位毎平方センチメートル〔emu/cm 2 〕で、Iの記号で表す。1[Wb/m 2]=10 4 /4π[emu/cm ...

• Magnetization definition of Magnetization in the Free Online ...

magnetization [‚mag·nəd·ə′zā·shən] (electromagnetism) The property and in particular, the extent of being magnetized; quantitatively, the magnetic moment per unit volume of a substance. Also known as magnetic dipole density ...

• Magnetization - ResearchGate

ResearchGate is a network dedicated to science and research. Connect, collaborate and discover scientific publications, jobs and conferences. All for free. ... Particles with less magnetization , large particle size (~250nm) but large ...

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magnetization

　 　

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「demagnetization」

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demagnetize