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Encyclopedia > Magnetization

Magnetization is a property of some materials (e.g. magnets) that describes to what extent they are affected by magnetic fields, and also determines the magnetic field that the material itself creates. Magnetization is defined as the amount of magnetic moment per unit volume. The origin of the magnetic moments that create the magnetization can be either microscopic electric currents corresponding to the motion of electrons in atoms, or the spin of the electrons. It has been suggested that this article or section be merged with Magnetism. ... Current (I) flowing through a wire produces a magnetic field () around the wire. ... A bar magnet. ... Electric current is by definition the flow of electric charge. ... e- redirects here. ... Properties In chemistry and physics, an atom (Greek ἄτομος or átomos meaning indivisible) is the smallest particle still characterizing a chemical element. ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ...


In some materials (e.g., ferromagnets) magnetization can exist even without an external magnetic field (spontaneous magnetization). In other types of materials, magnetization is induced only when an external magnetic field is present. Magnetization is not always homogeneous within a body, but rather a function of position. A ferromagnet is a piece of ferromagnetic material, in which the microscopic magnetized regions, called domains, have been aligned by an external magnetic field (e. ... Spontaneous magnetization is the term used to describe the appearance of an ordered spin state at zero applied magnetic field in a ferromagnetic or ferrimagnetic material below a critical point called the Curie temperature or TC. At temperatures above TC, the material is paramagnetic and its magnetic behavior is dominated... In physics, homogeneity is the quality of having all properties independent of the position. ...

Contents

Magnetization in Maxwell's equations

The behavior of magnetic fields (mathbf{B}, mathbf{H}), electric fields (mathbf{E}, mathbf{D}), charge density (rho,), and current density (mathbf{J}) is described by Maxwell's equations. The role of the magnetization is described below. Current (I) flowing through a wire produces a magnetic field () around the wire. ... In physics, an electric field or E-field is an effect produced by an electric charge that exerts a force on charged objects in its vicinity. ... Charge density is the amount of electric charge per unit volume. ... In electricity, current is the rate of flow of charges, usually through a metal wire or some other electrical conductor. ... In electromagnetism, Maxwells equations are a set of equations, developed in the latter half of the nineteenth century by James Clerk Maxwell. ...


Relations between B, H and M

The magnetization defines the auxiliary magnetic field mathbf{H} as

which is convenient for various calculations.


A relation between mathbf{M} and mathbf{H} exists in many materials. In diamagnets and paramagnets, the relation is usually linear: Diamagnetism is a very weak form of magnetism that is only exhibited in the presence of an external magnetic field. ... Simple Illustration of a paramagnetic probe made up from miniature magnets. ...

mathbf{M} = chi_mmathbf{H}

where chi_m, is called the magnetic susceptibility. In physics and electrical engineering, the magnetic susceptibility is the degree of magnetization of a material in response to an applied magnetic field. ...


In ferromagnets there is no one-to-one correspondence between mathbf{M} and mathbf{H} because of hysteresis. A ferromagnet is a piece of ferromagnetic material, in which the microscopic magnetized regions, called domains, have been aligned by an external magnetic field (e. ... Hysteresis is a property of systems (usually physical systems) that do not instantly follow the forces applied to them, but react slowly, or do not return completely to their original state: that is, systems whose states depend on their immediate history. ...


Magnetization current

The magnetization mathbf{M} makes a contribution to the current density mathbf{J}, known as the magnetization current or bound current: In electricity, current is the rate of flow of charges, usually through a metal wire or some other electrical conductor. ...

mathbf{J_m} = nablatimesmathbf{M}

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

mathbf{J} = mathbf{J_f} + nablatimesmathbf{M} + frac{partialmathbf{P}}{partial t}

where mathbf{J_f} is the electric current density of free charges, the second term is the contribution from the magnetization, and the last term is related to the electric polarization mathbf{P}. In classical electromagnetism, the polarization density (or electric polarization, or simply polarization) is the vector field that expresses the density of permanent or induced electric dipole moments in a dielectric material. ...


Magnetostatics

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

These equations can be easily solved in analogy with electrostatic problems where Electrostatics is the branch of physics that deals with the force exerted by a static (i. ...

mathbf{nablacdot E} = frac{rho}epsilon_0 qquad qquad qquad mathbf{nablatimes E} = 0

In this sense plays the role of a "magnetic charge density" analogous to the electric charge density rho,.


Magnetization is volume density of magnetic moment. That is: if a certain volume has magnetization mathbf{M} then volume element dV has magnetic moment of d mathbf{m} = mathbf{M} dV. A bar magnet. ...


Types of magnetism

Diamagnetism

This is the most common magnetic behavior. The diamagnetic magnetization is proportional and opposing to the applied magnetic field. All materials present a diamagnetic response, although it may be shadowed by stronger magnetic behaviors. Diamagnetism can be explained by the normal response of the orbiting electrons considering the Lenz's law. This is a weak form of magnetism that is non permanent and persists only while external field is applied. The magnitude of induced magnetic moment is very small and in a direction opposite to that of applied field.Therefore, relative permeability is less than 1 and magnetic susceptiveness is negative. When placed between the poles of a strong electromagnet, diamagnetic materials are attracted towards the region where field is weak. Diamagnetism is a very weak form of magnetism that is only exhibited in the presence of an external magnetic field. ... e- redirects here. ... Lenzs law (pronounced (IPA) ) was formulated by German physicist Heinrich Lenz in 1833 and gives the direction of the induced electromotive force (emf) resulting from electromagnetic induction. ...


Paramagnetism

Paramagnetic materials present a magnetization that is proportional to the applied field and reinforces it. This arises from the existence of magnetic dipoles in the material. Paramagnetism varies inversely with temperature and is characterized by the material's saturation magnetization. Paramagnetism is the tendency of the atomic magnetic dipoles, due to quantum-mechanical spin, in a material that is otherwise non-magnetic to align with an external magnetic field. ... This article is about the electromagnetic phenomenon. ... Look up inverse in Wiktionary, the free dictionary. ... Fig. ...


Superparamagnetism

Superparamagnetic materials are paramagnetic materials whose magnetization saturates at very large fields. They are obtained using magnetic nanoparticle aggregates with large net magnetic moments. Each particle is a single magnetic domain . Consequently, the alignment of spins under applied field is no longer impeded by domain walls. Above the blocking temperature, thermal vibrations randomly fluctuate the net spins, cancelling one another and the net moment of the collective particles is zero at zero field (no coercive field). If a magnetic field is applied, the particles will align producing a net moment. This behavior is characteristic of paramagnetic materials, but the difference is that each nanoparticle has a large net moment, so the saturation of magnetization occurs at very large fields of several Tesla. It has been suggested that this article or section be merged into Superparamagnetic effect. ...


Ferromagnetism

Ferromagnetic materials present a magnetization much larger than other materials. Ferromagnetism arises from the strong coupling between the magnetic dipoles in the material. Ferromagnetic materials can present spontaneous magnetization, and this gives rise to the hysteresis loops. Ferromagnetic materials can be characterized by their permeability, Curie temperature (temperature of the phase change to paramagnetic behavior), coercive field (field strength needed do demagnetize the material) and remnant magnetization (magnetization at zero external field). Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ... Hysteresis is a property of systems (usually physical systems) that do not instantly follow the forces applied to them, but react slowly, or do not return completely to their original state: that is, systems whose states depend on their immediate history. ... In electromagnetism, permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. ... In physics, the Curie point, or Curie temperature, is the temperature above which a ferromagnet loses its ferromagnetic ability to possess a net (spontaneous) magnetization in the absence of an external magnetic field. ...


See also

Look up magnetization in Wiktionary, the free dictionary.

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