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Spontaneous magnetization
 
 
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Spontaneous magnetization is the term used to describe the appearance of an ordered spin
Spin (physics)

In quantum mechanics, spin is a fundamental property of atomic nucleus, hadrons, and elementary particles. For particles with non-zero spin, spin direction is an important intrinsic degrees of freedom ....
 state (magnetization
Magnetization

Magnetization is defined as the quantity of magnetic moment per unit volume. 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....
) at zero applied magnetic field in a ferromagnetic or ferrimagnetic material below a critical point called the Curie temperature or TC.






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Spontaneousmagnetization
Spontaneous magnetization is the term used to describe the appearance of an ordered spin
Spin (physics)

In quantum mechanics, spin is a fundamental property of atomic nucleus, hadrons, and elementary particles. For particles with non-zero spin, spin direction is an important intrinsic degrees of freedom ....
 state (magnetization
Magnetization

Magnetization is defined as the quantity of magnetic moment per unit volume. 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....
) 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 by spin wave
Spin wave

Spin waves are propagating disturbances in the ordering of magnetic materials. These low-lying collective excitations occur in magnetic lattices with continuous symmetry....
s or magnon
Magnon

A magnon is a collective excitation of the electron' spin structure in a crystal lattice. In contrast, a phonon is a collective excitation of the crystal lattice atoms or ions....
s, which are boson
Boson

In particle physics, bosons are subatomic particle which obey Bose-Einstein statistics; they are named after Satyendra Nath Bose and Albert Einstein....
 collective excitations with energies in the meV range. The magnetization that occurs below TC is a famous example of the "spontaneous" breaking
Spontaneous symmetry breaking

In physics, spontaneous symmetry breaking occurs when a system that is symmetry in physics with respect to some symmetry group goes into a vacuum state that is not symmetric....
 of a global symmetry, a phenomenon that is described by Goldstone's theorem. The term "symmetry breaking" refers to the choice of a magnetization direction by the spins, which have spherical symmetry above TC, but a preferred axis (the magnetization direction) below TC.

To first order, the temperature dependence of spontaneous magnetization is given by Bloch's Law
Felix Bloch

Felix Bloch was a Switzerland physicist, working mainly in the U.S....
. The decrease in spontaneous magnetization at higher temperatures is caused by the increasing excitation of spin waves. In a particle description, the spin waves correspond to magnons, which are the massless Goldstone boson
Goldstone boson

In particle physics and condensed matter physics, Goldstone bosons are bosons that appear in models with spontaneously broken symmetry. First formulated by Jeffrey Goldstone, the Goldstone bosons correspond to the broken symmetry generators ? they can be thought of as the excitations of the field in the symmetric "directions" ? and are mass...
s corresponding to the broken symmetry
Continuous symmetry

In mathematics, continuous symmetry is an intuitive idea corresponding to the concept of viewing some symmetries as Motion s, as opposed to e.g....
.

See also

  • Magnetization
    Magnetization

    Magnetization is defined as the quantity of magnetic moment per unit volume. 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....
  • Ferromagnetism
    Ferromagnetism

    Ferromagnetism is the basic mechanism by which certain materials form permanent magnets and/or exhibit strong interactions with magnets; it is responsible for most phenomena of magnetism Magnet#Common uses of magnets ....
  • Ferrimagnetism
    Ferrimagnetism

    In physics, a ferrimagnetic material is one in which the magnetic moment of the atoms on different sublattices are opposed, as in antiferromagnetism; however, in ferrimagnetic materials, the opposing moments are unequal and a spontaneous magnetization remains....


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