Magnon

Magnon

A magnon is a collective excitation of the electrons' spin structure in a crystal lattice. In contrast, a phonon is a collective excitation of the crystal lattice atoms or ions. In the equivalent wave picture of quantum mechanics, a magnon can be viewed as a quantized spin wave. As a quasiparticle, a magnon carries a fixed amount of energy and lattice momentum. It also possesses a spin of ħ (where ħ is the reduced Planck constant).

Brief history

  • The concept of a magnon was introduced in 1930 by Felix Bloch in order to explain the reduction of the spontaneous magnetization in a ferromagnet. At absolute zero temperature, a ferromagnet reaches the state of lowest energy, in which all of the atomic spins (and hence magnetic moments) point in the same direction. As the temperature increases, more and more spins deviate randomly from the common direction, thus increasing the internal energy and reducing the net magnetization. If one views the perfectly magnetized state at zero temperature as the vacuum state of the ferromagnet, the low-temperature state with a few spins out of alignment can be viewed as a gas of quasiparticles, in this case magnons. Each magnon reduces the total spin along the direction of magnetization by one unit of ħ and the magnetization itself by γħ , where γ is the gyromagnetic ratio.
  • The quantitative theory of quantized spin waves, or magnons, was developed further by Theodore Holstein and Henry Primakoff (1940) and Freeman Dyson (1956). By using the formalism of second quantization they showed that the magnons behave as weakly interacting quasiparticles obeying the Bose-Einstein statistics (the bosons).
  • For a brief outline of the theory see spin wave. A comprehensive treatment can be found in Kittel's textbook or in the article by Van Kranendonk and Van Vleck.
  • A direct experimental detection of magnons by means of inelastic neutron scattering in ferrite was achieved in 1957 by Bertram Brockhouse. Since then magnons have been detected in ferromagnets, ferrimagnets, and antiferromagnets.
  • The fact that magnons obey the Bose-Einstein statistics was confirmed at latest by the light scattering experiments from magnons in 1960s-1980s. According to the classical theory the intensity of the Stokes and anti-Stokes lines in the light scattering spectrum should be the same. However, experimentally it was shown that if the energy of magnon ħω is comparable or smaller than the thermal energy kBT, the Stokes line becomes more intensive as it is followed from the Bose-Einstein statistics. The effect of Bose-Einstein condensation of magnons was proven recently in an antiferromagnet at low temperatures by Nikuni et al. and in a ferrimagnet by Demokritov et al. at room temperature. See the news report by Schewe and Stein and the scientific articles by Nikuni et al. and Demokritov et al. for more details.

See also

References

  • C. Kittel, Introduction to Solid State Physics, 7th edition (Wiley, 1995). ISBN 0-471-11181-3.
  • F. Bloch, Z. Physik 61, 206 (1930).
  • T. Holstein and H. Primakoff, Phys. Rev. 58, 1098 (1940). online
  • F. J. Dyson, Phys. Rev. 102, 1217 (1956). online
  • B. N. Brockhouse, Phys. Rev. 106, 859 (1957). online
  • J. Van Kranendonk and J. H. Van Vleck, Rev. Mod. Phys. 30, 1 (1958). online
  • T. Nikuni, M. Oshikawa, A. Oosawa, and H. Tanaka, Phys. Rev. Lett. 84, 5868 (1999). online
  • S. O. Demokritov, V. E. Demidov, O. Dzyapko, G. A. Melkov, A. A. Serga, B. Hillebrands, and A. N. Slavin, Nature 443, 430 (2006).online
  • P. Schewe and B. Stein, Physics News Update 746, 2 (2005). online
  • A.V. Kimel, A. Kirilyuk and T.H. Rasing, Laser & Photon Rev. 1, No. 3, 275-287 (2007). online

Wikimedia Foundation. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • Magnon — Les magnons sont des modes d excitation ou ondes de spin. Dans un milieu ferromagnétique isotrope en dessous de la température de Curie, ou dans un milieu antiferromagnétique en dessous de la température de Néel, les moments magnétiques des… …   Wikipédia en Français

  • MAGNON — MAG Quasi particule utilisée en théorie quantique du ferromagnétisme, de l’antiferromagnétisme et du ferrimagnétisme pour décrire les états collectifs faiblement excités représentés par les «ondes de spin». Dans certains corps cristallisés,… …   Encyclopédie Universelle

  • Magnon — Illustration eines ferromagnetischen Magnons. Als Magnon bzw. Magnon Quasiteilchen bezeichnet man den elementaren Anregungszustand einer magnetischen Spinwelle in Festkörpern. Voraussetzung dafür ist das Vorhandensein einer magnetischen Ordnung,… …   Deutsch Wikipedia

  • Magnon — magnonas statusas T sritis fizika atitikmenys: angl. magnon vok. Magnon, n rus. магнон, m pranc. magnon, m …   Fizikos terminų žodynas

  • magnon — magnonas statusas T sritis fizika atitikmenys: angl. magnon vok. Magnon, n rus. магнон, m pranc. magnon, m …   Fizikos terminų žodynas

  • magnon — ▪ physics       small quantity of energy corresponding to a specific decrease in magnetic (magnet) strength that travels as a unit through a magnetic substance.       In a magnetic substance, such as iron, each atom acts as a small individual… …   Universalium

  • Magnon Solutions — is a web design firm based in New Delhi, India. Smart Techie awarded them one of the Top 25 Most Promising Internet Companies in India. [1] Magnon s CEO, Vineet Bajpai, has been featured on CNBC and has authored a book on entrepreneurship titled… …   Wikipedia

  • Magnon-Magnon-Wechselwirkung — magnonų sąveika statusas T sritis fizika atitikmenys: angl. magnon magnon interaction vok. Magnon Magnon Wechselwirkung, f rus. магнон магнонное взаимодействие, n pranc. interaction magnon magnon, f …   Fizikos terminų žodynas

  • magnon-magnon interaction — magnonų sąveika statusas T sritis fizika atitikmenys: angl. magnon magnon interaction vok. Magnon Magnon Wechselwirkung, f rus. магнон магнонное взаимодействие, n pranc. interaction magnon magnon, f …   Fizikos terminų žodynas

  • magnon spectrum — magnonų spektras statusas T sritis fizika atitikmenys: angl. magnon spectrum vok. Magnonenspektrum, n; Magnonspektrum, n rus. магнонный спектр, m; спектр магнонов, m pranc. spectre des magnons, m; spectre magnonique, m …   Fizikos terminų žodynas

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”