Ferromagnetism

of three examples of a ferrousmagnetic order of a linear chain of magnetic moments.

The ferromagnetism (v. lat.: ferrum = iron + v. griech.: magnetis (lithos) = stone from Magnesien) a cooperative phenomenon is by solids which by the fact is characterized that elementary magnetic moments one parallel order exhibit. One calls ferrousmagnetic solids ferrous magnet. The ranges of same magnetization are called “domains” or” Weiss districts “. They arise in sizes of 0.01 mm up to 1 mm and are not not uniformly oriented in the unmagnetisierten condition (the substance).

Those magnetic order is broken open at high temperatures, the ferrous magnets is then only paramagnetic. The temperature, starting from which the ferrousmagnetic order disappears, becomes as curie temperature <math> T_ {\ mathrm {C}}< /math> (after Pierre curie, the man of Marie curie) designates. The paramagnetism remains for all temperatures upto the curie temperature receive, even after transition of the solid body to liquid phase or gaseous phase.

Substance <math> T_ {\ mathrm {C}}< /math> in K
CO 1395
Fe 1033
ever 627
CrO 2 ,390
Gd 289
Dy 85
EuO 70
Ho 20

ferrousmagnetic characteristics at ambient temperature do not show the elements iron, nickel and cobalt. At lower temperatures also the Lanthanoide gadolinium , dysprosium , holmium , erbium and terbium becomes ferrousmagnetic. In practice one uses frequently ferrousmagnetic alloys like e.g. AlNiCo, SmCo, lp 2 Fe 14 B, NiFe („Permalloy “), or NiCuCo („Mumetall “).Remarkable is that under certain circumstances also some connections do not exhibit generally ferrousmagnetic elements ferrousmagnetic behavior, for example chromium oxide or Europiumoxid.

physical origin

carrier of the elementary magnetic moments are the electron spins. As is the case for other cooperative magnetic phenomena is also withFerromagnetism the magnetic reciprocal effect much too weakly, in order to be responsible for the order of the spins. During the ferrousmagnetic order it is still added that the parallel adjustment of magnetic moments is energetically unfavorable. For the parallel spin order of the ferrous magnet the exchange reciprocal effect is responsible. A descriptiveRepresentation for this gives the Bethe Slater curve, which shows the exchange reciprocal effect in dependence of the relative atomic spacing. The relative atomic spacing is here the relationship of the atomic spacing of the neighbouring atoms to the diameter of the not locked electron shell.

In a sentence: „ The order of the magnetic moments becomes by the exchange reciprocal effectmediate, not by magnetic reciprocal effect! “

domains

the exchange reciprocal effect works only between fermions, whose wave functions a substantial overlap exhibit, usually thus only between nearby particles. The magnetic reciprocal effect works however also between far removes for lying magnetic moments. Therefore risesin an expanded ferrous magnet the magnetic energy expenditure sometime over the energy gain of the exchange reciprocal effect. The ferrousmagnetic order of the solid body disintegrates then into differently oriented domains. The ranges of the solid body, within which differently oriented domains meet one another, are called domain wall. Depending upon direction of rotation of the magnetization in the wallone speaks of Blochwand or Néelwand. The training of the domain wall requires performing of work against the exchange reciprocal effect, the reduction of the domains (the volume of a coherent domain) reduces the magnetic energy of a solid body. This work can be computed from the surface of the BH loop. Due tothe continuously not taking place adjustment of the Weiss districts under the influence of outside magnetic fields so-called can. Bark living jumps to be observed.

see also

 

  > German to English > de.wikipedia.org (Machine translated into English)