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Magnetism (Read 6327 times)
Gerrit-Jan Linker
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Posts: 75
03.01.10 at 22:50:13
Magnetism describes how materials respond on the microscopic level to an applied magnetic field; to categorize the magnetic phase of a material.  
The magnetic state (or phase) of a material depends on temperature, pressure, applied magnetic field, ...
Without an external field:
Random orientation of magnetic moments in para and diamagnets.
Oriented magnetic moments in ferro (all same direction), anti-ferro (alternating directions) and ferrimagnets.
With the applicatino of an external field:
Alignment of magnetic moments along with the field for para, ferro, anti-ferro and ferrimagnets.
Alignment of magnetic moments in opposite direction of the field for diamagnets.
  • Paramagnetic materials are attracted to magnetic fields, hence they have a relative magnetic permeability of ≥1. The magnetic moment induced by the applied field is linear in the field strength and rather weak.
  • Paramagnets do not retain any magnetization in the absence of an externally applied agnetic field, because thermal motion causes the spins to become randomly oriented without it.
  • These materials have a positive magnetic susceptibility.
  • Pauli paramagnetism: this is the effect that upon the application of a magnetic field, alpha and beta spin electronic bands split with a higher population of one type of spin as a result. This is a weak form of paramagnetism.

Diamagnetic materials are caused to create a magnetic field in opposition to an externally applied magnetic field. These materials have a negative magnetic susceptibility.
Most molecules are diamagnetic with two electrons of opposite spin in a closed shell configration in the HOMO.
Ferromagnetic materials exhibit the basic mechanism by which certain materials (such as iron) form permanent magnets and/or exhibit strong interactions with magnets.
In ferromagnetism all of the materials magnetic ions add a positive contribution to the net magnetization.
A ferrignetic material is a permanent magnet in which some of the magnetic ions subtract from the net magnetization (if they are partially anti-aligned).
An antiferromagnetic material is a material in which the moments of the aligned and anti-aligned ions balance completely so as to have zero net magnetization, despite the magnetic ordering.
Temperature independent magnetic susceptibility : Pauli (elaborate!).
Wikipedia - Magnetism
Wikipedia - Paramagnetism
Wikipedia - Ferromagnetism
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« Last Edit: 13.01.14 at 09:34:33 by Gerrit-Jan Linker »  


Gerrit-Jan Linker
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