What is the Difference Between Magnetic Moment and Magnetic Domain?

[gbaby370]

Just for clarification, I was wondering if someone could clarify what the difference between a magnetic moment and magnetic domain is. My understanding is a magnetic moment is when the atom aligns it's subatomic particles relative to the magnetic field, and that a magnetic domain is groups of magnetic moments that align relative to the magnetic field.

If anyone could clear that up for me that would be great.

 

[tiny-tim]

hi gbaby370!

a magnetic moment is simply one or more loops of current, facing in a particular direction

all materials have these, but in most materials their directions are random

in a ferromagnetic material, they aren't random …

the material is divided into "magnetic domains", and the magnetic moments in one domain all point in the same direction, but different domains have different directions

see http://en.wikipedia.org/wiki/Magnetic_domain for details

 

[gbaby370]

So if we apply a magnetic field, for example to a hydrogen atom. What would it be called when it's protons and electrons align themselves relevant to the applied magnetic field?

 

[tiny-tim]

So if we apply a magnetic field, for example to a hydrogen atom. What would it be called when it's protons and electrons align themselves relevant to the applied magnetic field?

a single hydrogen atom? it only has one proton and one electron

i suppose we'd call it "alignment"

 

[Hassan2]

From what I remember :
Each electron has two magnetic moments: spin magnetic moment and orbital magnetic moment . The two have equal magnitudes but reacts differently to the applied field. Spin moment tends to align with the applied field but the orbit one does not alight but rather precess around the the field because they have angular momentum. The result of this precession is a small induced magnetization "opposite" to the applied field ( diamagnetism).
On the other hand, spin moment tends to align with the applied field ( after some periods of damped precession) and results in an induced magnetization "parallel" with the applied field. Spin moments of paired electrons are cancelled. For unpaired electrons, the sum of orbital and spin moments determines the magnetization of the material though it spin contribution is larger by about 3 orders of magnitudes.

Except for ferromagnetic materials, the parallelization of spin moments is partial because electrostatic interactions and thermal energy does not allow it. In ferromagnetic materials, there is exchange interaction which keeps the spins of neighboring atoms parallel. Exchange interaction is so strong that it keeps the spins parallel for temperature bellow the material's Curie temperature and form domains which are a a large number of parallel moments. Note that the direction of spins in a domain is not necessarily parallel with the applied field.

In Hydrogen molecules ( H2) we have two electrons in S orbit so their spin moments are canceled and H2 becomes diamagentic.

 

[tiny-tim]

nice summary, Hassan2!