# Alignment of micro dipoles in magnetic material in external magnetic field.

• yungman

#### yungman

I just want to verify that the dipole moment $\vec{m}$ in the presence of external magnetic field $\vec{B}$ will line up in the the same direction and parallel with the external field. This is according to the right hand rule that if magnetic field is the direction of the thumb, the current will circulate in the direction of the finger. So the $\vec{m}$ will be in same direction of the external magnetic field.

Also the point of the $\vec{m}$ is the north pole.

But the electron orbital will spin at opposite direction of the current since electron direction is opposite to current.

Can anyone confirm this?

Thanks

Alan

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I am also confuse why diamagnetic material which mainly consist of dipoles formed by orbital electrons ( not spin electrons) that will opposed to the external magnetic field instead of in the same direction like in the magnetic materials?

Lenz's law:
An induced current is always in such a direction as to oppose the motion or change causing it

That is why all material containing orbiting electrons are diamagnetic to some extent.

I think I got the answer already. The diamagnetic material mainly have dipoles make of orbital electrons and the magnetizing vector is in opposite direction as the external magnetic field.

In paramagnetic material, the spining electrons is the main source of dipoles and it's magnetization vector is in the same direction as the external magnetic field.

Both source are very week and the permeability is still very very close to in vacuum.

Please tell me whether I am correct.

Thanks

Your first statement about diamagnetism is correct, orbiting electrons create a magnetic field so as to oppose the external field.

If an atom contains uncoupled electrons, their magnetic moments will align either parallel or anti-parallel to the external field. Because laying parallel (in the direction) of the field is the lowest energy configuration, the majority will do this, thus their magnetisation adds to the external field. This is known as paramagnetism.

Paramagnetism and diamagnetism only exist in the presence of external field. The relative sizes of these two effects depends on the substances involved so I couldn't comment on how comparable they are to a vacuum. How close to a vacuum do you need them to be? At what point would you no longer consider it significant? It depends on what you're doing!

There is also nuclear paramagnetism, but this can be thousands of times small than other effects so difficult to measure.

Thanks

Alan