The difference between diamagnetism and paramagnetism?

[jeebs]

Hi,
I am struggling to see the difference in the origins of diamagnetism and paramagnetism.

My understanding of things is that the electrons orbitting an atom constitute a tiny circular current loop, which corresponds to a magnetic dipole moment pointing normal to the plane of that loop.

When a magnetic field is applied, apparently a diamagnetic material will allow its dipoles to align themselves such that they oppose the applied field, as a consequence of Lenz's law.

However, from what I can gather, paramagnetism also results from tiny atomic current loops that create a magnetic dipole moment, but these do not oppose the field and I do not know why.

The Hyperphysics website states that:
"All materials are inherently diamagnetic, but if the atoms have some net magnetic moment as in paramagnetic materials, or if there is long-range ordering of atomic magnetic moments as in ferromagnetic materials, these stronger effects are always dominant."

This particularly confuses me, because surely a diamagnetic atom has some net magnetic moment too, or else what the hell is it aligning with the applied field? Surely an atom with no net magnetic moment will have no reaction whatsoever to an applied field?

I'd really appreciate a swift answer to this because my magnetism exam is tomorrow.

Thanks.

 

[kuruman]

This particularly confuses me, because surely a diamagnetic atom has some net magnetic moment too, or else what the hell is it aligning with the applied field?

The orbital current loops. Diamagnetism is present in all atoms. Paramagnetism arises in atoms with unpaired spins which not all atoms or have. People who measure paramagnetic susceptibilities routinely apply diamagnetic corrections found in tables to separate the paramagnetic contribution from the unavoidable diamagnetic contribution.

 

[Meir Achuz]

"If the atoms have some net magnetic moment"
I think that is just loose language in the text. I think they must mean something like 'intrinsic' instead of 'net'.