# Diamagnetism vs. paramagnetism

Simple question, kind of. I know that paramagnetic materials, when in the presence of a magnetic field will have its dipoles orient with the field while diamagnetic materials when introduced to a magnetic field orient opposite to the field. I've read that this has something to do with Lentz's Law, but is there someone that could help put this in slightly better perspective?

## Answers and Replies

apiri said:
Simple question, kind of. I know that paramagnetic materials, when in the presence of a magnetic field will have its dipoles orient with the field while diamagnetic materials when introduced to a magnetic field orient opposite to the field. I've read that this has something to do with Lentz's Law, but is there someone that could help put this in slightly better perspective?

http://www.cmp.liv.ac.uk/frink/thesis/thesis/node35.html

Gokul43201
Staff Emeritus
Gold Member
Lenz's law makes things oppose the change of applied field. So when a diamagnetric material experiences and increasing field, it lines up its spins in the opposite direction to reduce the net field inside the material. This is not really an explanation. More of a hand-waving argument.

Last edited:
ZapperZ
Staff Emeritus
Gokul43201 said:
Lenz's law makes things oppose the change of applied field. So when a diamagnetric material experiences and increasing field, it lines up its spins in the opposite direction to reduce the net field inside the material. This is not really an explanation. More of a hand-waving argument.

I don't think we can dismiss Lenz's law simply as "hand-waving". For one, it has a very detailed mathematical formulation. This implies it makes quantitative description and predictions. Hand-waving arguments very seldom have that.

It is also a direct consequence of the conservation of energy. Now that principle is certainly not hand-waving.

It is also from one of Maxwell's equations. So it is part of a well-established formulation of classical E&M.

What you might have wanted to say was that it is a phenomenology, which I have no arguments with. Classical E&M, as per Maxwell equations, is really phenomenology - none of those equations can be derived from classical First Principles formulations. Coulomb's law, for example, was not derived - it is a description of a phenomena.

[I purposely did not bring QED into this.]

Zz.

Gokul43201
Staff Emeritus