# Passing current through a magnet

1. Dec 30, 2010

### Pranav Jha

I think magnet has to be a conductor of electricity if is made of iron or steel. So, What happens when we pass a direct current through a magnet? What if we pass through AC? Does the passage of current effect the strength of the magnet?

2. Dec 30, 2010

### cragar

If we passed dc current through the magnet it will create another magnetic field out side the magnet, But im not sure how this will affect the existing magnetic field. And im not sure how the free current will affect the magnetic moments of the iron atoms. I know that when they make magnets they run current through them to magnetize them. Hopefully someone else can answer your question.

3. Dec 30, 2010

### trini

you usually don't run a current directly through a magnet to magnetize it(what would be the direction of magnetization if you did this?) they usually use solenoids with thick wire and high pulse current for rare earth magnets. if u ran a current through a magnet you would likely lose strength as the induced magnetic field would be in the opposite direction to the magnets polarization for at least half of the space, maybe you won't lose all, but a fair bit, depending on the type of magnet it is(bonded, sintered etc)

4. Dec 30, 2010

### Studiot

The simple answer is that we don't do this because the electrical resistivity of magnetic materials is relatively high.

So, although a real iron magnet will conduct electricity it will have significant electrical resistance.
This means that significant resistive heating will occur.
It may even be that the iron temperature will be raised sufficiently to destroy the magnetism, or even melt the iron.

This property is used in resistive welding, although no magnetism is involved, to input the necessary heat for the welding.

5. Dec 30, 2010

### cragar

I saw them do this on how its made, they ran current through the magnet. It does seem strange though. Putting it inside a solenoid seems better.

Last edited by a moderator: Sep 25, 2014
6. Dec 31, 2010

### graphene

OP's question remains unanswered.
The magnetic field produced by the current through the magnet is small to affect its already present magnetization.
(In case, you somehow keep the magnet cool so that resistive heating effects do not come into play)
Well, the magnet was a magnet because the spins were aligned. Would the passage of (not too large a) current affect the spins?

7. May 19, 2011

### zampaz

What a fun question! Current involves the movement of electrons, a specific number of electrons through a cross-section area of a material in a given amount of time.
And we are told that "magnets" as in the case of a simple permanent bar magnet have molecules that are organized as groups called "magnetic domains" when the original molecules valance electrons are ordered by an external magnetic field.
These domains have unpaired electrons arranged such that the spin of the unpaired electrons have an additive magnetic moment and as a group are in a more stable energy state.
So as an electron does it's quantum walk from valance to hole what happens to it's spin? You can easily see that if you push 6E23 electrons per second through a cross section of a small bar magnet the molecules are going to get really excited and get hot, oh boy! Remember it's valence electrons that are keeping things neatly organized.
So maybe we shouldn't add so much current and consider what would happen if we had a way to ensure electrons maintained their spin as they hopped from hole to hole. Would using another external magnetic field keep things organized at the electron hop?
Keep in mind the right hand rule...

8. May 23, 2011

### cragar

I wonder what would happen to the magnet if we cooled it down to superconducting temperatures.