# I Magnetism at the atomic level

1. Mar 28, 2016

### Prannu

If a magnet is cut in half, it is still a magnet (dipole). If the magnet is continuously cut in half until it is only an atom, it still remains a magnet. My question is, what part of the atom generates the magnet field?

I understand that magnets form primarily from the spin and angular momentum alignments of electrons, but in an individual atom, don't the electrons' spins cancel each other out?

2. Mar 28, 2016

### ZapperZ

Staff Emeritus
Not if you have unpaired electrons! Count the number of electrons in each element of the periodic table, and fill in each orbital. Why would every single one of them have even number of electrons and have their spins cancel out?

Zz.

3. Apr 3, 2016

### Prannu

What parts of the atom would be the North/South pole then?

4. Apr 3, 2016

### ZapperZ

Staff Emeritus
Does this mean then that you have finally accepted and understood that an atom may have a magnetic moment?

Zz.

5. Apr 3, 2016

### Prannu

Well, sort of. So you're saying that even if one left over electron exists (without a spin partner), it's enough to cause a magnetic field in the atom?

6. Apr 3, 2016

### ZapperZ

Staff Emeritus
Why don't you look up "electron paramagnetic resonance" or "electron spin resonance"?

Besides, where do you think magnetism in solids come from?

Zz.

7. Apr 3, 2016

### Prannu

I knew magnetism comes from the net sum of election spins, and orbital magnetic moments for all the atoms of the solid, but was wondering: if for a single atom, there is a non zero spin for the electrons, what orientation is the magnetic field in for the atom?

I will look up the terms you mentioned. Thank you for answering my original question.

8. Apr 3, 2016

### Staff: Mentor

The orientation isn't set. It can change, especially under the influence of external magnetic fields.

9. Apr 3, 2016

Suggestion to the OP is to look up magnetism in Griffith's E&M textbook where he discusses magnetic surface currents. He does it rather quickly and it is mixed in with some detailed calculations that include the calculation of a magnetic vector potential $A$. In any case, the magnetism in the materials is shown in the textbook to be a result of magnetic surface currents. The pole model of magnetism (with north and south poles) is actually a mathematical shortcut to the real source of the magnetic field which is the magnetic surface currents which are the residual effect of magnetic (electron) currents at the atomic level throughout the material that are aligned the same way (e.g. in the counterclockwise direction.) There is no net current at any point inside a uniformly magnetized material-essentially adjacent electron currents (i.e. of adjacent atoms in the material) cancel each other, but at the surface boundaries of the material there will be uncancelled currents. These magnetic surface currents are what creates the magnetic field of a permanent magnet both inside and outside of the material.