There are three magnetic fields in an atom. The nucleus, due its spinning motion, generates a small magnetic force. Electrons also generate a magnetic field from spinning. The resultant magnetic field (using vector addition of the nucleus and electron fields) is the third field in an atom. This resultant magnetic field is the overall magnetic field of the atom.

In non-magnetic atoms, for each electron spinning in one direction, there is another electron spinning in the opposite direction. The atom is said to be in a state of magnetic balance. A helium atom, with two electrons spinning in opposite directions, is non-magnetic.

A state of magnetic unbalance exists when there are more electrons spinning in one direction than the opposite direction. Lithium, for example, has three electrons, two spinning in one direction and one spinning in the opposite direction. Lithium has a resultant magnetic field, but the field strength is so miniscule that it is classified as a non-magnetic atom. The magnetic properties of an atom increase in direct proportion to the number of electrons that are not compensated for (more spinning one way than another). Iron, for example, has 26 electrons, 15 rotating in one direction and 11 rotating in the opposite direction. It has four uncompensated electrons, therefore it has a large magnetic field strength.

In an atom's natural state, these electrons are not aligned exactly. The overall magnetic field is reduced. If you apply a strong external magnetic field, the electrons are brought into alignment, and the resultant magnetic field is greatly increased. As an example, if you rub a magnet against a screwdriver made of ferrous (iron-based) metal, the screwdriver itself becomes magnetic. You are aligning the magnetic fields to work with each other.