Why are only a few metals magnetic?

Only the metals iron, nickel, cobalt and some of their alloys can be made into strong magnets. However, an electric current also gives a strong magnetic field when if flows through a coil. The Earth has magnetic field too, probably because of electric currents circulation in its core.

There is a connection here. The atoms of which all substances are made contain electrons in motion. This movements produces a magnetic field, as do the moving electrons in an electric current. But in most substances, the magnetic fields of the electrons in their atoms cancel each other out, and the substances are not magnetic. In magnetic metals, the fields reinforce each other.