Why are some metals magnetic?

Some metals are magnetic due to the alignment of their unpaired electrons in their atomic structure.

In more detail, magnetism in metals is a result of the behaviour of electrons within the atomic structure of the metal. Electrons have a property called 'spin', which can be thought of as a tiny magnetic field. In most atoms, electrons are paired up and their spins cancel each other out, making the atom non-magnetic. However, in some metals, such as iron, nickel, and cobalt, there are unpaired electrons whose spins align in the same direction. This alignment creates a net magnetic field, making the metal magnetic.

The alignment of these unpaired electrons is influenced by the metal's crystal structure. In ferromagnetic metals (those that are strongly magnetic like iron, nickel, and cobalt), the crystal structure allows the magnetic fields of the unpaired electrons to line up and reinforce each other. This is why these metals can be permanently magnetised - the aligned spins of the unpaired electrons create a strong, stable magnetic field.

On the other hand, in paramagnetic metals (those that are weakly magnetic), the crystal structure doesn't allow the unpaired electrons' magnetic fields to align as effectively. These metals can only be temporarily magnetised when an external magnetic field is applied, and they lose their magnetism when the external field is removed.

In summary, whether a metal is magnetic or not depends on the presence and alignment of unpaired electrons in its atomic structure, and how its crystal structure allows these magnetic fields to interact.