Non-ferromagnetic materials tend to have electrons in each orbital

Non-ferromagnetic materials tend to have paired electrons in each orbital or very less unpaired electrons.

Example - Neon, its atomic number is 10 and all the electrons are pared. Now, Aluminum. Its atomic number is 13 with the electronic configuration 3 i.e. only one unpaired electron in the p- orbital. Now, consider iron its atomic number is 26 and its configuration is 3. It has more number of unpaired electrons.  Thus, neon is non-magnetic, aluminum is also non-magnetic but iron is magnetic.