[Fyron]

Because they are ferromagnetic elements. Such atoms are capable of remembering magnetic alignment, so materials made of them can be "magnets." Other elements and compounds are paramagnetic or diamagnetic. I forget which was which, but essentially, they are completely incapable of remembring a magnetic field. A field can be induced in them, but it is fairly weak (much weaker in one class than the other, though I forget which).