Must be too late for the piece of art, I regret...
Ferromagnetism is not an atomic property but a molecular one. For instance, Zn-Mn alloys are used in electronics as magnetic cores called there "ferrite", and CrO2 is a permanent magnet from the time of magnetic tapes. In contrast, Fe-Ni austenitic stainless steel is non-magnetic, unless a deformation (= same atoms) without heating can transform some of it to martensite. There are even ferromagnetic plastics, made of banal organic elements.
While iron sulphate would be easy to buy or produce, don't expect a ferromagnetic behaviour from it.
Induction lines are aesthetic and could make a nice piece of art. Usually done with iron powder. Electromagnets are preferred: switch off to clean the powder away.