An effect apparent, and without matter to act upon is of no effect. A field is an abstraction, the cause is myriad nuclear spin momenta entangled over a distance with superluminal speed. The effect apparent is realized upon a mass, influenced by myriad nuclear alignments produced across disparate moments in time, individually unique from entanglement, as if the mass experienced force.
Moreover, the total mass involved with the experience of the 'force' will also couple into any equations relating the cause and effect of magnetism.
This entails an air-core (or vacuum) electromagnetic loop coil creates magnetism having an inductive quality that is dependent not upon the magnetic permanence of air or vacuum, but is rather an effect apparent due to the coupling of magnetic moment created by electron flow with the atomic mass of the copper atoms (nuclear spin mass).