Magnetism of a gaseous metal?

If one was, for instance, to create a mass driver that accelerated a ball bearing to a speed such that the friction with the air inside the barrel caused it to vaporise, the gaseous metal would be just as useful as a propellant as if the bearing maintained its solid state, right? Or do the magnetic properties of a excited metal change?

Iron loses its magnetic characteristics when melted. I believe it has to do with the crystal structure – the iron atoms need to be immobile relative to each other for magnetism to impart any motion to the mass. When the material is molten (or, by extension, gaseous) the individual atoms will just wiggle in place when exposed to a magnetic field.

Well before melting actually, 1043K (cite) …cherry red heat.

No ferromagnetic material holds a ferromagnetic charge above a temperature specific to that material, called its Curie point. (I specify ferromagnetic as meaning “magnetic” in everyday speech, because physicists will speak of ferrimagnetism, antiferrimagnetism, paramagnetism, and other more subtle phenomena.) For iron and nickel, the Curie point is in the 500s C IIRC, for cobalt I don’t recall, for gadolinium (the other ferromagnetic element) and various “ceramic” alloys/compounds it’s over 100 degrees below zero.

However, almost any ionized material can be manipulated by a magnetic field; while I’m not clear on my physics here, I suspect strongly something accelerated to its melting point by a mass driver would in fact be at least partly ionized.

This is true, but I think this is an important nit to pick for comprehension’s sake: ionization is not the same thing as magnetization. Ionization happens when atoms gain or lose electrons, so they have a net positive or negative charge. Since they are electrically charged they can be pushed or pulled around by electromagnetic fields.

Magnetization, on the other hand, happens when atoms carrying a magnetic dipole moment (say, because of how their electrons move around the nucleus – electric acceleration → magnetic field) start aligning. At the scale of atoms this is all but assured that neighboring atoms will point in the same direction. But as these little areas of agreement grow they bump into each other and you have a patchwork – one clump points all one way, and the next clump points all another way. Magnetization at the macroscopic scale is when these patches all start agreeing with each other and all pointing the same way.

The problem is that when you dump in heat energy the atoms start pointing every which way. They don’t need to be stingy with their energy by all pointing the same way, so they have no incentive to agree, and the whole thing falls apart. By the time a material has melted it’s far too late. At that point the atoms don’t even have an incentive to stay in the same relative positions, let alone to point in the same direction.