From high school, I remember that Aluminium has 13 electrons and thus has an unpaired electron in the 3p shell. This should make Aluminium magnetic. However, the wiki page of Aluminium says its non-magnetic at one place(with a citation needed tag though) and at another place says it's paramagnetic. Doing a google search shows up some contradictory results. So what is the truth?
Note:The context of the question is this answer on scifi.SE about magneto.
Answer
It really depends on what you mean by "magnetic," because there are different kinds of magnetic properties.
Materials like iron are ferromagnetic, which means that once you align the individual magnetic dipoles in the material, they will tend to stay aligned even without an external magnetic field. Ferromagnetic materials are the ones that permanent magnets are made out of, and they are probably what most people think of when they imagine a magnetic material. There are only three elements (as far as I know) that are ferromagnetic: iron, cobalt, and nickel, although other elements can be combined to make ferromagnetic polyatomic crystals.
Other materials that aren't ferromagnetic can (and typically do) have interesting magnetic properties, though - in other words, just because a material isn't a ferromagnet doesn't mean it doesn't interact magnetically at all. Paramagnetism is one such interaction. When you put a paramagnetic material in a magnetic field, its individual dipoles tend to align with the magnetic field, and thus with each other, thereby making the material magnetic. When this happens, the paramagnetic material is attracted to the magnetic field. The difference is that when you take the external magnetic field away, the individual dipoles in a paramagnetic material don't retain their orientation. Instead, thermal motion takes over and reorients them randomly. So a paramagnetic material only has a net magnetic moment while it is in an external magnetic field.
If Magneto is able to control magnetic fields, then that would potentially allow him to control all sorts of magnetic materials - not just ferromagnets (iron etc.) but also all paramagnetic and perhaps diamagnetic materials, since he can create the external field necessary to magnetize those materials. In fact, all materials, even non-metals, are diamagnetic to some (small) extent. However, paramagnetism and especially diamagnetism are generally much weaker effects than ferromagnetism, so it stands to reason that Magneto would have a harder time controlling non-ferromagnetic materials.
The closest thing to a scientific explanation for Magneto's abilities that I can come up with is that he's able to generate magnetic fields that are strong enough to have a significant effect on ferromagnetic and some of the more paramagnetic materials, but with diamagnetic materials, the magnetic fields he can produce are not strong enough to override other natural forces acting on those materials. Of course, I'm sure that wouldn't really hold up if you really look at the comics or the movie closely... but with comic books you probably don't want to ask too many questions ;-)
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