In Avengers vs. X-Men #2, Magneto clashes with Iron Man. According to the comic, "if you think this is no contest, you've never met Tony Stark.". I freely admit never meeting Tony Stark, so why isn't this no contest?
Tony has a carbon fiber suit and, I think, Stark manipulated some Kree or Shi'ar tech to make a useful suit for a fight against Magneto.
I have one word for you, to quote Jarvis from AvX Round 2 (11 pages in): Anti-magnetism Safeguards
Ok, that's two words, or three depending on how you slice it. Regardless carbon nanotubes alone won't help Tony. The 'extreme magnetic fields' Jarvis detects would fry the electronics in the suit as eddy currents, and other currents were induced in the magnetic field.
With my knowledge of physics I don't know how Stark could enact 'anti-magnetism safeguards' that wouldn't let Magneto abuse the Meissner effect (the thing that allows magnetic levitation of superconductors) or something similar.
Magnetic metals include iron, nickel, cobalt and most of their alloys. Some forms of steel are magnetic, while others are not. Non magnetic metals include aluminium, copper, lead, tin, titanium and zinc, and alloys such as brass and bronze. Precious metals such as gold, silver and platinum are also not magnetic.
Identifying Common Materials in Antiques: A Pocket Guide (page 61)
These metals can be used by Iron Man to make his non-magnetic suite.
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