I'm skeptical about this report though. The magnetosphere extends way beyond the atmosphere where the space junk burns up. And most metal fragments reach the surface. The metal dust that may remain suspended in the ionosphere doesn't have the ability to block the magnetic field (the ionosphere already has a distinct sodium layer). All that aside, there are tonnes of metallic meteoroids entering the atmosphere every day without any issues.
The other reports I've seen suggest damage to the ozone layer and ionosphere due to rocket exhaust during the ascent.