Is this an overlooked possibility... ? A few meteorites/asteroids are composed of nickel-iron-cobalt and are essentially large ferromagnets. None has reached our surface as a strong permanent magnet AFAIK (unless that part of the Excalibur myth). Even if one became permanently magnetized on its journey through space, it would exceed its Curie temp on contact with Earth's atmosphere and lose most of its polarization ... so it is unlikely that the magnetic field of earth would play much of role in altering any "near miss" orbit of a megaton magnet.
But what about the extreme situation of a nickel iron cobalt meteorite with a few rare earth elements - becoming strongly polarized like the best permanent magnet - and also picking up a coating of ice in the Oort cloud to protect it from exceeding its Curie point for several minutes, so that it was attracted to one of Earth's poles. Unlikely, of course ... but is it out of the realm of possibility?
