Note that you get the same effect, albeit magnified greatly, due to direct DC bias. (An external magnet doesn't have a closed path, so they are relatively insensitive that way, but self-bias does of course.) Ferrite chips aren't good for more than 10s or 100s of mA. Beads on leads, and cable beads and rings, aren't good for, much more than say 1-10At, depending on aspect ratio and material.
Tim